Intraoperative Neurophysiological Monitoring

Number: 0697

Table Of Contents

Policy
Applicable CPT / HCPCS / ICD-10 Codes
Background
References


Policy

Scope of Policy

This Clinical Policy Bulletin addresses intraoperative neurophysiological monitoring.

  1. Medical Necessity

    Aetna considers intraoperative neurophysiological monitoring medically necessary (unless otherwise specified) for the following indications when criteria are met:

    1. Intraoperative electromyographic (EMG) monitoring for the following indications (unless otherwise specified):

      1. Facial nerve for members undergoing any of the following intracranial neuro-otological surgeries:

        1. Cochlear implant surgery; or
        2. During canalplasty/external canal reconstruction; or
        3. Microvascular decompression of the facial nerve for hemifacial spasm; or
        4. Resection of temporal bone; or
        5. Surgery for acoustic neuroma, congenital auricular lesions, or cranial base lesions; or
        6. Surgery for cholesteatoma, including mastoidotomy or mastoidectomy; or
        7. Surgical excision of neuromas of the facial nerve; or
        8. Vestibular neurectomy for Meniere's disease; or
        9. Vestibular schwannoma surgery;
      2. During selective dorsal rhizotomy when selection criteria for the procedure set in CPB 0362 - Spasticity Management are met;
      3. Of any of the following cranial nerves for surgical excision of neuromas of these cranial nerves:

        1. Abducens nerve
        2. Glossopharyngeal nerve
        3. Hypoglossal nerve
        4. Oculomotor nerve
        5. Recurrent laryngeal nerve
        6. Spinal accessory
        7. Superior laryngeal nerve
        8. Trochlear nerve;
      4. For any of the following:

        1. Brachial plexus surgery
        2. Cross-facial nerve grafting
        3. Excision of branchial cleft anomalies (cysts, fistulae, or sinuses)
        4. Location of the hypoglossal nerve during implantation of an Inspire hypoglossal nerve stimulator
        5. Resection of skull base tumors including posterior fossa tumor (cranial nerve monitoring)
        6. Resection of spinal cord tumors (e.g., cauda equina tumor, nerve root tumor including schwannoma, and neurofibroma, and sacral chordoma)
        7. Tethered cord release;
      5. Stimulation of vagus nerve/recurrent laryngeal nerve and assessment of vocal fold response to nerve stimulation for thyroidectomy/lobectomy or thyroid reoperations; or
      6. Combined use of intraoperative EMG monitoring of facial nerve and intraoperative monitoring of somato-sensory evoked potentials is considered not medically necessary;
    2. Intraoperative somatosensory evoked potentials (SEPs, SSEPs) performed either alone, or in combination with motor evoked potentials (MEPs)

      1. For monitoring the integrity of the spinal cord to detect adverse changes before they become irreversible during spinal, intracranial, orthopedic, or vascular procedures, when the following criteria are met:

        1. A specially trained physician or a certified professional practicing within the scope of their license, who is not a member of the surgical team contemporaneously interprets the intraoperative evoked potentials during the operation; and
        2. The evoked potential monitoring is performed in the operating room by dedicated trained technician; and
        3. The clinician who performs the interpretation is monitoring no more than 3 surgical procedures at the same time; and
        4. The clinician who performs the interpretation may do so remotely, but must provide direct, immediate communication of intraoperative evoked potential results to the technician and surgeon during the operation;
      2. Intraoperative SEP monitoring, with or without MEPs, may be appropriate for the following types of surgery (not an all-inclusive list):

        1. Spinal surgeries:

          1. Correction of scoliosis or deformity of the spinal cord involving traction on the cord
          2. Decompression of the spinal cord where function of the spinal cord is at riskFootnote*
          3. During incision and drainage of paraspinal/epidural abscess of cervical spine
          4. During invasive spinal rod lengthening
          5. Removal of spinal cord tumors (including sacral tumors)
          6. Surgery as a result of traumatic injury to the spinal cord
          7. Surgery for arteriovenous (AV) malformation of the spinal cord
          8. Tethered cord release;
        2. Intracranial surgeries:

          1. Chiari malformation surgery
          2. Correction of cerebral vascular aneurysms (e.g., cerebral aneurysm clipping, coil embolization)
          3. Deep brain stimulation
          4. Endolymphatic shunt for Meniere's disease
          5. Microvascular decompression of cranial nerves (e.g., optic, trigeminal, facial, auditory nerves)
          6. Oval or round window graft
          7. Removal of cavernous sinus tumors
          8. Removal of tumors that affect cranial nerves
          9. Resection of brain tissue close to the primary motor cortex and requiring brain mapping
          10. Resection of epileptogenic brain tissue or tumor
          11. Surgery as a result of traumatic injury to the brain
          12. Surgery for intracranial AV malformations
          13. Surgery for intractable movement disorders
          14. Surgery for moyamoya disease
          15. Vestibular section for vertigo;
        3. Vascular surgeries:

          1. Arteriography, during which there is a test occlusion of the carotid artery
          2. Circulatory arrest with hypothermia (does not include surgeries performed under circulatory bypass such as CABG, and ventricular aneurysms)
          3. Distal aortic procedures, where there is risk of ischemia to the spinal cord
          4. Surgery of the aortic arch, its branch vessels, or thoracic aorta, including carotid artery surgery (e.g., carotid endarterectomy), when there is risk of cerebral ischemia.

      Intraoperative SSEPs with or without MEPs are considered experimental, investigational, or unproven for all other indications (e.g., scapula-thoracic fusion surgery) because their effectiveness for indications other than the ones listed above has not been established.

      Note: Depending on the clinical condition being investigated, it may be medically necessary to test several nerves in one extremity and compare them with the opposite limb.

      Footnote1*Intraoperative evoked potential studies have no proven value for lumbar surgery below (distal to) the end of the spinal cord; the spinal cord ends at L1-L2.

      Note: Post-operative SEP or MEP monitoring is not considered medically necessary for individuals who have undergone intraoperative SEP or MEP monitoring. 

      Note: The NIM-Spine System received 510(k) clearance from the Food and Drug Administration (FDA) in June 2003.  It offers 2 types of monitoring modalities: electromyography and MEP.

      Note on documentation requirements: The physician's SEP report should note which nerves were tested, latencies at various testing points, and an evaluation of whether the resulting values are normal or abnormal. See appendix for additional details on documentation requirements;

    3. Brain Stem Auditory Evoked Response (BAER)Footnote**

      1. For cerebral vascular surgery; or
      2. For Chiari malformation surgery; or
      3. For intraoperative monitoring during microvascular decompression of cranial nerve when decompression is performed via the intra-cranial posterior fossa approach; or
      4. For intraoperative monitoring during resection of chordoma , odontoidectomy, decompression of tumor from anterior brainstem/high spinal cord; or
      5. For intraoperative monitoring of other surgeries involving the posterior fossa (including resection of pineal mass) to help assess brainstem function and preserve hearing; 

      BAERs are considered experimental, investigational, or unproven for all other indications (except for additional indications listed in CPB 0181- Evoked Potential Studies) because their effectiveness for indications other than the ones listed above has not been established.

      Footnote2**Also known as auditory brainstem response (ABR), auditory evoked potentials (AEPs), brainstem auditory evoked potentials (BAEP), BERA, BSER, and BSRA.

    4. Intraoperative neuromonitoring (IONM) during eligible lower extremity and buttock reconstruction.
  2. Experimental, Investigational, or Unproven

    Aetna considers the following intraoperative neurophysiological monitoring modalities experimental, investigational, or unproven for the following indications (not an all-inclusive list) because the effectiveness of these approaches has not been established for these indications:

    1. Intraoperative EMG monitoring:

      1. During aortic aneurysm repair
      2. During biopsy of anterior cervical chain lymph nodes
      3. During carotid endarterectomy
      4. During Chiari malformation decompression surgery
      5. During craniotomy for meningioma
      6. During decompression, neurectomy, radiosurgery or rhizotomy of the trigeminal nerve
      7. During decompression of the jugular vein
      8. During decompression of peroneal (fibular) nerve
      9. During excision of sentinel lymph nodes
      10. During hip dysplasia surgery / hip replacement surgery
      11. During knee arthroscopy/repair
      12. During intra-cranial tumor resections (unless the resection involves a cranial nerve)
      13. During intra-thecal pump adjustment
      14. During lymph node biopsy for individuals with pelvic mass
      15. During Moyamoya surgery
      16. During open reduction internal fixation (ORIF) of the finger
      17. During ossiculoplasty
      18. During pharyngoplasty
      19. During placement of dorsal column stimulator
      20. During prostatectomy/prostate surgery
      21. During radiofrequency ablation (RFA) of the genicular nerve
      22. During radiofrequency thermal coagulation for any spinal procedures
      23. During rectal cancer surgery
      24. During repair of posterior inferior cerebellar artery aneurysm
      25. During rotator cuff repair
      26. During sacroiliac joint injection
      27. During shoulder labral repair
      28. During supra-cerebellar infratentorial craniotomy
      29. During supra-clavicular first rib resection and scalenectomy for thoracic outlet syndrome
      30. During sural nerve grafting
      31. During submandibular gland resection
      32. During tibial neurectomy
      33. During wrist arthroscopy
      34. EMG monitoring and neuromuscular junction testing for the following (not an all-inclusive list):

        • Celiac plexus block
        • Epidural injections
        • Facet joint injections
        • Lumbar sympathetic block
        • Medial branch block
        • Radiofrequency facet neurolysis;
      35. Intraoperative EMG monitoring and neuromuscular junction testing during spinal surgery (including anterior cervical procedures) because there is insufficient evidence that this technique provides useful information to the surgeon in terms of assessing the adequacy of nerve root decompression, detecting nerve root irritation, or improving the reliability of placement of pedicle screws at the time of surgery;
      36. Intraoperative EMG monitoring of the recurrent laryngeal nerve/intra-operative neuromonitoring during parathyroid surgery;
      37. intraoperative surface EMG monitoring;
      38. Of the facial nerve during parotid gland surgery, sinus surgery, stapedotomy for otosclerosis, thyroid surgery, tympanoplasty without mastoidotomy or mastoidectomy, or maxillo-facial surgery;
    2. Intraoperative evoked potential studies (see CPB 0181 - Evoked Potential Studies for additional indications):

      1. Auditory evoked potentials during surface electroencephalography (sEEG) implantation into the brain cortex;
      2. Auditory evoked potential monitoring during cochlear implantation;
      3. Evoked potential monitoring during degenerative cervical spine surgery;
      4. Intraoperative BAER** during stapedectomy, tympanoplasty and ossicle reconstruction;
      5. Intraoperative MEP during implantation of a spinal cord stimulator;
      6. Intraoperative neuromonitoring during carpal tunnel release;
      7. Intraoperative neuromonitoring during cervical lymphadenectomy (modified radical neck dissection);
      8. Intraoperative neuromonitoring during craniotomy repair of cerebrospinal fluid leak;
      9. Intraoperative neuromonitoring during femur, tibia/fibula osteotomy and ankle arthrodesis;
      10. Intraoperative neuromonitoring during femoroacetabular surgery;
      11. Intraoperative neuromonitoring during implantation, removal, and adjustment of vertical expandable prosthetic titanium rib (VEPTR);
      12. Intraoperative neuromonitoring during lymph node biopsy;
      13. Intraoperative neuromonitoring during removal of spinal cord stimulator;
      14. Intraoperative neuromonitoring during resection of a middle ear mass;
      15. Intraoperative neuromonitoring during rib resection;
      16. Intraoperative neuromonitoring during rotator cuff repair;
      17. Intraoperative neuromonitoring during sacretomy;
      18. Intraoperative neuromonitoring during sacroiliac joint fusion;
      19. Intraoperative neuromonitoring during scalenectomy;
      20. Intraoperative neuromonitoring during sciatic nerve biopsy;
      21. Intraoperative neuromonitoring during sciatic nerve tumor removal;
      22. Intraoperative neuromonitoring during shoulder surgery;
      23. Intraoperative neuromonitoring during spinal cord stimulator placement and removal;
      24. Intraoperative neuromonitoring during stapedectomy/ossicular chain reconstruction;
      25. Intraoperative neuromonitoring during surgery for the correction of thoracic outlet syndrome;
      26. Intraoperative neuromonitoring during surgery for the treatment of priformis syndrome;
      27. Intraoperative neuromonitoring during thoracotomy for resection of mediastinal mass (unless the mass is around the spinal cord or it involves the aorta or the radicular arteries branching off the aorta);
      28. Intraoperative neuromonitoring during total knee arthroplasty;
      29. Intraoperative neuromonitoring during total hip replacement;
      30. Intraoperative neuromonitoring during Zenkers diverticulectomy;
      31. Intraoperative neuromuscular junction testing in member with anoxic brain injury;
      32. Intraoperative saphenous nerve somatosensory evoked potential for monitoring the femoral nerve during transpoas lumbar lateral interbody fusion;
      33. Intraoperative SSEP monitoring during hip dysplasia and labral repair surgery;
      34. Intraoperative SSEP during open reduction internal fixation of acetabulum fracture;
      35. Intraoperative SSEP during transforaminal epidural steroid injections;
      36. Intraoperative SSEP of the facial nerve for submandibular gland excision or parotid gland surgery, during hip replacement surgery, implantation of a spinal cord stimulator, off-pump coronary artery bypass surgery, and for thyroid surgery and parathyroid surgery (because they have not been proven necessary to aid in diagnosis or alter the management of individual undergoing surgical treatment);
      37. Intraoperative SSEP, with or without MEPs, for cochlear implantation, implantation of vagus nerve stimulator, monitoring spinal injections (e.g., epidural injections, facet joint, interlaminar and transforminal epidural), open reduction internal fixation (ORIF) of the finger, radiofrequency ablation of facet medial branch, rotator cuff repair, or wrist arthroscopy repair;
      38. Intraoperative visual evoked potentials (e.g., for pituitary surgery, during intra-cranial surgery for arterio-venous malformation);
      39. Motor evoked potential monitoring for peripheral nerve ablation;
      40. Motor evoked potentials other than for intraoperative use with SSEPs (e.g., facial MEPs during cerebellopontine angle and skull base tumor surgery);
      41. SEPs for pectus excavatum surgery;
      42. SEPs for prostate surgery;
      43. SEPs monitoring during trigger point injection for management of low back pain;
      44. Stimulus evoked response during radical prostatectomy.
  3. Related Policies


Table:

CPT Codes / HCPCS Codes / ICD-10 Codes

Code Code Description

Intra-operative neurophysiological monitoring add-on codes:

Other CPT codes related to the CPB:

+95940 Continuous intraoperative neurophysiology monitoring in the operating room, one on one monitoring requiring personal attendance, each 15 minutes (List separately in addition to code for primary procedure)
+95941 Continuous intraoperative neurophysiology monitoring, from outside the operating room (remote or nearby) or for monitoring of more than one case while in the operating room, per hour (List separately in addition to code for primary procedure)

HCPCS codes covered if selection criteria are met:

G0453 Continuous intraoperative neurophysiology monitoring, from outside the operating room (remote or nearby), per patient, (attention directed exclusively to one patient) each 15 minutes (list in addition to primary procedure)

ICD-10 codes covered if selection criteria are met (not all-inclusive):

C30.1 Malignant neoplasm of middle ear
C44.201 - C44.299 Other and unspecified malignant neoplasm of skin of ear and external auricular canal
C47.0 Malignant neoplasm of peripheral nerves of head, face, and neck
C49.0 Malignant neoplasm of connective and soft tissue of head, face, and neck
C72.1 Malignant neoplasm of cauda equina
D04.20 - D04.22 Carcinoma in situ of skin of ear and external auricular canal
D14.0 Benign neoplasm of middle ear, nasal cavity and accessory sinuses
D21.0 Benign neoplasm of connective and other soft tissue of head, face, and neck
D22.20 - D22.22, D23.20 - D23.22 Benign neoplasm of skin of ear and external auditory canal
D36.10 Benign neoplasm of peripheral nerves and autonomic nervous system, unspecified [schwannoma, neurofibroma]
G51.0 - G52.9 Facial nerve disorders and disorders of other cranial nerves
H71.00 - H71.93 Cholesteatoma of middle ear
H74.40 - H74.43 Polyp of middle ear
H81.01 - H81.09 Meniere's disease
H95.00 - H95.03 Recurrent cholesteatoma of postmastoidectomy cavity

ICD-10 codes not covered for indications listed in the CPB (not all-inclusive):

A52.01 Syphilitic aneurysm of aorta
C19 Malignant neoplasm of rectosigmoid junction
C20 Malignant neoplasm of rectum
C61 Malignant neoplasm of prostate
C71.0 - C71.9 Malignant neoplasm of brain
C76.0 Malignant neoplasm of head, face, and neck
C78.5 Secondary malignant neoplasm of large intestine and rectum
C79.31 - C79.32 Secondary malignant neoplasm of brain and cerebral meninges
D01.2 Carcinoma in situ of rectum
D32.0 - D32.9 Benign neoplasm of meninges
D33.0 - D33.3 Benign neoplasm of brain, cranial nerves, or cerebral meninges
D43.0 - D43.3 Neoplasm of uncertain behavior of brain
G50.0 - G50.9 Disorders of trigeminal nerve
H70.001 - H70.93, H72.00 - H74.399, H74.8X1 - H75.83, H95.111 - H95.199 Mastoiditis and related conditions, other disorders of tympanic membrane, and other disorders of middle ear and mastoid
I67.5 Moyamoya disease
I71.10 - I71.9 Aortic aneurysm
K11.0 - K11.9 Diseases of the salivary glands
M26.00 - M26.9 Dentofacial anomalies, including malocclusion
M75.100 - M75.122 Rotator cuff tear or rupture of unspecified shoulder, not specified as traumatic
R19.00 - R19.09 Intra-abdominal and pelvic swelling, mass and lump
S02.400+ - S02.42x+, S02.600+ - S02.69x+ Fracture of mandible, malar, and maxillary bones
S03.00x+ - S03.02x+ Dislocation of jaw
S25.01xA - S25.09xS Minor laceration of thoracic aorta
S43.421A - S43.429S Sprain of rotator cuff capsule
S46.001A - S46.099S Injury of muscle(s) and tendon(s) of the rotator cuff of shoulder

Intra-operative electromyographic (EMG) monitoring primary procedure codes:

CPT codes covered if selection criteria are met:

51784 Electromyography studies (EMG) of anal or urethral sphincter, other than needle, any technique
51785 Needle electromyography studies (EMG) of anal or urethral sphincter, any technique
95860 Needle electromyography; one extremity with or without related paraspinal areas
95861     two extremities with or without related paraspinal areas
95863     three extremities with or without related paraspinal areas
95864     four extremities with or without related paraspinal areas
95865 Needle electromyography; larynx
95866     hemidiaphragm
95867 Needle electromyography; cranial nerve supplied muscle(s), unilateral
95868     cranial nerve supplied muscles; bilateral
95869     thoracic paraspinal muscles (excluding T1 or T12)
95870 Needle electromyography; limited study of muscles in one extremity or non-limb (axial) muscles (unilateral or bilateral), other than thoracic paraspinal, cranial nerve supplied muscles, or sphincters
95872 Needle electromyography using single fiber electrode, with quantitative measurement of jitter, blocking and/or fiber density, any/all sites of each muscle studied
95885 Needle electromyography, each extremity, with related paraspinal areas, when performed, done with nerve conduction, amplitude and latency/velocity study; limited (List separately in addition to code for primary procedure)
95886     complete, five or more muscles studied, innervated by three or more nerves or four or more spinal levels (List separately in addition to code for primary procedure)
95887 Needle electromyography, non-extremity (cranial nerve supplied or axial) muscle(s) done with nerve conduction, amplitude and latency/velocity study (List separately in addition to code for primary procedure)
95937 Neuromuscular junction testing (repetitive stimulation, paired stimuli), each nerve, any 1 method

CPT codes for surgery where intra-operative EMG is covered if selection criteria is met:

0442T Ablation, percutaneous, cryoablation, includes imaging guidance; nerve plexus or other truncal nerve (eg, brachial plexus, pudendal nerve)
42810 Excision branchial cleft cyst or vestige, confined to skin and subcutaneous tissues
42815 Excision branchial cleft cyst, vestige, or fistula, extending beneath subcutaneous tissues and/or into pharynx
60110 - 60212, 60220 - 60225, 60240 - 60271 Partial, total thyroid lobectomy and Thyroidectomy
61518 Craniectomy for excision of brain tumor, infratentorial or posterior fossa; except meningioma, cerebellopontine angle tumor, or midline tumor at base of skull
61520 Cerebellopontine angle tumor [Vestibular schwannoma surgery]
61521 Midline tumor at base of skull
61526 Craniectomy bone flap craniotomy, transtemporal (mastoid) for excision of cerebellopontine angle tumor [Vestibular schwannoma surgery]
61530 Combined with middle/posterior fossa craniotomy/craniectomy [Vestibular schwannoma surgery]
61591 Infratemporal post-auricular approach to middle cranial fossa (internal auditory meatus, petrous apex, tentorium, cavernous sinus, parasellar area, infratemporal fossa) including mastoidectomy, resection of sigmoid sinus, with or without decompression and/or mobilization of contents of auditory canal or petrous carotid artery
61595 Transtemporal approach to posterior cranial fossa, jugular foramen or midline skull base, including mastoidectomy, decompression of sigmoid sinus and/or facial nerve, with or without mobilization
61597 Transcondylar (far lateral) approach to posterior cranial fossa, jugular foramen or midline skull base, including occipital condylectomy, mastoidectomy, resection of C1-C3 vertebral body(s), decompression of vertebral artery, with or without mobilization
63185 Laminectomy with rhizotomy; 1 or 2 segments [selective dorsal rhizotomy]
63190 Laminectomy with rhizotomy; more than 2 segments [selective dorsal rhizotomy]
63200 Laminectomy, with release of tethered spinal cord, lumbar
63275 - 63290 Laminectomy for biopsy/excision of intraspinal neoplasm
64568 Incision for implantation of cranial nerve (eg, vagus nerve) neurostimulator electrode array and pulse generator
64713 Neuroplasty, major peripheral nerve, arm or leg, open; brachial plexus
64861 Suture of; brachial plexus
64885 Nerve graft (includes obtaining graft), head or neck; up to 4 cm in length [cross-facial nerve grafting]
64886 Nerve graft (includes obtaining graft), head or neck; more than 4 cm length [cross-facial nerve grafting]
69145 Excision soft tissue lesion, external auditory canal
69310 Reconstruction of external auditory canal (meatoplasty) (eg, for stenosis due to injury, infection) (separate procedure)
69320 Reconstruction external auditory canal for congenital atresia, single stage
69501 Transmastoid antrotomy (simple mastoidectomy)
69502 - 69511 Mastoidectomy
69530 Petrous apicectomy including radical mastoidectomy
69535 Resection temporal bone, external approach
69601 - 69605 Revision mastoidectomy
69635 - 69637 Tympanoplasty with antrotomy or mastoidotomy (including canalplasty, atticotomy, middle ear surgery, and/or tympanic membrane repair)
69641 - 69646 Tympanoplasty with mastoidectomy (including canalplasty, middle ear surgery, tympanic membrane repair)
69910 Labyrinthectomy; with mastoidectomy
69930 Cochlear device implantation, with or without mastoidectomy

CPT codes for surgery where intra-operative EMG is not covered for indications listed in the CPB:

Sural nerve grafting, decompression of peroneal (fibular) nerve, ossiculoplasty, supra-cerebellar infratentorial craniotomy, decompression of the jugular vein - no specific code:

0184T Excision of rectal tumor, transanal endoscopic microsurgical approach (ie, TEMS), including muscularis propria (ie, full thickness)
0213T Injection(s), diagnostic or therapeutic agent, paravertebral facet (zygapophyseal) joint (or nerves innervating that joint) with ultrasound guidance, cervical or thoracic; single level
+0214T     second level
+0215T     third and any additional level(s)
0216T Injection(s), diagnostic or therapeutic agent, paravertebral facet (zygapophyseal) joint (or nerves innervating that joint) with ultrasound guidance, lumbar or sacral; single level
+0217T     second level
+0218T     third and any additional level(s)
21010 - 21499 Surgery of skull, facial bones, and temporomandibular joint
21615 Excision first and/or cervical rib
21616 Excision first and/or cervical rib; with sympathectomy
21700 Division of scalenus anticus; without resection of cervical rib
21705 Division of scalenus anticus; with resection of cervical rib
22010 - 22865 Surgery of musculoskeletal system, spine (vertebral column)
23410 Repair of ruptured musculotendinous cuff (eg, rotator cuff) open; acute
23412 Repair of ruptured musculotendinous cuff (eg, rotator cuff) open; chronic
23420 Reconstruction of complete shoulder (rotator) cuff avulsion, chronic (includes acromioplasty)
23455 Capsulorrhaphy, anterior; with labral repair (eg, Bankart procedure)
26735 Open treatment of phalangeal shaft fracture, proximal or middle phalanx, finger or thumb, includes internal fixation, when performed, each
26765 Open treatment of distal phalangeal fracture, finger or thumb, includes internal fixation, when performed, each
27096 Injection procedure for sacroiliac joint, anesthetic/steroid, with image guidance (fluoroscopy or CT) including arthrography when performed
27130 Arthroplasty, acetabular and proximal femoral prosthetic replacement (total hip arthroplasty), with or without autograft or allograft
29827 Arthroscopy, shoulder, surgical; with rotator cuff repair
29840 Arthroscopy, wrist, diagnostic, with or without synovial biopsy (separate procedure)
29843 Arthroscopy, wrist, surgical; for infection, lavage and drainage
29844 Arthroscopy, wrist, surgical; synovectomy, partial
29845 Arthroscopy, wrist, surgical; synovectomy, complete
29847 Arthroscopy, wrist, surgical; internal fixation for fracture or instability
29866 – 29887 Arthroscopy, knee
31000 – 31299 Accessory sinuses surgery
33858 - 33877 Thoracic aortic aneurysm grafts
34701 - 34702 Endovascular repair of infrarenal aorta by deployment of an aorto-aortic tube endograft including pre-procedure sizing and device selection, all nonselective catheterization(s), all associated radiological supervision and interpretation, all endograft extension(s) placed in the aorta from the level of the renal arteries to the aortic bifurcation, and all angioplasty/stenting performed from the level of the renal arteries to the aortic bifurcation
34703 - 34706 Endovascular repair of infrarenal aorta and/or iliac artery(ies) by deployment of an aorto-uni-iliac endograft including pre-procedure sizing and device selection, all nonselective catheterization(s), all associated radiological supervision and interpretation, all endograft extension(s) placed in the aorta from the level of the renal arteries to the iliac bifurcation, and all angioplasty/stenting performed from the level of the renal arteries to the iliac bifurcation
34707 - 34708 Endovascular repair of iliac artery by deployment of an ilio-iliac tube endograft including pre-procedure sizing and device selection, all nonselective catheterization(s), all associated radiological supervision and interpretation, and all endograft extension(s) proximally to the aortic bifurcation and distally to the iliac bifurcation, and treatment zone angioplasty/stenting, when performed, unilateral
34709 Placement of extension prosthesis(es) distal to the common iliac artery(ies) or proximal to the renal artery(ies) for endovascular repair of infrarenal abdominal aortic or iliac aneurysm, false aneurysm, dissection, penetrating ulcer, including pre-procedure sizing and device selection, all nonselective catheterization(s), all associated radiological supervision and interpretation, and treatment zone angioplasty/stenting, when performed, per vessel treated (List separately in addition to code for primary procedure)
34710 - 34711 Delayed placement of distal or proximal extension prosthesis for endovascular repair of infrarenal abdominal aortic or iliac aneurysm, false aneurysm, dissection, endoleak, or endograft migration, including pre-procedure sizing and device selection, all nonselective catheterization(s), all associated radiological supervision and interpretation, and treatment zone angioplasty/stenting, when performed
34808 - 34834 Endovascular repair of abdominal aortic aneurysm
35301 Thromboendarterectomy, including patch graft, if performed; carotid, vertebral, subclavian, by neck incision
38500 Biopsy or excision of lymph node(s); open, superficial
38505 Biopsy or excision of lymph node(s); by needle, superficial (eg, cervical, inguinal, axillary)
38510     open, deep cervical node(s)
38520     open, deep cervical node(s) with excision scalene fat pad
38525     open, deep axillary node(s)
38530     open, internal mammary node(s)
38531     open, inguinofemoral node(s)
42300 - 42699 Surgery of salivary gland and ducts
42950 Pharyngoplasty (plastic or reconstructive operation on pharynx)
53850 Transurethral destruction of prostate tissue; by microwave thermotherapy
53852 Transurethral destruction of prostate tissue; by radiofrequency thermotherapy
55801 Prostatectomy, perineal, subtotal (including control of postoperative bleeding, vasectomy, meatotomy, urethral calibration and/or dilation, and internal urethrotomy).
55810 Prostatectomy, perineal radical
55812 Prostatectomy, perineal radical; with lymph node biopsy(s) (limited pelvic lymphadenectomy)
55815 Prostatectomy, perineal radical; with bilateral pelvic lymphadenectomy, including external iliac, hypogastric and obturator nodes
55821 Prostatectomy (including control of postoperative bleeding, vasectomy, meatotomy, urethral calibration and/or dilation, and internal urethrotomy); suprapubic, subtotal, 1 or 2 stages.
55831 Prostatectomy (including control of postoperative bleeding, vasectomy, meatotomy, urethral calibration and/or dilation, and internal urethrotomy); retropubic, subtotal
55840 Prostatectomy, retropubic radical, with or without nerve sparing
55842 Prostatectomy, retropubic radical, with or without nerve sparing; with lymph node biopsy(s) (limited pelvic lymphadenectomy)
55845 Prostatectomy, retropubic radical, with or without nerve sparing; with bilateral pelvic lymphadenectomy, including external iliac, hypogastric, and obturator nodes
55860 Exposure of prostate, any approach, for insertion of radioactive substance
55862 Exposure of prostate, any approach, for insertion of radioactive substance; with lymph node biopsy(s) (limited pelvic lymphadenectomy)
55865 Exposure of prostate, any approach, for insertion of radioactive substance; with bilateral pelvic lymphadenectomy, including external iliac, hypogastric and obturator nodes
55873 Cryosurgical ablation of the prostate (includes ultrasonic guidance and monitoring)
55875 Transperineal placement of needles or catheters into prostate for interstitial radioelement application, with or without cystoscopy
55876 Placement of interstitial device(s) for radiation therapy guidance (eg, fiducial markers, dosimeter), prostate (via needle, any approach), single or multiple
60000 Incision and drainage of thyroglossal duct cyst, infected
60100 Biopsy thyroid, percutaneous core needle
60200 Excision of cyst or adenoma of thyroid, or transection of isthmus
60280 Excision of thyroglossal duct cyst or sinus
60281     recurrent
60500 - 60505 Parathyroidectomy or exploration of parathyroid
60512 Parathyroid autotransplantation
61343 Craniectomy, suboccipital with cervical laminectomy for decompression of medulla and spinal cord, with or without dural graft (eg, Arnold-Chiari malformation)
61450 Craniectomy, subtemporal, for section, compression, or decompression of sensory root of gasserian ganglion [trigeminal nerve]
61458 Craniectomy, suboccipital; for exploration or decompression of cranial nerves [trigeminal nerve]
61460     for section of one or more cranial nerves [trigeminal nerve]
61519 Craniectomy for excision of brain tumor, infratentorial or posterior fossa; meningioma
61545 Craniotomy for excision of craniopharyngioma
61698 Surgery of complex intracranial aneurysm, intracranial approach; vertebrobasilar circulation
61702 Surgery of simple intracranial aneurysm, intracranial approach; vertebrobasilar circulation
61708 Surgery of aneurysm, vascular malformation or carotid-cavernous fistula; by intracranial electrothrombosis
61796 Stereotactic radiosurgery (particle beam, gamma ray, or linear accelerator); 1 simple cranial lesion [trigeminal nerve]
+61797     each additional cranial lesion, simple (List separately in addition to code for primary procedure) [trigeminal nerve]
61798     1 complex cranial lesion [trigeminal nerve]
+61799     each additional cranial lesion, complex (List separately in addition to code for primary procedure) [trigeminal nerve]
+61800 Application of stereotactic headframe for stereotactic radiosurgery (List separately in addition to code for primary procedure) [trigeminal nerve]
62164 Neuroendoscopy, intracranial; with excision of brain tumor, including placement of external ventricular catheter for drainage
62263 - 63182, 63191 - 63273, 63295 - 63746 Surgery of spine and spinal cord
64451 Injection(s), anesthetic agent(s) and/or steroid; nerves innervating the sacroiliac joint, with image guidance (ie, fluoroscopy or computed tomography)
64479 - 64484 Injection, anesthetic agent and/or steroid, transforaminal epidural with imaging guidance (fluoroscopy or CT)
64490 - 64495 Facet joint injections
64520 Injection, anesthetic agent; lumbar or thoracic (paravertebral sympathetic)
64530 Injection, anesthetic agent; celiac plexus, with or without radiologic monitoring
64561 Percutaneous implantation of neurostimulator electrode array; sacral nerve (transforaminal placement) including image guidance, if performed
64581 Incision for implantation of neurostimulator electrodes; sacral nerve (transforaminal placement)
64600 Destruction by neurolytic agent; trigeminal nerve; supraorbital, infraorbital, mental, or inferior alveolar branch
64605     second and third division branches at foramen ovale
64610     second and third division branches at foramen ovale under radiologic monitoring
64622 - 64627 Destruction by neurolytic agent, paravertebral facet joint nerve; lumbar or sacral; cervical or thoracic
64633 Destruction by neurolytic agent, paravertebral facet joint nerve(s) with imaging guidance (fluoroscopy CT); cervical or thoracic, single facet joint
64634     cervical or thoracic, each additional facet joint (List separately in addition to code for primary procedure)
64635     lumbar or sacral, single facet joint
64636      lumbar or sacral, each additional facet joint (List separately in addition to code for primary procedure)
64640 Destruction by neurolytic agent; other peripheral nerve or branch [genicular nerve]
64742 Transection or avulsion of; facial nerve, differential or complete [trigeminal nerve]
64772 Transection or avulsion of other spinal nerve, extradural
64861 Suture of; brachial plexus
69631 - 69633 Tympanoplasty without mastoidectomy
69660 - 69662 Stapedectomy or stapedotomy

Intra-operative somatosensory evoked potentials (SSEPs) performed either alone, or in combination with motor evoked potentials (MEPs):

CPT codes covered if selection criteria are met:

95925 Short-latency somatosensory evoked potential study, stimulation of any/all peripheral nerves or skin sites, recording from the central nervous system; in upper limbs
95926      in lower limbs
95927      in the trunk or head
95938      in upper and lower limbs

Intra-operative SSEP monitoring, with or without MEPs, may be appropriate for the following types of surgery (not all-inclusive):

CPT codes covered if selection criteria are met for intraoperative SEPs:

22210 - 22212, 22216 - 22222, 22226 Osteotomy of spine
22305 - 22319, 22326 - 22328 Treatment of fracture and/or dislocation of vertebrae
22513 Percutaneous vertebral augmentation, including cavity creation (fracture reduction and bone biopsy included when performed) using mechanical device (eg, kyphoplasty), 1 vertebral body, unilateral or bilateral cannulation, inclusive of all imaging guidance; thoracic
+22515      each additional thoracic or lumbar vertebral body (List separately in addition to code for primary procedure)
22532, 22534 - 22556, 22585, 22590 - 22610, 22614, 22800 - 22819 Arthrodesis [not covered for monitoring the femoral nerve during transpsoas lumbar lateral interbody fusion]
22840 - 22855 Spinal instrumentation
22856 Total disc arthroplasty (artificial disc), anterior approach, including discectomy with end plate preparation (includes osteophytectomy for nerve root or spinal cord decompression and microdissection); single interspace, cervical
+22858      second level, cervical (List separately in addition to code for primary procedure)
31200 - 31230 Ethmoidectomy and maxillectomy
33320 - 33335 Repair of aorta or great vessels
33400 - 33417 Aortic valve procedures
33800 - 33853 Aortic anomalies procedures
33860 - 33877 Thoracic aortic aneurysm repair
61000 - 61070 Injection, drainage, or aspiration of skull meninges, and brain
61105 - 61253 Twist drill, burr hole(s), or trephine
61304 - 61576 Craniectomy or craniotomy
61600 - 61616 Definitive procedures of skull base
61618 - 61619 Repair and/or reconstruction of surgical defects of skull base
61623 - 61626 Endovascular therapy
61680 - 61711 Surgery for aneurysm, arteriovenous malformation or vascular disease
61720 - 61791 Stereotaxis, intracranial
61850 - 61888 Neurostimulators (intracranial)
62000 - 62148 Repair of skull
62160 - 62165 Neuroendoscopy
62263 - 62280, 62284 - 62327 Injection, drainage, or aspiration of spine and spinal cord
63001 - 63003, 63015 - 63016, 63020, 63035 - 63040, 63043, 63045 - 63046, 63048 - 63055, 63057 - 63101, 63103 Exploration/decompression of spinal cord
63170 - 63199, 63250 - 63266, 63268, 63270 - 63271, 63273, 63275 - 63276, 63278, 63280 - 63281, 63283, 63285 - 63302, 63304 - 63306, 63308 Incision/excision intraspinal
63200 Laminectomy, with release of tethered spinal cord, lumbar
63600 - 63615 Stereotaxis, spinal
63700 - 63710 Repair (spinal)
64716 Neuroplasty and/or transposition; cranial nerve (specify)
67570 Optic nerve decompression (e.g., incision or fenestration of optic nerve sheath)
69666 Repair of oval window fistula
69667 Repair of round window fistula
69720 Decompression facial nerve, intratemporal; lateral to geniculate ganglion
69725      including medial to geniculate ganglion
69740 Suture facial nerve, intratemporal, with or without graft or decompression; lateral to geniculate ganglion
69745     including medial to geniculate ganglion
69805 Endolymphatic sac operation; without shunt
69806     with shunt
69915 Vestibular nerve section, translabyrinthine approach
69950 Vestibular nerve section, transcranial approach
69955 Total facial nerve decompression and/or repair (may include graft)
99173 Screening test of visual acuity, quantitative, bilateral

CPT codes not covered for indications listed in the CPB for intraoperative SSEPs:

Implantation or removal of vertical expandable prosthetic titanium rib (VEPTR) - no specific code
0213T Injection(s), diagnostic or therapeutic agent, paravertebral facet (zygapophyseal) joint (or nerves innervating that joint) with ultrasound guidance, cervical or thoracic; single level
+0214T      second level
+0215T      third and any additional level(s)
0216T Injection(s), diagnostic or therapeutic agent, paravertebral facet (zygapophyseal) joint (or nerves innervating that joint) with ultrasound guidance, lumbar or sacral; single level
+0217T      second level
+0218T      third and any additional level(s)
0309T Arthrodesis, pre-sacral interbody technique, including disc space preparation, discectomy, with posterior instrumentation, with image guidance, includes bone graft, when performed, lumber, L4-L5 interspace (List separately in addition to code for primary procedure)
11646 Excision, malignant lesion including margins, face, ears, eyelids, nose, lips; excised diameter over 4.0 cm
13132 Repair, complex, forehead, cheeks, chin, mouth, neck, axillae, genitalia, hands and/or feet; 2.6 cm to 7.5 cm
14060 Adjacent tissue transfer or rearrangement, eyelids, nose, ears and/or lips; defect 10 sq cm or less
15100 Split-thickness autograft, trunk, arms, legs; first 100 sq cm or less, or 1% of body area of infants and children (except 15050)
15120 Split-thickness autograft, face, scalp, eyelids, mouth, neck, ears, orbits, genitalia, hands, feet, and/or multiple digits; first 100 sq cm or less, or 1% of body area of infants and children (except 15050)
15260 Full thickness graft, free, including direct closure of donor site, nose, ears, eyelids, and/or lips; 20 sq cm or less
15275 Application of skin substitute graft to face, scalp, eyelids, mouth, neck, ears, orbits, genitalia, hands, feet, and/or multiple digits, total wound surface area up to 100 sq cm; first 25 sq cm or less wound surface area
15732 Muscle, myocutaneous, or fasciocutaneous flap; head and neck (eg, temporalis, masseter muscle, sternocleidomastoid, levator scapulae)
15760 Graft; composite (eg, full thickness of external ear or nasal ala), including primary closure, donor area
15769 Grafting of autologous soft tissue, other, harvested by direct excision (eg, fat, dermis, fascia)
15770 Graft; derma-fat-fascia
15771 Grafting of autologous fat harvested by liposuction technique to trunk, breasts, scalp, arms, and/or legs; 50 cc or less injectate
+15772     each additional 50 cc injectate, or part thereof (List separately in addition to code for primary procedure)
15773 Grafting of autologous fat harvested by liposuction technique to face, eyelids, mouth, neck, ears, orbits, genitalia, hands, and/or feet; 25 cc or less injectate
+15774      each additional 25 cc injectate, or part thereof (List separately in addition to code for primary procedure)
20552 Injection(s); single or multiple trigger point(s), 1 or 2 muscle(s)
20553      single or multiple trigger point(s), 3 or more muscles
20680 Removal of implant; deep (eg, buried wire, pin, screw, metal band, nail, rod or plate)
20900 Bone graft, any donor area; minor or small (eg, dowel or button)
20926 Tissue grafts, other (eg, paratenon, fat, dermis)
+20985 Computer-assisted surgical navigational procedure for musculoskeletal procedures, image-less (List separately in addition to code for primary procedure)
21235 Graft; ear cartilage, autogenous, to nose or ear (includes obtaining graft)
21554 Excision, tumor, soft tissue of neck or anterior thorax, subfascial (eg, intramuscular); 5 cm or greater
21556 Excision, tumor, soft tissue of neck or anterior thorax, subfascial (eg, intramuscular); less than 5 cm
21600 Excision of rib, partial
21700 Division of scalenus anticus; without resection of cervical rib
21705      with resection of cervical rib [for correction of thoracic outlet syndrome]
22214 Osteotomy of spine, posterior or posterolateral approach, 1 vertebral segment; lumbar
22224 Osteotomy of spine, including discectomy, anterior approach, single vertebral segment; lumbar
22325 Open treatment and/or reduction of vertebral fracture(s) and/or dislocation(s), posterior approach, 1 fractured vertebra or dislocated segment; lumbar
22514 Percutaneous vertebral augmentation, including cavity creation (fracture reduction and bone biopsy included when performed) using mechanical device (eg, kyphoplasty), 1 vertebral body, unilateral or bilateral cannulation, inclusive of all imaging guidance; lumbar
22533 Arthrodesis, lateral extracavitary technique, including minimal discectomy to prepare interspace (other than for decompression); lumbar
22558 Arthrodesis, anterior interbody technique, including minimal discectomy to prepare interspace (other than for decompression); lumbar
22586 Arthrodesis, pre-sacral interbody technique, including disc space preparation, discectomy, with posterior instrumentation, with image guidance, includes bone graft when performed, L5-S1 interspace
22612 Arthrodesis, posterior or posterolateral technique, single level; lumbar (with lateral transverse technique, when performed)
22630 Arthrodesis, posterior interbody technique, including laminectomy and/or discectomy to prepare interspace (other than for decompression), single interspace; lumbar
+22632      each additional interspace (List separately in addition to code for primary procedure)
22633 Arthrodesis, combined posterior or posterolateral technique with posterior interbody technique including laminectomy and/or discectomy sufficient to prepare interspace (other than for decompression), single interspace and segment; lumbar
+22634      each additional interspace and segment (List separately in addition to code for primary procedure)
22899 Unlisted procedure, spine
23000 - 23921 Shoulder Surgery
26715 Open treatment of metacarpophalangeal dislocation, single, includes internal fixation, when performed
26735 Open treatment of phalangeal shaft fracture, proximal or middle phalanx, finger or thumb, includes internal fixation, when performed, each
26746 Open treatment of articular fracture, involving metacarpophalangeal or interphalangeal joint, includes internal fixation, when performed, each
26765 Open treatment of distal phalangeal fracture, finger or thumb, includes internal fixation, when performed, each
26785 Open treatment of interphalangeal joint dislocation, includes internal fixation, when performed, single
27130 - 27138 Total hip arthroplasty (includes conversion and revision to previous surgery)
27161 Osteotomy, femoral neck (separate procedure)
27227 Open treatment of acetabular fracture(s) involving anterior or posterior (one) column, or a fracture running transversely across the acetabulum, with internal fixation
27228 Open treatment of acetabular fracture(s) involving anterior and posterior (two) columns, includes T-fracture and both column fracture with complete articular detachment, or single column or transverse fracture with associated acetabular wall fracture, with internal fixation
27279 Arthrodesis, sacroiliac joint, percutaneous or minimally invasive (indirect visualization), with image guidance, includes obtaining bone graft when performed, and placement of transfixing device
27280 Arthrodesis, open, sacroiliac joint, including obtaining bone graft, including instrumentation, when performed
27360 Partial excision (craterization, saucerization, or diaphysectomy) bone, femur, proximal tibia and/or fibula (eg, osteomyelitis or bone abscess)
27437 Arthroplasty, patella; without prosthesis
27443 Arthroplasty, femoral condyles or tibial plateau(s), knee; with debridement and partial synovectomy
27446 Arthroplasty, knee, condyle and plateau; medial OR lateral compartment
27447      medial AND lateral compartments with or without patella resurfacing (total knee arthroplasty)
27448 Osteotomy, femur, shaft or supracondylar; without fixation
27450     with fixation
27454 Osteotomy, multiple, with realignment on intramedullary rod, femoral shaft (eg, Sofield type procedure)
27455 Osteotomy, proximal tibia, including fibular excision or osteotomy (includes correction of genu varus [bowleg] or genu valgus [knock-knee]); before epiphyseal closure
27457     after epiphyseal closure
27705 Osteotomy; tibia
27707      fibula
27709      tibia and fibula
29805 - 29828 Shoulder arthroscopy
29843 - 29847 Wrist arthroscopy repair
29848 Endoscopy, wrist, surgical, with release of transverse carpal ligament
29914 Arthroscopy, hip, surgical; with femoroplasty (ie, treatment of cam lesion)
29915      with acetabuloplasty (ie, treatment of pincer lesion)
29916 Arthroscopy, hip, surgical; with labral repair
29999 Unlisted procedure, arthroscopy
31525 Laryngoscopy direct, with or without tracheoscopy; diagnostic, except newborn
31536 Laryngoscopy, direct, operative, with biopsy; with operating microscope or telescope
31575 Laryngoscopy, flexible fiberoptic; diagnostic
31610 Tracheostomy, fenestration procedure with skin flaps
31622 Bronchoscopy, rigid or flexible, including fluoroscopic guidance, when performed; diagnostic, with cell washing, when performed (separate procedure)
33510 - 33548 Coronary artery bypass surgery
35301 Thromboendarterectomy, including patch graft, if performed; carotid, vertebral, subclavian, by neck incision
36556 Insertion of non-tunneled centrally inserted central venous catheter; age 5 years or older
37799 Unlisted procedure, vascular surgery
38500 - 38531 Biopsy or excision of lymph node(s)
38720 Cervical lymphadenectomy (complete)
38724 Cervical lymphadenectomy (modified radical neck dissection)
41120 Glossectomy; less than one-half tongue
42410 - 42426 Excision of parotid tumor or parotid gland
42440 Excision of submandibular (submaxillary) gland
43130 Diverticulectomy of hypopharynx or esophagus, with or without myotomy; cervical approach
43135      thoracic approach
43180 Esophagoscopy, rigid, transoral with diverticulectomy of hypopharynx or cervical esophagus (eg, Zenker's diverticulum), with cricopharyngeal myotomy, includes use of telescope or operating microscope and repair, when performed
43191 Esophagoscopy, rigid, transoral; diagnostic, including collection of specimen(s) by brushing or washing when performed (separate procedure)
49215 Excision of presacral or sacrococcygeal tumor
51785 Needle electromyography studies (EMG) of anal or urethral sphincter, any technique
60000 - 60512 Thyroid and parathyroid surgery
60699 Unlisted procedure, endocrine system
61450 Craniectomy, subtemporal, for section, compression, or decompression of sensory root of gasserian ganglion
61458 Craniectomy, suboccipital; for exploration or decompression of cranial nerves
61460      for section of 1 or more cranial nerves
61546      for section of 1 or more cranial nerves
61548 Craniectomy, suboccipital; for exploration or decompression of cranial nerves
61460      for section of 1 or more cranial nerves
61546 Craniotomy for hypophyesctomy or excision of pituitary tumor, intracranial approach
61548 Hypophyesctomy or excision of pituitary tumor, transnasal or transseptal approach, nonsterotatic
61796 Stereotactic radiosurgery (particle beam, gamma ray, or linear accelerator); 1 simple cranial lesion
+61797 each additional cranial lesion, simple (List separately in addition to code for primary procedure)
61798 Stereotactic radiosurgery (particle beam, gamma ray, or linear accelerator); 1 complex cranial lesion
+61799      each additional cranial lesion, complex (List separately in addition to code for primary procedure)
+61800 Application of stereotactic headframe for stereotactic radiosurgery (List separately in addition to code for primary procedure)
62100 Craniotomy for repair of dural/cerebrospinal fluid leak, including surgery for rhinorrhea/otorrhea
62165 Neuroendoscopy, intracranial; with excision of pituitary tumor, transnasal or trans-sphenoidal approach
62281 Injection/infusion of neurolytic substance (eg, alcohol, phenol, iced saline solutions), with or without other therapeutic substance; epidural, cervical or thoracic
62282      epidural, lumbar, sacral (caudal)
62320 - 62327 lnterlaminar epidural injections
63005 Laminectomy with exploration and/or decompression of spinal cord and/or cauda equina, without facetectomy, foraminotomy or discectomy (eg, spinal stenosis), 1 or 2 vertebral segments; lumbar, except for spondylolisthesis
63011     sacral
63012 Laminectomy with removal of abnormal facets and/or pars inter-articularis with decompression of cauda equina and nerve roots for spondylolisthesis, lumbar (Gill type procedure)
63017 Laminectomy with exploration and/or decompression of spinal cord and/or cauda equina, without facetectomy, foraminotomy or discectomy (eg, spinal stenosis), more than 2 vertebral segments; lumbar
63030 Laminotomy (hemilaminectomy), with decompression of nerve root(s), including partial facetectomy, foraminotomy and/or excision of herniated intervertebral disc; 1 interspace, lumbar
63042 Laminotomy (hemilaminectomy), with decompression of nerve root(s), including partial facetectomy, foraminotomy and/or excision of herniated intervertebral disc, reexploration, single interspace; lumbar
+63044      each additional lumbar interspace (List separately in addition to code for primary procedure)
63047 Laminectomy, facetectomy and foraminotomy (unilateral or bilateral with decompression of spinal cord, cauda equina and/or nerve root[s], [eg, spinal or lateral recess stenosis]), single vertebral segment; lumbar
63052 Laminectomy, facetectomy, or foraminotomy (unilateral or bilateral with decompression of spinal cord, cauda equina and/or nerve root[s] [eg, spinal or lateral recess stenosis]), during posterior interbody arthrodesis, lumbar; single vertebral segment (List separately in addition to code for primary procedure)
63056 Transpedicular approach with decompression of spinal cord, equina and/or nerve root(s) (eg, herniated intervertebral disc), single segment; lumbar (including transfacet, or lateral extraforaminal approach) (eg, far lateral herniated intervertebral disc)
63102 Vertebral corpectomy (vertebral body resection), partial or complete, lateral extracavitary approach with decompression of spinal cord and/or nerve root(s) (eg, for tumor or retropulsed bone fragments); lumbar, single segment
63267 Laminectomy for excision or evacuation of intraspinal lesion other than neoplasm, extradural; lumbar
63268      sacral
63272 Laminectomy for excision of intraspinal lesion other than neoplasm, intradural; lumbar
63273      sacral
63277 Laminectomy for biopsy/excision of intraspinal neoplasm; extradural, lumbar
63278     extradural, sacral
63282      intradural, extramedullary, lumbar
63283      intradural, sacral
63303 Vertebral corpectomy (vertebral body resection), partial or complete, for excision of intraspinal lesion, single segment; extradural, lumbar or sacral by transperitoneal or retroperitoneal approach
63307      intradural, lumbar or sacral by transperitoneal or retroperitoneal approach
63650 Percutaneous implantation of neurostimulator electrode array, epidural
63655 Laminectomy for implantation of neurostimulator electrodes, plate/paddle, epidural
63661 Removal of spinal neurostimulator electrode percutaneous array(s), including fluoroscopy, when performed
63662 Removal of spinal neurostimulator electrode plate/paddle(s) placed via laminotomy or laminectomy, including fluoroscopy, when performed
63664 Revision including replacement, when performed, of spinal neurostimulator electrode plate/paddle(s) placed via laminotomy or laminectomy, including fluoroscopy, when performed
63685 Insertion or replacement of spinal neurostimulator pulse generator or receiver, direct or inductive coupling
63688 Revision or removal of implanted spinal neurostimulator pulse generator or receiver
64479 - 64484 Transforaminal injections
64490 Injection(s), diagnostic or therapeutic agent, paravertebral facet (zygapophyseal) joint (or nerves innervating that joint) with image guidance (fluoroscopy or CT), cervical or thoracic; single level
64491      second level
64492      third and any additional level(s) level
64493 Injection(s), diagnostic or therapeutic agent, paravertebral facet (zygapophyseal) joint (or nerves innervating that joint) with image guidance (fluoroscopy or CT), lumbar or sacral; single level
64494      second level
64495      third and any additional level(s) level
64553 Percutaneous implantation of neurostimulator electrode array; cranial nerve
64568 Incision for implantation of cranial nerve (eg, vagus nerve) neurostimulator electrode array and pulse generator
64569 Revision or replacement of cranial nerve (eg, vagus nerve) neurostimulator electrode array, including connection to existing pulse generator
64580 Incision for implantation of neurostimulator electrode array; neuromuscular
64600 Destruction by neurolytic agent, trigeminal nerve; supraorbital, infraorbital, mental, or inferior alveolar branch
64605      second and third division branches at foramen ovale
64610      second and third division branches at foramen ovale under radiologic monitoring
64633 Destruction by neurolytic agent, paravertebral facet joint nerve(s), with imaging guidance (fluoroscopy or CT); cervical or thoracic, single facet joint
+64634      each additional facet joint (List separately in addition to code for primary procedure)
64640 Destruction by neurolytic agent; other peripheral nerve or branch
64708 Neuroplasty, major peripheral nerve, arm or leg, open; other than specified
64713      brachial plexus
64718 Neuroplasty and/or transposition; ulnar nerve at elbow
64721      median nerve at carpal tunnel
+64727 Internal neurolysis, requiring use of operating microscope (List separately in addition to code for neuroplasty) (Neuroplasty includes external neurolysis)
64742 Transection or avulsion of; facial nerve, differential or complete
64784 Excision of neuroma; major peripheral nerve, except sciatic
64786      sciatic nerve
64790 Excision of neurofibroma or neurolemmoma; major peripheral nerve
64795 Biopsy of nerve
64886 Nerve graft (includes obtaining graft), head or neck; more than 4 cm length
64905 Nerve pedicle transfer; first stage
64886 Nerve graft (includes obtaining graft), head or neck; more than 4 cm length
64905 Nerve pedicle transfer; first stage
64912 Nerve repair; with nerve allograft, each nerve, first strand (cable)
64913      with nerve allograft, each additional strand (List separately in addition to code for primary procedure)
64999 Unlisted procedure, nervous system
69140 Excision exostosis(es), external auditory canal
69145 Excision soft tissue lesion, external auditory canal
69310 Reconstruction of external auditory canal (meatoplasty) (eg, for stenosis due to injury, infection) (separate procedure)
69320 Reconstruction external auditory canal for congenital atresia, single stage
69436 Tympanostomy (requiring insertion of ventilating tube), general anesthesia
69440 Middle ear exploration through postauricular or ear canal incision
69501 - 69511 Mastoidectomy
69530 Petrous apicectomy including radical mastoidectomy
69535 Resection temporal bone, external approach
69540 Excision aural polyp
69550 Excision aural glomus tumor; transcanal
69552      transmastoid
69554      extended (extratemporal)
69620 Myringoplasty (surgery confined to drumhead and donor area)
69631 Tympanoplasty without mastoidectomy (including canalplasty, atticotomy and/or middle ear surgery), initial or revision; without ossicular chain reconstruction
69632      with ossicular chain reconstruction (eg, postfenestration)
69633      with ossicular chain reconstruction and synthetic prosthesis (eg, partial ossicular replacement prosthesis [PORP], total ossicular replacement prosthesis [TORP])
69635 Tympanoplasty with antrotomy or mastoidotomy (including canalplasty, atticotomy, middle ear surgery, and/or tympanic membrane repair); without ossicular chain reconstruction
69636      with ossicular chain reconstruction
69637      with ossicular chain reconstruction and synthetic prosthesis (eg, partial ossicular replacement prosthesis [PORP], total ossicular replacement prosthesis [TORP])
69641 Tympanoplasty with mastoidectomy (including canalplasty, middle ear surgery, tympanic membrane repair); without ossicular chain reconstruction
69642      with ossicular chain reconstruction
69643      with intact or reconstructed wall, without ossicular chain reconstruction
69644      with intact or reconstructed canal wall, with ossicular chain reconstruction
69645      radical or complete, without ossicular chain reconstruction
69646      radical or complete, with ossicular chain reconstruction
69650 Stapes mobilization
69660 Stapedectomy or stapedotomy with reestablishment of ossicular continuity, with or without use of foreign material;
69661      with footplate drill out
69662 Revision of stapedectomy or stapedotomy
69930 Cochlear device implantation, with or without mastoidectomy

Other CPT codes related to the CPB:

+34717 Endovascular repair of iliac artery at the time of aorto-iliac artery endograft placement by deployment of an iliac branched endograft including pre-procedure sizing and device selection, all ipsilateral selective iliac artery catheterization(s), all associated radiological supervision and interpretation, and all endograft extension(s) proximally to the aortic bifurcation and distally in the internal iliac, external iliac, and common femoral artery(ies), and treatment zone angioplasty/stenting, when performed, for rupture or other than rupture (eg, for aneurysm, pseudoaneurysm, dissection, arteriovenous malformation, penetrating ulcer, traumatic disruption), unilateral (List separately in addition to code for primary procedure)
+34718 Endovascular repair of iliac artery, not associated with placement of an aorto-iliac artery endograft at the same session, by deployment of an iliac branched endograft, including pre-procedure sizing and device selection, all ipsilateral selective iliac artery catheterization(s), all associated radiological supervision and interpretation, and all endograft extension(s) proximally to the aortic bifurcation and distally in the internal iliac, external iliac, and common femoral artery(ies), and treatment zone angioplasty/stenting, when performed, for other than rupture (eg, for aneurysm, pseudoaneurysm, dissection, arteriovenous malformation, penetrating ulcer), unilateral

HCPCS codes not covered for indications listed in the CPB:

C7555 Thyroidectomy, total or complete with parathyroid autotransplantation
G0259 Injection procedure for sacroiliac joint; arthrography
G0260      provision of anesthetic, steroid and/or other therapeutic agent, with or without arthrography
S2348 Decompression procedure, percutaneous, of nucleus pulposus of intervertebral disc, using radiofrequency energy, single or multiple levels, lumbar
S2350 - S2351 Diskectomy, anterior, with decompression of spinal cord and/or nerve root(s), including osteophytectomy; lumbar, single interspace or each additional interspace (list separately in addition to code for primary procedure)

Other HCPCS codes related to the CPB:

S8040 Topographic brain mapping

ICD-10 codes covered if selection criteria are met for intraoperative SEPs:

C41.0 Malignant neoplasm of bones of skull and face [except mandible]
C41.2 Malignant neoplasm of vertebral column [excluding sacrum and coccyx]
C41.4 Malignant neoplasm of pelvic bones, sacrum, and coccyx
C70.0 - C70.9, C72.0 - C72.9 Malignant neoplasm of cranial nerves, cerebral meninges, spinal cord, and spinal meninges
C71.0 - C71.9 Malignant neoplasm of brain
C79.31, C79.49 Secondary malignant neoplasm of brain and other parts of nervous system [spinal cord]
C79.32 Secondary malignant neoplasm of cerebral meninges
D16.6 Benign neoplasm of vertebral column [excluding sacrum and coccyx]
D16.8 Benign neoplasm of pelvic bones, sacrum, and coccyx
D32.0 - D33.4 Benign neoplasm of brain, cranial nerves, cerebral meninges, spinal cord, and spinal meninges
D42.0 - D43.2, D43.4 Neoplasm of uncertain behavior of brain and spinal cord, or meninges
D49.6 Neoplasm of unspecified behavior of brain
G10 Huntington's disease
G23.0 - G26 Extrapyramidal and movement disorders [intractable]
G40.001 - G40.919 Epilepsy [resection of brain tissue or tumor]
G50.8 Disorders of trigeminal nerve [compression]
G51.8 Other disorders of facial nerve [compression]
G93.5 Compression of brain
G93.6 Cerebral edema
H47.091 - H47.099 Other disorders of optic nerve, not elsewhere classified [compression]
H81.01 - H81.09 Meniere's disease [endolymphatic shunt placement]
H81.391 - H81.399 Other and unspecified peripheral vertigo [vestibular resection]
H81.41 - H81.49 Vertigo of central origin [vestibular resection]
H93.3x1 - H93.3x9 Disorders of acoustic nerve [compression]
I06.0 - I06.9 Diseases of aortic valve
I35.0 - I35.9 Nonrheumatic aortic valve disorders
I70.0 Atherosclerosis of aorta
I71.00 - I71.9 Dissection of aorta
I72.0 Aneurysm of carotid artery (common) (external) (internal, extracranial portion)
I74.01 - I74.09 Embolism and thrombosis of abdominal aorta
I74.11 Embolism and thrombosis of thoracic aorta
I77.71 Dissection of carotid artery
M41.00 - M41.05, M41.112 - M41.115, M41.122 - M41.125, M41.26 - M41.27, M41.30 - M41.35, M41.82 - M41.85, M96.5 Idiopathic and thoracogenic scoliosis and kyphoscoliosis [correction involving traction] [cervical, thoracic, thoracolumbar]
M41.41 - M41.45, M41.52 - M41.55 Neuromuscular and other secondary scoliosis [correction involving traction] [cervical, thoracic, thoracolumbar]
M47.14 - M47.15 Other spondylosis with myelopathy, thoracic and thoracolumbar region
M50.00 - M50.03, M51.04 - M51.05 Intervertebral disc disorder, with myelopathy
M96.1 Postlaminectomy syndrome, not elsewhere classified
P91.0 - P91.1, P91.3 - P91.5 Other disturbances of cerebral status of newborn
Q01.0- Q01.9 Encephalocele
Q04.0 - Q04.3 Congenital reduction deformities of brain
Q07.00 - Q07.03 Arnold-Chiari syndrome
Q28.2 Arteriovenous malformation of cerebral vessels
Q28.8 Other specified congenital malformations of circulatory system [arteriovenous malformation spine]
Q65.89 Other specified congenital deformities of hip
Q67.5, Q76.3, Q76.425 - Q76.429 Congenital musculoskeletal deformities of spine [correction involving traction]
R25.0 - R25.9 Abnormal involuntary movements [intractable movement disorder]
R40.20 - R40.236 Coma [unconscious]
R42 Dizziness and giddiness [vertigo NOS]
R56.9 Unspecified convulsions [resection of brain tissue or tumor]
S02.0xx+ - S02.42x+, S02.600+ - S02.92x+ Fracture of skull and facial bones [conscious]
S06.0X0A - S06.A1XS Intracranial injury
S12.000+ - S12.9xx+, S22.000+ - S22.089+, S32.000+ - S32.2xx+ Fracture of vertebral column
S14.0xx+ - S14.159+, S24.0xx+ - S24.159+, S34.01x+ - S34.139+ Spinal cord injury
T84.010+ - T84.59x+ Complication of internal orthopedic prosthetic devices, implants, and grafts
T84.50x+ - T84.7xx+ Infection and inflammatory reaction due to other internal orthopedic device, implant, and graft
T84.81x+ - T84.9xx+ Other specified complications of internal orthopedic devices, implants, and grafts
Z47.2, Z51.89 Aftercare involving internal fixation device

ICD-10 codes not covered for indications listed in the CPB for intraoperative SEPs:

C07 Malignant neoplasm of parotid gland
C08.0 Malignant neoplasm of submandibular gland
C76.0 Malignant neoplasm of head, face, and neck
D00.0 - D00.08 Carcinoma in situ of lip, oral cavity, and pharynx
D11.0 - D11.9 Benign neoplasm of major salivary glands
D37.030 - D37.039 Neoplasm of uncertain behavior of major salivary glands
D49.0 Neoplasm of unspecified behavior of digestive system
E00.0 - E07.9 Disorders of the thyroid gland
K11.0 - K11.9 Diseases of the salivary glands
M41.06 - M41.08, M41.116 - M41.119, M41.126 - M41.129, M41.20, M41.26 - M41.27, M41.80, M41, 86 - M41.87 Idiopathic scoliosis [lumbar, sacral, unspecified]
M41.40, M41.46 - M41.47, M41.50, M41.56 - M41.57 Neuromuscular and other secondary scoliosis [lumbar, sacral, unspecified]
M43.26 - M43.28 Fusion of spine, lumbar, lumbosacral, sacral or sacrococcygeal region
M47.16 Other spondylosis with myelopathy, lumbar region
M47.26 - M47.28 Other spondylosis with radiculopathy, lumbar, lumbosacral, sacral or sacrococcygeal region
M47.816 - M47.818 Spondylosis without myelopathy or radiculopathy, lumbar, lumbosacral, sacral, or sacrococcygeal region
M47.896 - M47.898 Other spondylosis, lumbar, lumbosacral, sacral or sacrococcygeal region
M51.06 Intervertebral disc disorder with myelopathy, lumbar region
M51.16 - M51.17 Intervertebral disc disorders with radiculopathy, lumbar or lumbosacral region
M51.26 - M51.27 Other intervertebral disc displacement, lumbar or lumbosacral region
M51.36 - M51.37 Other intervertebral disc degeneration, lumbar or lumbosacral region
M51.86 - M51.9 Other and unspecified intervertebral disc disorders, lumbar, lumbosacral, sacral or sacrococcygeal region
M53.2X6 - M53.2X9 Spinal instabilities, lumbar, lumbosacral, sacral or sacrococcygeal region
M53.3 Sacrococcygeal disorders, not elsewhere classified
M53.86 - M53.9 Other specified and unspecified dorsopathies, lumbar, lumbosacral, sacral or sacrococcygeal region
M54.05 Low back pain
M54.16 - M54.18 Radiculopathy, lumbar, lumbosacral, sacral or sacrococcygeal region
N35.010 - N35.92, N99.110 - N99.12 Urethral stricture
N40.0 - N40.1 Enlarged prostate
N40.2 - N40.3 Nodular prostate
Q67.6 Pectus excavatum

Intra-operative brain stem auditory evoked response (BAER) monitoring:

CPT codes covered if selection criteria are met:

92650 Auditory evoked potentials; screening of auditory potential with broadband stimuli, automated analysis
92651      for hearing status determination, broadband stimuli, with interpretation and report
92652      for threshold estimation at multiple frequencies, with interpretation and report
92653      neurodiagnostic, with interpretation and report

Intra-operative brain stem auditory evoked response (BAER) monitoring may be appropriate for the following types of surgery:

CPT codes covered if selection criteria are met:

22100 Partial excision of posterior vertebral component (eg, spinous process, lamina or facet) for intrinsic bony lesion, single vertebral segment; cervical
+22103      each additional segment (List separately in addition to code for primary procedure)
22110 Partial excision of vertebral body, for intrinsic bony lesion, without decompression of spinal cord or nerve root(s), single vertebral segment; cervical
+22116      each additional vertebral segment (List separately in addition to code for primary procedure)
22210 Osteotomy of spine, posterior or posterolateral approach, 1 vertebral segment; cervical
+22216      each additional vertebral segment (List separately in addition to code for primary procedure)
22220 Osteotomy of spine, including discectomy, anterior approach, single vertebral segment; cervical
+22226      each additional vertebral segment (List separately in addition to code for primary procedure)
22548 Arthrodesis, anterior transoral or extraoral technique, clivus-C1-C2 (atlas-axis), with or without excision of odontoid process
61343 Craniectomy, suboccipital with cervical laminectomy for decompression of medulla and spinal cord, with or without dural graft (eg, Arnold-Chiari malformation)
61575 Transoral approach to skull base, brain stem or upper spinal cord for biopsy, decompression or excision of lesion
61576      requiring splitting of tongue and/or mandible (including tracheostomy)
62164 Neuroendoscopy, intracranial; with excision of brain tumor, including placement of external ventricular catheter for drainage
62165      with excision of pituitary tumor, transnasal or trans-sphenoidal approach
63001 Laminectomy with exploration and/or decompression of spinal cord and/or cauda equina, without facetectomy, foraminotomy or discectomy, (eg, spinal stenosis), one or two vertebral segments; cervical

ICD-10 codes covered if selection criteria are met:

C41.0 Malignant neoplasm of bones of skull and face
C41.2 Malignant neoplasm of vertebral column
C71.7 Malignant neoplasm of brain stem
C72.0 Malignant neoplasm of spinal cord
Q75.0 - Q75.9 Other congenital malformations of skull and face bones

Brain stem auditory evoked response (BAER) monitoring, may not be appropriate for the following types of surgery:

CPT codes not covered for indications listed in the CPB:

61531 Subdural implantation of strip electrodes through 1 or more burr or trephine hole(s) for long-term seizure monitoring
61533 Craniotomy with elevation of bone flap; for subdural implantation of an electrode array, for long-term seizure monitoring
69930 Cochlear device implantation, with or without mastoidectomy

Motor evoked potentials not covered intraoperatively:

CPT codes not covered for indications listed in the CPB:

95928 Central motor evoked potential study (transcranial motor stimulation); upper limbs
95929      lower limbs
95939      in upper and lower limbs

Surgical procedures where motor evoked potentials are not covered for indications listed in the CPB:

CPT codes not covered for indications listed in the CPB:

63650 Percutaneous implantation of neurostimulator electrode array, epidural
63655 Laminectomy for implantation of neurostimulator electrodes, plate/paddle, epidural
63663 Revision including replacement, when performed, of spinal neurostimulator electrode percutaneous array(s), including fluoroscopy, when performed
63664 Revision including replacement, when performed, of spinal neurostimulator electrode plate/paddle(s) placed via laminotomy or laminectomy, including fluoroscopy, when performed
63685 Insertion or replacement of spinal neurostimulator pulse generator or receiver, direct or inductive coupling
63688 Revision or removal of implanted spinal neurostimulator pulse generator or receiver
92517 Vestibular evoked myogenic potential (VEMP) testing, with interpretation and report; cervical (cVEMP)
92519      cervical (cVEMP) and ocular (oVEMP)

ICD-10 codes not covered for indications listed in the CPB:

G43.801 - G43.819 Other migraine [vestibular migraine]
H81.01 - H81.09 Meniere's disease
H81.10 - H81.13 Benign paroxysmal vertigo
H81.20 - H81.23 Vestibular neuronitis

Background

Intraoperative neurophysiological monitoring (IONM) modalities are available to assess the function of the brain, brainstem, spinal cord, cranial nerves, and peripheral nerves in order to avoid permanent neurologic injury during surgical procedures. These modalities include: evoked potentials including somatosensory evoked potential (SSEP), motor evoked potential (MEP), brainstem auditory evoked potential (BAEP), visual evoked potential (VEP), electroencephalography (EEG), and electromyography (EMG) (Ghatol and Widrich, 2022). This CPB addresses intraoperative EMG, SSEP, MEP, and BAER. For additional information on evoked potentials, see CPB 0181 - Evoked Potential Studies. For EEG, see CPB 0221 - Quantitative EEG (Brain Mapping)CPB 0289 - Grid Monitoring and Intraoperative ElectroencephalographyCPB 0322 - Electroencephalographic (EEG) Video Monitoring, and CPB 0425 - Ambulatory Electroencephalography. See Glossary of Terms for definition of these modalities.

Intraoperative EMG Monitoring

Facial Nerve

Electromyographic monitoring of the facial nerve (7th CN) is used to predict post-operative facial function after skull base surgery, which is associated with considerable risk to the functioning of the cerebral hemispheres, the brain stem and the CNs.  This risk is due to problems associated with maintaining an adequate blood flow while exposing and removing the tumor, as well as direct or indirect trauma to the brain, perineural tissues and CNs.

Harner and associates (1987) compared with the results of patients who underwent acoustic neuroma resection with (n = 48) or without (n = 48) intra-operative monitoring of facial nerve. They reported that anatomical preservation of the facial nerve in patients with large tumors was substantially improved in the monitored patients (67 %) when compared with those without monitoring (33 %).  Although no difference was noted in facial nerve function in the 2 groups of patients immediately post-operatively, the degree of improvement in the monitored group exceeded that observed for those who were not monitored at 3 months, particularly in those with medium-sized and large tumors.

Kwartler and colleagues (1991) compared a group of monitored translabyrinthine acoustic tumor removals (n = 89) to a similar un-monitored group (n = 155) in regard to facial nerve function.  Function was assessed immediately post-operatively, at time of discharge, and at 1 year post-operatively using the House 6-point scale.  Results were grouped as satisfactory, intermediate, or poor, and were analyzed by tumor size.  Facial nerve results were better at all time intervals in the monitored groups, although the difference was not statistically significant at the 1-year interval.  There was no difference between monitored and un-monitored patients in the subgroups with tumors smaller than 2.5 cm in diameter.  The findings of this study supported the usefulness of intra-operative facial nerve monitoring in improving facial nerve results, especially in larger tumors.

Olds et al (1997) stated that “routine facial nerve monitoring is not considered the standard of care in most communities; however risk of facial nerve injury appears to be greatly reduced when this adjunctive technique is employed”.  Spielholz (1997) stated that intra-operative facial nerve monitoring is especially helpful during removal of large (4 cm or greater) acoustic neuromas in which the incidence of facial weakness can reach 31 %.  Fabregas and Gomar (2001) noted that facial nerve monitoring for surgery of acoustic neuromas should be considered an absolute standard of care in neurosurgery.  This is in agreement with the observation of Ingelmo et al (2003) who stated that intra-operative EMG monitoring of the facial nerve should be used routinely in acoustic neuroma surgery to reduce the degree of post-operative neurological impairment.

Wilson et al (2003) assessed the cost-effectiveness of intra-operative facial nerve monitoring during middle ear or mastoid surgery.  The authors concluded that facial nerve monitoring is cost-effective, and its routine use should be adopted to reduce the risk of iatrogenic facial nerve injury during otologic surgery.

The American Academy of Otolaryngology-Head and Neck Surgery (1998) recognized the proven effectiveness of neurophysiologic monitoring of the facial nerve (7th CN), which may minimize the risk of injury to the nerve during surgical procedures in which the nerve is vulnerable due to site of lesion or extent of disease.  The American Academy of Neurology (AAN, 1990; Lopez, 2004) stated that brainstem AEPs and cranial nerve EMG monitoring is safe and effective during surgeries performed in the region of the brainstem or inner ear.  Nevertheless, clinical situations need to be chosen carefully, avoiding those in which the nervous system is only at low-risk.

A Tech Brief by the American Medical Association (1994) stated that the safety and effectiveness of intra-operative monitoring of the facial nerve by the use of either nerve conduction studies or EMG as a means of determining the integrity of the nerve during surgery for acoustic neuromas, cranial base lesions, or congenital auricular lesions were considered to be established by an expert panel.  This is in agreement with the reviews by Harper (1998, 2004) who stated that there are controlled data to suggest that monitoring reduces the risk of injury to the facial nerve during resection of acoustic neuromas and other tumors in the posterior fossa.

The facial nerve is often embedded by fibrous tissues in recurrent tumor of the parotid gland.  Studies have suggested that facial nerve-monitored patients undergoing parotidectomy for recurrent tumors have a 0 to 4 % risk of permanent facial paralysis.  Dulguerov et al (1999) analyzed the incidence and factors responsible for post-parotidectomy facial nerve paralysis when the surgery is performed with the routine use of facial nerve monitoring (n = 70).  The authors concluded that despite a stringent accounting of post-operative facial nerve deficits, the data compared favorably to the literature with or without the use of monitoring.  An overall incidence of 27 % for temporary facial paralysis and 4 % for permanent facial paralysis was found.  Although the lack of a control group precluded definitive conclusions on the role of EMG-based facial nerve monitoring in routine parotidectomy, the authors found its use very helpful.  Brennan et al (2001) studied the effectiveness of continuous intra-operative EMG monitoring in patients who underwent parotidectomies, thyroidectomies, and parathyroidectomies (44 facial nerves, and 96 recurrent laryngeal nerves).  These investigators concluded that continuous intra-operative nerve monitoring was associated with extremely low rates of temporary and permanent nerve paralysis.  However, these reports were not randomized, controlled studies.  Therefore, it remains unclear whether facial nerve monitoring significantly lowers the risk of facial nerve injury.

In a retrospective, case-controlled study, Terrell et al (1997) evaluated whether continuous facial nerve monitoring during parotidectomy is associated with a lower incidence of facial nerve paresis or paralysis compared with parotidectomy without monitoring (n = 117).  The authors found that continuous EMG monitoring of facial muscle during primary parotidectomy reduced the incidence of short-term post-operative facial paresis, but did not change the incidence of permanent paralysis.  Furthermore, Witt (1998) compared post-operative facial nerve function after monitored (n = 20) and unmonitored (n = 33) parotid surgical procedures.  No patient showed permanent facial paralysis.  In 9 patients (17 %), transient nerve paralysis developed: 5 (15 %) of the 33 patients who underwent lateral parotidectomy without the use of a nerve-integrity monitor and 4 (20 %) of the 20 patients who underwent lateral parotidectomy with the use of a nerve-integrity monitor.  Therefore, the clinical value of facial nerve monitoring during parotidectomy is still in question and its routine use in clinical setting awaits findings of well-designed randomized controlled studies.

In a prospective, controlled clinical two-center trial, Grosheva and colleagues (2009) analyzed the benefit of EMG neuromonitoring during primary surgery on benign parotid lesions for post-operative facial function compared to visual observation only.  Using an operation microscope, 100 parotidectomies in 96 patients were performed: 50 procedures with a continuous EMG monitoring plus visual facial observation (EMG group), and 50 procedures with only visual facial control (control group).  The rate of post-operative facial weakness was detected.  Patients with post-operative facial paralysis were followed-up until total recovery or defective healing by repeated EMG examinations.  A total of 79 superficial and 21 total parotidectomies were performed.  Histological analysis found pleomorphic adenoma in 38 patients, cystadenolymphoma in 39, and chronic parotitis in 18.  Immediate post-operative facial paralysis was evident in 41 patients.  Six patients had permanent paralysis; in this group definitive defective healing was detected by EMG in 5 cases.  Electromyography was not classifiable in 1 case.  Intra-operative EMG monitoring had no significant effect on immediate post-operative or definitive facial outcome (p = 0.23 and p = 0.45, respectively).  The duration of superficial, but not of a total parotidectomy, was diminished in the EMG group (p = 0.02 and p = 0.61, respectively).  This result was independent of the specimen's histology.  The authors concluded that EMG monitoring in parotid surgery in addition to visual facial observation did not diminish either the incidence of post-operative facial paralysis or the final facial outcome.  Nevertheless, the duration of surgery for superficial parotidectomy could be reduced by using EMG monitoring.

Shan et al (2014) analyzed the benefits of facial nerve EMG monitoring during parotid tumor surgery.  In this study, 92 patients with parotid tumor who underwent surgery were surveyed.  The study group consisted of 46 patients who underwent intra-operative EMG monitoring, and 46 patients served as the control group.  The incidence of post-operative facial nerve weakness and the operation time were recorded.  In primary parotid tumor resection, the operation time of the study group (6 cases) was (50.0 ± 9.1) mins, that of control group (7 cases) was (42.9 ± 5.2) mins (p = 0.064) when the facial nerve needed no dissecting; the operation time of the study group (32 cases) was (74.7 ± 28.0) mins, that of control group (33 cases) was (75.6 ± 29.8) mins (p = 0.893) when the facial nerve needed dissecting.  For patients with revision surgery, the mean operation time in the study group [(117.5 ± 37.8) mins] was significantly lower than that of the control group [(175.0 ± 47.8) mins], p < 0.05.  In the study group, 8 patients suffered from post-operative facial nerve weakness because of tumor characteristics; in the control group, 6 patients suffered from post-operative facial nerve weakness, with 4 cases because of tumor characteristic, and 2 cases because of operator error.  The authors concluded that these findings suggested that continuous EMG monitoring of facial nerve during parotidectomy reduces the mean operation time in patients with revision surgery, but not the incidence of post-operative facial paralysis.

Leonetti et al (1990) noted that while identification of the intra-temporal portion of the facial nerve is mandatory in most otologic surgical procedures, inadvertent instrumentation, traction, or thermal injury may still result from inaccurate delineation, purposeful avoidance, or false protection of this critical structure.  Improved functional preservation of the facial nerve has been achieved in acoustic neuroma surgery through the monitoring of evoked facial EMG activity.  This technique may also be used during otologic procedures in which facial nerve manipulation is anticipated in the management of recurrent cholesteatoma, temporal bone trauma, congenital deformity, or purposeful access for cochlear implantation.  The authors stated that intra-operative monitoring can assist the surgeon in isolating the facial nerve when chronic inflammation, traumatic injury, or anomalous development has resulted in distortion or absence of micro-anatomic landmarks.

Selesnick and Lynn-Macrae (2001) identified the incidence of facial nerve dehiscence in patients undergoing surgery for cholesteatoma.  An assessment of all cases performed by the senior author from 1991 to 1999 revealed 59 patients with adequate data available for analysis.  These patients ranged in age from 3 to 92 years; a total of 67 surgical procedures.  Main outcome measure was the presence of facial nerve bony dehiscence after exenteration of disease, and post-operative facial nerve function.  In 33 % of the total procedures analyzed, 30 % of the initial procedures, and 35 % of the revision procedures, patients were found to have facial nerve bony dehiscence.  The dehiscence was present in the tympanic portion of the facial nerve in the vast majority of patients.  Of the 97 % of patients with normal pre-operative facial nerve function, all retained normal function post-operatively.  The authors concluded that facial nerve dehiscence in this series was far greater than that reported in the literature, underscoring the fact that this is an under-appreciated condition.  These findings suggested that surgeons should be highly vigilant when dissecting near the facial nerve.  The authors stated that intra-operative facial nerve monitoring (FNM) has been shown to be of value in facial nerve preservation during acoustic neuroma resections, and may have a role during surgery for cholesteatoma.

In a prospective, non-randomized study, Di Martino et al (2005) investigated fallopian canal dehiscences in order to assess the risk of encountering an unprotected facial nerve during routine ear surgery.  The intra-operative appearance of the facial canal in 357 routine ear operations was compared with 300 temporal bone specimens from 150 autopsies.  Intra-operatively, a dehiscence was detected in 6.4 % (23/357) of the operations, most frequently at the oval niche region (16/23 cases).  The incidence increased with the number of operations (p < 0.0002).  Cholesteatoma surgery had the highest relative risk (RR 4.6) of exposing an unprotected facial nerve.  Post-operatively, no persistent facial paralysis was observed.  In 4 of 5 cases with a transient facial palsy due to local anesthetics, a bony dehiscence could be found.  The anatomical study revealed fallopian canal dehiscences in 29.3 % (44/150) of the autopsies. One-third (15/44) of the individuals affected displayed bilateral findings; thus resulting in 19.7 % (59/300) of temporal bones affected.  A total of 17/59 bones showed micro-dehiscences, and most (55/59) were located at the oval niche.  The actual prevalence of fallopian canal dehiscences was significantly higher than intra-operative findings suggested.  The oval niche is the most affected region.  The authors stated that high-resolution computed tomography is of diagnostic value only in selected cases.  Facial paralysis following local anesthesia is the most significant clinical sign.  Vigilance in acute facial palsy after local anesthetics and in cholesteatoma surgery and adequate intra-operative exposure help to prevent iatrogenic injury of the uncovered nerve.  In unclear cases, FNM can facilitate a safe outcome.

Jiang and associates (2006) studied the application of FNM and estimated the therapeutic effectiveness of the total decompression of facial nerve during the surgery for cholesteatoma in petrous bone by middle cranial fossa-mastoid process approach.  A total of 8 patients who suffered from chronic suppurative otitis media (cholesteatoma type) in petrous bone were treated with open technique, 3 other cholesteatoma cases whose tympanic membranes were intact was treated with close technique.  Monitoring for facial nerve integrity during operation was applied.  Total decompression of facial nerve was performed in all patients.  House-Brackmann grading system was used to evaluate the recovery of facial nerve function.  Facial paralysis recovered gradually during the period of 3 to 6 months after operation.  After 6 to 12 months follow-up in 11 cases, 1 case regained basically normal status, 9 cases recovered to mild facial paralysis and 1 case still needed further follow-up.  There was no recurrence of cholesteatoma in all patients.  The authors concluded that middle cranial fossa-mastoid process combining approach technique is effective for cholesteatoma in petrous bone and total decompression of facial nerve at the same stage.  They stated that FNM is helpful in orientating facial nerve during operation and in preventing possible damage to the facial nerve.

Hu and colleagues (2014) stated that there is a growing trend for the routine use of the FNM in chronic ear surgery. These investigators aimed to examine current patterns in the use of FNMs in chronic ear surgery. A 10-question survey was designed to identify level of training, scope of practice, specific otologic surgeries where monitoring was most used, and the opinion of respondents regarding the use of FNMs as standard of care for chronic and/or middle ear surgery. A randomized list of 2,000 board-certified members of the American Academy of Otolaryngology-Head and Neck Surgery was generated; a total of 1,000 subjects received a mailed survey with a self-addressed return envelope and 1,000 subjects received an emailed survey through Surveymonkey.com. There were 359 (36 %) surveys returned by mail and 258 (26 %) surveys returned electronically – 43 % of respondents were in private practice, and 31 % were fellowship-trained in otology/neurotology; 65 % used a FNM in their training and 95 % had regular access to a FNM. Revision mastoid surgery, cholesteatoma, canal wall down mastoidectomy, and facial recess approach were the settings where a FNM was most used. Forty-nine percent of respondents felt that a FNM should be used as the standard of care in chronic ear surgery; this represents an increase from 32 % in a similar study done approximately 10 years ago. The authors concluded that there is a growing trend for routine facial nerve monitoring in the setting of chronic ear surgery.

Prell and colleagues (2017) stated that in vestibular schwannoma surgery, facial nerve injury with consecutive functional impairment is one of the most important complications.  Intraoperative monitoring of facial nerve function has been developed in order to avoid this complication.  These investigators evaluated the methods and their ability to achieve the goals of intraoperative monitoring.  Intraoperative functional monitoring aims to identify and map the facial nerve in the surgical field during surgery.  It also aims to identify potentially damaging events and allow for intraoperative prognosis of functional outcome.  Available methods are direct electrical stimulation, free-running EMG, facial nerve EPs, and processed EMG.  The authors concluded that identification and mapping of the facial nerve in the surgical field can be reliably achieved by direct electrical stimulation; potentially dangerous events can be identified in real time by the free-running EMG and the processed EMG, and almost in real time by facial nerve EPs.  However, they stated that intraoperative prognostics are hampered by false-positive results with all available methods and have limited reliability.

Hermann et al (2004) stated that neuromonitoring has been advocated to reduce the risk of vocal cord palsy and to predict post-operative vocal cord function.  These researchers examined the ability of neuromonitoring to predict post-operative outcome in patients undergoing thyroid surgery for different indications.  A total of 328 patients (502 nerves at risk) were studied prospectively at a single center.  Neuromonitoring was performed with the Neurosign 100 device by trans-ligamental placement of the recording electrode into the vocalis muscles.  Cumulative distribution of stimulation thresholds was determined by step-wise decreases in current (1 mA to 0.05 mA) for both the vagus nerve and the RLN.  Patients were grouped according to surgical risk (benign and malignant disease, re-operation for benign and for malignant disease).  If the electrophysiological response was correlated to post-operative vocal cord function, the sensitivity of neuromonitoring was modest (86 % in surgery for benign disease) to low (25 % in re-operation for malignant disease); PPV was modest (overall rate 62 %) but acceptable (87 %) if corrected for technical problems.  Specificity and NPV were high (i.e., overall greater than 95 %).  Stimulation thresholds were not augmented in 11 patients, in whom post-operative palsy developed despite normal intra-operative recordings.  Similarly, an electrical field response was elicited in 14 of 21 patients with pre-operative vocal cord palsy; EMG recordings did not reveal an abnormal amplitude or a decline in nerve conduction velocity.  The authors concluded that neuromonitoring was useful for identifying the RLN, in particular if the anatomic situation was complicated by prior surgery, large tissue masses, aberrant nerve course.  However, neuromonitoring did not reliably predict post-operative outcome.  Facial nerve was not monitored in this study.

Furthermore, an UpToDate review on “Thyroidectomy” (Wang et al, 2020) states that “Intraoperative nerve monitoring (IONM) has been advocated with the goal of reducing the rate of RLN injury.  Although its routine use remains controversial, it could potentially assist in the identification, dissection, and prediction of postoperative function of the RLN”.

Recurrent Laryngeal Nerve

The recurrent laryngeal nerve (RLN) is one of the branches of the vagus nerve (10th CN).  After the RLN leaves the vagus nerve, it travels into the chest and then loops back up to supply nerves to the larynx.  Injury to the RLN is rare but may occur as a complication of surgery in the neck or chest.  In this regard, damage to the RLN remains one of the most devastating complications of thyroid surgery.  The nerve can also be injured by tumors or swollen lymph nodes in the mediastinum.  Damage to the RLN causes laryngeal palsy on the affected side.  Symptoms include hoarseness, difficulty in speaking, and difficulty in swallowing.

During thyroidectomy, the RLN is visually identified and dissected away from the thyroid gland.  It has been advocated that intra-operative knowledge of the status of the nerve after dissection could potentially provide the surgeon with important decision-making information.  However, it has not been established that intra-operative EMG monitoring of the RLN reduces the incidence of RLN injury during thyroidectomy.  There are studies that have calculated the positive-predictive value (PPV) and negative-predictive value (NPV) of RLN monitoring during thyroid surgery.  Most recently, Beldi and co-workers (2004) reported that the NPV of intra-operative RLN monitoring was 99 %, but the PPV was only 33 %.  These results are similar to those of Otto and Cochran (2002) who reported a NPV of 98.6 % and a PPV of 33.3 %.  Beldi et al (2004) concluded that although an intact nerve can be verified by RLN monitoring, the loss of nerve function can not be reliably identified, and that the incidence of RLN lesions was not lowered by intra-operative monitoring.  This is in agreement with the findings of Robertson et al (2004) who reported that there were no statistically significant differences in RLN paralysis, paresis, or total injury rates between control and continuous laryngeal nerve integrity monitoring among patients who underwent thyroidectomy (n = 165).

In a prospective study (n = 328 patients with 502 nerves at risk), Hermann et al (2004) examined the ability of neuromonitoring to predict post-operative outcome in patients undergoing thyroid surgery for different indications.  These authors concluded that neuromonitoring is useful for identifying the RLN, in particular if the anatomical situation is complicated by prior surgery, large tissue masses, aberrant nerve course.  However, neuromonitoring does not reliably predict post-operative outcome.  Thus, the value of intra-operative EMG monitoring of the RLN has not been established.

Chiang et al (2008) determined the causes of RLN palsy and identified potentially reversible causes of RLN injury during thyroid surgery with the use of intra-operative neuromonitoring (IONM).  A total of 113 patients with 173 nerves at risk were enrolled in this study.  All operations were performed by the same surgeon.  The 4-step procedure of IONM was designed to obtain EMG signals from the vagus nerve and RLN before and after resection of thyroid lobe.  A total of 16 nerves had loss of EMG signals after thyroid dissection, and the causes of nerve injuries were well elucidated with the application of IONM.  One nerve injury was caused by inadvertent transection, which led to permanent RLN palsy.  Among the remaining 15 nerves, 1 injury was caused by a constricting band of connective tissue, which was detected precisely and released intra-operatively, 2 by inadvertent clamping of the nerve, and 12 by apparent over-stretching at the region of Berry's ligament (5 nerves regained signals before closing the wound, but 1 showed impaired cord movement.  Another 7 nerves did not regain signals before closing the wound, and all developed temporary RLN palsy).  The authors concluded that their 4-step procedure of IONM is useful and helpful in elucidating the potential operative pitfalls during dissection near the RLN.  However, the rates of RLN palsy were not decreased in this study.

The National Institute for Health and Clinical Excellence's (NICE) guidance on intra-operative nerve monitoring during thyroid surgery (2008) noted that the evidence raises no major safety concerns.  However, only 2 of the 9 specialist advisers stated that this procedure is useful for teaching; while 1 adviser stated that there are significantly different opinions between surgeons as to whether this technology improves outcomes or whether it gives false reassurance to inexperienced surgeons.

The NICE (2008) assessment reported that 4 non-randomized studies of 16,448, 684, 639 and 136 patients (29,998, 1,043, 1,000 and 190 nerves) reported permanent rates of vocal cord paralysis ranging from 0 % to 2 % in the intra-operative nerve monitoring groups, compared with 0 % to 1 % in the control groups (visual recurrent laryngeal nerve identification or no recurrent laryngeal nerve identification).  No statistically significant differences were seen between procedures undertaken with or without intra-operative nerve monitoring.  The NICE assessment also found that 3 case series of 328, 288 and 171 patients reported rates of permanent vocal cord paralysis using intra-operative nerve monitoring in 3 % (15/502), 1 % (6/429) and 1 % (2/271) of recurrent laryngeal nerves, respectively.

The NICE (2008) assessment also indicated that 4 non-randomized studies of 684, 639, 165 and 136 patients (1,043, 1,000, 236 and 190 nerves) reported rates of transient vocal cord paralysis ranging from 3 % to 5 % in the intra-operative nerve monitoring groups, compared with 3 % to 4 % in the control groups (none was statistically significant).  The NICE assessment stated that another non-randomized study reported that vocal cord immobility was detected at 3-month follow-up in 6 % (6/104) of patients when intra-operative nerve monitoring was used and 5 % (5/100) of patients when intra-operative nerve monitoring was not used (p = 0.55).  The 3 case series of 328, 288 and 171 patients reported rates of transient recurrent laryngeal nerve palsy as 9 % (43/502), 9 % (37/429) and 5 % (13/271), respectively.

The NICE (2008) assessment stated that the non-randomized study of 639 patients (1,000 nerves at risk), which compared intra-operative nerve monitoring with visual identification of the recurrent laryngeal nerve, reported that intra-operative nerve monitoring indicated no nerve damage in 10 out of 21 vocal cords that were paralyzed as a result of surgery.  Conversely, intra-operative nerve monitoring indicated nerve damage in 27 out of 480 patients who were found to have normal post-operative vocal cord function.

Barczyński and colleagues (2009) tested the hypothesis that identification of the RLN during thyroid surgery reduces injury, and that IONM may be of additional benefit.  A total of 1,000 patients scheduled to have bilateral thyroid surgery were randomized to standard protection or additional nerve monitoring.  The primary outcome measure was prevalence of RLN injury.  Of 1,000 nerves at risk in each group, transient and permanent RLN injuries were found respectively in 38 and 12 nerves without RLN monitoring (p = 0.011) and 19 and 8 nerves with RLN monitoring (p = 0.368).  The prevalence of transient RLN paresis was lower in patients who had RLN monitoring by 2.9 % in high-risk patients (p = 0.011) and 0.9 % in low-risk patients (p = 0.249).  The NPV and PPV of RLN monitoring in predicting post-operative vocal cord function were 98.9 and 37.8 %, respectively.  The authors concluded that nerve monitoring decreased the incidence of transient but not permanent RLN paresis compared with visualization alone, particularly in high-risk patients.

In a retrospective case control study with 993 patients, Cavicchi et al (2009) examined the accuracy of neurostimulation with laryngeal palpation (NSLP) and IONM to predict the post-operative function of RLN in thyroid surgery.  The control group (799 patients with 1,450 nerves at risk) included patients who underwent NSLP and the case group (194 patients with 354 nerves at risk) consisted of those who underwent NSLP in association with IONM.  Sensitivity, specificity, PPV, NPV, and accuracy were calculated for NSLP and IONM, with nerve palsy as the target outcome.  A significant difference in nerve injury between the case and the control group (p = 0.31) was not observed.  The presence or absence of laryngeal twitch (LT) (p < 0.0001) and the acoustic response to electrical stimulation (p = 0.003) were significantly associated with nerve function at the end of the surgery.  The authors concluded that these findings indicated that NSLP is a safe and reliable intraoperative method of RLN monitoring.  Moreover, these results confirmed that IONM is not a helpful tool to reduce the rate of palsy in thyroid surgery.

Harrison and Triponez (2009) reviewed the evidence regarding the use of intra-operative parathyroid hormone (PTH), radio-guided parathyroidectomy (RGP), methylene blue (MB), frozen section, and IONM during surgery for primary hyper-parathyroidism (PHPT).  A Medline keyword search of English-language articles led to the production of a draft document, subsequently revised by committee, containing levels of evidence and the grading of recommendations as proposed by the Agency for Healthcare Research and Quality.  Literature review provided the basis for clear recommendations on the use of intra-operative PTH at surgery for PHPT.  In contrast, there is little evidence to support the use of RGP, MB, routine frozen section, and IONM.

Kiviniemi and colleagues (2010) stated that the knowledge of the anatomy for the parathyroid and thyroid glands helps a surgeon to localize important details and lessen complications, especially laryngeal palsy and hypo-parathyroidism.  The ligament of Berry and tuberculum Zuckerkandl cover the recurrent laryngeal nerve in the upper part of the thyroid lobes.  The recurrent laryngeal nerve or its branches are exposed during the mobilization of these structures during total thyreoidectomy.  The upper parathyroid gland can be found on the upper part of the tuberculum Zuckerkandl behind the recurrent laryngeal nerve, whereas the lower parathyroid gland can be found in front of the nerve on the under surface of the thyroid lobe or in the thymus below.  The tertiary branches of blood vessels are cut preserving the function of the parathyroid glands.  If the parathyroid has lost its blood circulation, it is made into pieces and transplanted into the pockets of sternocleidomastoideus muscle.  Exposing the recurrent laryngeal nerve during operation seems to decrease permanent recurrent laryngeal nerve injury.  The authors noted that the role of neuromonitoring during parathyroid and thyroid surgery is still controversial.

Dionigi et al (2013) stated that IONM contributes in several ways to RLN protection.  Notwithstanding these advantages, surgeons must be aware that the current, intermittent mode of IONM (I-IONM) has relevant limitations.  To overcome these I-IONM limitations, a continuous IONM (C-IONM) technology has been proposed.  These investigators performed a PubMed indexed literature review of the current limitations of I-IONM and provided a commentary about C-IONM; presenting the preliminary results of research on this topic.  These researchers concluded that RLN traction injury is still the most common cause of RLN injury and is difficult to avoid with the application of I-IONM in thyroid surgery.  Continuous-IONM is useful to prevent the imminent traction injury by detecting progressive decreases in electromyographic amplitude combined with progressive latency increases; C-IONM seems to be a technological improvement.  Likely, C-IONM by vagal nerve stimulation should enhance the standardization process, RLN intraoperative information, documentation, protection, training, and research in modern thyroid surgery.  They stated that although C-IONM is a promising technology at the cutting edge of research in thyroid surgery, more studies to assess in an evidence-based way all its advantages are needed.

Other Cranial Nerves

Schlake et al (2001) reported that EMG is effective as a mapping tool for intra-operative localization and identification of ocular motor nerves – the oculomotor nerve (3rd CN) and the abducens nerve (6th CN) in skull base surgery.  However, the predictive value of conventional neurophysiological parameters for clinical outcomes appears to be rather poor.  Further investigations on a larger number of patients are thus needed to develop new quantification techniques which enable an intra-operative prediction of ocular motor nerve deficits.  More studies are also needed to extend this technique to the trochlear nerve (4th CN).  Furthermore, in a review on the electrophysiological examination of CNs, Vial and Bouhour (2004) stated that intra-operative monitoring of various CNs can be useful but techniques still need to be validated.

There are no controlled studies that examined whether EMG monitoring of the oculomotor, trochlear, and abducens nerves during surgery in the middle cranial fossa reduces the risk of post-operative ophthalmoplegia.  Moreover, although there are reports of monitoring, either alone or in combination, of glossopharyngeal, laryngeal branches of the vagus (e.g., the superior laryngeal nerve and the recurrent laryngeal nerve), spinal accessory, and hypoglossal nerves during skull base surgeries such as surgical resection of tumors in the region of the foramen magnum, jugular foramen, hypoglossal foramen, and clivus, there are no controlled data to indicate that the risk of CN injury is reduced by monitoring (Harper, 2004).  Thus, the clinical value of intra-operative monitoring of the oculomotor, trochlear, abducens, glossopharyngeal, laryngeal branches of the vagus, spinal accessory, and hypoglossal nerves has not been established.

During Intra-Cranial Tumor Resections

Grabb and colleagues (1997) reviewed the results of continuous intra-operative EMG monitoring of muscles innervated by cranial nerves in 17 children whose pre-operative imaging studies showed compression or infiltration of the 4th ventricular floor by tumor to determine how intra-operative EMG activity correlated with post-operative cranial nerve morbidity.  Bilateral lateral rectus (6th) and facial (7th) nerve musculatures were monitored in all children.  Cranial nerve function was documented immediately post-operatively and at 1 year.  Of the 68 nerves monitored, 9 new neuropathies occurred in 6 children (6th nerve in 4 children and 7th nerve in 5 children).  In 5 new neuropathies, intra-operative EMG activity could be correlated in 1 of 4 6th nerve injuries and 4 of 5 7th nerve injuries.  Electromyographic activity could not be correlated in 4 children with new neuropathies.  Of 59 cranial nerves monitored that remained unchanged, 47 had no EMG activity.  Twelve cranial nerves (3 6th nerves and 9 7th nerves) had EMG activity but no deficit.  Of 4 children with lateral rectus EMG activity, 3 had new 7th nerve injuries.  Lateral rectus EMG activity did not predict post-operative abducens injury.  The absence of lateral rectus EMG activity did not assure preserved abducens function post-operatively.  Likely because of the close apposition of the intra-pontine facial nerve to the abducens nucleus, lateral rectus EMG activity was highly predictive of 7th nerve injury.  The authors noted that although facial muscle EMG activity was not an absolute predictor of post-operative facial nerve dysfunction, the presence of facial muscle EMG activity was associated statistically with post-operative facial paresis.  The absence of facial muscle EMG activity was rarely associated with facial nerve injury.  The authors speculated that EMG activity in the facial muscles may have provided important intra-operative information to the surgeon so as to avoid facial nerve injury.

Kombos et al (2000) stated that intra-operative cranial nerve monitoring has improved the preservation of facial nerve function following surgery in the cerebello-pontine angle (CPA).  Facial EMG was performed in 60 patients during CPA surgery.  Pairs of needle electrodes were placed subdermally in the orbicularis oris and orbicularis oculi muscles.  The duration of facial EMG activity was noted.  Facial EMG potentials occurring in response to mechanical or metabolic irritation of the corresponding nerve were made audible by a loudspeaker.  Immediate (4 to 7 days after tumor excision) and late (6 months after surgery) facial nerve function was assessed on a modified House-Brackmann scale.  Late facial nerve function was good (House-Brackmann 1 to 2) in 29 of 60 patients, fair (House-Brackmann 3 to 4) in 14, and poor (House-Brackmann 5 to 6) in 17.  Post-manipulation facial EMG activity exceeding 5 minutes in 15 patients was associated with poor late function in 5, fair function in 6, and good function in 4 cases.  Post-manipulation facial EMG activity of 2 to 5 minutes in 30 patients was associated with good late facial nerve function in 20, fair in 8, and poor in 2.  The loss of facial EMG activity observed in 10 patients was always followed by poor function.  Facial nerve function was preserved post-operatively in all 5 patients in whom facial EMG activity lasted less than 2 minutes.  The authors concluded that facial EMG is a sensitive method for identifying the facial nerve during surgery in the CPA.  EMG bursts are a very reliable indicator of intra-operative facial nerve manipulation, but the duration of these bursts do not necessarily correlate with short- or long-term facial nerve function despite the fact that burst duration reflects the severity of mechanical aggression to the facial nerve.

Furthermore, UpToDate reviews on "Clinical manifestations and initial surgical approach to patients with malignant gliomas" (Batchelor and Curry, 2012) and "Overview of the management of central nervous system tumors in children" (Lau and Teo, 2012) do not mention the use of intra-operative EMG.

During Placement of Dorsal Column Stimulator

Shils and Arle (2012) demonstrated that spinal cord stimulators (SCSs) may be placed safely and accurately under general anesthesia (GA) and that the proposed evaluation method activates structures predominantly in the dorsal columns.  Data were retrospectively analyzed from 172 electrodes implanted with spinal cord SCSs at the Lahey Clinic between September 2008 and July 2011.  All patients had their SCS placed under GA.  Electromyography was recorded from upper or lower limb muscle groups related to the placement of the stimulator electrode.  Lateralization was performed based on electromyographic responses and electrode pairs stimulated.  In a select group of patients, standard neurophysiologic tests, paired pulse, and collision studies were performed to demonstrate that the pain stimuli were activating the dorsal columns.  A total of 155 patients had standard thoracic or cervical SCS placement.  Pre-operatively this cohort of patients had a visual analog score (VAS) of 7.51 ± 1.93, while post-operatively the VAS was 3.63 ± 2.43 (a reduction of 52.11 %).  Based on the electromyographic recording technique, the electrodes were re-positioned intra-operatively in 15.9 % of patients.  The recovery time (initial approximately 70 msec and complete approximately 150 to 300 msec) in both the paired-pulse tests and the collision studies showed that the stimulation used to elicit the compound muscle action potentials came from antidromic activation of the dorsal columns and not from the cortico-spinal tract.  The authors concluded that GA-SCS is safe and appears to be at least as accurate and efficacious as using the awake-SCS placement technique based on a 50 % improvement in the VAS.  In addition, the technique presented herein demonstrated that the test stimuli activate the same fiber tracts as that of the therapeutic stimulation.

Mammis and Mogilner (2012) noted that placement of spinal cord stimulating paddle leads has traditionally been performed under local anesthesia with intravenous sedation to allow intraoperative confirmation of appropriate placement.  It may be difficult to maintain appropriate sedation in certain patients because of medical co-morbidities.  Furthermore, patients undergoing lead revision frequently have extensive epidural scarring, requiring multi-level laminectomies to place the electrode appropriately.  These investigators reported their technique of neurophysiologic monitoring that allows these procedures to be performed under GA.  Data from 78 patients who underwent electromyography during laminectomy for paddle lead placement were retrospectively reviewed; 70 patients presented for first-time permanent system placement after a successful trial, and 8 were referred for revision or replacement of previously functioning systems.  Surgeries were performed under GA with fluoroscopic guidance.  Electromyography was used to help define the physiological midline of the spinal cord and to guide appropriate lead placement.  Somatosensory evoked potentials were used as an adjunct to minimize the possibility of neural injury.  Immediately post-operatively, 75 of 78 patients reported that the paresthesia coverage was as good as (or better than) that of the spinal cord stimulation trial.  At the long-term follow-up, 1 system was removed for infection, and 6 systems were explanted for lack of efficacy.  A total of 64 of the 78 implanted patients reported continued pain relief with stimulator use.  Revision surgery was performed in 9 patients.  The authors concluded that the use of intra-operative electrophysiology for the placement of spinal cord stimulation paddle leads under GA is a safe and efficacious alternative to awake-surgery.

Also, an eMedicine review on “Intraoperative Neurophysiological Monitoring” lists the following clinical uses of intra-operative EMG:

  • Facial nerve/other cranial nerve monitoring
  • Pedicle screw placement
  • Selective dorsal rhizotomy
  • Tethered spinal cord release.

Placement of spinal cord stimulator is not one of the listed indications.

Manuals of implantation of SCSs provide no recommendations for EMG neuromonitoring.

During Surgical Intervention of the Trigeminal Nerve

Brock et al (2004) reported the findings of the first 45 consecutive patients undergoing microvascular decompression (MVD) surgery for trigeminal neuralgia, studied with peri-operative brainstem auditory evoked potentials (BAEPs) and EMG.  These researchers observed a good correlation between the intra-operative BAEP modifications and post-operative hearing function.  BAEP monitoring was useful in identifying the maneuvers that may compromise cochlear nerve function.  This improved the surgical technique in the subsequent cases and reduced the incidence of iatrogenic hearing deficits after the learning period.  There were no correlations between the entity of the intra-operative EMG discharges and the post-operative facial and trigeminal function.  The authors noted that intra-operative EMG monitoring can be useful during the period of learning as a means of identifying the different nerves in the cisternal tract.

Minahan and Mandir (2011) noted that the trigeminal and facial nerves are placed at risk in a number of surgical procedures.  The use of EMG, nerve conduction studies, SSEPs, MEPs, and other techniques were described.  Application to specific surgical types and the associated evidence for impact on surgical outcomes were discussed.  The authors discussed the use of intra-operative evoked potential studies of the trigeminal nerve; but not intra-operative EMG.

Furthermore, an UpToDate review on “Trigeminal neuralgia’ (Bajwa et al, 2015) does not mention intra-operative EMG monitoring during surgical interventions (e.g., MVD, peripheral neurectomy, radiosurgery, and rhizotomy) of trigeminal neuralgia.

During Brachial Plexus Repair

An UpToDate review on “Brachial plexus syndromes” (Bromberg, 2018) does not mention intraoperative EMG.

During Decompression of Peroneal (Fibular) Nerve

Yamasaki and colleagues (2020) carried out intra-operative EMG of the fibularis longus and tibialis anterior muscles during nerve decompression (ND) of the common fibular nerve (CFN) in patients with symptomatic diabetic sensorimotor peripheral neuropathy.  Patient demographics and clinical attributes were compared against changes in EMG after ND and analyzed for possible correlations.  Intraoperative changes in CFN EMG were analyzed for correlations against sex, age, body mass index (BMI), hemoglobin A1c (A1c), and type and duration of diabetes.  Statistically significant changes were found between EMG changes and patient attributes, but no individual correlations were established.  Significant EMG improvement was observed for both men and women (p < 0.0001 and p < 0.05, respectively), age groups (4th decade: p < 0.05; 5th decade: p < 0.05; 6th decade: p < 0.01; 7th decade: p < 0.005), diabetes duration (0 to 9 years: p = 0.002; 10 to 19 years: p = 0.002; 20 to 29 years: p = 0.03), and for type 1 and 2 diabetes (type 1: p < 0.005; type 2: p < 0.001).  EMG improvement was greater in patients with the highest BMI levels (30 to 34.9: p = 0.014; 35 to 39.9: p = 0.013; greater than 39.9: p = 0.043), and highest A1c levels (greater than 6.4 %; p < 0.0001).  The authors concluded that although long-term clinical studies are needed, these results provided insight into which patients might benefit most from this surgery.  These findings also suggested that surgical ND can produce an acute improvement in nerve function for both men and women, for people with type 1 and 2 diabetes, and across a wide range of ages, BMI, A1c levels, and disease duration.

Furthermore, an UpToDate review on “Overview of lower extremity peripheral nerve syndromes” (Rutkove, 2021) does not mention intraoperative EMG as a management option.

During Knee Arthroscopy / Repair

Niemi-Murola and Paloheimo (2005) stated that Bromage scale (0 to 3) is used to measure the degree of motor block during spinal anesthesia.  However, an estimation of motor block is difficult during surgery.  These researchers examined the feasibility of surface electromyography (EMG) describing spontaneous muscular activity in the lower extremities during spinal anesthesia.  In part I of the study, 13 patients undergoing day case surgery were studied.  They received 10-mg hyperbaric bupivacaine at interspace L3 to L4.  EMG, sensory and muscular block were measured at 5-min intervals during the first 30 mins and then every 15 mins until the patient was able to flex the knee.  In part II of the study, 16 patients undergoing knee arthroplasty received 10-mg bupivacaine through spinal catheter at interspace L3 to L4 (Group CSA).  An additional bolus of 2.5-mg was administered using EMG-guidance, if needed.  Another group, 15 patients, received a single bolus of bupivacaine (15 to 20 mg) at L3 to L4 (Group Bolus).  EMG, muscular and sensory block were monitored as described above.  The epidural catheter was used as rescue.  Part I: EMG compared to modified Bromage scale showed a significant correlation (p < 0.01, Spearman rank correlation).  Part II: The amount of bupivacaine was significantly reduced with EMG guidance when compared with the single bolus group (14.0 mg versus 17.0 mg) (p < 0.05 Mann-Whitney U).  Motor block started to recover before the sensory block in 7/15 CSA patients versus 1/15 Bolus patient.  The authors concluded that stable maximal sensory block did not necessarily correlate with adequate motor block in patients receiving spinal anesthesia induced with small bolus doses.  In spite of electrical noise, EMG-guided administration of spinal anesthesia significantly reduced the amount of bupivacaine compared to the hospital routine.  Moreover, these researchers stated that further studies are needed to develop the method.

Figueroa et al (2008) noted that the incidence of IBSN injury to the infrapatellar branch of the saphenous nerve (IBSN) in anterior cruciate ligament (ACL) surgery using the hamstrings technique has been reported to be between 30 % and 59 %.  These researchers examined the incidence of IBSN injury in ACL surgery with the hamstrings technique via clinical and electrophysiological evaluation.  They also examined potential risk factors of IBSN injury related to the surgical incision.  Between November 2003 to September 2004, a total of 21 consecutive patients (22 knees) with an acute ACL rupture suitable for reconstruction were included.  Patients with previous surgeries or scars around the knee and those with any degree of osteoarthritis (OA) were excluded.  Clinical and electrophysiological evaluations were carried out in all the cases.  Hypoesthesia of the IBSN territory was found in 17 knees (77 %) with an average area of 36 cm(2) (1 to 120 cm(2)).  Injury to the IBSN was electrophysiologically detected in 15 knees (68 %); 2 patients also had an injury to the saphenous nerve (9 %).  The authors concluded that the presence of sensory loss associated with damage to the IBSN did not correlate with the size of the incision or the distance to the tibial tubercle.  This injury probably occurred during tendon harvesting as found by an injury to the saphenous nerve in 2 of the patients; however, the sensory loss did not impair normal daily activities in these patients.

Furthermore, UpToDate reviews on “Anterior cruciate ligament injury” (Friedberg, 2021) and “Total knee arthroplasty” (Martin and Harris, 2021) do not mention intraoperative electromyography/EMG as a management/therapeutic tool.    

During Pedicle Screw Placement

Available studies of intraoperative EMG for pedicle screw placement (e.g., Raynor et al, 2002 and Shi et al, 2003) focused on the relationship between threshold testing to hardware position, but include no data on clinical outcomes.  In addition, studies have not examined the clinical consequence of unnecessary screw revisions or removal. Considering that a false-positive finding can result in the temporary removal of a pedicle screw to evaluate the screw tract, performing a laminotomy to check screw position, repositioning or complete removal of a pedicle screw, or aborting a planned portion of the procedure, the potential for significant adverse effects on outcome exists. There is yet to be any published data showing reduced postoperative neurologic deficit or improved clinical outcomes from using intraoperative EMG to confirm satisfactory placement of pedicle screws at any spinal level to justify the time, effort and potential adverse consequences involved.  Additional prospective study of these recordings is recommended to further specify the relationship of electrophysiological breach to clinical outcomes.

In a prospective study, Glassman and colleagues (1995) performed an analysis of intra-operative EMG monitoring of pedicle screw placement with CT scan confirmation.  A total of 90 patients underwent lumbar pedicle screw instrumentation; 512 screws were tested intra-operatively using electrical stimulation.  The accuracy of this technique was verified after surgery by CT.  Screws (total, 512) in 90 patients were stimulated intra-operatively, and stimulation threshold was recorded.  Computed tomographic scans were taken after surgery to document pedicle screw position; EMG thresholds and CT data were evaluated independently and compared to evaluate the accuracy of the EMG stimulation technique.  Intra-operative screw stimulation was extremely accurate in confirming the adequacy of screw position.  A stimulation threshold greater than 15 mA provided a 98 % confidence that the screw was within the pedicle.  In 8 of 90 patients (9 %), EMG monitoring detected a screw mal-position that was not identified on lateral radiograph.  The authors concluded that screw stimulation monitoring is a valuable and effective adjunct to lumbar pedicle screw instrumentation.  They stated that a stimulation threshold greater than 15 mA reliably indicated adequate screw position.  A stimulation threshold between 10 and 15 mA was generally associated with adequate screw position, although exploration of the pedicle is recommended; a stimulation threshold of less than 10 mA was associated with a significant cortical perforation in most instances.  The main drawback of this study was that it focused on the relationship between EMG threshold testing to hardware position, but lacked data on clinical outcomes.

In a prospective clinical study, Raynor et al (2002) assessed the sensitivity of recording rectus abdominis-triggered EMG to evaluate placement of thoracic screw.  A total of 677 thoracic screws were inserted into 92 patients.  Screws placed from T-6 and T-12 were evaluated using an ascending method of stimulation until a CMAP was obtained from the rectus abdominis.  Threshold values were compared both in absolute terms and also in relation to other intra-patient values.  Screws were divided into 3 groups: group A (n = 650 screws) had thresholds greater than 6.0 mA and intra-osseus placement; group B (n = 21) had thresholds less than 6.0 mA but an intact medial pedicle border on re-examination and radiographical confirmation; and group C (n = 6) had thresholds less than 6.0 mA and medial wall perforations confirmed by tactile and/or visual examination.  Thus, 3.9 % (27 of 677) of all screws had thresholds less than 6.0 mA.  Only 22 % (6 of 27) had medial perforation.  Group B screws averaged a 54 % decrease from the mean as compared with a 69 % decrease for group C screws (p = 0.016).  There were no post-operative neurological deficits or radicular chest wall complaints.  These investigators concluded that for assessment of thoracic pedicle screw placement, triggered EMG thresholds of less than 6.0 mA, coupled with values 60 to 65 % decreased from the mean of all other thresholds in a given patient, should alert the surgeon to suspect a medial pedicle wall breach.  These investigators further stated that although this retrospective analysis of electrophysiological observations and subsequent guidelines are not currently validated, this electrophysiological approach can be used in conjunction with precise surgical techniques, careful pedicle tract palpation, as well as intra-operative biplanar fluoroscopy and/or radiography to create the safest environment for placement of thoracic screw.  They noted that further investigations of these guidelines will be carried out to validate this electrophysiological approach.

It is interesting that the conclusion of the study by Raynor et al (2002) was directly opposite to that by Reidy et al (2001), who, in a prospective study, examined the use of inter-costal EMG monitoring as an index of the accuracy of the placement of pedicle screws in the thoracic spine.  A total of 95 thoracic pedicle screws in 17 patients were studied.  Prior to insertion of the screw, the surgeon recorded his assessment of the integrity of the pedicle track, and then stimulated the track using a K-wire pedicle probe connected to a constant current stimulator.  A CMAP was recorded from the appropriate inter-costal or abdominal muscles.  Post-operative computed tomography (CT) was performed to establish the position of the screw.  The stimulus intensity needed to evoke a muscle response was correlated with the position of the screw on the CT scan.  There were 8 unrecognized breaches of the pedicle.  Using 7.0 mA as a threshold, the sensitivity of EMG was 0.50 in detecting a breached pedicle and the specificity was 0.83.  Thoracic pedicle screws were accurately placed in more than 90 % of patients.  These investigators concluded that EMG monitoring did not significantly improve the reliability of placement of the screw.

Regarding the observations by Raynor and colleagues (2002), Finkelstein (2003) stated that “the value of a screening test should be such that the outcome could be altered by the prediction of an adverse event.  The protocol of the study by Raynor et al would suggest that the damage of a medially placed screw would have already occurred by the time the screws were tested for CMAP and then compared to the other screws, determining an ”average“ of all other thresholds.  Aside from improving the radiograph, it would seem to have little clinical utility”.  Finkelstein also noted that the utility of a screening test is defined by its sensitivity and specificity, as well as its positive predictive value.  These were assessed in the study by Reidy and associates, and deemed unable to improve the accuracy beyond an experienced surgeon's knowledge of well described anatomical landmarks.

Ajiboye and colleagues (2017) conducted a retrospective, national data-base study to evaluate the trends in the use of EMG for instrumented postero-lateral lumbar fusions (PLFs) in the United States; and examine the risk of neurological injury following PLFs with and without EMG.  Neurologic injuries from iatrogenic pedicle wall breaches during screw placement are known complications of PLFs.  The routine use of IONM such as EMG during PLF to improve the accuracy and safety of pedicle screw implantation remains controversial.  A retrospective review was performed using the PearlDiver Database to identify patients who had PLF surgery with and without EMG for lumbar disorders from 2007 to 2015.  Patients undergoing concomitant interbody fusions or spinal deformity surgery were excluded.  Demographic trends and risk of neurological injuries were assessed.  During the study period of 2007 to 2015, a total of 9,957 patients underwent PLFs.  Overall, EMG was used in 2,495 (25.1 %) of these patients.  There was a steady increase in the use of EMG from 14.9 % in 2007 to 28.7 % in 2009, followed by a steady decrease to 21.9 % in 2015 (p < 0.0001).  The risk of post-operative neurological injuries following PLFs was 1.35 % (134/9,957) with a risk of 1.36 % (34/2,495) with EMG and 1.34 % (100/7,462) without EMG (p = 0.932); EMG is used most commonly for PLFs in the Southern part of the United States.  The authors concluded that there was a steady increase in the routine use of EMG for PLFs followed by a steady decline; and regional differences were observed in the utility of EMG for PLFs.  These researchers stated that the risk of neurological complications following PLF in the absence of spinal deformity was low and the routine use of EMG for PLF may not decrease the risk.

During Prostatectomy / Prostate Surgery

An UpToDate review on “Radical prostatectomy for localized prostate cancer” (Klein, 2022) does not mention intraoperative EMG monitoring.

During Rectal Cancer Surgery

Wałega and colleagues (2017) presented their preliminary experience with intra-operative neuro-monitoring during rectal resection.  These investigators qualified 4 patients (2 women, 2 men; age of 42 to 53 years) with rectal cancer for surgery with intra-operative neuro-monitoring.  In all patients, functional tests of the anorectal area were performed before surgery.  Action potentials from the sphincter complex in response to nerve fiber stimulation were recorded with electrodes implanted before surgery.  Moreover, these researchers inserted a standard, 18FR Foley's urinary catheter to which a T-tube was connected to allow urine outflow and measurement of pressure changes in the bladder induced by detrusor contractions during stimulation.  Setting up neuro-monitoring prolonged surgery time by 30 to 40 minutes, or even by 60 to 80 minutes in the case of the first 2 patients.  Neuro-monitoring itself took additional 20 to 30 minutes during surgery.  In all patients, these investigators stimulated branches of the inferior hypogastric plexus in their anatomical position during dissection.  In 3 patients, these researchers evoked responses both from the bladder and the sphincter in all planes of stimulation.  In 1 patient, there was no response from the left side of the bladder, and in the same patient, these investigators observed symptoms of neurogenic bladder.  Based on the available literature and their own experience, the authors stated that monitoring of bladder pressure and EMG signals from rectal sphincters enabled visualization and preservation of autonomic nervous system structures, both sympathetic and parasympathetic.  They noted that intra-operative signals appeared to be correlated with clinical presentation and functional examinations after surgery.  They stated that in order to objectify their findings, it is necessary to perform functional examinations before and after surgery in a larger group of patients.

During Resection of Skull Base Tumors / Spinal Tumors

Fehlings et al (2010) carried out a systematic review of the literature to examine if IOM is able to sensitively and specifically detect intra-operative neurologic injury during spine surgery and to examine if IOM results in improved outcomes for patients during these procedures.  They conducted a review of the English language literature for articles published between 1990 and March 2009.  Medline, Embase, and Cochrane Collaborative Library databases were searched, as were the reference lists of published articles examining the use of IOM in spine surgery.  Two independent reviewers assessed the level of evidence quality using the GRADE criteria, and disagreements were resolved by consensus.  A total of 103 articles were initially screened and 32 met the pre-determined inclusion criteria.  These investigators determined that there is a high level of evidence that multi-modal IOM was sensitive and specific for detecting intra-operative neurologic injury during spine surgery.  There was a low level of evidence that IOM reduced the rate of new or worsened peri-operative neurologic deficits.  There was very low evidence that an intra-operative response to a neuromonitoring alert reduced the rate of peri-operative neurologic deterioration.  The authors concluded that based on strong evidence that multi-modality IOM (MIOM) was sensitive and specific for detecting intra-operative neurologic injury during spine surgery, it is recommended that the use of MIOM be considered in spine surgery where the spinal cord (SC) or nerve roots (NRs) are deemed to be at risk, including procedures involving deformity correction and procedures that require the placement of instrumentation.

Scibilia et al (2016) noted that spinal tumor (ST) surgery carries the risk of new neurological deficits in the post-operative period; and IONM represents an effective method of identifying and monitoring in real time the functional integrity of both the SC and the NRs.  Despite consensus favoring the use of IONM in ST surgery, in this era of evidence-based medicine, there is still a need to demonstrate the effective role of IONM in ST surgery in achieving an oncological cure, optimizing patient safety, and considering medicolegal aspects.  These investigators focused on the rationale for and the accuracy (sensitivity, specificity, PPVs and NPVs) of IONM in ST surgery in light of more recent evidence in the literature, with specific emphasis on the role of IONM in reducing the incidence of post-operative neurological deficits.  This review confirmed the role of IONM as a useful tool in the workup for ST surgery.  The authors concluded that individual monitoring and mapping techniques are inadequate to account for the complex function of the SC and NRs.  Conversely, multi-modal IONM is highly sensitive and specific for anticipating neurological injury during ST surgery and represents an important tool for preserving neuronal structures and achieving an optimal post-operative functional outcome.

Elangovan et al (2016) examined the value of IONM using EMG, BAEPs, and SSEPs to predict and/or prevent post-operative neurological deficits in pediatric patients undergoing endoscopic endonasal surgery (EES) for skull base tumors.  All consecutive pediatric patients with skull base tumors who underwent EES with at least 1 modality of IONM (BAEP, SSEP, and/or EMG) at the authors’ institution between 1999 and 2013 were retrospectively reviewed.  Staged procedures and repeat procedures were identified and analyzed separately.  To evaluate the diagnostic accuracy of significant free-run EMG activity, the prevalence of cranial nerve (CN) deficits and the sensitivity, specificity, PPV and NPV were calculated.  A total of 129 patients underwent 159 procedures; 6 patients had a total of 9 CN deficits.  The incidences of CN deficits based on the total number of nerves monitored in the groups with and without significant free-run EMG activity were 9 % and 1.5 %, respectively.  The incidences of CN deficits in the groups with 1 staged and more than 1 staged EES were 1.5 % and 29 %, respectively.  The sensitivity, specificity, and NPVs (with 95 % CIs) of significant EMG to detect CN deficits in repeat procedures were 0.55 (0.22 to 0.84), 0.86 (0.79 to 0.9), and 0.97 (0.92 to 0.99), respectively.  Two patients had significant changes in their BAEPs that were reversible with an increase in mean arterial pressure.  The authors concluded that IONM could be employed effectively during EES in children.  These investigators stated that EMG monitoring was specific for detecting CN deficits and could be an effective guide for dissecting these procedures.  They stated that triggered EMG (tEMG) should be elicited intra-operatively to check the integrity of the CNs during and after tumor resection.  Given the anatomical complexity of pediatric EES and the unique challenges encountered, multi-modal IONM could be a valuable adjunct to these procedures.

Shkarubo et al (2017) stated that intra-operative identification of CNs is crucial for safe surgery of skull base tumors.  Currently, only a small number of published papers described the technique of tEMG in ESS for removal of such tumors.  In a pilot study, these researchers examined the effectiveness of tEMG in preventing intra-operative CN damage in endoscopic endonasal surgery of skull base tumors.  A total of 9 patients were operated on using the endoscopic endonasal approach within a 1-year period.  The tumors included large skull base chordomas and trigeminal neurinomas localized in the cavernous sinus.  During the surgical process, CN identification was performed using mono-polar and bi-polar t-EMG methods.  Assessment of CN functional activity was carried out both before and after tumor removal.  These investigators mapped 17 CNs in 9 patients; 3rd, 5th, and 6th CNs were identified intra-operatively.  There were no cases of post-operative functional impairment of the mapped CNs.  In 1 case, these researchers were unable to get an intra-operative response from the 4th CN and observed its post-operative transient plegia (the function was normal before surgery).  The authors concluded that tEMG allowed surgeons to control the safety of the CNs both during and after skull base tumor removal, rendering it a promising method of intra-operative neuromonitoring, which needs further investigation.

Shkarubo et al (2018) stated that preservation of anatomic integrity and function of the CNs during the removal of skull base tumors is one of the most challenging procedures in EES.  It is possible to use intra-operative mapping and identification of the CNs to facilitate their preservation.  These researchers examined the effectiveness of intra-operative tEMG in prevention of iatrogenic damage to the CNs.  A total of 23 patients with various skull base tumors (chordomas, neuromas, pituitary adenomas, meningiomas, cholesteatomas) underwent mapping and identification of CNs during tumor removal using the EE approach (EEA) in the Department of Neurooncology of Federal State Autonomous Institution "N.N. Burdenko National Medical Research Center of Neurosurgery" of the Ministry of Health of the Russian Federation from 2013 to 2018.  During the surgical interventions, mapping and identification of the CNs were performed using EMG in triggered mode.  The effectiveness of the method was examined based on a comparison with a control group (41 patients).  In the main group of patients, 44 CNs were examined during surgery using tEMG.  During the study, the 3rd, 5th, 6th, 7th, and 12th CNs were identified intra-operatively.  Post-operative CN deficiency was observed in 5 patients in the study group and in 13 patients in the control group.  The average length of hospitalization was 9 days.  These investigators did not receive statistically significant data supporting the fact that intra-operative identification of CNs using tEMG lowered the incidence of post-operative complications in the form of CN deficits (p = 0.56); however, the odds ratio (OR = 0.6) suggested a less frequent occurrence of complications in the study group.  The authors considered tEMG a promising methodology, even though it unquestionably requires further research.

Ferreira et al (2021) proposed to present reference parameters for trigeminal (5th) and facial (7th) CNs-tEMG during EEA skull base surgeries to allow more precise and accurate mapping of these CNs.  These investigators retrospectively reviewed EEA procedures conducted at the University of Pittsburgh Medical Center between 2009 and 2015.  tEMG recorded in response to stimulation of CNs V and VII was analyzed.  Analysis of tEMG waveforms included latencies and amplitudes.  Medical records were reviewed to determine the presence of peri-operative neurologic deficits.  A total of 28 patients were included.  tEMG from 34 CNs (22 V and 12 VII) were analyzed.  For CN V, the average onset latency was 2.9 ± 1.1 ms and peak-to-peak amplitude was 525 ± 436.94 μV (n = 22).  For CN VII, the average onset latency and peak-to-peak amplitude were 5.1 ± 1.43 ms and 315 ± 352.58 μV for the orbicularis oculi distribution (n = 9), 5.9 ± 0.67 ms and 517 ± 489.07 μV on orbicularis oris (n = 8), and 5.3 ± 0.98 ms 303.1 ± 215.3 μV on mentalis (n = 7), respectively.  The authors concluded that these findings supported the notion that onset latency may be a feasible parameter in the differentiation between the CNs V and VII during the crosstalk phenomenon in EEA surgeries; however, the particularities of this type of procedure should be taken into consideration. 

Ruschel et al (2021) stated that intra-medullary SC tumors (IMSCT) account for approximately 2 % to 4 % of all CNS tumors.  Surgical resection is the mainstay of treatment; but might cause damage to functional tissues.  IONM is an adopted measure to decrease surgical complications.  These investigators described the results of IMSCT submitted to surgery under IONM at a tertiary institution.  The sample consisted of consecutive patients with IMSCT admitted to the Neurological Institute of Curitiba from January 2007 to November 2016.  A total of 47 patients were surgically treated; 23 (48.9 %) were men and 24 (51.1 %) were women; and the mean age was 42.77 years.  The mean follow-up time was 42.7 months.  Neurological status improved in 29 patients (62 %), stable in 6 (13 %), and worse in 12 (25 %).  Patients who presented with motor symptoms at initial diagnosis had a worse outcome compared to patients with sensory impairment and pain (p = 0.026).  Patients with a change in EMG had worse neurological outcomes compared to patients who did not show changes in monitoring (p = 0.017).  The authors concluded that no prospective, randomized, high evidence study has been carried out to-date to compare clinical evolution following surgery with or without monitoring.  In this cohort, surgical resection was well succeeded mainly in oligosymptomatic patients with low pre-operative McCormick classification and no worsening of IONM during surgery.  These researchers believed that microsurgical resection of IMSCT with simultaneous IONM is the gold standard treatment and achieved with good results.

During Rotator Cuff Repair

An UpToDate review on “Management of rotator cuff tears” (Martin and Martin, 2018) does not mention intraoperative EMG monitoring.

During Sacroiliac Joint Injection

An UpToDate review on “Subacute and chronic low back pain: Nonsurgical interventional treatment” (Chou, 2020) states that “Sacroiliac joint injection — The sacroiliac joints are thought to be the source of low back pain in some patients.  Effective methods for diagnosing and treating sacroiliac joint pain in patients without spondyloarthropathy remain controversial.  Periarticular steroid injection does not require radiographic guidance.  One small (n = 24), randomized trial found periarticular sacroiliac joint glucocorticoid injection more effective than local anesthetic injection for pain relief (change in pain of -40 versus -13 mm on a 100 mm visual analogue scale one month after injection) in patients with chronic pain in the sacroiliac joint area and at least one physical exam finding for sacroiliac pain.  These results should be considered preliminary, due to the small sample size and relatively short-term follow-up.  There are no randomized trials of intraarticular sacroiliac joint steroid injection versus a sham procedure in patients without spondyloarthropathy”.  This review does not mention EMG monitoring for sacroiliac joint injection.

During Shoulder Labral Repair

In a prospective, cohort study, Esmail et al (2005) examined the ability of a novel intra-operative neurophysiologic monitoring method used to locate the axillary nerve, predict relative capsule thickness, and identify impending injury to the axillary nerve during arthroscopic thermal capsulorrhaphy of the shoulder.  A total of 20 consecutive patients with glenohumeral instability were monitored prospectively during arthroscopic shoulder surgery.  Axillary nerve mapping and relative capsule thickness estimates were recorded before the stabilization portion of the procedure.  During labral repair and/or thermal capsulorrhaphy, continuous and spontaneous EMG recorded nerve activity.  In addition, trans-spinal MEPs of the 4th and 5th cervical roots and brachial plexus electrical stimulation, provided real-time information about nerve integrity.  Axillary nerve mapping and relative capsule thickness were recorded in all patients.  Continuous axillary nerve monitoring was successfully performed in all patients; 11 of the 20 patients underwent thermal capsulorrhaphy alone or in combination with arthroscopic labral repair; 9 patients underwent arthroscopic labral repair alone.  In 4 of the 11 patients who underwent thermal capsulorrhaphy, excessive spontaneous neurotonic EMG activity was noted, thereby altering the pattern of heat application by the surgeon.  In 1 of these 4 patients, a small increase in the motor latency was noted after the procedure but no clinical deficit was observed.  There were no neuromonitoring or clinical neurologic changes observed in the labral repair group without thermal application.  At last follow-up, no patient in either group had any clinical evidence of nerve injury or complications from neurophysiologic monitoring.  The authors successfully evaluated the use of intra-operative nerve monitoring to identify axillary nerve position, capsule thickness, and provided real-time identification of impending nerve injury and function during shoulder thermal capsulorrhaphy.  These researchers stated that the use of intra-operative nerve monitoring altered the heat application technique in 4 of 11 patients and may have prevented nerve injury.

During Supraclavicular First Rib Resection and Scalenectomy for Thoracic Outlet Syndrome

An UpToDate review on “Overview of thoracic outlet syndromes” (Goshima, 2022) does not mention electromyography and electroencephalography as management tools.   

During Tibial Neurectomy

Sitthinamsuwan et al (2013) stated,that selective tibial neurotomy (STN) is an effective neurosurgical intervention for treating ankle spasticity.  These investigators used intraoperative EMG for selecting targeted fascicles and determined the degree of fascicular resection in STN.  Participants who underwent STN with utilization of intraoperative EMG were recruited.  Modified Ashworth Scale (MAS), passive range of motion (PROM) of the ankle in plantar flexion and dorsiflexion, Massachusetts General Hospital Functional Ambulatory Classification (MGHFAC) and ability to attain full plantigrade stance were assessed pre- and post-operatively.  A total of 21 STNs were performed in 15 patients.  The mean pre- and post-operative MAS and PROM were 2.8 and 0.4 (p < 0.001), 39.5(o) and 66.0(o) (p < 0.001), respectively.  The mean level of MGHFAC was improved from 3.3 pre-operatively to 4.9 post-operatively (p < 0.01); 6 non-ambulators had significant amelioration in MGHFAC level.  Post-operatively, 19 of 21 lower limbs achieved full plantigrade, and 6 patients could perform selective voluntary motor control of the ankle.  The authors concluded that STN is an effective procedure for spastic ankle in well-selected cases; intraoperative EMG aided in selection of targeted fascicles, increased objectivity in neurotomy and prevents excessive denervation.  This was a small, uncontrolled study; the clinical value of intraoperative EMG in this setting needs to be further investigated.

During Excision of Branchial Cleft Anomalies (Cysts, Fistulae, or Sinuses)

Isaacson and Martin (2000) carried out a retrospective review of consecutive surgical procedures by a single surgeon, using a consistent technique during a 9-year period to examine the safety and efficacy of surgical excision of selected 1st branchial cleft cysts using electrophysiological rather than anatomical location of the facial nerve in 11 children with 1st branchial cleft cysts.  Selected 1st branchial cleft cysts were removed using a smaller surgical approach than that generally advocated.  The facial nerve was localized using electrophysiological means rather than superficial parotidectomy and identification of the nerve trunk and branches.  Facial nerve EMG was performed using a 2-channel system with visual display and audio output (NIM or NIM-2).  One pair of needle electrodes was placed in the lateral margin of the orbicularis oculi, and another pair was placed in the lateral orbicularis oris muscles on the side that was operated on.  Each pair was routed to 1 of 2 input channels on the EMG system.  A needle ground electrode was placed in the high-midline forehead.  A 60-millisecond time base was used to visually monitor the spontaneous, mechanically evoked and electrically evoked EMG activity of both channels.  A trained clinical neurophysiologist conducted the EMG monitoring.  Main outcome measures included successful removal of the lesion, avoidance of facial nerve injury, incidence of Fry syndrome, and cosmesis.  A total of 11 patients underwent surgical excision of 1st branchial cleft cysts during a 9-year period; 10 lesions were removed without the need for anatomical localization of the facial nerve trunk.  There was no facial weakness, recurrence of the lesions, or Fry syndrome during a follow-up of 6 months to 7 years; and cosmesis was superior.  The authors concluded that electrophysiological location of the facial nerve may, in the appropriate setting, replaced anatomical localization for 1st branchial cleft cysts that are superior to the stylomastoid foramen and not previously infected or surgically violated.

During Excision of Sentinel Lymph Nodes

An UpToDate review on “Technique of axillary lymph node dissection” (Margenthaler, 2021) does not mention intraoperative EMG as a management tool.

Facial Nerve during Vestibular Schwannoma Surgery

Huang and colleagues (2018) examined the predictive utility of stimulation threshold (ST) of intra-operative EMG monitoring for FN outcomes among vestibular schwannoma (VS) patients post-operatively.  These researchers enrolled 103 unilateral VS patients who underwent surgical resection into a prospective cohort observational study from January 2013 to April 2015 in their hospital; ST values were used to categorize 81 patients into the "low current" (ST less than or equal to 0.05 mA) group and 22 patients into the control (ST greater than 0.05 mA) group.  The FN function outcomes were summarized and correlated with these 2 groups at 1, 3, 6, and 12 months after surgery.  Binary regression analysis revealed that the percentage of "good" FN outcome, defined by House-Brackmann (HB) classification of facial function (I to II), in the "low current" group was significantly higher than that of the control group (42.0 versus 4.5 % at 1 month, p = 0.015; 64.2 versus 31.8 % at 3 months, p = 0.024; 72.8 versus 40.9 % at 6 months, p = 0.021; 84.0 versus 45.5 % at 12 months, p = 0.002).  Ordinal regression analysis showed that the distribution of HB scores was shifted in a favorable direction in the "low current" group at 1, 3, 6, and 12 months post-operatively.  For patients with HB IV at the 1st month post-operative period, the recovery rate of the "low current" group was significantly higher than that of control group (p = 0.003).  "Low current" can predict FN function outcomes better and has faster recovery rates than that of the control group.

The Congress of Neurological Surgeons’ systematic review and evidence-based guidelines on “Intraoperative cranial nerve monitoring in vestibular schwannoma surgery” (Vivase et al, 2018) provided the following recommendations:

  • Intra-operative FN monitoring be routinely utilized during VS surgery to improve long-term facial nerve function.
  • Intra-operative FN monitoring can be used to accurately predict favorable long-term FN function after VS surgery.  Specifically, the presence of favorable testing reliably portends a good long-term FN outcome.  However, the absence of favorable testing in the setting of an anatomically intact FN does not reliably predict poor long-term function and therefore cannot be used to direct decision-making regarding the need for early re-innervation procedures.

Intraoperative EMG and Evoked Potential Studies

During Hip Dysplasia Surgery

Pring and colleagues (2002) stated that peri-acetabular osteotomy (PAO) has become the procedure of choice in many centers for the treatment of symptomatic hip dysplasia.  Intra-operative real-time nerve monitoring has been advocated during acetabular fracture repair and complex total hip arthroplasties to prevent iatrogenic sciatic nerve injury.  To the authors' knowledge there is no information concerning the use of intra-operative EMG monitoring during PAO.  These researchers examined the use of intra-operative continuous EMG monitoring during PAO in a relatively large consecutive series of patients as a mechanism to prevent nerve injury during surgery and as a prognostic indicator of neurologic function after PAO.  From September 1992 to July 1999, a total of 140 consecutive PAOs were performed in 127 patients at the authors' institution.  There were 96 women and 31 men, with an average age of 32 years at the time of surgery.  All patients had intra-operative EMG monitoring of femoral and sciatic innervated muscles.  All patients were followed-up for a minimum of 1 year, until complete resolution of neurologic deficits, or both; 36 patients (26 %) had abnormal EMG activity recorded during surgery; 7 patients (5 %) had peroneal nerve deficits post-operatively including extensor hallucis longus and tibialis anterior weakness with loss of sensation in the first web space.  Abnormal EMG activity was observed intra-operatively in 5 of the 7 patients with post-operative deficits; 6 of the 7 injuries resolved completely; 1 patient with intra-operative EMG activity (0.7 %) had a post-operative foot-drop that persisted for greater than 1 year.  There were no femoral, tibial, or obturator nerve deficits observed.  The authors concluded that intra-operative EMG monitoring appeared to provide prediction of post-operative neurologic deficit.

Commenting on the afore-mentioned study, Sierra and colleagues (2012) noted that “Pring et al [2002] specifically studied nerve injuries after PAO at one institution and reported an incidence of 5 %, of which 0.7 % of injuries were permanent.  They recommended the use of intraoperative EMG to decrease the risk of nerve injury and as a prognostic tool in cases when injury had occurred.  Its use during PAO, however, has been debatable and is currently surgeon-dependent.  Its drawbacks include cost and the fact that it requires specialized personnel present for its interpretation during the case.  It also has certain limitations because it cannot identify all nerve irritation or trauma.  A sharp laceration of the nerve, for example, may not produce neurotonic discharges and may not be recorded.  The presence of EMG could potentially provide the surgeon a false sense of safety that could lead to inadvertent injury to the nerve.  It may be useful in surgery, however, because it may identify situations in which the nerve is at risk, such as during placement of retractors in inappropriate locations and it may identify over-lengthening of the extremity.  It also could help the surgeon in determining whether exploration of the nerve may be warranted, such as in cases when the EMG fires during a specific maneuver that may injure the nerve”.  

Novais and associates (2017) noted that sciatic nerve palsy after PAO is a serious complication.  These researchers examined if a multi-modal sciatic monitoring technique allows for identification of surgical steps that place the sciatic nerve at risk.  Transcranial electrical motor evoked potentials (TcMEPs), SSEPs, and spontaneous EMG were monitored in a consecutive series of 34 patients (40 hips) who underwent PAO for the treatment of symptomatic hip dysplasia between January 2012 and November 2014.  There were 29 females (85 %) and 5 males (15%) with an average age of 19 years (range of 12 to 36 years) at the time of surgery.  These investigators detected 8 temporary sciatic nerve monitoring alerts in 6 patients (incidence of 15 %).  The events included decrease in amplitude of the TcMEPs related to the position of the hip during incomplete ischium osteotomy and placement of a retractor in the sciatic notch during the posterior column osteotomy (n = 3), generalized bilateral decrease in TcMEPs during fragment manipulation and fixation in association with acute blood loss (n = 2), and a change in SSEPs during a superior pubic osteotomy and supra-acetabular osteotomy (n = 1).  At the end of the procedure, TcMEPs and SSEPs were at baseline and there was no abnormal pattern on EMG in all patients.  Post-operatively, at 2, 6, 12 weeks, and 6 and 12 months, no motor weakness or sensory deficits were noted.  The authors concluded that multi-modal neuro-monitoring allowed for identification of intra-operative steps and maneuvers that potentially place the sciatic nerve at higher risk of injury.

During Moyamoya Surgery

An UpToDate review on “Moyamoya disease: Treatment and prognosis” (Suwanwela, 2019) does not mention SSEP / somatosensory evoked potentials and EMG / electromyography as management tools.

During Spinal Surgery

Spinal surgery is associated with a risk of injury to the spinal cord.  Methods to intraoperatively monitor spinal function have been employed to minimize such risks.  These neurophysiological techniques include EMG, somato-sensory evoked potentials (SSEPs), dermatosensory evoked potentials (DSEPs), and motor evoked potentials (MEPs). The main objective of intraoperative neurophysiological monitoring of spinal cord or nerve root function is to identify induced neurophysiological alterations so that they can be detected as they occur and corrected during surgery; thus avoiding post-surgical complications such as myelopathy or radiculopathy, as well as permanent injury.

Weiss (2001) discussed the application of intra-operative neurophysiological monitoring to surgical treatment of lumbar stenosis.  The author noted that benefits of SSEP and MEP studies during surgical correction of spinal deformity are well known and documented.  Continuous free-running and stimulus-triggered electromyography (EMG) monitoring during placement of pedicle screw is an accepted practice at many institutions.  Moreover, the functional integrity of spinal cord, cauda equina, and nerve roots should be monitored throughout every stage of surgery including exposure and decompression.  Continuous free-running EMG provides feedback regarding the location and potential for surgical injury to the lumbo-sacral nerve roots within the operative field, while stimulus-triggered EMG can confirm that transpedicular instrumentation has been positioned correctly within the bony cortex.  Continuous free-running EMG is monitored from muscles innervated by nerves or nerve roots considered to be at risk during spinal surgery.  Surgical trauma to these nerve roots and motor nerves will produce high-frequency spikes or trains of motor unit potentials in monitored muscles.  These neural discharges can be used to alert the surgeon of inadvertent trauma to nerve roots/peripheral nerves, and avoid more severe or irreversible injury.  Multiple channels of continuous free-running EMG activity can be monitored simultaneously, providing real-time information regarding lumbosacral nerve root motor function throughout the operation (Holland, 2002).

Electro-stimulation of intact motor nerves will elicit compound muscle action potentials (CMAP) in innervated muscles.  Intra-operative CMAP responses (all-or-none) are usually recorded by means of intra-muscular needle electrodes and submaximal stimulation, in contrast to those measured in diagnostic EMG laboratories where surface electrodes and maximal stimulation are employed.  Electro-stimulation is usually performed by the surgeon using a hand-held monopolar or bipolar device within the operative field.  The advantage of bipolar stimulation is that it evokes a localized stimulating current, thus avoiding unwanted current spreading to nearby nerves.  This is especially useful during peripheral nerve or plexus surgeries, when multiple nerves lie in close proximity.  Two examples of stimulus-triggered EMG monitoring are as follows:
  1. the presence of a stimulus-triggered CMAP response can be used to differentiate nerve root from fibrous bands during surgical dissection for tethered cord release (Legatt et al, 1992), and
  2. the failure to produce a CMAP response from stimulation of pedicle screws and holes at a stimulus intensity of 7 to 11 mA is the electrophysiological criterion most commonly used to exclude a pedicular cortical perforation (Maguire et al, 1995). 

However, since the expected finding is negative (i.e., no CMAP responses), it is always beneficial to test and document a positive control response to confirm the reliability of the test results.  This is best achieved by directly stimulating an exposed nerve or nerve root at the same stimulus intensity (Holland, 2002).

Although intra-operative monitoring of EMG has been used to monitor spinal cord function during spinal surgery, there is disagreement regarding its clinical value.

In a clinical trial, Owen and colleagues (1994) examined the use of mechanically elicited EMG during placement of pedicle screws in patients undergoing surgery for spinal stenosis (n = 89).  Mechanically elicited EMG was recorded in muscle groups innervated by cervical or lumbar nerve roots.  Confirmation of surgical activity with the level of the EMG was correlated.  Results of this study indicated that mechanically elicited EMG is very sensitive to nerve root irritation.  Compared to other neurophysiological methods, EMG is a viable alternative.  These authors concluded that mechanically elicited EMG is sensitive and specific to nerve root firings and should be considered for use during the dynamic phases of surgery.

In a case series study, Beatty et al (1996) discussed their experiences with the use of continuous intra-operative EMG recording during spinal surgery.  A total of 150 patients underwent spinal surgery for radiculopathy (120 underwent lumbar surgery and 30 had cervical operations).  All of the surgeries were performed to alleviate symptoms due to disc herniation, spondylosis, or both.  During the surgical procedures, continuous intra-operative EMG recordings were taken from the muscle corresponding to the involved nerve root.  In baseline recordings taken in the operating room 10 minutes before lumbar surgery, electrical discharge or firing was recorded from the muscle in 18 % (22 of 120 patients) of the cases.  Once the nerve was decompressed, muscle firing ceased.  Electrical discharges were produced with regularity on nerve root retraction.  These authors concluded that continuous EMG monitoring can be accomplished easily and yields valuable information that indicates when the nerve root is adequately decompressed or when undue retraction is exerted on the root.  The findings of Owen et al (1994) as well as Beatty et al (1996) are in congruous with that of Limbrick and Wright (2005) who stated that surgeon-driven evoked EMG threshold testing may provide a simple, effective adjunct to lumbar microendoscopic diskectomy for intra-operative verification of nerve root decompression as well as that of Jimenez and co-workers (2005) who reported that the incidence of post-operative C-5 palsies was lowered from 7.3 to 0.9 % as a consequence of intra-operative continuous EMG monitoring.  Jimenez et al (2005) also noted that no patient suffered a post-operative C-5 palsy when intra-operative evidence of root irritation was absent.

Continuous intra-operative EMG plus SSEP have also been used in spinal surgery to prevent neural injury.  However, only limited data are available on the sensitivity, specificity, and predictive values of intra-operative electrophysiological changes with regard to the occurrence of new post-operative neurological deficits.  Gunnarsson and colleagues (2004) retrospectively analyzed a prospectively accrued series of 213 consecutive patients who underwent intra-operative monitoring with EMG and SSEP during thoraco-lumbar spine surgery.  The authors examined data on patients who underwent intra-operative monitoring with continuous lower limb EMG and SSEP.  The analysis focused on the correlation of intra-operative electrophysiological changes with the development of new neurological deficits.  A total of 213 patients underwent surgery on a total of 378 levels; 32.4 % underwent an instrumented fusion.  Significant EMG activation was observed in 77.5 % of the patients and significant SSEP changes in 6.6 %.  Fourteen patients (6.6 %) had new post-operative neurological symptoms.  Of those, all had significant EMG activation, but only 4 had significant SSEP changes.  Intra-operative EMG activation had a sensitivity of 100 % and a specificity of 23.7 % for the detection of a new post-operative neurological deficit, while SSEP had a sensitivity of 28.6 % and specificity of 94.7 %.  These investigators concluded that intra-operative EMG activation has a high sensitivity for the detection of a new post-operative neurological deficit but a low specificity.  In contrast, SSEP has a low sensitivity but a high specificity.  They noted that combined intra-operative monitoring with EMG and SSEP is helpful for predicting and possibly preventing neurological injury during thoracolumbar spine surgery.

The aforementioned study by Gunnarson et al (2004) was 1 of 2 studies of intraoperative EMG that met inclusion criteria in the recent systematic evidence review of intraoperative neuromonitoring for spinal surgery by Fehlings, et al. (2010). The other study, by Kelleher, et al. (2008), looked at the predictive value of intraoperative EMGs and evoked potentials in cervical spine surgery. The aforementioned study by Gunnarsson, et al. (2004) reported on EMGs and SSEPs in 213 patients undergoing thoracolumbar surgery. EMG activation occurred in more than three-fourths of patients, including all of 14 patients who were found to have new or exacerbated neurologic symptoms postoperatively. The authors found that intraoperative EMG had a negative predictive value of 1.0 but a positive predictive value of 0.085. The authors posited that the low specificity of intraoperative EMG may be because the surgeon was able to avoid injury by changing the surgical strategy based upon the monitoring. However, the study did not report whether and what type of changes in surgical strategy were made as a result of EMG neuromonitoring.  Significant limitations of this study include retrospective analysis, lack of standardized method of case ascertainment, and lack of blinding of clinical outcome assessment. Nonobjective outcomes are particularly problematic for assessing the usefulness of intraoperative neuromonitoring because of the potential for diagnostic suspicion bias. Without masked clinical outcome assessment and a standardized method of case ascertainment, patients with a positive EMG result could be more thoroughly evaluated for neurologic deficits than persons with a normal intraoperative neuromonitoring result. This bias would tend to exaggerate the usefulness of intraoperative EMG.

In a review on intra-operative EMG monitoring during thoracolumbar spinal surgery, Holland (1998) stated that this approach has a number of potential limitations, including:
  1. EMG is sensitive to blunt lumbosacral nerve root irritation or injury, but may provide misleading results with “clean” nerve root transaction,
  2. EMG must be recorded from muscles belonging to myotomes appropriate for the nerve roots considered at risk from surgery,
  3. EMG can be effective only with careful monitoring and titration of pharmacological neuromuscular junction blockade,
  4. when transpedicular instrumentation is stimulated, an exposed nerve root should be stimulated directly as a positive control whenever possible,
  5. pedicle holes and screws should be stimulated with single shocks at low-stimulus intensities when pharmacological neuromuscular blockade is excessive, and
  6. chronically compressed nerve roots that have undergone axonotmesis (wallerian degeneration) have higher thresholds for activation from electrical and mechanical stimulation. 

Hence, whenever axonotmetic nerve root injury is suspected, the stimulus thresholds for transpedicular holes and screws must be specifically compared with those required for the direct activation of the adjacent nerve root (and not published guideline threshold values).

Krassioukov et al (2004) examined the neurological outcomes after complex lumbo-sacral surgery in patients undergoing multi-modality neurophysiological monitoring.  A total of 61 patients were consecutively enrolled in this study.  These subjects underwent complex intra- and extra-dural lumbosacral procedures with concomitant intra-operative EMG monitoring of the lower-limb muscles, external anal and urethral sphincters (EAS and EUS), and lower-limb SSEP.  Long-term (minimum of 2 years) clinical follow-up data were obtained in all cases.  Most subjects were treated for spinal/spinal cord tumors (61 %) or adult tethered cord syndrome (25 %).  Recordable lower-extremity SSEP were reported in 54 patients (89 %).  New post-operative neurological deficits occurred in only 3 patients (4.9 %), and remained persistent in only 1 patient (1.6 %) at long-term follow-up examination.  In only 1 of these cases was a significant decrease in SSEP amplitude detected.  Spontaneous EMG activity was observed in the lower-extremity muscles and/or EAS and EUS in 51 cases (84 %).  Intra-operatively, EMG demonstrated activity only in the EUS in 5 % of patients and only in the EAS in 28 %.  In 7 patients (11 %) spontaneous intra-operative EMG activity was observed in both the EAS and the EUS; however, in only 3 of these cases was EMG activity recorded in both sphincters simultaneously.  In addition to spontaneously recorded EMG activity, electrically evoked EMG activity was also used as an intra-operative adjunct.  A bipolar stimulating electrode was used to identify functional neural tissue before undertaking microsurgical dissection in 58 individuals (95 %).  In the majority of these patients, evoked EMG activity occurred either in 1 (33 %) or in 2 muscles (9 %) simultaneously.  The presence of electrically evoked EMG activity in structures encountered during microdissection altered the plan of treatment in 24 cases (42 %).  The investigators concluded that the combined SSEP and EMG monitoring of lower-limb muscles, EAS, and EUS is a practical and reliable method for obtaining optimal electrophysiological feedback during complex neurosurgical procedures involving the conus medullaris and cauda equina.  Analysis of the results indicates that these intra-operative adjunctive modalities positively influence decision making with regard to microsurgery and reduce the risk of peri-operative neurological complications.  Moreover, the authors noted that validation of the clinical value of these approaches, however, will require further assessment in a larger prospective cohort of patients.

In a review on electrophysiological intra-operative monitoring for spinal surgeries, Slimp (2004) stated that the advent of equipment capable of performing SSEP, MEP, and EMG in a multi-plexed fashion, and in a timely manner brings a new level of monitoring that far exceeds the previous basic monitoring done with SSEP only.  However, the author noted that whether this more comprehensive monitoring will result in greater protection of the nervous system awaits future analysis.  It is also interesting to note that when Erickson and co-workers (2005) from the technology assessment unit of the McGill University Health Center developed a report on the use of intra-operative neurophysiological monitoring during spinal surgery, they only examined the use of SSEP and MEP.  These investigators recommended that combined SSEP/MEP should be available for all cases of spinal surgery for which there is a risk of injury to the spinal cord.

The American Association of Neurological Surgeons/Congress of Neurological Surgeons' guidelines for the performance of fusion procedures for degenerative disease of the lumbar spine (Resnick et al, 2005) stated that there does not appear to be support for the hypothesis that any type of intra-operative monitoring improves patient outcomes after spinal surgery such as lumbar decompression or fusion procedures for degenerative spinal disease.  The report noted that evidence does indicate that a normal evoked EMG response is predictive for intra-pedicular screw placement (high negative predictive value for breakout); while the presence of an abnormal EMG response does not, however, exclude intra-pedicular screw placement (low PPV).  The majority of clinically apparent post-operative nerve injuries are associated with intra-operative changes in SSEP and/or DSEP monitoring.  Thus, changes in DSEP/SSEP monitoring appear to be sensitive to nerve root injury.  However, there is a high false-positive rate, and changes in DSEP and SSEP recordings are often not associated with nerve injury.  A normal study has been shown to correlate with the lack of a significant post-operative nerve injury.  There is insufficient evidence that the use of intra-operative monitoring of any kind provides clinically useful information to the surgeon in terms of assessing the adequacy of nerve root decompression at the time of surgery.  Furthermore, the authors stated that a randomized prospective study comparing clinical and radiographical outcomes in similar groups of patients undergoing lumbosacral fusion with or without intra-operative monitoring would provide Class I evidence (well-conducted randomized prospective trials) supporting or refuting the hypothesis that the added expense associated with the use of intra-operative monitoring is justified by a clinical benefit.

In a prospective analysis, Paradiso and colleagues (2006) evaluated the sensitivity, specificity, as well as PPV and NPV of multi-modality intra-operative neurophysiological monitoring in surgery for adult tethered cord syndrome.  The results of multi-modality intra-operative neurophysiological monitoring were compared with the "gold standard" (neurological outcomes).  Multi-modality intra-operative neurophysiological monitoring included posterior tibial nerve SSEPs, continuous EMG monitoring of the L2 to S4 myotomes, and evoked EMG.  Follow-up neurological evaluations were performed for at least 1 year.  A total of 44 consecutive patients, including 19 males and 25 females (aged 43 +/- 15 years), who underwent microsurgery for adult tethered cord syndrome were evaluated.  After surgery, new neurological deficits, including 1 transient and 1 permanent, developed in 2 patients.  There was 1 patient who had persistent posterior tibial nerve SSEP amplitude reduction following microsurgical manipulation.  In 1 patient, a transient posterior tibial nerve SSEP amplitude reduction prompted a change in microneurosurgical strategy.  This patient awoke with no new post-operative neurological deficits.  For SSEPs, the sensitivity was 50 % and specificity 100 %.  Electromyographical bursts were recorded in 36 patients (82 %).  The 2 patients with post-operative neurological worsening had EMG activity in the myotomes, where their new deficits presented.  Continuous EMG had a sensitivity of 100 % and a specificity of 19 %.  The authors concluded that this was the largest series to date reporting the use of multi-modality intra-operative neurophysiological monitoring in the surgical management of adult tethered cord syndrome.  Posterior tibial nerve SSEPs have high specificity, but low sensitivity, for predicting new neurological deficits.  In contrast, continuous EMG showed high sensitivity and low specificity.  Evoked EMG accurately identified functional neural tissue.  The combined recording of SSEPs in concert with continuous and evoked EMGs may provide a useful adjunct to complex microsurgery for adult tethered cord syndrome.

In a systematic review, Fehlings and colleagues (2010) examined if intra-operative monitoring (IOM) is able to sensitively and specifically detect intra-operative neurologic injury during spine surgery and to assess whether IOM results in improved outcomes for patients during these procedures.  A review of the English language literature was undertaken for articles published between 1990 and March 2009.  Medline, Embase, and Cochrane Collaborative Library databases were searched, as were the reference lists of published articles examining the use of IOM in spine surgery.  Two independent reviewers assessed the level of evidence quality using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) criteria, and disagreements were resolved by consensus.  A total of 103 articles were initially screened and 32 ultimately met the pre-determined inclusion criteria.  These researchers determined that there is a high level of evidence that multi-modal (SSEP and MEP) IOM is sensitive and specific for detecting intra-operative neurologic injury during spine surgery.  There is a low level of evidence that IOM reduces the rate of new or worsened peri-operative neurologic deficits (a grade of "low" means that further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate).  There is very low evidence that an intra-operative response to a neuromonitoring alert reduces the rate of peri-operative neurologic deterioration (a grade of "very low" means that any estimate of effect is very uncertain).  The authors concluded that based on strong evidence that multi-modality intra-operative neuromonitoring is sensitive and specific for detecting intra-operative neurologic injury during spine surgery, it is recommended that the use of multi-modality intra-operative neuromonitoring be considered in spine surgery where the spinal cord or nerve roots are deemed to be at risk, including procedures involving deformity correction and procedures that require the placement of instrumentation.  Furthermore, they stated that there is a need to develop evidence-based protocols to deal with intra-operative changes in multi-modality intra-operative neuromonitoring and to validate these prospectively.  Intra-operative EMG monitoring was not recommended as a means of neurophysiological monitoring during spinal surgery.

Kundnani et al (2010) reported the analysis of prospectively collected intra-operative neurophysiological monitoring data of 354 consecutive patients undergoing corrective surgery for adolescent idiopathic scoliosis (AIS) to establish the efficacy of multi-modal neuromonitoring and to evaluate comparative sensitivity and specificity.  The study group consisted of 354 patients (45 males and 309 females) undergoing spinal deformity corrective surgery between 2004 and 2008.  Patients were monitored using electrophysiological methods including SSEP and MEP simultaneously.  Mean age of patients was 13.6 years (+/- 2.3 years).  The operative procedures involved were instrumented fusion of the thoracic/lumbar/both curves.  Baseline SSEP and neurogenic MEP (NMEP) were recorded successfully in all cases.  Thirteen cases expressed significant alert to prompt reversal of intervention.  All these 13 cases with significant alert had detectable NMEP alerts, whereas significant SSEP alert was detected in 8 cases.  Two patients awoke with new neurological deficit (0.56 %) and had significant intra-operative SSEP and NMEP alerts.  There were no false-positives with SSEP (high specificity) but 5 patients with false-negatives with SSEP (38 %) reduced its sensitivity.  There was no false-negative with NMEP but 2 of 13 cases were false-positive with NMEP (15 %).  The specificity of SSEP (100 %) is higher than NMEP (96 %); however, the sensitivity of NMEP (100 %) is far better than SSEP (51 %).  Due to these results, the overall sensitivity, specificity and PPV of combined multi-modality neuromonitoring in this adult deformity series was 100 %, 98.5 % and 85 %, respectively.  The authors concluded that NMEP monitoring appears to be superior to conventional SSEP monitoring for identifying evolving spinal cord injury.  Used in conjunction, the sensitivity and specificity of combined neuromonitoring may reach up to 100 %.  Multi-modality monitoring with SSEP and NMEP should be the standard of care.

In a cross-sectional study of non-consecutive cases (level III evidence), de Bla et al (2012) reported the findings of a series of young patients with thoracic scoliosis who were treated with pedicle screw constructs.  Data obtained from triggered EMG (t-EMG) screw stimulation and post-operative computed tomographic scans were matched to find different threshold limits for the safe placement of pedicle screws at the concavity (CC) and convexity (CV) of the scoliotic curves.  The influence of the distance from the medial pedicle cortex to the spinal cord on t-EMG threshold intensity was also investigated at the apex segment.  A total of 23 patients who underwent posterior fusions using 358 pedicle thoracic screws were reviewed.  All patients presented main thoracic scoliosis, with a mean Cobb angle of 58.3 degrees (range of 46 to 87 degrees).  Accuracy of the screw placement was tested at surgery by the t-EMG technique.  During surgery, 8 screws placed at the CC showed t-EMG threshold values below 7 mA and were carefully removed.  Another 25 screws disclosed stimulation thresholds within the range of 7 to 12 mA.  After checking the screw positions by intraoperative fluoroscopy, 15 screws were removed because of clear signs of mal-positioning.  Every patient underwent a pre-operative magnetic resonance imaging examination, in which the distances from the spinal cord to the pedicles of the concave and convex sides at 3 apex vertebrae were measured.  Post-operative computed tomographic scans were used in all patients to detect screw mal-positioning of the final 335 screws.  According to post-operative computed tomographic scans, 44 screws (13.1 %) showed different mal-positions: 40 screws (11.9 %) perforated the medial pedicle wall, but only 11 screws (3.2 %) were completely inside the spinal canal.  If these researchers considered the 23 screws removed during surgery, the true rate of misplaced screws increased to 18.7 %.  In those screws that preserved the pedicle cortex (well-positioned screws), EMG thresholds from the CC showed statistically significantly lower values than those registered at the CV of the deformity (21.1 ± 8.2 versus 23.9 ± 7.7 mA, p < 0.01).  In the concave side, t-EMG threshold values under 8 mA should be unacceptable because they correspond to screw mal-positioning.  Threshold values above 14 mA indicate an accurate intrapedicular position with certainty.  At the convex side, threshold values below 11 mA always indicate screw mal-positioning, and values above 19 mA imply accurate screw placement.  At the 3 apex vertebrae, the average pedicle-spinal cord distance was 2.2 ± 0.7 mm at the concave side and 9.8 ± 4.3 mm at the convex side (p < 0.001).  In well-positioned screws, a correlation between pedicle-dural sac distance and t-EMG threshold values was found at the concave side only (Pearson r = 0.467, p < 0.05).  None of the patients with misplaced screws showed post-operative neurological impairment.  The authors concluded that independent of the screw position, average t-EMG thresholds were always higher at the CV in the apex and above the apex regions, presuming that the distance from the pedicle to the spinal cord plays an important role in electrical transmission.  They stated that the t-EMG technique has low sensitivity to predict screw mal-positioning and can not discriminate between medial cortex breakages and complete invasion of the spinal canal.

Also, an UpToDate review on “Treatment and prognosis of adolescent idiopathic scoliosis” (Scherl, 2012) mentions the use of intra-operative SEP and MEP monitoring; but not intra-operative EMG monitoring.

In a retrospective, controlled clinical study, Ovadia and associates (2011) evaluated the contribution of an electronic conductivity device (ECD) to the safety of pedicle screw insertion in pediatric scoliosis surgery.  Pedicle screw insertion was analyzed in 248 pediatric scoliosis patients (idiopathic, congenital, neuromuscular, syndromatic).  Group I included 150 procedures without the aid of the ECD and group II included 98 ECD-aided procedures.  The 2 groups were matched by age, sex, etiology, Cobb angle, and surgical criteria.  Data on screw position and concomitant neuro-monitoring alarms were compared.  Group I consisted of patients operated with both the hybrid construct and pedicle screw instrumentation, while group II consisted of patients operated solely with pedicle screws.  Both groups were operated on by a single surgeon with the same neurophysiologic methodology.  Clinically relevant misplaced pedicle screws were established by intra-operative monitoring alarms concomitant with pedicle screw insertion.  A total of 1,270 pedicle screw placements were analyzed in group I and compared with 1,400 pedicle screw placements in group II.  Neuro-monitoring alarms concomitant with screw placement occurred in 10 procedures in group I (6.6 %) compared with 3 in group II (3.0 %).  The contribution of the electronic device to reducing the number of neurophysiologic alarms was significant (p = 0.048, Fisher exact test); 9 of the 13 monitoring alarms (69 %) were associated with implantation adjacent to the apex of the spinal curve.  The authors concluded that the use of an ECD significantly reduced the incidence of clinically relevant misplaced screws in a variety of scoliosis patients, thereby increasing the safety of pedicle screw implantation.  This study did not appear to provide evidence for intra-operative EMG.

Lee and associates (2015) noted that triggered EMG (t-EMG) for pedicle screw placement was introduced to prevent the misplacement of screws; however, its diagnostic value is still debated. These researchers attempted to clarify the diagnostic value of t-EMG and to compare thresholds.  They searched Medline, Embase, and the Cochrane Library, and 179 studies were identified.  Among them, 11 studies were finally enrolled.  The pooled sensitivity, specificity, diagnostic odds ratio (DOR), and summary receiver operating characteristics (SROC) plots were analyzed.  The enrolled studies included 13,948 lumbar and 2,070 thoracic screws.  The overall summary sensitivity/specificity/DOR values of t-EMG were 0.55/0.97/42.16 in the lumbar spine and 0.41/0.95/14.52 in the thoracic spine, respectively, indicating a weak diagnostic value.  However, subgroup analysis by each threshold value showed that the cut-off value of 8 mA in the lumbar spine indicated high sensitivity (0.82), specificity (0.97), and DOR (147.95), thereby showing high diagnostic accuracy of identifying misplaced screws.  The authors concluded that the most useful application of t-EMG may be as a warning tool for lumbar pedicle screw mal-positioning in the presence of positive stimulation at a threshold of less than or equal to 8 mA.

Mikula and colleagues (2016) determined the ability of t-EMG to detect misplaced pedicle screws (PSs).  These investigators searched the U.S. National Library of Medicine, the Web of Science Core Collection database, and the Cochrane Central Register of Controlled Trials for PS studies.  A meta-analysis of these studies was performed on a per-screw basis to determine the ability of t-EMG to detect misplaced PSs.  Sensitivity, specificity, and ROC area under the curve (AUC) were calculated overall and in subgroups.  A total of 26 studies were included in the systematic review.  These researchers analyzed 18 studies in which t-EMG was used during PS placement in the meta-analysis, representing data from 2,932 patients and 15,065 screws.  The overall sensitivity of t-EMG for detecting misplaced PSs was 0.78, and the specificity was 0.94.  The overall ROC AUC was 0.96.  A t-EMG current threshold of 10 to 12 mA (ROC AUC 0.99) and a pulse duration of 300 µsec (ROC AUC 0.97) provided the most accurate testing parameters for detecting misplaced PSs.  Screws most accurately conducted EMG signals (ROC AUC 0.98).  The authors concluded that t-EMG has very high specificity but only fair sensitivity for detecting mal-positioned PSs.

In a prospective, randomized study, Bernhardt and co-workers (2016) evaluated the impact of intra-operative pedicle screw monitoring on screw positioning. These investigators enrolled 22 patients and they were split into 2 equal groups:
  1. dorsal instrumentation was supplemented with intra-operative nerve root monitoring using the INS-1-System (NuVasive, San Diego, CA), and
  2. screws were inserted without additional pedicle monitoring. 

All patients underwent mono-segmental instrumentation with "free hand implanted" pedicle screws; a total of 44 screws were inserted in each group.  The screw position was evaluated post-operatively using CT scans.  The position of the screws in relation to the pedicle was measured in 3 different planes:

  1. sagittal,
  2. axial and
  3. coronal. 

The accuracy of the screw position was described using the Berlemann classification system.  Screw position is classified in 3 groups:

  1. type 1 correct screw position,
  2. type 2 encroachment on the inner cortical wall, and
  3. type 3 pedicle cortical perforation. 

Screw angulation and secondary operative criteria were also evaluated.  The use of neuro-monitoring did not influence the distance between the center of the screws and the pedicle wall.  Distances only depended on the implantation side (right and left) and the height of implantation (caudal or cranial screw).  Because of the low number of cases, no conclusion could be reached about the influence of root monitoring on the correct positioning of the screws.  There was at least a non-significant trend towards more frequent perforation of the pedicle in the monitor group.  In the present study, these researchers showed that root monitoring had a significant effect on the scattering of transversal angles.  These were increased compared to the control group.  Otherwise, the implantation angle was not shown to depend on the use of neuro-monitoring.  They noted that neuro-monitoring did not influence blood loss or operative time.  The authors concluded that the data did not permit any conclusion as to whether this technique can minimize the frequency of pedicle screw mal-position.  The 4 coronal plane distances did not depend on the use of neuro-monitoring.  The inclination angle was also unaffected by neuro-monitoring.  The only parameter for which the authors found any effect was the transverse angle.  The mean values were similar in both groups, but the variances were not equal.  They stated that the effect of monitoring on the only parameter which could not be evaluated by fluoroscopy is thus rather unfavorable.

Hussain (2015) stated that while prospective data regarding the clinical utility of IOM are conspicuously lacking, retrospective analyses continue to provide useful information regarding surgeon responses to reported waveform changes. Data regarding clinical presentation, operative course, IOM, and post-operative neurological examination were compiled from a database of 1,014 cranial and spinal surgical cases at a tertiary care medical center from 2005 to 2011.  Intra-operative monitoring modalities utilized included SSEP, transcranial MEP, pedicle screw stimulation, and EMG.  Surgeon responses to changes in IOM waveforms were recorded.  Changes in IOM waveforms indicating potential injury were present in 87 of 1,014 cases (8.6 %).  In 23 of the 87 cases (26.4 %), the surgeon responded by re-positioning the patient (n = 12), re-positioning retractors (n = 1) or implanted instrumentation (n = 9), or by stopping surgery (n = 1).  Loss of IOM waveforms predicted post-operative neurological deficit in 10 cases (11.5 % of cases with IOM changes).  In the largest IOM series to-date, the authors reported that the surgeon responded by appropriate interventions in over 25 % of cases during which there were IOM indicators of potential harm to neural structures.  Moreover, they stated that prospective studies remain to be needed to adequately evaluate the utility of IOM in changing surgeon behavior.

Spitz et al (2015) stated that although advances have been made in surgical technique and IOM, the rate of post-operative C5 palsy remains the same. These researchers attempted to define characteristics which may predict risk of developing post-operative C5 palsy.  Retrospective chart review identified 644 patients undergoing cervical procedures.  Anterior cervical discectomy and fusion was performed in 456, anterior cervical corpectomy and fusion (ACCF) in 78, posterior laminectomy and fusion (PLF) in 106, and posterior open-door laminoplasty in 4 patients.  All patients had neurophysiologic monitoring (SSEP, spontaneous EMG, and/or MEP).  Post-operative C5 root palsy occurred in 5 (2 with ACCF and 3 with PLF) cases (1.4 %).  In all cases, there were no changes in intra-operative neurophysiologic monitoring; C5 palsy did not occur before post-operative day 2.  The authors concluded that patients undergoing cervical decompression remain at risk for C5 root palsy despite use of IOM.  They stated that given that all patients experienced delayed onset of C5 palsy, MEP, SSEP, and EMG may not be sensitive enough to assess the risk of developing C5 palsy.

Thirumala and colleagues (2016) conducted a systematic review of reports of patients with cervical spondylotic myelopathy and evaluated the value of IOM, including SSEP, transcranial MEP and EMG, in anterior cervical procedures. A search was conducted to collect a small database of relevant papers using key words describing disorders and procedures of interest.  The database was then shortlisted using selection criteria and data was extracted to identify complications as a result of anterior cervical procedures for cervical spondylotic myelopathy and outcome analysis on a continuous scale.  In the 22 studies that matched the screening criteria, only 2 involved the use of IOM.  The average sample size was 173 patients.  In procedures done without IOM a mean change in Japanese Orthopaedic Association score of 3.94 points and Nurick score by 1.20 points (both less severe post-operatively) was observed.  Within our sub-group analysis, worsening myelopathy and/or quadriplegia was seen in 2.71 % of patients for studies without IOM and 0.91 % of patients for studies with IOM.  Variations persisted in the existing literature in the evaluation of complications associated with anterior cervical spinal procedures.  The authors concluded that based on the review of published studies, sufficient evidence does not exist to make recommendations regarding the use of different IOM modalities to reduce neurological complications during anterior cervical procedures.  However, they stated that future studies with objective measures of neurological deficits using a specific IOM modality may establish it as an effective and reliable indicator of injury during such surgeries.

In a large, single-institution, case-series study involving all levels of the spinal column and all spinal surgical procedures, Raynor and associates (2016) categorized and evaluated IOM failure to detect neurologic deficits occurring during spinal surgery.   Multi-modality IOM included SSEPs, descending neurogenic evoked potentials (DNEPs), transcranial MEP, DSEP, and spontaneous electromyography (spEMG) and t-EMG.  These investigators reviewed 12,375 patients who underwent surgery for spinal pathology from 1985 to 2010.  There were 7,178 females (59.3 %) and 5,197 males (40.7 %); 9,633 (77.8 %) primary surgeries and 2,742 (22.2 %) revisions.  Procedures by spinal level were: cervical 29.7 % (3,671), thoracic/thoracolumbar 45.4 % (5,624) and lumbosacral 24.9 % (3,080).  Age at surgery was: greater than 18 years 72.7 % (8,993), less than 18 years 27.3 % (3,382); 45 of the 12,375 patients (0.36 %) had false negative outcomes.  False negative results by modality were as follows: spEMG (n = 22, 48.8 %), t-EMG (n = 8, 17.7 %), DSEP (n = 4, 8.8 %), DNEP (n = 4, 8.8 %), SSEP (n = 3, 6.6 %), DSEP/spEMG (n = 3, 6.6 %), t-EMG/spEMG (n = 1, 2.2 %); 37 patients had immediate post-operative deficits un-identified by IOM; 30 (81 %) involved nerve root monitoring, 4 had spinal cord deficits, and 3 had peripheral sensory deficits; 8 patients had permanent neurologic deficits, 6 (0.048 %) were nerve root and 2 (0.016 %) were spinal cord in nature.  The authors concluded that despite correct application and usage, IOM data failed to identify 45 (0.36 %) patients with false negative outcomes out of 12,375 surgical patients; 8 (0.064 %) of these 45 patients had permanent neurologic deficits, 6 were nerve root in nature and 2 were spinal cord.  They stated that although admittedly small, this represented the risk of undetected neurologic deficits even when properly using IOM.  Deficits were at a higher risk to remain unresolved when not detected by IOM.  (Level of Evidence = IV)

In summary, there is insufficient scientific evidence that intra-operative monitoring of EMG during spinal surgery provides useful information to the surgeon in terms of assessing the adequacy of nerve root decompression, detecting nerve root irritation, or improving the reliability of placement of pedicle screw at the time of surgery.

In a retrospective study, Kaliya-Perumal and colleagues (2017) investigated the effectiveness of intraoperative EMG monitoring to detect potential pedicle breach and examined if re-operation rates were significantly reduced.  Patients who underwent posterior stabilization with pedicle screws for various pathologies were analyzed and those with screws among L1 to S1 levels were short-listed.  They were divided into 2 groups: Group 1 included patients in whom t-EMG was used to confirm appropriate screw placement, and Group 2 included those in whom it was not used.  Responses to t-EMG and corresponding stimulation thresholds were recorded for Group 1 patients.  The sensitivity and specificity of the test was calculated.  Re-operation rates due to post-operative neurologic compromise caused by mal-positioned screws were compared between both the groups.  A total of 518 patients had 3,112 pedicle screws between L1 to S1 levels.  Among Group 1 [n = 296; screws = 1,856], 145 screws (7.8 %) showed a positive response for t-EMG at stimulation thresholds ranging between 2.6 to 19.8 mA. The sensitivity and specificity of t-EMG to diagnose potential pedicle breach was found to be 93.33 % and 92.88 % respectively.  Only 1 patient among Group 1 needed re-operation. However, among Group 2 [n = 222; screws = 1,256], 6 patients needed re-operation.  This indicated a significant decrease in the number of mal-positioned screws that caused neurological compromise [p = 0.02], leading to subsequent decrease in re-operation rates [p = 0.04] among Group 1 patients.  The authors concluded that these findings suggested that t-EMG can be considered highly sensitive and specific for identifying potential pedicle breach by a mal-positioned screw that can cause neurologic compromise; but, undetected breaches may still exist.  However, t-EMG monitoring in combination with palpatory and radiographic assessment will aid safe and secure pedicle screw placement.  It can also reduce re-operation rates due to neurologic compromise provoked by a mal-positioned screw.

These researchers noted that this analysis may be subject to secular influences regarding certain factors due to the retrospective nature of this study.  Regarding selection of samples, these investigators only included patients with pedicle screws among L1 to S1 segments, excluding dysmorphic pedicles.  However, it should be understood that, not all pedicles are anatomically similar and there can be variants or anomalies.  The underlying pathology for which the surgery was done may have affected the pedicle anatomy.  The pedicles of patients in one group may be more prone for a breach when compared to the other group.  This may have influenced the analysis of re-operation rates.  The overall number of screws and the number of screws per patient in Group 1 was significantly higher than that of Group 2.  Besides that, the decision to use intraoperative EMG was purely based on availability.  These factors may have contributed for a selection bias and could have influenced these findings.

Intraoperative Evoked Potential Studies

Somatosensory evoked potentials (SEPs or SSEPs) (also known as cerebral sensory evoked potentials) augment the sensory examination and are most useful in assessing the spinal nerve roots, spinal cord, or brain stem for evidence of delayed nerve conduction. Dermatomal somatosensory evoked potentials (DSEPs) are elicited by stimulating the skin "signature" areas of specific nerve roots. Both techniques involve production and recording of small electrophysiological responses of the central nervous system that follow sequential electrical stimulation of peripheral nerves. These small electrophysiological responses are extracted from the background noise of electroencephalography (EEG), usually by signal averaging techniques. Delays in signal propagation suggest lesions of the central sensory pathways. Although controversial, evoked potentials have been used to assess the prognosis of children with spinal cord lesions, brain malformations, and neurodegenerative diseases, as well as young children who are at risk for brain injury, such as preterm infants. Somatosensory evoked potentials measurements have been used to predict outcome in spinal cord injury; however, signal changes on MRI actually may be more useful in determining the severity of injury. Hemorrhage within the spinal cord is readily identified on MRI, and such hemorrhage is predictive of injury severity. Intra-operative SSEP measurements are useful in complex neurologic, orthopedic, and vascular surgical procedures as a means of gauging nerve injury during surgery (e.g., resection of cord tumors).

Magnetic stimulation of the brain and spine elicits so-called motor evoked potentials (MEPs) (Goetz, 2003). The latency of the motor responses can be measured, and central conduction time can be estimated by comparing the latency of the responses elicited by cerebral and spinal stimulation. Abnormalities have been described in patients with a variety of central disorders including multiple sclerosis, amyotrophic lateral sclerosis, stroke, and certain degenerative disorders. An assessment by the McGill University Health Centre on use of intraoperative neurophysiological monitoring during spinal surgery stated that there is sufficient evidence to support the conclusion that intraoperative spinal monitoring using SSEPs and MEPs during surgical procedures that involve risk of spinal cord injury is an effective procedure that is capable of substantially diminishing this risk (Erickson et al, 2005). The report explained that intra-operative spinal cord injury during spinal surgery generally compromises both motor and somatosensory pathways; therefore the use of both of these independent techniques in parallel has been proposed and is seen as a safeguard should one of the monitoring techniques fail. Combination of SSEP monitoring with MEP monitoring is also proposed to reduce false-positive results, and eliminate the need for the wake-up test. The assessment identified 11 studies, all case series, of the combined use of SSEPs and MEPs in neurophysiological monitoring during spinal surgery. The assessment found that, in several reports, combined SSEP and MEP monitoring was shown to have greater sensitivity than SSEP alone. The report also noted that the addition of MEP monitoring where SSEP monitoring is already being performed is considered to be relatively straightforward, adding little to the overall effort and resources employed in intraoperative neurophysiological monitoring.

A study by Schwartz et al (2007) illustrated the advantage of intraoperative monitoring of spinal cord motor tracts directly by recording motor evoked potentials in addition to somatosensory evoked potentials. Investigators reviewed the intraoperative neurophysiological monitoring records of 1121 consecutive patients (834 female and 287 male) with adolescent idiopathic scoliosis (mean age, 13.9 years) treated between 2000 and 2004 at four pediatric spine centers. The same group of experienced surgical neurophysiologists monitored spinal cord function in all patients with use of a standardized multimodality technique with the patient under total intravenous anesthesia. A relevant neurophysiological change (an alert) was defined as a reduction in amplitude (unilateral or bilateral) of at least 50% for somatosensory evoked potentials and at least 65% for transcranial electric motor evoked potentials compared with baseline. The investigators reported that 38 (3.4%) of the 1121 patients had recordings that met the criteria for a relevant signal change (i.e., an alert). Of those 38 patients, 17 showed suppression of the amplitude of motor evoked potentials in excess of 65% without any evidence of changes in somatosensory evoked potentials. In nine of the 38 patients, the signal change was related to hypotension and was corrected with augmentation of the blood pressure. The remaining 29 patients had an alert that was related directly to a surgical maneuver. Three alerts occurred following segmental vessel clamping, and the remaining 26 were related to posterior instrumentation and correction. Nine (35%) of these 26 with an instrumentation-related alert, or 0.8% of the cohort, awoke with a transient motor and/or sensory deficit. Seven of these nine patients presented solely with a motor deficit, which was detected by intraoperative monitoring of motor evoked potentials in all cases, and two patients had only sensory symptoms. The investigators reported that somatosensory evoked potential monitoring failed to identify a motor deficit in four of the seven patients with a confirmed motor deficit. Furthermore, when changes in somatosensory evoked potentials occurred, they lagged behind the changes in transcranial electric motor evoked potentials by an average of approximately five minutes. With an appropriate response to the alert, the motor or sensory deficit resolved in all nine patients within one to 90 days.

A systematic evidence review of multimodality intraoperative monitoring (MIOM), including somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) recording, during spinal cord/spinal column surgery, reached the following conclusions (Hadley, et al., 2017): "Robust class I medical evidence supports the use of electrophysiological monitoring including SSEP and MEP recordings during spinal cord/spinal column surgery as a diagnostic adjunct to assess spinal cord integrity in the perioperative setting. IOM, applied in this way, is a valid and sensitive means to detect neurological injury during spinal cord and spinal column surgical procedures.

The systematic review concluded (Hadley, et al., 2017): "The use of IOM as a therapeutic tool during spinal surgery, however, has not been shown to be successful in reducing the rate of perioperative neurological deterioration or to improve neurological outcome during spinal surgery procedures. To date, there is no meaningful medical evidence (ie, class I or II) to support a therapeutic relationship between the use of IOM in spinal cord/spinal column surgery and neurological outcome. Two class II medical evidence studies on this issue are negative/refute the utility of IOM as a therapeutic adjunct in surgery within and around the spinal cord. For this reason, the use of IOM during spinal cord or spinal column surgery cannot be considered a “standard of care.”

The clinical utility of MEPs outside of the operative setting, however, is unclear and at the present time the magnetic stimulation of central structures is regarded as investigational (Goetz, 2003; Miller, 2005).

In a prospective consecutive case series study, Lee et al (2009) evaluated the side effects of microvascular decompression (MVD) on hearing and described the main intra-operative ABR changes. The study included 22 patients who underwent MVD with monitoring of ABRs. The latency prolongation and wave loss were analyzed at each surgical step, which were decided arbitrarily. Patients were divided into 4 groups depending on degree of change of wave V. Group 1 consisted of minimal change, whereas group 4 was permanent loss of wave V. Hearing changes were evaluated in 20 patients in the 4 groups who were available for post-operative hearing results. Loss of wave I, III, and V occurred with 6 %, 13 %, and 9 % of surgical actions, respectively. Wave III disappearance was identified as the earliest and most sensitive sign and was usually preceded by the disappearance of wave V. The greatest prolongation of wave V at more than 1.0 ms developed statistically significant sensorineural hearing loss in the range of 10 dB. One patient in group 4 experienced deafness. The authors concluded that in addition to the significant delay of wave V, useful recognition of early changes of wave III is possible and enables a change of microsurgical maneuvers to favor ABR recovery.

Polo and Fischer (2009) stated that BAEP monitoring is a useful tool to decrease the danger of hearing loss during pontocerebellar angle surgery, particularly in MVD.  Critical complications arising during MVD surgery are the stretching of the VIII nerve – the main cause of hearing loss – labyrinthine artery manipulation, direct trauma with instruments, or a nearby coagulation, and at end of the surgery neocompression of the cochlear nerve by the prosthesis positioned between the conflicting vessel(s) and the VIIth-VIIIth nerve complex.  All these dangers warrant the use of BAEP monitoring during the surgical team's training period.  Based on delay in latency of peak V, these investigators established warning thresholds that can provide useful feedback to the surgeon to modify the surgical strategy: the initial signal at 0.4 ms is considered the safety limit.  A second signal threshold at 0.6 ms (warning signal for risk) corresponds to the group of patients without resultant hearing loss.  The third threshold characterized by the delay of peak V is at 1 ms (warning signal for a potentially critical situation).  BAEP monitoring provides the surgeon with information on the functional state of the auditory pathways and should help avoid or correct maneuvers that can harm hearing function.  BAEP monitoring during VIIth-VIIIth complex surgery, particularly in MVD of facial nerves for hemifacial spasm (HFS) is very useful during the learning period.

Huang and colleagues (2009) determined the reliability of
  1. intra-operative monitoring by stimulated electromyography (EMG) of the facial nerve to predict the completeness of MVD for HFS, and
  2. BAEP to predict post-operative hearing disturbance. 

These investigators conducted a prospective study of 36 patients who received MVD for HFS.  They confirmed the disappearance of an abnormal muscle response in the facial nerve EMG to predict the completeness of MVD, and performed BAEP monitoring to predict post-operative hearing disturbance.  The sensitivity, specificity and accuracy of facial nerve EMG and BAEP monitoring were evaluated.  The sensitivity, specificity and accuracy of facial nerve EMG were 0.97, 1.0 and 0.97, respectively, and that for BAEP monitoring were 1.0, 0.94 and 0.94, respectively.  There was 1 false-positive result for facial nerve EMG, and 2 false-positive results for BAEP monitoring.  No false-negative result was encountered for either EMG or BAEP monitoring.  Facial nerve EMG correctly predicted whether MVD was successful in 35 out of 36 patients, and BAEP correctly predicted whether there was post-operative hearing disturbance in 34 out of 36 patients.  The authors concluded that intra-operative facial nerve EMG provides a real-time indicator of successful MVD during an operation while BAEP monitoring may provide an early warning of hearing disturbance after MVD.

Evoked Potential Monitoring During Degenerative Cervical Spine Surgery

Di Martino and colleagues (2019) stated that intraoperative SSEP and TcMEP monitoring are frequently used in spinal as well as spinal cord surgery for so-called IONM, while the combination of these techniques is known as concomitant multi-modal intraoperative monitoring (MIOM).  These investigators collected available evidence concerning use of IONM and MIOM in cervical decompression surgery in the degenerative setting and identified the best practice to be advocated.  They carried out a review of the PubMed and Medline databases and Cochrane Central Registry of Controlled Trials.  Studies were included if they involved patients who underwent cervical spine decompression surgery for degenerative stenosis with use of IONM or MIOM and where sensitivity/specificity was reported.  In the identified studies, the sensitivity of SSEP was estimated to be between 22 % and 100 % with constant specificity of 100 % . In the included studies, the sensitivity of MEP was estimated to be between 78 % and 100 % with specificity ranging from 83.2 % to 100 %.  The authors concluded that on the basis of available evidence, MIOM could be a helpful tool in decompression cervical spine surgery in patients affected by degenerative spinal stenosis, since it was associated with high specificity and sensitivity for detection of intraoperative neural damage.  However, these researchers stated that given the lack of appropriate evidence, they recommended that better and more focused studies be performed to examine if the combination of SSEP and MEP is more sensitive and specific than either method alone.  Furthermore, evidence concerning appropriate selection of patients in whom monitoring is indicated is still lacking, and this should be a focus of future studies on this topic.

Intraoperative Brainstem Neuromonitoring During Coil Embolization for the Treatment of Cerebral Aneurysms

Horowitz et al (2003) reported a case of intra-operative aneurysm rupture during endovascular therapy and documented the effects of rupture on cerebral transit times and neurophysiologic monitoring.  A 42-year old man with Hunt and Hess grade 1, Fisher grade-3 subarachnoid hemorrhage (SAH) secondary to a 5-mm anterior communicating artery aneurysm underwent coil embolization.  Endovascular therapy was complicated by intra-procedural aneurysm rupture.  Changes in cerebral transit time and electroencephalography (EEG) along with SSEPs were documented as were improvement in these parameters following aneurysm obliteration and ventriculostomy placement.  The patient awoke without deficit and was discharged 2 weeks later with a grossly normal examination.  The authors concluded that early recognition of aneurysm rupture during coil embolization and prompt aneurysm obliteration and reduction in intra-cranial hypertension could lead to acceptable patient outcomes.  These researchers stated that the use of neurophysiologic monitoring in the intubated patient could help the neurosurgeon determine the need for cerebrospinal fluid (CSF) drainage in such situations.

In a prospective study, Chen (2010) examined the efficacy of neurophysiological monitoring (NPM) techniques in the detection of ischemic changes that may be observed during endovascular treatment of cerebral aneurysms.  A total of 63 patients underwent NPM during 1st-stage endovascular treatment of cerebral aneurysms.  The endovascular procedures included coil embolization (26 patients), balloon-remodeling coiling (16 patients), stent-assisted coiling (10 patients), balloon-stent-assisted coiling (9 patients), and balloon test occlusion (2 patients).  NPM included EEG, SSEP, and (BAEP, depending on the location of the aneurysm and its associated vascular territory.  NPM changes were observed in 3 (4.8 %) patients and the procedures were altered immediately.  No neurological changes were found post-endovascularly; 10 patients demonstrated abnormal angiographic findings without concurrent NPM changes, of which 5 patients developed visual disturbance or hemiparesis.  The author concluded that NPM was a valuable monitoring tool for endovascular treatment of cerebral aneurysms.  A combination of SSEP, EEG, BAEP or MEP may be particularly useful in situations in which neurological examination is not possible (such as when the patient is under general anesthesia) or when a patient's condition (such as obtunded SAH) precluded neurological examination.  It should also be emphasized that the decision-making and changing of endovascular procedures would not only be based on NPM changes, but also the real-time abnormal angiographic findings.  The author stated that BAEP monitoring detected functional changes along the auditory brain stem pathways; BAEP changes were most often caused by a brain stem insult, which could result from vertebrobasilar ischemia.  However, ischemia in the cerebellum or posterior cerebral artery territories could still be missed.  Other technical limitations include confounding anesthesia-related effects, which may mimic cerebral ischemia.

Ares et al (2018) noted that SSEP monitoring is used extensively for early detection and prevention of neurological complications in patients undergoing many different neurosurgical procedures.  However, the predictive ability of SSEP monitoring during endovascular treatment of cerebral aneurysms is not well detailed.  These researchers evaluated the performance of intra-operative SSEP in the prediction post-procedural neurological deficits (PPNDs) after coil embolization of intra-cranial aneurysms.  This population-based cohort study included patients of greater than or equal to 18 years of age undergoing intra-cranial aneurysm embolization with concurrent SSEP monitoring between January 2006 and August 2012.  The ability of SSEP to predict PPNDs was analyzed by multiple regression analyses and assessed by AUC.  In a population of 888 patients, SSEP changes occurred in 8.6 % (n = 77); 28 patients (3.1 %) suffered PPNDs.  A 50 % to 99 % loss in SSEP waveform was associated with a 20-fold increase in risk of PPND; a total loss of SSEP waveform, regardless of permanence, was associated with a greater than 200-fold risk of PPND.  SSEPs displayed very good predictive ability for PPND, with AUC of 0.84 (95 % CI: 0.76 to 0.92).  The authors concluded that this study supported the predictive ability of SSEPs for the detection of PPNDs.  The magnitude and persistence of SSEP changes was clearly associated with the development of PPNDs.  The utility of SSEP monitoring in detecting ischemia may provide an opportunity for neuro-interventionalists to respond to changes intra-operatively to mitigate the potential for PPNDs.  These researchers stated that although further analysis of the clinical outcomes of patients who experienced changes in SSEP monitoring is needed, especially the long-term outcomes of patients with sub-total loss of signals, regular use of SSEP monitoring may allow the opportunity to respond to changes in monitoring in a way that minimizes both short- and long-term clinical deficits.

The authors stated that this study had several drawbacks.  The limitations of such a retrospective analysis were fairly self-evident and well described in the literature.  Subjective data, such as consistent documentation of neurological examinations prior to and after the procedure and self-reporting by the proceduralist for documentation of procedural complications, was always prone to bias; however, great care was taken to maximize fidelity of this data, and no gross mis-representations were noted during data collection.  Furthermore, the focus on immediate PPNDs and lack of long-term follow-up may both over-state the gravity and permanence of these deficits and under-estimate the long-term differences between the sub-categorical SSEP changes.

Intraoperative Motor Evoked Potentials During Descending and Thoraco-Abdominal Aortic Aneurysm Repair

Fok and colleagues (2015) stated that paraplegia remains the most feared and a devastating complication after descending and thoraco-abdominal aneurysm operative repair (DTA and TAAAR).  Neuro-monitoring, particularly use of MEPs, for this surgery has gained popularity.  However, ambiguity remains regarding its use and benefit.  These researchers systematically reviewed the literature to evaluate the benefit and applicability of neuro-monitoring in DTA and TAAAR.  Electronic searches were performed on 4 major databases from inception until February 2014 to identify relevant studies.  Eligibility decisions, method quality, data extraction, and analysis were performed according to predefined clinical criteria and end-points.  Among the studies matching the inclusion criteria, a total of 1,297 patients had MEP monitoring during DTA and TAAAR.  In-hospital mortality was low (6.9 % ± 3.6).  Immediate neurological deficit was low (3.5 % ± 2.6).  In 1/3 of patients (30.4 % ± 14.2), the MEPs dropped below threshold, which were 30.4 % and 29.4 % with threshold levels of 75 % and 50 %, respectively.  A range of surgical techniques were applied after reduction in MEPs.  Most patients whose MEPs dropped and remained below threshold had immediate permanent neurological deficit (92.0 % ± 23.6).  Somatosensory-evoked potentials were reported in 1/3 of papers with little association between loss of SEPs and permanent neurological deficit (16.7 % ± 28.9 %).  The authors concluded that they demonstrated that MEPs are useful at predicting paraplegia in patients who lose their MEPs and did not regain them intra-operatively.  Moreover, they stated that to date, there is no consensus regarding the applicability and use of MEPs; current evidence does not mandate or support MEP use.

Intraoperative Neuromonitoring During Carpal Tunnel Release

An UpToDate review on “Surgery for carpal tunnel syndrome” (Hunter and Simmons, 2018) does not mention neuromonitoring, neuromuscular junction monitoring, or somatosensory evoked potential monitoring as a management tool.

Intraoperative Neuromonitoring During Cervical Lymphadenectomy (Modified Radical Neck Dissection)

Calo et al (2014) examined the ability of IONM in reducing the post-operative recurrent laryngeal nerve (RLN) palsy rate by a comparison between patients submitted to thyroidectomy with IONM and with routine identification alone.  Between June 2007 and December 2012, a total of 2,034 consecutive patients underwent thyroidectomy by a single surgical team.  These researchers compared patients who have had neuromonitoring and patients who have undergone surgery with nerve visualization alone.  The number of patients in which neuromonitoring was not utilized (Group A) was 993, and the number of patients in which neuromonitoring was utilized (group B) was 1,041.  In group A, 28 RLN injuries were observed (2.82 %), 21 (2.11 %) transient and 7 (0.7 %) permanent.  In group B, 23 RLN injuries were observed (2.21 %), in 17 cases (1.63 %) transient and in 6 (0.58 %) permanent.  Differences were not statistically significative.  The authors concluded that visual nerve identification remains the gold standard of RLN management in thyroid surgery.  Neuromonitoring helped to identify the nerve, in particular in difficult cases, but it did not decrease nerve injuries compared with visualization alone.  Moreover, these researchers stated that future studies are needed to evaluate the benefit of IONM in thyroidectomy, especially in conditions in which the RLN is at high risk of injury.

Brauckhoff et al (2016) stated that continuous vagal IONM (CIONM) of the RLN may reduce the risk of RLN lesions during high-risk endocrine neck surgery such as operation for large goiter potentially requiring trans-sternal surgery, advanced thyroid cancer, and recurrence.  A total of 55 consecutive patients (41 women, median age of 61 years, 87 nerves at risk) underwent high-risk endocrine neck surgery.  CIONM was performed using the commercially available NIM-Response 3.0 nerve monitoring system with automatic periodic stimulation (APS) and matching endotracheal tube electrodes.  All CIONM events (decreased amplitude/increased latency) were recorded; APS malfunction occurred on 3 sides (3 %).  A total of 138 CIONM events were registered on 61 sides.  Of 138, 47 (34 %) events were assessed as imminent (13 events) or potentially imminent (34 events) lesions, whereas 91 (66 %) were classified as artifacts.  Loss of signal was observed in 7 patients.  Actions to restore the CIONM baseline were undertaken in 58/138 (42 %) events with a median 60 s required per action; 4 RLN palsies (3 transient, 1 permanent) occurred: 1 in case of CIONM malfunction, 2 sudden without any significant previous CIONM event, and 1 without any CIONM event.  The APS vagus electrode led to temporary damage to the vagus nerve in 2 patients.  The authors concluded that CIONM using the APS system may be a useful tool in high-risk thyroid and parathyroid surgery in order to reduce the risk of RLN lesions.  Moreover, these researchers noted that even though the technology has matured, a major development effort is needed to reduce EMG artifacts and improve the safety of CIONM systems. They also stated that randomized studies are needed in order to obtain reliable estimates of cost benefit.

The authors stated that this study had several drawbacks.  First, the restricted number of patients undergoing high-risk surgery limited the number of relevant clinical events (loss of signal and RLN palsy).  Second, due to the non-randomized study design, no final conclusion regarding the potential benefit of CIONM could be drawn.  Third, even though classification of events as intrinsic versus artifactual was based on several objective parameters, it ultimately rested on the subjective evaluation by the surgeon.  Therefore, these investigators could not exclude that some artifactual events were related to sub-clinical nerve damage and vice versa.  Fourth, the protocol was not completely standardized (e.g., use of needle electrodes); however, this reflected clinical practice.  Last, the results pertained to high-risk surgery and a specific device (APS) and could perhaps not be transferred to the systems by other manufacturers.

Yang et al (2017) stated that IONM has been a commonly used technology during thyroid surgery aimed at reducing the incidence of RLN palsy (RLNP), which is a severe complication and leads to significant impacts on a patient's life.  In a systematic review and meta-analysis, these researchers provided a comprehensive assessment for potential benefits and disadvantage of IONM; they discussed RLNP rate, predictive power, CIONM, and emphasized on application during thyroid cancer surgeries.  These investigators carried out a literature search in the following electronic databases: PubMed, Embase, and the Cochrane library from January 1, 2004 to July 30, 2016.  After applying inclusion and exclusion criteria, a total of 24 studies, including 4 prospective, randomized trials, were selected.  Heterogeneity of studies was checked by the Cochran Q test.  Publication bias was assessed by funnel plots with Egger's linear regression test of asymmetry; OR was calculated by random effects model.  A total of 9,203 patients and 17,203 nerves at risk (NAR) were included.  Incidence of overall, transient, and persistent RLNP in IONM group were, respectively, 3.15 %, 1.82 %, and 0.67 %, whereas for the visual identification group, they were 4.37 %, 2.58 %, and 1.07 %.  The summary OR of overall, transient, and persistent RLNP compared using IONM and ID were, respectively, 0.81 (95 % CI: 0.66 to 0.99), 0.76 (95 % CI: 0.61 to 0.94), and 0.78 (95 % CI: 0.55 to 1.09).  The authors presented data showed benefits of reducing RLNP rate by using IONM, but without statistical significance for persistent RLNP rate.  For patients with thyroid cancer who undergo total thyroidectomy, using IONM may improve the outcome by reducing amount of residual thyroid tissue.  However, no benefits were found for thyroid re-operation; visual identification and careful dissection remain standard for this challenging procedure.  Furthermore, the relative low positive predictive power indicated intermittent IONM (IIONM) may not be reliable; but CIONM was showed to be a more promising method, with prudent approach.  These researchers stated that future studies may include larger patient number, and multi-center, prospective, randomized trials; and PPV of IONM should be improved through the establishment of standardized criteria for RLNP diagnosis.

Cirocchi et al (2019) stated that injuries to the recurrent inferior laryngeal nerve (RILN) remain one of the major post-operative complications after thyroid and parathyroid surgery.  Damage to this nerve can result in a temporary or permanent palsy, which is associated with vocal cord paresis or paralysis.  Visual identification of the RILN is a common procedure to prevent nerve injury during thyroid and parathyroid surgery.  Recently, IONM has been introduced in order to facilitate the localization of the nerves and to prevent their injury during surgery; IONM allows nerve identification using an electrode, where, in order to measure the nerve response, the electric field is converted to an acoustic signal.  In a Cochrane review, these researchers examined the effects of IONM versus visual nerve identification for the prevention of RILN injury in adults undergoing thyroid surgery.  They searched CENTRAL, Medline, Embase, ICTRP Search Portal and ClinicalTrials.gov.  The date of the last search of all data-bases was August 21, 2018.  These investigators did not apply any language restrictions.  They included RCTs comparing IONM nerve identification plus visual nerve identification versus visual nerve identification alone for prevention of RILN injury in adults undergoing thyroid surgery; 2 review authors independently screened titles and abstracts for relevance.  One review author carried out screening for inclusion, data extraction and “risk of bias” assessment and a 2nd review author checked them.  For dichotomous outcomes, these researchers calculated risk ratios (RRs) with 95 % CIs.  For continuous outcomes, they calculated mean differences (MDs) with 95 % CIs; and assessed trials for certainty of the evidence using the GRADE instrument.  A total of 5 RCTs with 1,558 participants (781 participants were randomly assigned to IONM and 777 to visual nerve identification only) met the inclusion criteria; 2 trials were performed in Poland and 1 trial each was performed in China, Korea and Turkey.  Inclusion and exclusion criteria differed among trials: previous thyroid or parathyroid surgery was an exclusion criterion in 3 trials.  In contrast, this was a specific inclusion criterion in another trial.  Three trials had central neck compartment dissection or lateral neck dissection and Graves' disease as exclusion criteria.  The mean duration of follow-up ranged from 6 to 12 months.  The mean age of participants ranged between 41.7 and 51.9 years.  There was no firm evidence of an advantage or disadvantage comparing IONM with visual nerve identification only for permanent RILN palsy (RR 0.77, 95 % CI: 0.33 to 1.77; p = 0.54; 4 trials; 2,895 nerves at risk; very low-certainty evidence) or transient RILN palsy (RR 0.62, 95 % CI: 0.35 to 1.08; p = 0.09; 4 trials; 2,895 nerves at risk; very low-certainty evidence).  None of the trials reported health-related quality of life (HR-QOL).  Transient hypoparathyroidism as an adverse event (AE) was not substantially different between intervention and comparator groups (RR 1.25; 95 % CI: 0.45 to 3.47; p = 0.66; 2 trials; 286 participants; very low-certainty evidence).  Operative time was comparable between IONM and visual nerve monitoring alone (MD 5.5 mins, 95 % CI: -0.7 to 11.8; p = 0.08; 3 trials; 1,251 participants; very low-certainty evidence); 3 of 5 included trials provided data on all-cause mortality: no deaths were reported.  None of the trials reported socioeconomic effects.  The evidence reported in this review was mostly of very low certainty, particularly because of risk of bias, a high degree of imprecision due to wide CIs and substantial between-study heterogeneity.  The authors concluded that the findings from this systematic review and meta-analysis indicated that there is currently no conclusive evidence for the superiority or inferiority of IONM over visual nerve identification only on any of the outcomes measured.  These researchers stated that well-designed RCTs with a larger number of participants and longer follow-up, employing the latest IONM technology and applying new surgical techniques are needed.

Stankovic et al (2020) noted that although the history of IONM dates back to the 19th century, the method did not evolve further than the mere differentiation of nerves until recently.  Only the development of CIONM has allowed for non-stop analysis of excitation amplitude and latency during surgical procedures, which is nowadays integrated into the software of almost all commercially available neuromonitoring devices.  The objective of CIONM is real-time monitoring of nerve status in order to recognize and prevent impending nerve injury and predict post-operative nerve function.  Despite some drawbacks such as false-positive/negative alarms, technical artefacts, and rare AEs, CIONM remains a good instrument which is still under development.  Active (aCIONM) and passive (pCIONM) methods of CIONM were described in the literature.  The main fields of CIONM implementation are currently thyroid surgery (in which the vagal nerve is continuously stimulated) and surgery to the cerebello-pontine angle (in which the facial nerve is either continuously stimulated or the discharge signal of the nerve is analyzed via pCIONM).  In the latter surgery, continuous monitoring of the cochlear nerve is also established.  The authors provided the following conclusions:

  • Continuous IONM is a new evolving instrument destined to help surgeons in performing surgical maneuvers in close proximity to neural structures.
  • It cannot and does not replace good operative technique and patency; however, it does provide reliable and safe assistance.
  • The safety of active CIONM (aCIONM) has been demonstrated in animal and human studies.
  • The field appears to be open for future studies, especially in surgery of the parotid gland where to-date neither aCIONM nor pCIONM has been applied.

Furthermore, UpToDate reviews on “Neck dissection for differentiated thyroid cancer” (Sippel, 2020) and “Treatment of locoregionally advanced head and neck cancer: The oropharynx” (Worden et al, 2020) do not mention intraoperative neuromonitoring as a management option.

Intraoperative Neuromonitoring During Craniotomy Repair of Cerebrospinal Fluid Leak

Feng et al (2014) noted that CSF leak may occur during the preparation of trajectory of thoracic pedicle screws in scoliosis surgery.  The strategy for management of such situation is controversial.  There is limited literature regarding the CSF leak and concomitant neuromonitoring change.  In a retrospective study, these researchers analyzed CSF leak during the thoracic pedicle screw fixation in spinal deformities, the relative IONM changes and the strategy for management.  A total of 695 patients with spinal deformity subjected to correction by posterior instrumentation using thoracic pedicle screw fixation from 2008 January to 2010 December and followed-up for more than 2 years were retrospectively analyzed for CSF leak during pedicle screw placement and the concomitant neuromonitoring changes.  The cases with CSF leak and with complete information regarding neuromonitoring were reviewed.  A total of 7,284 thoracic pedicle screws were inserted in the thoracic level (10.4 screws/patient).  All the procedures were carried out under the IONM.  There were 8 cases of CSF leak with the rate of 0.11 % during the screw trajectory preparation; 7 of the screws located at the concave side; 5 cases presented with concomitant positive IONM changes. The holes were sealed for 3 of them, and patients presented with reversible monitoring changes and intact neurological function.  Negligence of the CSF leak and screw insertion caused the deterioration of neuromonitoring even neurological deficit that needed revision surgery; 3 cases presented without IONM changes and woke-up without neurological deficit.  The authors concluded that the factors impacting the safety of screw placement for CSF leak included screw position, segment of vertebra, and concomitant neuromonitoring changes.  Commonly, it was unnecessary to repair the dural tear and sealing the pedicle hole with bone wax for the case with reversible neuromonitoring changes was all that needed.  A lateral entry point to the initial one could be used and to continue the screw placement when neuromonitoring demonstrated reversible positive changes.  Level of Evidence = IV.

Silverstein et al (2018) stated that transcranial MEP (TCMEP) and direct cortical MEP (DCMEP) paradigms have historically been used contemporaneously or independently for supratentorial craniotomies.  DCMEP provides focal stimulation to the cortical surface, whereas TCMEP stimulation is more variable and may be activating structures deeper than those at risk during a supratentorial craniotomy.  These researchers presented the case of a 65-year old woman who underwent a supratentorial craniotomy for the clipping of a right-sided unruptured middle cerebral artery (MCA) aneurysm.  DCMEP recordings of the upper extremity (UE) degraded after the parent vessel was temporarily occluded with a clip.  The recordings returned once the clip was released.  The DCMEP lower extremity (LE) recordings did not deviate from their established baseline.  TCMEP recordings (UEs and LEs) also did not deviate from their established baselines.  The permanent clip was placed without incident, and the patient awoke neurologically intact.  This case study demonstrated the specificity and sensitivity of DCMEP versus TCMEP.  DCMEP activated the corticospinal tract more superficially; thus, it was evident by the loss of the UE DCMEPs without the loss of LE DCMEPs that the temporary vessel occlusion caused an ischemic event focal to the cortical area perfused by the MCA.  This ischemic event was not detected by TCMEP.  The authors concluded that TCMEP and DCMEP are part of the neurophysiologist’s and neurosurgeon’s armamentarium and should be used accordingly.  DCMEPs are shown to be more specific and more sensitive than TCMEPs in supratentorial craniotomy and should be employed when feasible.  TCMEPs should not be discarded or discontinued, as they do have benefits in cranial surgery.  For example, the establishment of pre-incision baseline data can be used as a pilot to what should be expected from DC stimulation.  However, the expectations of their utility as an indicator of the cortical function should be managed, and if only using TCMEP, it should be understood that the risk of a false-negative occurring is increased, even if the neurophysiologist has controlled for the “crossover” response.  This was a single-case study that examined the use of MEP.

Beck et al (2019) stated that spinal CSF leaks are the cause of spontaneous intracranial hypotension (SIH).  These investigators proposed a surgical strategy, stratified according to anatomic location of the leak, for sealing all CSF leaks around the 360° circumference of the dura through a single tailored posterior approach.  All consecutive SIH patients undergoing spinal surgery were included.  The anatomic site of the leak was localized.  These researchers used a tailored hemi-laminotomy and IONM for all cases.  Neurological status was examined before and up to 90 d after surgery.  A total of 47 SIH patients had an identified CSF leak between the levels C6 and L1.  Leaks, anterior to the spinal cord, were approached by a transdural trajectory (n = 28).  Leaks lateral to the spinal cord by a direct extradural trajectory (n = 17) and foraminal leaks by a foraminal microsurgical trajectory (n = 2).  The transdural trajectory necessitated cutting the dentate ligament accompanied by elevation and rotation of the spinal cord under continuous neuromonitoring (spinal cord release maneuver, SCRM); 4 patients had transient deficits, none had permanent neurological deficits.  These researchers proposed an anatomic classification of CSF leaks into I ventral (77 %, anterior dural sac), II lateral (19 %, including nerve root exit, lateral, and dorsal dural sac), and III foraminal (4 %).  The authors concluded that safe sealing (with IONM) of all CSF leaks around the 360° surface of the dura was feasible through a single posterior approach.  The exact surgical trajectory was selected according to the anatomic category of the leak.

Intraoperative Neuromonitoring During Femoroacetabular Surgery

Ochs and associates (2012) noted that arthroscopic hip surgery is used to treat many of the causes of hip pain, hip instability, and hip disorders.  Hip pain and instability are often caused by injuries to the acetabular labrum.  Repairing labral tears, suturing, and debridement involve stabilizing the hip and placing the operative side leg in traction to allow for instrument clearance and to avoid iatrogenic injury to the chondral surfaces.  This places the sciatic nerve in a stretched position and may cause temporary or permanent nerve injury.  Transient neuropraxia is the most common injury occurring in 5 % of the patients undergoing arthroscopic hip surgery.  In this study, a total of 35 patients (24 women and 11 men, a total of 36 surgeries) were monitored with IONM using SSEPs during hip arthroscopy for labral repair and femoral head osteoplasty.  They ranged in age from 15 to 59 years; mean age of 39.81 years.  During surgery 19 (54 %) patients experienced significant SSEP waveform changes.  Time from placement of traction to loss of signals in those patients experiencing SSEP changes ranged from 7 mins to 46 mins.  Recovery of SSEP signals ranged from 2 mins to over 15 mins when the traction of the leg was released.  Surgeries ranged from 2 to 4 hours; mean of 2.78 hours.  The authors concluded that these findings showed that neuromonitoring during hip arthroscopic labral repair and debridement procedures might be useful to prevent temporary and permanent neural tissue injuries.

Hesper and colleagues (2017) stated that nerve injuries can occur from major hip surgeries, and some may be significant.  These investigators examined the feasibility and safety of neuromonitoring during hip preservation surgery and the incidence of alerting events during such monitoring.  A total of 25 adult patients underwent surgical hip dislocation for femoro-acetabular impingement (FAI).  Upper and lower extremity SSEPs, lower extremity transcranial MEPs, and lower extremity EMG were recorded.  They observed a temporary reduction of the monitored parameters in 12 patients (48 %) during surgery. There were no clinically significant neurological deficits post-operatively in any cases.  The authors concluded that neuromonitoring demonstrated events during hip surgery in this case-series study.  Although it may not be practical to use neuromonitoring in all major hip surgeries, it may be prudent from the perspective of patient safety to use it in high-risk cases, including those requiring prolonged surgical time; in patients with high body mass index (BMI), excessive deformity correction, and pre-existing neuropathy; and in revision cases, among others.

The authors stated that this study had several drawbacks.  With a sample size of 25 patients, this rather small study group did not allow for proof of reliability of IONM to predict permanent impairments of nerve function during this particular procedure, as sciatic nerve injury with post-operative deficiency in neuromuscular function has been described in less than 1% of cases after surgical hip dislocation.  Furthermore, as alerting events apparently appeared to be dependent on leg positioning while the hip was dislocated, different surgical assistants (who were holding the legs during these cases) might have possibly biased these findings.  However, all surgeries were performed by 1 single surgeon, and efforts were made to ensure similar patient positioning during each case.  Because of the need of muscle relaxants for endotracheal intubation, ease of dislocation and surgical exposures, and less tension on muscle structures, intraoperative EMG and TcMEP evaluation done during the usage of muscle relaxants might have been impaired. Until the relaxants wore off, SSEPs were the predominant predictor of nerve injury.  However, evaluation of SSEPs were based on calculated averages that were recorded, and thus, transient nerve injury might have sometimes occurred several minutes before notification.  In a study by Hilibrand et al (2004), changes in SSEPs were shown to occur with an average delay of 16 minutes after alterations in MEPs were noted.  With respect to the present findings, these results indicated that, in case of an alerting event, transient sciatic nerve injury might occur earlier than the average time of 36.7 ± 13.9 minutes that was noted in this study, and should likely be considered as such in dealing with the event.  However, because no patient exhibited a post-operative deficit in neuromuscular function, it appeared unlikely that irreversible neurological injury had occurred at that point, that is, within the time span of an event in these patients.

Intraoperative Neuromonitoring During Femur, Tibia/Fibula Osteotomy and Ankle Arthrodesis

Li et al (2018) noted that transcranial motor evoked potential (TcMEP) is widely used intra-operatively to monitor spinal cord and nerve root function.  To the authors’ knowledge, there is no report regarding TcMEP signal loss purely caused by patient positioning during the spinal procedure.  In a retrospective, case report, these investigators reported an intra-operative TcMEP signal loss of a patient with fixed sagittal imbalance posture along with mild hip contractures.  A 57-year old man had fixed sagittal imbalance and flexed hip contractures.  For a reconstruction surgery of T10 to the sacrum/ilium and L5 pedicle subtraction osteotomy (PSO), he was put in a prone position on a Jackson table.  In order to accommodate his fixed hip flexion contracture, thigh pads were not used; and pillows were placed under his bilateral thighs for cushioning.  TcMEPs were used to evaluate lumbar nerve root function.  Ten minutes after incision, bilateral vastus medialis TcMEPs were lost during spine exposure whereas all other data remained normal at baseline.  The bilateral lower extremities were re-positioned, with the knees flexed into a sling position to increase hip flexion.  Five minutes after re-positioning, the bilateral vastus medialis TcMEPs gradually improved and maintained baseline amplitude during the remainder of the surgery.  No muscle weakness was detected immediately after surgery.  The patient was discharged 6 days post-operatively with markedly improved posture and alignment.  The authors concluded that insufficient hip flexion in patients with fixed sagittal imbalance and hip flexion contractures may cause TcMEP signal changes in the quadriceps response.  TcMEP monitoring of bilateral lower extremities is highly recommended for patients with sagittal imbalance and hip contractures, with consideration for lower extremity re-positioning when data degradation did not correlate with the actual spinal procedure being performed.

Furthermore, an UpToDate review on “Total joint replacement for severe rheumatoid arthritis” (Rinaldi, 2021) does not mention intra-operative neuromonitoring as a management tool.

Intraoperative Neuromonitoring During Implantation/Removal and Adjustment of Vertical Expandable Prosthetic Titanium Rib

Skaggs and colleagues (2009) stated that the vertical expandable prosthetic titanium rib (VEPTR) device is used in the treatment of thoracic insufficiency syndrome and certain types of early-onset spinal deformity.  These researchers evaluated the risk of neurologic injury during surgical procedures involving use of the VEPTR and determined the effectiveness of intra-operative spinal cord neuro-monitoring (IONM).  Data were collected prospectively during a multi-center study.  Surgical procedures were divided into 3 categories:
  1. primary device implantation,
  2. device exchange, and
  3. device lengthening.

Further retrospective evaluation was undertaken in cases of neurologic injury or changes detected with neuro-monitoring.  There were 1,736 consecutive VEPTR procedures at 6 centers: 327 (in 299 patients) consisted of a primary device implantation, 224 were a device exchange, and 1,185 were a device lengthening.  Peri-operative clinical neurologic injury was noted in 8 (0.5 %) of the 1,736 cases: these injuries were identified after 5 (1.5 %) of the 327 procedures for primary device implantation, 3 (1.3 %) of the 224 device exchanges, and none of the 1,185 device-lengthening procedures.  Of the 8 cases of neurologic injury, 6 involved the upper extremity and 2 involved the lower extremity.  The neurologic deficit was temporary in 7 patients and permanent in 1 patient, who had persistent neurogenic arm and hand pain; IONM demonstrated changes during 6 (0.3 %) of the 1,736 procedures: 5 (1.5 %) of the 327 procedures for primary device implantation and 1 (0.08 %) of the 1,185 device-lengthening procedures.  The surgery was altered in all 6 cases, with resolution of the monitoring changes in 5 cases and persistent signal changes and a neurologic deficit (upper-extremity brachial plexopathy) in 1; 2 patients had false-negative results of monitoring of SEPs, and 1 had false-negative results of monitoring of SEPs and MVPs during implant surgery; 2 had a brachial plexopathy and 1 had monoplegia post-operatively, with all 3 recovering.  The authors concluded that neurologic injury during VEPTR surgery occurred much more frequently in the upper extremities than in the lower extremities.  The rates of potential neurologic injuries (neurologic injuries plus instances of changes detected by monitoring) during primary implantation of the VEPTR (2.8 %) and during exchange of the VEPTR (1.3 %) justified the use of IONM of the upper and lower extremities during those procedures.  As neuro-monitoring did not demonstrate any changes in children without a previous VEPTR-related monitoring change and there were no neurologic injuries during more than 1,000 VEPTR-lengthening procedures, IONM may not be necessary during those procedures in children without a history of a neurologic deficit during VEPTR surgery.

Roper (2010) noted that the titanium rib procedure is a safe and effective way of surgically treating pediatric patients with thoracic insufficiency syndrome and scoliosis.  As with any invasive surgical procedure, it is not without risks.  This investigator explained the potential risks to neurological structures while outlining the surgical approach and the neurological anatomy in the vicinity of the implanted instrumentation.  The types of potential nerve injury involve ischemia, trauma, compression, and stretch.  Furthermore, a suitable compilation of modalities of IONM is recommended to detect and avoid long-term nerve or spinal cord insult.  The authors concluded that overall, there are potential risks to the peripheral nerves and spinal cord during the implantation and subsequent lengthening of the vertical expandable prosthetic titanium rib (VEPTR) device.  However, utilizing the appropriate IONM modalities as a tool and intervention may prevent or significantly reduce the severity of any post-operative deficit, thereby influencing the outcome and artificially raising the quantity of false-positive cases.  An appropriate monitoring plan offers real-time feedback on a patient’s neurological conduction status.  If potential compromise is communicated properly among the surgical team, it is possible to reverse trauma to nervous tissue so the insult is only temporary and does not become permanent.  This is the goal of utilizing an appropriate IONM regimen during a VEPTR procedure.  The author stated that IONM should be a part of the initial surgical implantation of the device as well as any VEPTR replacements of the devise as neurological risks are potentially present in all.

Intraoperative Neuromonitoring During Rotator Cuff Repair

An UpToDate review on “Management of rotator cuff tears” (Martin and Martin, 2018) does not mention intra-operative neuromonitoring as a management tool.

Intraoperative Neuromonitoring During Sacroiliac Joint Fusion

In a retrospective, case-series, single-center study, Woods et al (2014) documented the clinical utility of intra-operative neuromonitoring during minimally invasive surgical sacroiliac joint (SIJ) fusion for patients diagnosed with SIJ dysfunction (as a direct result of SIJ disruptions or degenerative sacroiliitis) and determined stimulated electromyography (EMG) thresholds reflective of favorable implant position.  A medical chart review of consecutive patients treated with minimally invasive surgical SIJ fusion was undertaken at a single center.  Baseline patient demographics and medical history, intra-operative EMG thresholds, and peri-operative adverse events (AEs) were collected after obtaining institutional review board (IRB) approval.  A total of 111 implants were placed in 37 patients.  Sensitivity of EMG was 80 % and specificity was 97 %; intra-operative neuromonitoring potentially avoided neurologic sequelae as a result of improper positioning in 7 % of implants.  The authors concluded that the findings of this study suggested that intra-operative neuromonitoring may be a useful adjunct to minimally invasive surgical SIJ fusion in avoiding nerve injury during implant placement.

The authors stated that the drawbacks of this study included its small sample size (n = 37 patients), single surgeon experience, and absence of a control group.  The small patient size was reflective of the number of patients available in the private practice office.  All patients included in this study were followed post-operatively for a minimum of 3 months.  The benefits of evaluating patients from a single center include a consistent diagnostic and therapeutic approach.  Hopefully, in the near future, other surgeons will add to this body of knowledge and help validate the outcomes of this limited study.

Shamrock et al (2019) performed a systematic review of the existing literature to determine the safety of minimally invasive (MI)-SIJ fusion via the determination of the rate of procedural and device-related intra-operative and post-operative complications.  All original studies with reported complication rates were included for analysis.  Complications were defined as procedural if secondary to the MI surgery and device-related if caused by placement of the implant.  Complication rates were reported using descriptive statistics.  Random-effects meta-analysis was carried out for pre-operative and post-operative visual analog score (VAS) pain ratings and Oswestry Disability Index (ODI) scores.  A total of 14 studies entailing 720 patients (499 females/221 males) with a mean follow-up of 22 months were included; 99 patients (13.75 %) underwent bilateral SI joint arthrodesis resulting in a total of 819 SI joints fused.  There were 91 reported procedural-related complications (11.11 %) with the most common AE being surgical wound infection/drainage (n = 17); 25 AEs were attributed to be secondary to placement of the implant (3.05 %) with nerve root impingement (n = 13) being the most common.  The revision rate was 2.56 %. MI-SIJ fusion reduced VAS scores from 82.42 (9 5% confidence interval [CI]: 79.34 to 85.51) to 29.03 (95 % CI: 25.05 to 33.01) and ODI scores from 57.44 (95 % CI: 54.73 to 60.14) to 29.42 (95 % CI: 20.62 to 38.21).  The authors concluded that MI-SIJ fusion was a relatively safe procedure but is not without certain risks.  These researchers stated that further investigation must be carried out to optimize the procedure's complication profile.  Possible areas of improvement include pre-operative patient optimization, operative technique, and use of intra-operative real-time imaging.  This review did not mention intra-operative neuromonitoring (electromyography, nerve conduction velocity study, motor evoked potential, and somatosensory evoked potential).

Intraoperative Neuromonitoring During Shoulder Surgery

In a prospective, cohort study, Esmail et al (2005) examined the ability of a novel IONM method used to locate the axillary nerve, predict relative capsule thickness, and identify impending injury to the axillary nerve during arthroscopic thermal capsulorrhaphy of the shoulder.  A total of 20 consecutive patients with glenohumeral instability were monitored prospectively during arthroscopic shoulder surgery.  Axillary nerve mapping and relative capsule thickness estimates were recorded before the stabilization portion of the procedure.  During labral repair and/or thermal capsulorrhaphy, continuous and spontaneous EMG recorded nerve activity.  Furthermore, trans-spinal MEPs of the 4th and 5th cervical roots and brachial plexus electrical stimulation, provided real-time information regarding nerve integrity.  Axillary nerve mapping and relative capsule thickness were recorded in all patients.  Continuous axillary nerve monitoring was successfully performed in all patients; 11 of the 20 patients underwent thermal capsulorrhaphy alone or in combination with arthroscopic labral repair; 9 patients underwent arthroscopic labral repair alone.  In 4 of the 11 patients who underwent thermal capsulorrhaphy, excessive spontaneous neurotonic EMG activity was noted, thereby altering the pattern of heat application by the surgeon.  In 1 of these 4 patients, a small increase in the motor latency was noted after the procedure but no clinical deficit was observed.  There were no neuromonitoring or clinical neurologic changes observed in the labral repair group without thermal application.  At last follow-up, no patient in either group had any clinical evidence of nerve injury or complications from neurophysiologic monitoring.  The authors successfully evaluated the use of IONM to identify axillary nerve position, capsule thickness, and provide real-time identification of impending nerve injury and function during shoulder thermal capsulorrhaphy.  The use of IONM altered the heat application technique in 4 of 11 patients and may have prevented nerve injury.  These findings need to be validated by well-designed studies.

Parisien et al (2016) compared the incidence and pattern of potential nerve injuries between reverse shoulder (RSA) and total shoulder arthroplasty (TSA) using IONM.  These researchers hypothesized that RSA has a greater risk of nerve injury than TSA due to arm lengthening.  They reviewed 36 consecutive patients who underwent RSA (n = 12) or TSA (n = 24) with IONM.  The number of nerve alerts was recorded for each stage of surgery.  Neurologic function was assessed pre-operatively and post-operatively at routine follow-up visits.  Predictive factors for increased intra-operative nerve alerts and clinically detectable neurologic deficits were determined.  There were nearly 5 times as many post-reduction nerve alerts per patient in the RSA cohort compared with the TSA cohort (2.17 versus 0.46).  There were 17 unresolved nerve alerts post-operatively, with only 2 clinically detectable nerve injuries, which fully resolved by 6 months post-operatively.  A pre-operative decrease in active forward flexion and the diagnosis of rotator cuff arthropathy were independent predictors of intra-operative nerve alerts.  The authors concluded that RSA had a higher incidence of intra-operative nerve alerts than TSA during the post-reduction stage due to arm lengthening.  Decreased pre-operative active forward flexion and the diagnosis of rotator cuff arthropathy were predictors of more nerve alerts.  Moreover, these investigators stated that the clinical utility of routine IONM remained in question given the high level of nerve alerts and lack of persistent post-operative neurologic deficits.

In a case-series study, Shinagawa et al (2019) examined the risk of nerve injury with IONM during reverse total shoulder arthroplasty.  This study included 15 shoulders of 15 patients (11 females and 4 males) who underwent RSA.  The mean age of the subjects was 74.8 ± 4.4 years; 9 shoulders had cuff tear arthropathy, 4 had massive rotator cuff tears, 2 had osteoarthritis (OA), and 1 had RA.  The SSEPs of the median nerve, transcranial MEPs, and free-EMGs from 6 upper-extremity muscles were measured intra-operatively.  These researchers defined a nerve alert as 50 % amplitude attenuation or 10 % latency prolongation of the SSEPs and transcranial MEPs and sustained neurotonic discharge on free-EMG.  A total of 31 alerts were recorded in 11 patients.  The axillary nerve was associated with 17 alerts; 11 alerts occurred during the glenoid procedure and 5 alerts occurred during the humeral procedure; 1 patient who did not recover from the alert of the axillary nerve had clinically incomplete paralysis of the deltoid muscle.  The authors concluded that the findings of this study suggested that the axillary nerve was the nerve most frequently exposed to the risk of injury, especially during glenoid and humeral implantation.  Level of Evidence = IV.

Intraoperative Neuromonitoring During Temporal Artery to Middle Cerebral Artery Bypass in Patients with Moyamoya Disease

Chen et al (1989) described the findings of 20 Japanese children with Moyamoya disease who were investigated by examining the multi-modality evoked potentials (BAEP, FVEP and SSEP).  BAEPs were abnormally prolonged wave I-III and wave III-V in each one (10 %).  FVEPs were abnormal in 6 (30 %), included prolonged latencies, reduced amplitudes and poor waveform in one each, and delayed latencies as well as reduced amplitudes in 3.  FVEPs significantly correlated with intellectual deterioration (p < 0.01).  SSEPs were abnormal in 13 (65 %) significantly more frequent than BAEPs and FVEPs (p < 0.01); reduction of N20 in 7, delayed latencies of N13-N20 in 4, and both delayed latencies and reduced amplitudes of N20 in 2.  The authors stated that these findings correlated well with the neurologic deficits, CT findings and EEG findings in this progressive cerebrovascular disease (Moyamoya disease) in children.

Intraoperative Neuromonitoring During Tethered Cord Release

Sala and colleagues (2002) performed a critical analysis of the role of intraoperative neurophysiological monitoring (INM) during various neurosurgical procedures, emphasizing the aspects that mainly concern the pediatric population.  Original papers related to the field of intraoperative neurophysiology were collected using Medline; INM consists of monitoring (continuous "on-line" assessment of the functional integrity of neural pathways) and mapping (functional identification and preservation of anatomically ambiguous nervous tissue) techniques.  These investigators attempted to delineate indications for intraoperative neurophysiological techniques according to their feasibility and reliability (specificity and sensitivity).  In compiling this review, controversies about indications, methodologies and the usefulness of some INM techniques have surfaced.  These discrepancies were often due to lack of familiarity with new techniques in groups from around the globe.  Accordingly, internationally accepted guidelines for INM are still far from being established.  Nevertheless, the studies reviewed provide sufficient evidence to enable clinicians to make the following recommendations.

  • INM is mandatory whenever neurological complications are expected on the basis of a known pathophysiological mechanism.  INM becomes optional when its role is limited to predicting post-operative outcome or it is used for purely research purposes.
  • INM should always be performed when any of the following are involved: supratentorial lesions in the central region and language-related cortex; brain stem tumors; intramedullary spinal cord tumors; conus-cauda equina tumors; rhizotomy for relief of spasticity; spina bifida with tethered cord.
  • Monitoring of MEPs is now a feasible and reliable technique that can be used under general anesthesia.  MEP monitoring is the most appropriate technique to assess the functional integrity of descending motor pathways in the brain, the brain stem and, especially, the spinal cord.
  • Monitoring of SEP is of value in assessment of the functional integrity of sensory pathways leading from the peripheral nerve, through the dorsal column and to the sensory cortex.  SEPs cannot provide reliable information on the functional integrity of the motor system (for which MEPs should be used).
  • Monitoring of brain stem auditory evoked potentials remains a standard technique during surgery in the brain stem, the cerebellopontine angle, and the posterior fossa.
  • Mapping techniques (such as the phase reversal and the direct cortical/subcortical stimulation techniques) are invaluable and strongly recommended for brain surgery in eloquent cortex or along subcortical motor pathways.
  • Mapping of the motor nuclei of the 8th, 9th to 10th and 12th cranial nerves on the floor of the 4th ventricle is of great value in identification of "safe entry zones" into the brain stem.  Techniques for mapping cranial nerves in the cerebellopontine angle and cauda equina have also been standardized.  Other techniques, although safe and feasible, still lack a strong validation in terms of prognostic value and correlation with the post-operative neurological outcome.  These techniques include monitoring of the bulbo-cavernosus reflex, monitoring of the corticobulbar tracts, and mapping of the dorsal columns.  These techniques, however, are expected to open up new perspectives in the near future.

Paradiso and associates (2005) stated that during complex micro-neurosurgery performed in patients with tethered cord syndrome (TCS), the conus medullaris and the roots that innervate the lower limbs, bladder and bowel are potentially exposed to damage.  The aim of multi-modality IOM is to reduce the risk of inadvertent injury of neural tissue.  These researchers simultaneously recorded tibial nerve SSEPs from the scalp and free-run EMG of limb muscles supplied by L2 to S2 roots, anal and urethral sphincters.  They also identified critical neural structures in the operative field, including the conus and exiting nerve roots, with a nerve stimulator to evoke EMG; SSEPs assessed the sensory pathways mainly mediated by the S1 roots.  Continuous EMG provided the surgeon with immediate auditory feedback resulting from irritative discharges triggered by manipulation of nerve fibers.  Micro-stimulation can distinguish the filum terminale, scar tissue and invasive tumors from functional neural tissue, thus minimizing the risk of iatrogenic injury.  The authors concluded that multi-modality IOM proved a valuable adjunct to micro-neurosurgery of the lumbosacral spine.

Husain and Shah (2009) noted that IONM is used in surgery for TCS.  These researchers determined if IONM is helpful in identifying which patients would have worsening symptoms after surgery.  The spinal cord was stimulated before and after untethering until a motor response was obtained.  The pre- and post-operative neurologic examination findings were noted.  The motor response thresholds before and after untethering were compared using Student t-tests.  A total of 40 patients were identified; 37 had higher motor response thresholds before untethering, whereas in 3 thresholds were higher after untethering.  Of the 37 patients, 2 had worsening of motor function.  All 3 patients with higher thresholds after untethering had worsening of motor function (p < 0.0001).  The authors concluded that an increase in the motor response threshold after surgical release of tethered cord syndrome indicated possible worsening of clinical symptoms; spinal cord stimulation during TCS surgery may help predict neurologic outcome.

Beyazova and co-workers (2010) stated that the TCS refers to a variety of lesions that can cause the conus medullaris to be low-lying or incapable of movement within the spinal canal.  Permanent or temporary neurological complications were reported following surgical release.  In this report, peri- and post-operative results in cases with TCS that were followed by multi-modal IONM (MIONM) methods were presented.  An IONM system (Nicolet CR Endeavor) was used for monitoring during TCS surgery; SEPs, MEPs, direct nerve root/rootlet stimulation, free-run EMG and F-waves were used during TCS surgery of 10 cases to prevent possible nerve injuries.  MEP and SEP recordings did not change in any of the cases during surgery.  The nervous tissue was identified and differentiated from connective tissue in 3 cases when motor responses were elicited with direct stimulation of nerve roots.  None of the cases had neurological deficits following the operation.  The authors concluded that direct nerve root/rootlet stimulation should be one of the components of MIONM during surgery for TCS to prevent post-operative neurological deficits.

Intraoperative Neuromonitoring During Thoracotomy for Resection of Mediastinal Mass

Husain et al (2007) noted that conventional surgery on the descending thoracic aorta for aneurysm or dissection repair typically involves open thoracotomy and cross-clamping of the aorta.  These procedures are associated with the potential for significant neurologic morbidity due to spinal cord ischemia.  Endovascular stent graft (EVSG) repair of the descending thoracic aorta precludes the need for aortic cross-clamping and appeared to be associated with fewer neurologic complications.  Several studies have demonstrated the utility of IONM during conventional aortic surgery; however, less information is available regarding IONM during EVSG repair.

Srivastava et al (2014) reported a rare case of benign thoracic dumb-bell tumor in the upper posterior mediastinum, which was successfully removed by posterolateral thoracotomy and foraminotomy, using intraoperative monitoring of spinal MEPs.  This technique has many advantages including minimal morbidity and mortality, a single incision, 1-step complete resection with adequate exposure, spinal stabilization, avoidance of laminectomy, nerve root identification, and good predicted post-operative function.

Mikai et al (2019) reported the findings of a 33-year old woman who presented with a right cervical mass.  Contrast computed tomography (CT) showed a multi-locular tumor with a clear border and heterogeneous contents including fat and calcification.  The tumor was located adjacent to the vagus and recurrent nerves.  To avoid injury of these nerves, these investigators resected the tumor through a median sternotomy and right cervical lateral incision; IONM was carried out using an NIM TriVantage EMG tube (Medtronic, Minneapolis, MN).  After the surgery, no neuropathy such as hoarseness was recognized.  Pathological diagnosis showed a benign mature teratoma.  The authors concluded that IONM was useful for superior mediastinal surgery around the vagus and recurrent nerves.

An UpToDate review on “Overview of open surgical repair of the thoracic aorta” (Burke, 2020) states that “For patients at high risk for spinal cord ischemia (i.e., extent I and II disease, e.g., descending thoracic aortic aneurysm and thoracoabdominal aortic aneurysm repair), cerebrospinal fluid drainage and perioperative monitoring of spinal perfusion pressure (mean arterial pressure - spinal pressure of greater than 80 mmHg) and spinal cord function are recommended.  In our protocol, we maintain intrathecal pressure ≤ 10 mmHg.  Intraoperative motor or somatosensory evoked potential monitoring can also be used to detect early spinal cord ischemia, which may help guide therapy.  It is reasonable to base the decision to use neurophysiologic monitoring on individual patient needs, institutional resources, the urgency of the procedure, and the surgical and perfusion techniques to be used during open thoracic aortic repair”.

Intraoperative Neuromonitoring During Thyroidectomy and Thyroid Re-Operations

Barczynski and colleagues (2013) stated that IONM during thyroid surgery has gained widespread acceptance as an adjunct to the gold standard of visual identification of the recurrent laryngeal nerve (RLN).  Contrary to routine dissection of the RLN, most surgeons tend to avoid rather than routinely expose and identify the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy or parathyroidectomy.  IONM has the potential to be utilized for identification of the EBSLN and functional assessment of its integrity; therefore, IONM might contribute to voice preservation following thyroidectomy or parathyroidectomy.  These investigators reviewed the literature and the cumulative experience of the multi-disciplinary International Neural Monitoring Study Group (INMSG) with IONM of the EBSLN.  A systematic search of the Medline database (from 1950 to the present) with pre-defined search terms (EBSLN, superior laryngeal nerve, stimulation, neuromonitoring, identification) was undertaken and supplemented by personal communication between members of the INMSG to identify relevant publications in the field.  The hypothesis explored in this review was that the use of a standardized approach to the functional preservation of the EBSLN could be facilitated by application of IONM resulting in improved preservation of voice following thyroidectomy or parathyroidectomy.  Level of Evidence: V.

Pisanu and co-workers (2014) stated that the role of IONM of the RLN during thyroid surgery is still debatable.  In a meta-analysis, these investigators evaluated the potential improvement of IONM versus RLN visualization alone (VA) in reducing the incidence of vocal cord palsy.  A literature search for studies comparing IONM versus VA during thyroidectomy was performed.  Studies were reviewed for primary outcome measures: overall, transient, and permanent RLN palsy per nerve and per patients at risk; and for secondary outcome measures: operative time; overall, transient and permanent RLN palsy per nerve at low and high risk; and the results regarding assistance in RLN identification before visualization.  A total of 20 studies comparing thyroidectomy with and without IONM were reviewed: 3 prospective, randomized trials, 7 prospective trials, and 10 retrospective, observational studies.  Overall, 23,512 patients were included, with thyroidectomy performed using IONM compared with thyroidectomy by VA.  The total number of nerves at risk was 35,513, with 24,038 nerves (67.7 %) in the IONM group, compared with 11,475 nerves (32.3 %) in the VA group.  The rates of overall RLN palsy per nerve at risk were 3.47 % in the IONM group and 3.67 % in the VA group.  The rates of transient RLN palsy per nerve at risk were 2.62 % in the IONM group and 2.72 % in the VA group.  The rates of permanent RLN palsy per nerve at risk were 0.79 % in the IONM group and 0.92 % in the VA group.  None of these differences was statistically significant, and no other differences were found.  The authors concluded that the current review with meta-analysis showed no statistically significant difference in the incidence of RLN palsy when using IONM versus VA during thyroidectomy.  However, they noted that these results must be approached with caution, as they were mainly based on data coming from non-randomized observational studies.  These researchers stated that further studies including high-quality multi-center, prospective, randomized trials based on strict criteria of standardization and subsequent clustered meta-analysis are needed to verify the outcomes of interest.

Barczynski and associates (2016) noted that surgical management of the EBSLN during thyroidectomy is complex.  These investigators hypothesized that there exist variations in surgical behaviors patterns in the management of the EBSLN during thyroidectomy.  They carried out a prospective Web-based anonymous survey.  The survey, consisting of 22 questions including surgeon demographics, laryngeal examination before and after surgery, and utilization of IONM for the management of the RLN and the EBSLN, was sent to 673 surgeons world-wide with known interest in thyroid surgery.  A total of 170/673 (25.3 %) surgeons from 5 continents with low-volume (11.2 %), moderate-volume (27.2 %), and high-volume practices (61.5 %) completed the survey.  Laryngeal pre-operative examination was performed by 94 % of respondents.  IONM was utilized in the RLN management by 95 % of respondents.  IONM was used for identification of the EBSLN by 26.3 % of low-volume versus 68.4 % of high-volume surgeons (p = 0.004), and 93 % of respondents felt EBSLN identification with IONM as necessary in voice professionals.  Staged thyroidectomy was performed for benign disease by 89.5 % of low-volume versus 63.2 % of high-volume surgeons (p = 0.031).  Post-thyroid surgery laryngeal examination was performed by 36.8 % of low-volume versus 64.9 % of high-volume surgeons (p = 0.032).  The authors concluded that laryngeal examination and IONM was used frequently.  However, the exact pattern of utilization varied notably with demographic information.  Generally, high-volume surgeons, those with otolaryngology background, and younger surgeons more commonly utilized IONM according to existing international neural monitoring study group guidelines.  These researchers stated that prospective multi-center studies are needed to guide an evidence-based management of the EBSLN during thyroidectomy.

Yang and colleagues (2017) noted that IONM has been a commonly used technology during thyroid surgery aimed at reducing the incidence of recurrent laryngeal nerve palsy (RLNP), which is a severe complication and leads to significant impacts on a patient's life.  In order to give a comprehensive assessment for potential benefits and disadvantage of IONM, this meta-analysis and systematic review discussed RLNP rate, predictive power, continuous IONM (CIONM), and emphasized application during thyroid cancer surgeries.  A literature search was performed in the following electronic databases: PubMed, Embase, and the Cochrane library from January 1, 2004 to July 30, 2016.  After applying inclusion and exclusion criteria, a total of 24 studies, including 4 prospective randomized trials, were selected.  Heterogeneity of studies was checked by the Cochran Q test.  Publication bias was assessed by funnel plots with Egger's linear regression test of asymmetry; OR was calculated by random effects model.  Overall, 9,203 patients and 17,203 nerves at risk (NAR) were included.  Incidence of overall, transient, and persistent RLNP in IONM group were, respectively, 3.15 %, 1.82 %, and 0.67 %, whereas for the ID group, they were 4.37 %, 2.58 %, and 1.07 %.  The summary OR of overall, transient, and persistent RLNP compared using IONM and ID were, respectively, 0.81 (95 % CI: 0.66 to 0.99), 0.76 (95 % CI: 0.61 to 0.94), and 0.78 (95 % CI: 0.55 to 1.09).  The authors concluded that the presented data showed benefits of reducing RLNP rate by using IONM, but without statistical significance for persistent RLNP rate.  For patients with thyroid cancer who underwent total thyroidectomy, the use of IONM may improve the outcome by reducing amount of residual thyroid tissue.  However, no benefits were found for thyroid re-operation; visual identification and careful dissection remain standard for this challenging procedure.  In addition, the relative low positive predictive power indicated intermittent IONM (IIONM) may not be reliable; but CIONM was showed to be a more promising method, with prudent approach.

Motos-Mico and associates (2017) stated that IONM of the RLN in thyroid surgery facilitates the identification of anatomical structures in cervical endocrine surgery reducing the frequency of vocal cord paralysis.  An In an observational, descriptive, prospective study, these investigators examined the normal electrophysiological values of the vagus nerve and RLN before and after thyroid surgery, and compared rates of injury of RLN before and after the introduction of the IONM in thyroid surgery.  This trial included a total of 490 patients, and was carried out between 2003 to 2010; surgery was performed on 411 patients (703 nerves at risk) with systematic identification of RLNs.  Between 2010 to 2011 neuromonitorization was also systematically performed on 79 patients.  Before the introduction of IONM of 704 nerves at risk, there were 14 RLN injuries. Since 2010, after the introduction of the intraoperative neuromonitoring in thyroid surgery, there has been no nerve injury in 135 nerves at risk.  The authors concluded that the systematic identification of the RLN is the “gold standard” in thyroid surgery and IONM of nerves can never replace visual nerve identification but can complement it.

Stopa and Barczynski (2017) stated that the diagnostic accuracy of IONM of the RLN remains controversial.  In a prospective study, these investigators examined IONM diagnostic accuracy in prognostication of post-operative nerve function in thyroid surgery.  This trial was conducted in 2011 to 2013; a total of 500 consenting patients qualified for total thyroidectomy with IONM (1,000 nerves at risk) using NIM 3.0 Response equipment were included.  Laryngoscopy was used to evaluate and follow-up RLN injury.  The primary outcome was diagnostic accuracy of IONM.  The receiver operating characteristics (ROC) were used for evaluation of IONM diagnostic accuracy.  Loss of signal (LOS) occurred in 31 cases, including 25 patients with LOS and corresponding vocal fold paresis found in post-operative laryngoscopy (2.5 %), including 20 (2.0 %) temporary and 5 (0.5 %) permanent nerve lesions.  The following diagnostic accuracy values were calculated for the criterion recommended by INMSG (V2 amplitude of less than or equal to 100 μV): sensitivity of 92.0 %, specificity of 99.3 %, PPV of 76.7 %, and NPV of 99.8 %.  The ROC curve analysis allowed for calculation of the most optimal criterion in prognostication of post-operative vocal fold paresis, namely, V2 amplitude of less than or equal to 189 μV.  For this criterion, PPV was 77.4 %, while NPV was 99.9 %.  The authors concluded that aAdherence to the standardized protocol recommended by the International Neural Monitoring Study Group allowed for optimizing predictive values of IONM in prognostication of post-operative RLN function.  Any changes in the cut-off values for the definition of LOS only marginally improve PPV and NPV of IONM and need to be carefully assessed in multi-center studies.

The authors stated that despite a prospective design, the current study had several drawbacks.  Not all eligible patients were included, as the employment of IONM in Poland is not reimbursed by the Polish National Health Fund, which is the main reason for using this technique on select patients depending on the individual surgeon’s preferences and availability of the equipment.  The operations were performed not by 1, but 2 surgeons.  However, in order to minimize the risk of any bias, all the surgeons involved in this study had a comparable background experience both in thyroid surgery and utilization of IONM during thyroidectomy.  Post-operative laryngoscopy was not performed immediately after surgery in the recovery room, but at post-operative day 1, which in theory might have led to under-estimation of the prevalence of short-lasting transient nerve injuries.

Calo and colleagues (2017) evaluated the diagnostic accuracy of IONM in predicting post-operative nerve function during thyroid surgery and its consequent ability to assist the surgeon in intra-operative decision-making.  A total of 2365 consecutive patients were submitted to thyroidectomy by the same surgical team.  Group A included 1,356 patients (2,712 nerves at risk) in whom IONM was utilized, and Group B included 1,009 patients (2,018 nerves at risk) in whom IONM was not utilized.  In Group A, loss of signal (LOS) was observed in 37 patients; there were 29 true-positive, 1,317 true-negative, 8 false-positive, and 2 false-negative cases.  Accuracy was 99.3 %, PPV was 78.4 %, NPV was 99.8 %, sensitivity was 93.6 %, and specificity was 99.4 %.  A total of 29 (2.1 %) cases of unilateral paralysis were observed, 23 (1.7 %) of which were transient and 6 (0.4 %) of which were permanent.  Bilateral palsy was observed in 2 (0.1 %) cases requiring a tracheostomy.  In Group A, 31 (2.3 %) injuries were observed, 25 (1.8 %) of which were transient and 6 (0.4 %) of which were permanent.  In Group B, 26 (2.6 %) unilateral paralysis cases were observed, 20 (2 %) of which were transient and 6 (0.6 %) of which were permanent; bilateral palsy was observed in 2 (0.2 %) cases.  In Group B, 28 (2.8 %) injuries were observed, 21 (2.1 %) of which were transient and 7 (0.7 %) of which were permanent.  Differences between the 2 groups were not statistically significant.  The authors concluded that these findings showed that IONM had a very high sensitivity and NPV, but also good specificity and PPV.  For these reasons, in selected patients with LOS, the surgical strategy should be reconsidered.  However, patients need to be informed pre-operatively about potential strategy changes during the planned bilateral surgery.  These researchers stated that future larger, multi-center studies are needed to confirm the benefits of this therapeutic strategy.

Wojtczak and associates (2018) examined the usefulness of IONM in identifying anatomical variants of the RLN during thyroidectomies, with emphasis on the nerve's relationship to the inferior thyroid artery (ITA), Zuckerkandl's tubercle, non-RLNs (NRLNs), and extra-laryngeal bifurcation.  A total of 128 subjects undergoing surgery for thyroid disorders were enrolled in the study, and the course and anatomical variants of RLN were assessed with IONM application.  The standard relationship between RLN and ITA was that the artery and nerve intersect (100 %).  The right RLN was below the ITA in 76.67 % of the patients, and the left RNL was below it in 75.81 %.  There were no statistically significant differences in the relationship between RLN and ITA on the 2 sides; and gender did not significantly influence the relationship between the RLN and ITA on either side.  In 1 patient a non-recurrent inferior laryngeal nerve was present on the right side (0.83 %); RLN bifurcation was observed in 33.33 % of the patients on the right and in 19.35 % on the left side; the difference between sides was statistically significant (p < 0.05).  Posterior tubercle (Zuckerkandl's tubercle) was observed on the right in 83 % of the subjects and on the left in 69 %.  The age, thyroid volume and body mass index (BMI) did not influence the size of the tumor.  The authors concluded that the utilization of IONM of the RLN in thyroid surgery added a new dimension to the standard of visual nerve identification allowing for functional nerve testing at the most vulnerable area of the dissection: at the level of Berry's ligament, posterior tubercle (Zuckerkandl's tubercle) and crossing of the RLN with the inferior thyroid artery.

The authors stated that this study had 2 main drawbacks.  First of all the study group comprised of 128 patients and hence it could be considered a relatively small study.  Second, all these anatomical variants were observed by a single high-volume thyroid surgeon, which may be difficult to follow by low-volume thyroid surgeons.

Mirallie and co-workers (2018) stated that the impact of IONM on RLNP remains debated.  In a prospective, multi-center, study, these researchers evaluated the potential protective effect of IONM on RLN during total thyroidectomy.  The use of IONM was left at the surgeons' choice.  Post-operative laryngoscopy was performed systematically at day 1 to 2 after operation and at 6 months in case of post-operative RLNP.  Uni-variate and multi-variate analyses and propensity score (sensitivity analysis) were performed to compare RLNP rates between patients operated with or without IONM.  Among 1,328 patients included (women 79.9 %, median age of 51.2 years, median BMI of 25.6 kg/m2), 807 (60.8 %) underwent IONM.  Post-operative abnormal vocal cord mobility was diagnosed in 131 patients (9.92 %), including 69 (8.6 %) and 62 (12.1 %) in the IONM and non-IONM groups, respectively; IONM was associated with a lesser rate of RLNP in uni-variate analysis (OR = 0.68, 95 % CI: 0.47 to 0.98, p = 0.04); but not in multi-variate analysis (OR = 0.74, 95 % CI: 0.47 to 1.17, p = 0.19), or when using a propensity score (OR = 0.76, 95 % CI: 0.53 to 1.07, p = 0.11).  There was no difference in the rates of definitive RLNP (0.8 % and 1.3 % in IONM and non-IONM groups respectively, p = 0.39).  The sensitivity, specificity, PPV and NPV of IONM for detecting abnormal post-operative vocal cord mobility were 29 %, 98 %, 61 %, and 94 %, respectively.  The authors concluded that the use of IONM did not decrease post-operative RLNP rate.  Due to its high specificity, however, IONM was useful to predict normal vocal cord mobility.

Furthermore, an UpToDate review on “Initial thyroidectomy” (Wang et al, 2018) states that “Intraoperative nerve monitoring (IONM) has been introduced with the goal of reducing the rate of RLN injury.  Although its routine use remains controversial, it could potentially assist in the identification, dissection, and prediction of postoperative function of the RLN”.

Wojtczak and associates (2017) stated that thyroid re-operations are at a high risk of RLN injury.  In a retrospective, cohort study, these investigators examined if the use of IONM could aid in the RLN identification and minimize the risk of its injury, in comparison with visual RLN identification.  This trial consisted patients who underwent thyroid re-operations with and without the use of IONM.  Primary end-point was the RLN identification rate.  The study entailed 61 patients undergoing thyroid re-operation among whom 24 were operated on with visual RLN identification only, while 37 procedures used IONM.  In the non-monitored re-operations, 44.4 % of the RLN were visually identified, as opposed to 91.6 % in the IONM group (p < 0.001).  Transient paresis occurred in 3 nerves with visualization (6.6 %), and in 1 in IONM group 1.6 % (p = 0.185).  Permanent paresis occurred in the group with visualization (6.6 %), as opposed to none with IONM.  The extent of resection in both groups was significantly different (p = 0.043).  Total, near-total thyroidectomies, Dunhill operations and subtotal thyroidectomies were performed in 71, 17, 4, and 8 % in the visualization group, and in 94, 0, 3, and 3 %, respectively, in the IONM group.  A non-anatomical RLN course was observed in 80 % of the re-operations with IONM.  The authors concluded that thyroid re-operation should be performed using IONM, because it allowed for a significantly improved RLN identification rate and a significantly more radical resection.

The authors stated that there is currently no hard evidence that IONM could diminish the prevalence of permanent vocal fold palsy, but more than 90 % of the respondents in the most recent international survey on the identification and neural monitoring of the EBSLN during thyroidectomy emphasized their confidence in IONM, and listed re-operative thyroid cases as the top indication – far higher than any other clinical situation – for the use of this technique during thyroid surgery.  Furthermore, these investigators noted that there is no consensus regarding the utility of IONM and its role is still evolving; i is not a standard of care in the majority of countries.

Sun and colleagues (2017) noted that the rate of RLNP is especially high in thyroid re-operations.  In a meta-analysis, these researchers examined if IONM reduces the prevalence of RLNP in thyroid re-operations.  A systematic literature search was conducted in the PubMed, SCIE and Wan Fang databases for studies published up to  August 31, 2016.  All data were analyzed using STATA (version 11) software.  Publication bias was assessed using Begg's funnel plot and Egger's test, and sensitivity analysis was performed.  A total of 9 studies including 2,436 at-risk nerves met the inclusion criteria.  The results were presented as pooled RRs with 95 % CI.  The overall RLNP rate was significantly lower in re-operations conducted with IONM than in those conducted without IONM (RR = 0.434, 95 % CI: 0.206 to 0.916, p = 0.029).  High heterogeneity was found (I2 = 70.2 %, p = 0.001).  The rates of transient RLNP with and without IONM did not differ significantly (RR = 0.607, 95 % CI: 0.270 to 1.366, p = 0.227).  The heterogeneity was high (I2 = 67.4 %, p = 0.005).  However, IONM was significantly associated with a reduction in permanent RLNP (RR = 0.426, 95 % CI: 0.196 to 0.925, p = 0.031).  No significant heterogeneity was found (I2 = 13.7 %, p = 0.325).  Funnel plots for overall and transient RLNP showed a possible publication bias.  The authors concluded that IONM was associated with a reduction in overall and permanent RLNP in thyroid re-operations.  However, these investigators stated that given the limited sample size and heterogeneity in this meta-analysis, further studies are needed to confirm these preliminary findings.

Intraoperative Neuromonitoring During Total Hip Replacement

Overzet et al (2018) noted that arthroscopic hip surgery is performed routinely for the treatment of various hip disorders.  Leg traction during labral tear repair, femoroplasty, and acetabuloplasty for hip stabilization can stretch the peripheral nerves.  This may cause temporary or permanent nerve injury.  This study examined the benefit of utilizing multi-modality intraoperative neurophysiological monitoring (IONM) during hip surgical procedures.  They performed a retrospective review of 10 arthroscopic hip surgeries with neurophysiological monitoring at 1 medical center.  Subjects consisted of 6 women and 4 men (mean age of 48.9 years).  The procedures were equally divided into left and right-sided procedures; IONM setup included posterior tibial, peroneal, and femoral or saphenous nerve SSEPs, transcranial electrical MEP (TCeMEP), train of 4(TOF), and EMG from the lower extremities.  All patients exhibited changes in IONM data during the surgical procedure.  Changes in the latency and amplitude or loss of the lower SSEPs on the surgical side occurred in 36 % of the monitorable SSEPs.  The surgeon instructed the team to reduce the leg lengthening by removing traction when changes were observed.  The SSEPs exhibited a full recovery in 75 % of the affected lower extremity SSEPs.  In the 2 instances of non-recovery, the SSEP responses remained increased in latency or decreased in amplitude at closing, but the waveform was intact.  There were 5 instances of complete loss of the waveform (4 in the ipsilateral leg, and 1in the contralateral leg) with recovery after traction was reduced.  TCeMEP changes occurred in 53 % of the ipsilateral lower muscles monitored.  Many of the TCeMEP changes were attributed to ischemia of the feet and could not be resolved intraoperatively.  The authors concluded that multi-modality IONM can be a beneficial and protective tool during surgical procedures involving hip and acetabular areas.  Early identification of changes in EPs during hip arthroscopy surgeries could minimize post-operative neurological deficits due to peripheral nerve injury and leg ischemia.  This was a small study (n = 10) on patients undergoing arthroscopic hip surgeries; not total hip replacement.

Furthermore, an UpToDate review on “Total hip arthroplasty” (Erens et al, 2019) does not mention intraoperative neuromonitoring as a management tool.

Intraoperative Neuromonitoring During Total Knee Arthroplasty / Replacement

An UpToDate review on “Total knee arthroplasty” (Martin and Roe, 2018) does not mention intra-operative neuromonitoring as a management tool.

Intraoperative Neuromonitoring During Zenkers Diverticulectomy

Ataka et al (2020) noted that Killian-Jamieson diverticulum is a rare pharyngo-esophageal diverticulum.  The risk of intra-operative injury of the recurrent laryngeal nerve (RLN) is high during surgical resection of Killian-Jamieson diverticulum because the RLN usually runs next to the base of the diverticulum.  These researchers presented a case of Killian-Jamieson diverticulum that was safely resected with effective use of an IONM system with a hand-held stimulating probe to prevent RLN injury.  This case entailed a 69-year old man who complained of dysphagia, and was diagnosed with Killian-Jamieson diverticulum and underwent open transcervical diverticulectomy.  Because the anterior aspect of the diverticulum was expected to be close to the RLN, the accurate location of the RLN was checked during dissection by intermittent stimulation using a hand-held probe of the IONM system to avoid mechanical and thermal injury.  The diverticulum was transected longitudinally using a linear stapler, and the staple line was buried using absorbable sutures from the distal end.  During its closure, RLN was identified very close to the diverticulum stump by IONM, and the upper side of the stump was left unburied to avoid RLN injury.  The post-operative course was uneventful and the patient was discharged on post-operative day 7.  Post-operative evaluation showed no vocal cord paralysis.  The authors concluded that IONM may be beneficial during open surgery for Killian-Jamieson diverticulum, which usually protrudes just lateral to the RLN.  The finding of this single-case study needs to be validated by well-designed studies.

Furthermore, an UpToDate review on “Zenker's diverticulum” (Schiff and van Delft, 2020) does not mention intraoperative nerve monitoring.

Intraoperative Somatosensory Evoked Potentials for Cochlear Implantation

American Academy of Neurology’s “Principles of Coding for Intraoperative Neurophysiologic Monitoring (IOM) and Testing” did not mention cochlear implantation.

American Speech-Language-Hearing Association (ASHA)’s Technical Report on “Cochlear Implants” did not mention somatosensory evoked potentials (SSEPs) as a management tool.

Intraoperative Somatosensory Evoked Potentials During Cervical Facet Injections

An UpToDate review on “Subacute and chronic low back pain: Nonsurgical interventional treatment” (Chou, 2017) does not mention “neuroimaging or intraoperative monitoring” for facet joint injection.

Intraoperative Somatosensory Evoked Potentials During Decompression of the Trigeminal Nerve

An UpToDate review on “Trigeminal neuralgia” (Bajwa et al, 2017) does not mention intraoperative monitoring or intraoperative SSEP monitoring.

Intraoperative Somatosensory Evoked Potentials During Hip Dysplasia and Labral Repair Surgery

Overzet et al (2018) noted that arthroscopic hip surgery is routinely carried out for the treatment of various hip disorders.  Leg traction during labral tear repair, femoroplasty, and acetabuloplasty for hip stabilization can stretch the peripheral nerves.  This may cause temporary or permanent nerve injury.  In a retrospective study, these researchers examined the benefit of employing multi-modality IONM during hip surgical procedures.  They conducted a review of 10 arthroscopic hip surgeries with neurophysiological monitoring at 1 medical center.  Subjects consisted of 6 women and 4 men (mean age of 48.9 years).  The procedures were equally divided into left and right-sided procedures.  IONM setup included posterior tibial, peroneal, and femoral or saphenous nerve SSEPs, transcranial electrical MEP (TCeMEP), train of 4 (TOF), and EMG from the lower extremities.  All subjects exhibited changes in IONM data during the surgical procedure.  Changes in the latency and amplitude or loss of the lower SSEPs on the surgical side occurred in 36 % of the monitorable SSEPs.  The surgeon instructed the team to reduce the leg lengthening by removing traction when changes were observed.  The SSEPs exhibited a full recovery in 75 % of the affected lower extremity SSEPs.  In the 2 instances of non-recovery, the SSEP responses remained increased in latency or decreased in amplitude at closing, but the waveform was intact.  There were 5 instances of complete loss of the waveform (4 in the ipsilateral leg, and 1 in the contralateral leg) with recovery after traction was reduced.  TCeMEP changes occurred in 53 % of the ipsilateral lower muscles monitored.  Many of the TCeMEP changes were attributed to ischemia of the feet and could not be resolved intra-operatively.  The authors concluded that multi-modality IONM could be a beneficial and protective tool during surgical procedures involving hip and acetabular areas.  Early identification of changes in evoked potentials during hip arthroscopy surgeries could minimize post-operative neurological deficits due to peripheral nerve injury and leg ischemia.

Murena et al (2021) stated that sciatic nerve injury is an uncommon but potentially devastating complication in hip and pelvis surgery; IONM was employed since the 1970s in neurosurgery and spine surgery.  To-date, IONM has gained popularity in other surgical specialties including orthopedic and trauma surgery.  In a systematic review, these investigators examined the available evidence on the effectiveness of intra-operative monitoring of sciatic nerve during pelvic and hip surgery.  Two reviewers independently identified studies by a systematic search of PubMed and Google Scholar from inception of database to January 10, 2021.  Inclusion criteria entailed English written papers, use of any type of IONM during traumatic or elective pelvic and hip surgery, comparison of the outcomes between patients who underwent nerve monitoring and patient who underwent standard procedures, all study types including case reports.  The present review was carried out in accordance with the 2009 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement.  The literature search produced 224 papers from PubMed and 594 from Google Scholar, with a total amount of 818 papers.  The 2 reviewers excluded 683 studies by title or duplicates.  Of the 135 remaining, 72 were excluded after reading the abstract, and 31 by reading the full text; therefore, 32 studies were finally included in the review.  The authors concluded that the use of IONM during hip and pelvis surgery was debated.  The review results were insufficient to support the routine use of IONM in hip and pelvis surgery.  The different IONM techniques have peculiar advantages and disadvantages and differences in sensitivity and specificity without clear evidence of superiority for any.  Results from different studies and different interventions were often in contrast.  However, there is general agreement in recognizing a role for IONM to define the critical maneuvers, positions or pathologies that could lead to sciatic nerve intra-operative damage.  Level of Evidence = II.

Intraoperative Somatosensory Evoked Potentials During Incision and Drainage of Paraspinal/Epidural Abscess of Cervical Spine

Abdelkader et al (2019) noted that monitoring of SSEPs serves as an early warning system to detect spinal cord injury and is correlated with post-operative sensory findings.  It is an indirect indicator of motor function.  These investigators examined the usefulness of intra-operative SSEPs monitoring as a stand-alone tool during spinal surgeries when MEPs are not available, to prevent and predict new post-operative neurologic deficits.  MEPs were not used as the equipment needed to record them was not available at the time of this study.  This trial included 50 patients, aged 14 to 67 years, undergoing extra-medullary manipulations, decompression of an epidural abscess or neoplasm, removal of intra-medullary tumor, or arterio-venous malformation (AVM) or spine correction procedures.  SSEPs were analyzed for latency and peak-to-peak amplitude.  Critical SSEP changes were defined as a 50 % decrease in amplitude or a 10 % increase in latency.  SSEPs had an overall sensitivity of 81.8 %, a specificity of 100 %, a PPV of 100 %, and a NPV of 91.3 %.  The authors concluded that intra-operative SSEPs have proven to be highly sensitive and specific for iatrogenic injury, mechanical stress caused by cord traction/compression, dural traction, lowered systemic blood pressure (SBP), and cord hypothermia.  The reversibility of intra-operative SSEP changes showed a highly significant relation to the number of cases with new post-operative deficits as well as type and site of pathologic study (p = 0.00, p = 0.01, and p = 0.00, respectively) but not with the level of pathologic study (p = 0.49).

Reddy et al (2021) stated that cervical decompression and fusion surgery remains a mainstay of treatment for a variety of cervical pathologies.  Potential intra-operative injury to the spinal cord and nerve roots poses non-trivial risk for consequent post-operative neurologic deficits.  Although neuromonitoring with intra-operative SSEPs is often used in cervical spine surgery, its therapeutic value remains controversial.   These researchers examined if significant SSEP changes could predict post-operative neurologic complications in cervical spine surgery.  A subgroup analysis was carried out to compare the predictive power of SSEP changes in both anterior and posterior approaches.  This study was a meta-analysis of the literature from PubMed, Web of Science, and Embase to identify prospective/retrospective studies with outcomes of patients who underwent cervical spine surgeries with intra-operative SSEP monitoring.  The total cohort consisted of 7,747 patients who underwent cervical spine surgery with intra-operative SSEP monitoring.  Inclusion criteria for study selection were as follows: prospective or retrospective cohort studies; studies conducted in patients undergoing elective cervical spine surgery not due to aneurysm, tumor, or trauma with intra-operative SSEP monitoring; studies that reported post-operative neurologic outcomes; studies conducted with a sample size 20 or more patients; studies with only adult patients 18 years of age or older; studies published in English; and studies inclusive of an abstract.  The sensitivity, specificity, diagnostic odds ratio (DOR), and likelihood ratios of overall SSEP changes, reversible SSEP changes, irreversible SSEP changes, and SSEP loss for predicting post-operative neurological deficit were calculated.  The total rate of post-operative neurological deficits was 2.50 % (194/7,747) and the total rate of SSEP changes was 7.36 % (570/7,747).  The incidence of post-operative neurological deficit in patients with intra-operative SSEP changes was 16.49 % (94/570) while only 1.39 % (100/7,177) in patients without.  All significant intra-operative SSEP changes had a sensitivity of 46.0 % and specificity of 96.7 % with a DOR of 27.32.  Reversible and irreversible SSEP changes had sensitivities of 17.7 % and 37.1 % and specificities of 97.5 % and 99.5 %, respectively.  The DORs for reversible and irreversible SSEP changes were 9.01 and 167.90, respectively.  SSEP loss had a DOR of 51.39, sensitivity of 17.3 % and specificity 99.6 %.  In anterior procedures, SSEP changes had a DOR of 9.60, sensitivity of 34.2 %, and specificity of 94.7 %.  In posterior procedures, SSEP changes had a DOR of 13.27, sensitivity of 42.6 %, and specificity of 94.0 %.  The authors concluded that SSEP monitoring was highly specific but weakly sensitive for post-operative neurological deficit following cervical spine surgery.  The analysis found that patients with new post-operative neurological deficits were nearly 27 times more likely to have had significant intra-operative SSEP change.  Loss of SSEP signals and irreversible SSEP changes appeared to indicate a much higher risk of injury than reversible SSEP changes.  These investigators stated that SSEPs could likely be used during cervical spine surgeries to accurately predict the risk of post-operative neurologic deficits.

Intraoperative Somatosensory Evoked Potentials During Rotator Cuff Repair

An UpToDate review on “Management of rotator cuff tears” (Martin and Martin, 2017) does not mention intraoperative SSEP monitoring.

Intraoperative SSEP During Open Reduction Internal Fixation (ORIF) of Acetabulum fracture

Calder et al (1994) examined the effectiveness of intra-operative sciatic nerve monitoring for 88 consecutive patients undergoing open reduction and internal fixation (ORIF) for acetabular fractures.  Intervention outcomes and pre- and post-operative electrophysiologic status were compared to post-operative functional findings.  Only 2 % of the patients demonstrated iatrogenic sciatic nerve palsies.  Functional and evoked potential (Eps) findings were in agreement for 89 % of the patients with post-operative palsies, while 26 % of the functionally normal patients showed abnormal EPs.  Intervention occurred in 55 surgeries; 80 % of interventions involved the peroneal nerve; 41 of the 55 patients who had interventions based on EP results showed recovery of responses to baseline.  Of the 14 patients with incomplete intervention recovery, 11 showed impaired post-operative responses.  Patients with pre-operative EP abnormalities did not show increased susceptibility to iatrogenic evoked potential changes.

In a retrospective, case-review study, Middlebrooks e al (1997) examined the incidence of sciatic nerve injury associated with the operative repair of acetabular fractures without SSEP monitoring.  These researchers reviewed prospectively documented pre- and post-operative physical examinations.  All the cases were reviewed of patients with ORIF of acetabular fractures who underwent posterior or extensile approaches (n = 129) performed by the 3 senior authors from January 1991 through March 1995.  Intraoperative SSEP monitoring was not used during any of the procedures.  The procedures included 65 Kocher-Langenbeck approaches, 34 combined Kocher-Langenbeck and ilio-femoral approaches, 4 extended ilio-femoral approaches, and 4 triradiate approaches; 1 case of iatrogenic nerve injury resulted in a sensory deficit.  No patient suffered an exacerbation of a pre-existing nerve injury.  The authors concluded that the findings of this study indicated that ORIF of acetabular fractures, using current techniques with visualization and protection of the sciatic nerve, can reduce the incidence of neurologic injury to a negligible level.  There did not appear to be justification for the addition of SSEP or EMG modalities to the operative routine of experienced surgeons.

Arrington et al (2000) stated that monitoring of motor evoked potentials (MEP) and SSEP provides instantaneous intraoperative assessment of a patient's neurologic status.  Monitoring of the sciatic nerve through MEP and SSEP can be used during ORIF of pelvic and acetabular fractures.  These investigators carried out a review of 12 pelvic and acetabular fractures treated with ORIF and evaluated with a combination of intraoperative MEP and SSEP monitoring.  Results revealed intraoperative MEP monitoring was 100 % sensitive and 100 % specific in predicting post-operative sciatic nerve deficits, whereas SSEP were not accurate in predicting post-operative sciatic nerve deficits.  The authors concluded that combined monitoring of the sciatic nerve with MEP and SSEP is beneficial at predicting post-operative sciatic nerve deficits during ORIF of pelvic and acetabular fractures.

In a retrospective, non-randomized study, Haidukewych et al (2002) described their experience with iatrogenic nerve injuries and examined the efficacy of intraoperative monitoring in a large consecutive series of operatively treated acetabular fractures from January 1, 1992 through December 31, 1998.  A total of 256 consecutive acetabular fractures were operatively treated at the authors’ institution; 140 unmonitored procedures and 112 monitored procedures were available for review.  The decision to use monitoring was at the discretion of the treating surgeon.  Intervention was ORIF of the acetabular fracture.  Pre-operative and post-operative neurologic examinations, fracture type, use of traction, dislocation, operative approach, and complications were analyzed.  Motor strength, sensation, the need for gait aids, orthoses, and extent of recovery were evaluated.  Traumatic nerve palsies were present in 11 of 140 (7.9 %) unmonitored and 13 of 112 (11.6 %) monitored fractures (p = 0.314).  There were 14 iatrogenic sciatic nerve palsies in 252 cases (5.6 %).  There were 4 iatrogenic sciatic palsies (2.9 %) in the unmonitored group and 10 iatrogenic palsies (8.9 %) in the monitored group (p = 0.037).  In the unmonitored group 1 of 81 Kocher-Langenbeck approaches (1.2 %), 2 of 52 ilio-inguinal (3.9 %), and 1 of 3 extended ilio-femoral approaches developed a sciatic palsy.  In the monitored group 6 of 77 Kocher-Langenbeck approaches (7.8 %), 3 of 25 ilio-inguinal (12 %), and 1 of 6 combined approaches (16.7 %) developed a sciatic palsy.  In 7 of the 10 iatrogenic palsies in the monitored group, the intraoperative monitoring was normal.  A total of 76 patients were monitored with SSEP alone, and 9 had iatrogenic injuries (11.8 %); 36 patients were monitored with SSEP and EMG, and 1 had an iatrogenic injury (2.8 %) (p = 0.164).  Clinical follow-up was available for 3 of the 4 patients with iatrogenic injuries in the unmonitored group, with a mean follow-up of 27 months (range of 8 to 60 months); 2 patients had full motor recovery at a mean of 6 months, and 1 had no recovery at 14 months.  The authors concluded that the use of intraoperative monitoring did not decrease the rate of iatrogenic sciatic palsy.  These researchers stated that further study involving larger prospective, randomized methodology appeared warranted.  Sciatic nerve injury was more common in ilio-inguinal approaches in both groups, likely due to reduction techniques for the posterior column performed with the hip flexed, placing the sciatic nerve under tension.

Facial Nerve Monitoring During Parotidectomy

In a systematic review and meta-analysis, Sood et al (2015) examined the effectiveness of intra-operative FNM in preventing immediate and permanent post-operative facial nerve weakness in patients undergoing primary parotidectomy.  Data sources included PubMed-NCBI database from 1970 to 2014.  Acceptable studies included controlled series that examined facial nerve function following primary parotidectomy with or without FNM (intra-operative nerve monitor versus control).  Primary and secondary endpoints were defined as immediate post-operative and permanent facial nerve weakness (House-Brackmann score of 2 or higher), respectively.  After a review of 1,414 potential publications, 7 studies met inclusion criteria, with a total of 546 patients included in the final meta-analysis.  The incidence of immediate post-operative weakness following parotidectomy was significantly lower in the FNM group compared to the unmonitored group (22.5 % versus 34.9 %; p = 0.001).  The incidence of permanent weakness was not statistically different in the long-term (3.9 % versus 7.1 %; p = 0.18).  The number of monitored cases needed to prevent 1 incidence of immediate post-operative facial nerve weakness was 9, given an absolute risk reduction of 11.7.  This corresponded to a 47 % decrease in the incidence of immediate facial nerve dysfunction (odds ratio [OR], 0.53; 95 % CI: 0.35 to 0.79; p = 0.002).  The authors concluded that in primary cases of parotidectomy, intra-operative FNM decreased the risk of immediate post-operative facial nerve weakness but did not appear to influence the final outcome of permanent facial nerve weakness.  Moreover, these researchers stated that additional studies are needed to determine if this reduction in short-term paresis would translate into improved patient quality of life (QOL) and satisfaction.

The authors noted that the key drawback of this study was that no facial nerve grading analysis could be performed, as reports of specific House-Brackmann scoring were not consistently reported in the literature.  The definition of ‘‘facial weakness’’ denoted a varied group of patients with slight-to-complete facial nerve paralysis (House-Brackmann of 2); thus, it was unclear if intra-operative FNM would reduce incidence of total paralysis (House-Brackmann of 6) or whether it only decreased marginal mandibular nerve weakness.  Furthermore, attempts were made to reduce bias and increase study validity by means of the Oxford Center for Evidence-Based Medicine grading system.  This analysis included only studies with grading A to B and studies with 2 arms where monitored and unmonitored patients were drawn from a relatively homogeneous population.  Although this greatly minimized the potential for bias, these investigators could not exclude the potential for bias on the part of surgeons in the absence of randomized controlled trials (RCTs).  However, it was expected that if bias were present, surgeons would be more likely to use FNM in cases that they determined to be at higher risk pre-operatively.

Chiesa-Estomba et al (2021) stated that facial nerve injury remains the most severe complication of parotid gland surgery; however, the use of intra-operative FNM (IFNM) during parotid gland surgery among otolaryngologist-head and neck surgeons continues to be a matter of debate.  These investigators carried out a systematic review and meta-analysis of the literature including studies from 1970 to 2019 to examine the effectiveness of IFNM in preventing immediate and permanent post-operative facial nerve weakness in patients undergoing primary parotidectomy.  Acceptable studies included controlled series that examined facial nerve function following primary parotidectomy with or without IFNM.  A total of 10 studies met inclusion criteria, with a total of 1,069 patients included in the final meta-analysis.  The incidence of immediate and permanent post-operative weakness following parotidectomy was significantly lower in the IFNM group compared to the unmonitored group (23.4 % versus 38.4 %; p = 0.001) and (5.7 % versus 13.6 %; p = 0.001) when all studies were included.  However, when these researchers analyzed just prospective data, they were unable to find any significant difference.  The authors concluded that the findings of this study suggested that IFNM may decrease the risk of immediate post-operative and permanent facial nerve weakness in primary parotid gland surgery.  However, due to the low evidence level, additional prospective-randomized trials are needed to determine if these results can be translated into improved surgical safety and improved patient satisfaction.

The authors stated that this study had several drawbacks.  First, the absence of uniformity across studies regarding the grading of facial nerve weakness made it impossible to carry out a proper analysis. Second, a correlation between the use of facial nerve monitoring and the rate of facial nerve weakness according to histology (Benign versus Malignant) was not possible, due to the absence of information in the studies included.  A specific House-Brackmann scoring was not consistently reported in the revised literature, with the definition of "facial weakness" encompassing a varied group of patients (House-Brackmann = 2to 6).  Third, a trend in favor of more limited resection in parotid gland surgery made it necessary to perform more specific studies regarding the need of IFNM and its influence in reducing the incidence of transient or permanent paralysis or single branch nerve weakness in partial superficial parotidectomy.  This analysis included 10 studies with grading A to B, with all of them having 2 arms (IFNM and WIFNM), drawn from a relatively homogeneous population.  Although this significantly minimized the potential for bias, these researchers could not exclude it all.  Attempts were made to reduce bias and increase the study validity by means of the Oxford Center for Evidence-Based Medicine grading system and the ROBIN-I.  The risk of bias analysis showed that the overall bias evaluation was considered to be at low-to-moderate risk in most studies, where the main reason for lowering the quality was the risk of bias due to missing data (due to short follow-up) and measurement of outcomes (absence of uniformity across studies).  Therefore, the main drawback of the studies included was possible risk of bias in selection of the reported results.

Sajisevi (2021) noted that facial nerve injury is the most feared complication during parotid surgery.  Intra-operative EMG nerve monitoring could be used to identify the facial nerve, map its course, identify surgical maneuvers detrimental to the nerve, and provide prognostic information.  Data regarding outcomes with FNM are heterogeneous.  In contrast, the incidence of permanent weakness has not been shown to be significantly affected by use of nerve monitoring.  For revision surgery, studies showed that monitored patients had weakness that was less severe with quicker recovery; and shorter operative times compared with unmonitored patients.

Chiang et al (2022) noted that FNM has been widely accepted as an adjunct during parotid surgery to facilitate identification of the FN main trunk, dissection of FN branches, confirmation of FN function integrity, detection of FN injury and prognostication of facial expression following tumor resection.  Although the use of FNM in parotidectomy is increasing, little uniformity exists in its application from the literature.  Therefore, not only are the results of many studies difficult to compare but the value of FNM technology is also limited.  These investigators reviewed the available evidence and proposed their standardized FNM procedures during parotid surgery, such as standards in FNM setup, standards in general anesthesia, standards in FNM procedures and application of stimulus currents, interpretation of electrophysiologic signals and prediction of the facial expression outcome and pre-/post-operative assessment of facial expressions.  The authors hoped that the FNM standardized procedures would provide greater uniformity, improve the quality of applications, help surgeons elucidate the mechanisms of FN injury and improve their surgical techniques and contribute to future studies of FNM technology.

Ruas et al (2023) stated that facial nerve dysfunction (FND) is a frequent and serious parotidectomy outcome; IFNM is an increasingly used technique to identify the FN and minimize its injury.  In a retrospective study, these researchers examined the determinant factors in the presence and severity of FND following parotidectomy, including IFNM.  A total of 48 patients consecutively submitted to parotidectomy between 2005 and 2020 in a tertiary hospital were analyzed.  The House-Brackmann Scale (HBS) was used to evaluate the severity of FND.  There was a mean age of 54.2 ± 17.8 years, 50 % were men.  Pleomorphic adenoma (41.7 %) and Warthin's tumor (25.0 %) were most common.  From the 23 patients (47.9 %) who developed some degree of FND (HBS score of 3.41 ± 1.53), 19 (82.6 %) showed facial movement recovery, with a mean recovery time of 4.78 ± 2.53 months.  IFNM was performed in 39.6 % of the surgeries.  The use of IFNM (p = 0.514), the type of surgery -- partial or total parotidectomy-(p = 0.853) and the type of histology -- benign or malignant lesion -- (p = 0.852) did not significantly influence the presence of FND in the post-operative period.  However, in the subgroup of patients who developed FND, the HBS value was significantly lower in cases of benign pathology (p = 0.002) and in patients who underwent IFNM (p = 0.017), denoting a significantly lower severity.  The authors concluded that in the present study, IFNM and the existence of a benign lesion have been shown to be associated with lower severity of FND.

Furthermore, an UpToDate review on “Parotidectomy” (Smith, 2023) states that “Intraoperative facial nerve monitoring -- The significant functional and psychological consequences of facial nerve dysfunction have prompted the utilization of facial nerve monitoring in an attempt to reduce the incidence of nerve injury and dysfunction.  Our group does not routinely incorporate facial nerve monitoring but selectively employs it for reoperation or surgeries that are complex and high-risk as defined by the surgeon.  At this time facial nerve monitoring during parotidectomy should not be considered standard of care, particularly since the long-term facial weakness results are the same with or without nerve monitoring”.

Intraoperative Neuromuscular Junction Testing

Anoxic Brain Injury

An UpToDate review on “Hypoxic-ischemic brain injury in adults: Evaluation and prognosis” (Weinhouse and Young, 2022) does not mention neuromuscular junction testing as a management option.

For Epidural Steroid Injections

An UpToDate review on “Subacute and chronic low back pain: Nonsurgical interventional treatment” (Chou, 2021) does not mention neuromuscular junction testing for epidural steroid injections.

Motor Evoked Potential Monitoring for Peripheral Nerve Ablation

A position statement on “Intraoperative motor evoked potential monitoring” by the American Society of Neurophysiological Monitoring (Macdonald et al, 2013) did not mention peripheral nerve ablation as an indication of MEP monitoring.

Stimulus Evoked Response During Radical Prostatectomy

Reeves et al (2016) employed nerve conduction studies (NCS) to clarify the functional innervation of the male urethral rhabdo-sphincter (RS), especially to test the hypothesis that in some men, fibers of the neurovascular bundle supply the RS.  These fibers may be at risk during radical prostatectomy (RP).  In this trial, men undergoing robot-assisted RP for clinically localized prostate cancer (PCa) were included.  Men with a history of pelvic surgery and/or radiation and/or trauma, obesity, or neurological diseases were excluded; NCS were carried out before and after prostate removal.  The St. Mark's pudendal electrode was used for pudendal (control) stimulation.  The ProPep Nerve-Monitoring System (ProPep Surgical, Austin, TX) was used to stimulate the neurovascular bundle at the level of the prostate base, mid, and apex.  ProPep needle electrodes inserted into the RS were used to measure evoked compound motor action potential (cMAP)response.  Results were only included if a valid pudendal control was elicited.  A total of 17 men underwent investigation.  Valid measurements were obtained after initial quality control in 7.  In 2 cases, evidence of sphincteric activation was observed, providing evidence to support neurovascular bundle innervation of the RS.  In the other 5 patients, no intra-pelvic nerve supply was demonstrated.  The authors concluded that somatic nerve supply to the RS was variable.  Direct intra-pelvic supply to the RS may exist in some men.  This may be one explanation as to why some patients unexpectedly develop severe urinary incontinence (UI) post-operatively despite technically satisfactory surgery.  Moreover, these researchers stated that further research is needed to validate these findings.

Furthermore, UpToDate reviews on “Radical prostatectomy for localized prostate cancer” (Klein, 2022), “Follow-up surveillance after definitive local treatment for prostate cancer” (Penson, 2022) and “Overview of approach to prostate cancer survivors” (Skolaru, 2022) do not mention stimulus evoked response as a management option.

Intraoperative Neuromonitoring During Thyroidectomy and Thyroid Re-Operations

Wojtczak et al (2023) stated that vocal fold paralysis after thyroid surgery is still a dangerous complication that significantly reduces patients' QOL.  Since the IONM technique has been introduced and standardized, the most frequently asked question is whether its use has significantly reduced the rate of RLN injury during thyroid surgery compared to VA.  In a retrospective, non-randomized, single-center study, these researchers attempted to prove the superiority of IONM over VA of the RLN during thyroid surgery in the prevention of vocal fold paralysis, considering risk factors for complications.  The medical records of 711 patients (1,265 RLNs at risk of injury) were analyzed retrospectively: in 257 patients/469 RLNs at risk, thyroid surgery was performed with IONM; in 454 patients/796 RLNs at risk, surgery was performed with VA.  The statistical analysis showed that in the group of patients with IONM only 1 risk factor -- the surgeon's experience-proved statistically significant (OR = 3.27; p = 0.0478) regarding the overall risk of vocal fold palsy.  In the group of patients where VA was used, 5 of the 12 factors analyzed were statistically significant: retrosternal goiter (OR = 2.23; p = 0.041); total thyroid volume (OR = 2.30; p = 0.0284); clinical diagnosis (OR = 2.5; p = 0.0669); gender (OR = 3.08; p = 0.0054), and risk stratification (OR = 3.30; p = 0.0041).  Furthermore, the cumulative risk, considering the simultaneous influence of all 12 factors, was slightly higher in the group of patients in whom only VA was used during the procedure: OR = 1.78.  This value was also considerably more statistically significant (p < 0.0001) than that obtained in the group of patients in whom IONM was used: OR = 1.73; p = 0.004.  The authors concluded that risk factors for complications in thyroid surgery were not significant for any increase in the rate of vocal fold paralysis as long as surgery was performed with IONM, in contrast to thyroid surgery performed only with VA; therefore, proving the superiority of IONM over VA for safety.

Gutierrez-Alvarez et al (2023) noted that the well-recognized risk of injury to the RLN during thyroidectomy has instigated various preventive measures.  One such measure involves directly visualizing the RLN, however, this is not always feasible in practice.  A more recent approach entails the use of IONM to identify and preserve the RLN.  In a retrospective, observational, and descriptive study, these researchers examined the effectiveness of IONM compared to single visualization of the RLN in averting nerve injury.  This trial included a cohort of 218 patients.  A Chi-square test was employed to determine the influence of IONM on the incidence of nerve injury, with p < 0.05 considered statistically significant.  These investigators used Jamovi software version 2.3.18 to analyze the data.  Of the 218 patients, IONM was used in 150 (68.8 %) cases; none of which resulted in nerve injury.  In contrast, 68 (31.2 %) patients underwent surgery without the use of neuromonitoring, with 2 (2.9 %) patients in this group experiencing nerve injury (p = 0.037).  In comparison, the risk of nerve injury was 0 % in the group monitored intra-operatively, and 2.94 % in the group that did not undergo intra-operatively neuromonitoring.  Furthermore, the RR of complications was 0.66 % in patients operated with IONM, while it was 5.88 % in the group operated without IONM; therefore, showing a clinically significant protective against vasculo-nervous complications.  The authors concluded that the findings of this study advocated for the use of IONM, whenever available, as it is a safe method for significantly decreasing the incidence of RLN injury during thyroidectomy compared with only visualization.

Mahvi et al (2023) stated that RLN injury is a significant complication after thyroidectomy.  Understanding risk factors for RLN injury and the associated post-operative complications may help inform quality improvement initiatives.  The American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) thyroidectomy-targeted database was employed for patients undergoing total thyroidectomy between 2016 and 2017.  Univariable and multi-variable regression were used to identify factors associated with RLN injury.  A total of 6,538 patients were identified.  The overall rate of RLN injury was 7.1 % (467/6,538).  Of these, 4,129 (63.1 %) patients had IONM, with an associated RLN injury rate of 6.5 % (versus 8.2 % without).  African American and Asian race, non-elective surgery, parathyroid auto-transplantation, and lack of RLN monitoring were all significantly associated with nerve injury on multi-variable analysis (p < 0.05).  Patients with RLN injury were more likely to experience cardiopulmonary complications, re-intubation, longer hospital length of stay, re-admission, and re-operation.  Patients who had IONM and sustained RLN injury remained at risk for developing significant post-operative complications, although the extent of cardiopulmonary complications was less severe in this cohort.  The authors concluded that RLN injury is common after thyroidectomy and is associated with significant morbidity, despite best practices.  Attention to pre-operative characteristics may help clinicians to further risk stratify patients before thyroidectomy.  Moreover, these investigators stated that while IONM does not mitigate all complications; the use of this technology may decrease severity of post-operative complications.

Veetil and Puzhakkal (2023) noted that total thyroidectomy (TT) in true sense is not total as evidenced by remnant uptake in radio-iodine scans and serum thyroglobulin.  These researchers examined the completeness of TT, operating time, and RLN injury with and without IONM.  This was a cross-sectional analytical study using retrospective data of patients undergoing TT for benign and malignant goiters.  Surgeries were performed by single surgeon.  Patients undergoing TT (2015 to 2022) were grouped into Group A (n = 400) and Group B (n = 400) based on use of IONM.  Subgroup of patients (Group A1 and B1) who had differentiated thyroid cancer were compared for completeness of thyroidectomy with diagnostic radioiodine whole-body scintigraphy (DxWBS) and serum thyroglobulin (TG).  Group A and B were compared for operating time and incidence of RLN palsy.  Of the 800 RLN at risk transient RLN palsy was lower with IONM (p = 0.048).  Mean operating time was significantly higher in Group-B (p = 0.0038).  Subgroup A1 showed lower radio-active iodine uptake percentage, higher number of patients with negative scan, TG of less than 1 ng/ml indicating better completeness of TT.  The authors concluded that the findings of this study showed better completeness of thyroidectomy, lower incidence of transient RLN palsy and shorter operating time with IONM.

Furthermore, an UpToDate review on “Thyroidectomy” (Wang et al, 2024) states that “Intraoperative nerve monitoring (IONM) has been advocated with the goal of reducing the rate of RLN injury.  Although its routine use remains controversial, it could potentially assist in the identification, dissection, and prediction of postoperative function of the RLN … Regardless of whether IONM is used during endocrine surgery, surgeons should exercise the same vigilance with surgical techniques to avoid RLN injury.  When IONM is used, it is to augment, rather than circumvent, the need for meticulous surgical techniques, including intraoperative visual identification of the RLN … Routine visual identification of the recurrent laryngeal nerve (RLN) decreases the incidence of injury and is regarded as the standard of care in thyroid surgery.  Intraoperative nerve monitoring is an adjunctive measure that can be used to identify the nerve with the goal of reducing the risk of nerve injury but should not be relied upon as a substitute for good surgical technique”.


Glossary of Terms

Table: Glossary of Terms
Term Definition
Brainstem Auditory Evoked Potential (BAEP) Monitors the function of the auditory nerve and auditory pathways in the brainstem
Electroencephalography (EEG) The electrical activity measured by EEG is generated by groups of pyramidal neurons, which has cell bodies in the 3rd and 5th layer of the cerebral cortex.
Electromyography (EMG) Monitors somatic efferent nerve activity and evaluates the functional integrity of individual nerves. Monitors intracranial, spinal, and peripheral nerves during surgeries.
Motor Evoked Potential (MEP) Monitors motor pathways, transcranial electrical stimulation elicits excitation of corticospinal projections at multiple levels
Somatosensory Evoked Potential (SSEP) Monitors the dorsal column–medial lemniscus pathway, which mediates tactile discrimination, vibration, and proprioception. Stimulation of sensory receptors in the skin initiates peripheral sensory nerves, which extend through the nerve root to the ipsilateral dorsal root ganglia at spinal levels.
Visual Evoked Potential (VEP) Measures the functional integrity of the optic pathways from the retina to the brain's visual cortex in response to light stimulus. Visual stimulus is converted into nerve signals in the retina. These signals are transmitted via the optic pathway to the brain, from the retina to the optic nerve, optic chiasma, optic tract, lateral geniculate body, optic radiation, and visual cortex occipital lobe.

Source: Ghatol and Widrich, 2022


Appendix

Documentation Requirements

  1. All medical necessity criteria must be clearly documented in the member's medical record and made available upon request.
  2. The member's medical record must contain documentation that fully supports the medical necessity for evoked potential studies. This documentation includes, but is not limited to, relevant medical history, physical examination, the anatomic location of the planned surgical procedure, the rationale for the location and modalities to be monitored, and results of pertinent diagnostic tests or procedures.
  3. For the BAERs, the member’s medical record should document the otologic exam describing both ear canals and tympanic membranes, as well as a gross hearing assessment. The medical record should also include the results of air and bone pure tone audiogram and speech audiometry.
  4. The physician’s evoked potential report should note which nerves were tested, latencies at various testing points, and an evaluation of whether the resulting values are normal or abnormal.
  5. Baseline testing prior to intraoperative neuromonitoring requires contemporaneous interpretation prior to the surgical procedure. To qualify for coverage of baseline testing, results of testing of multiple leads for signal strength, clarity, amplitude, etc., should be documented in the medical record. The time spent performing or interpreting the baseline electrophysiologic studies performed prior to surgery should not be counted as intraoperative monitoring, but represents separately reportable procedures. Testing performed during surgery does not qualify as baseline testing and is not a separately reportable procedure.
  6. For continuous intraoperative neurophysiology monitoring, from outside the operating room (remote or nearby) or for monitoring of more than one case while in the operating room, increments of less than 30 minutes should not be billed. For continuous intraoperative neurophysiology monitoring in the operating room with one on one monitoring requiring personal attendance, increments of less than 8 minutes should not be billed.

References

The above policy is based on the following references:

Monitoring of Facial Nerve

  1. American Academy of Otolaryngology - Head and Neck Surgery (AAO-HNS). Facial nerve monitoring. Position Statements. Alexandria, VA: AAO-HNS; submitted September 12, 1998.
  2. Brennan J, Moore EJ, Shuler KJ. Prospective analysis of the efficacy of continuous intraoperative nerve monitoring during thyroidectomy, parathyroidectomy, and parotidectomy. Otolaryngol Head Neck Surg. 2001;124(5):537-543.
  3. Chiang F-Y, Lien C-F, Wang C-C, et al. Proposals for standardization of intraoperative facial nerve monitoring during parotid surgery. Diagnostics (Basel). 2022;12(10):2387.
  4. Chiesa-Estomba CM, Larruscain-Sarasola E, Lechien JR, et al. Facial nerve monitoring during parotid gland surgery: A systematic review and meta-analysis. Eur Arch Otorhinolaryngol. 2021;278(4):933-943.
  5. Di Martino E, Sellhaus B, Haensel J, et al. Fallopian canal dehiscences: A survey of clinical and anatomical findings. Eur Arch Otorhinolaryngol. 2005;262(2):120-126.
  6. Dulguerov P, Marchal F, Lehmann W. Postparotidectomy facial nerve paralysis: Possible etiologic factors and results with routine facial nerve monitoring. Laryngoscope. 1999;109(5):754-762.
  7. Fabregas N, Gomar C. Monitoring in neuroanaesthesia: Update of clinical usefulness. Eur J Anaesthesiol. 2001;18(7):423-439.
  8. Grosheva M, Klussmann JP, Grimminger C, et al. Electromyographic facial nerve monitoring during parotidectomy for benign lesions does not improve the outcome of postoperative facial nerve function: A prospective two-center trial. Laryngoscope. 2009;119(12):2299-2305.
  9. Harner SG, Daube JR, Ebersold MJ, Beatty CW. Improved preservation of facial nerve function with use of electrical monitoring during removal of acoustic neuromas. Mayo Clin Proc. 1987;62(2):92-102.
  10. Harper C. Intraoperative cranial nerve monitoring. Muscle Nerve. 2004;29(3):339-351.
  11. Harper CM, Daube JR. Facial nerve electromyography and other cranial nerve monitoring. J Clin Neurophysiol. 1998;15(3):206-216.
  12. Hermann M, Hellebart C, Freissmuth M. Neuromonitoring in thyroid surgery: Prospective evaluation of intraoperative electrophysiological responses for the prediction of recurrent laryngeal nerve injury. Ann Surg. 2004;240(1):9-17.
  13. Hu J, Fleck TR, Xu J, et al. Contemporary changes with the use of facial nerve monitoring in chronic ear surgery. Otolaryngol Head Neck Surg. 2014;151(3):473-477.
  14. Ingelmo I, Trapero JG, Puig A, et al. Intraoperative monitoring of the facial nerve: Anesthesia and neurophysiology considerations. Rev Esp Anestesiol Reanim. 2003;50(9):460-471.
  15. Jiang L, Ma Y, Jiao Y. Decompression and monitor of facial nerve during cholesteatoma surgery in petrous part of temporal bone. Lin Chuang Er Bi Yan Hou Ke Za Zhi. 2006;20(16):741-743.
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  18. Lopez JR. The use of evoked potentials in intraoperative neurophysiologic monitoring. Phys Med Rehabil Clin N Am. 2004;15(1):63-84.
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  21. No authors listed. Intraoperative monitoring of the facial nerve - evoked potentials. Tech Brief. Chicago, IL: American Medical Association; March 1994.
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  27. Sajisevi M. Indications for facial nerve monitoring during parotidectomy. Otolaryngol Clin North Am. 2021;54(3):489-496.
  28. Selesnick SH, Lynn-Macrae AG. The incidence of facial nerve dehiscence at surgery for cholesteatoma. Otol Neurotol. 2001;22(2):129-132.
  29. Shan XF, Lin B, Lu XG, et al. Electromyographic monitoring of facial nerve during parotid surgery. Beijing Da Xue Xue Bao. 2014;46(1):48-52.
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  32. Terrell JE, Kileny PR, Yian C, et al. Clinical outcome of continuous facial nerve monitoring during primary parotidectomy. Arch Otolaryngol Head Neck Surg. 1997;123(10):1081-1087.
  33. Wang TS, Lyden ML, Sosa JA. Thyroidectomy. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed June 2020.
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Monitoring of Recurrent Laryngeal Nerve

  1. Barczyński M, Konturek A, Cichoń S. Randomized clinical trial of visualization versus neuromonitoring of recurrent laryngeal nerves during thyroidectomy. Br J Surg. 2009;96(3):240-246.
  2. Beldi G, Kinsbergen T, Schlumpf R. Evaluation of intraoperative recurrent nerve monitoring in thyroid surgery. World J Surg. 2004; 28(6):589-591.
  3. Brauckhoff M, Gimm O, Thanh PN, et al. First experiences in intraoperative neurostimulation of the recurrent laryngeal nerve during thyroid surgery of children and adolescents. J Pediatr Surg. 2002;37(10):1414-1418.
  4. Brennan J, Moore EJ, Shuler KJ. Prospective analysis of the efficacy of continuous intraoperative nerve monitoring during thyroidectomy, parathyroidectomy, and parotidectomy. Otolaryngol Head Neck Surg. 2001;124(5):537-543.
  5. Cavicchi O, Caliceti U, Fernandez IJ, et al. The value of neurostimulation and intraoperative nerve monitoring of inferior laryngeal nerve in thyroid surgery. Otolaryngol Head Neck Surg. 2009;140(6):866-870.
  6. Chiang FY, Lu IC, Kuo WR, et al. The mechanism of recurrent laryngeal nerve injury during thyroid surgery--the application of intraoperative neuromonitoring. Surgery. 2008;143(6):743-749.
  7. Dackiw AP, Rotstein LE, Clark OH. Computer-assisted evoked electromyography with stimulating surgical instruments for recurrent/external laryngeal nerve identification and preservation in thyroid and parathyroid operation. Surgery. 2002;132(6):1100-1106; discussion 1107-1108.
  8. Dimov RS, Doikov IJ, Mitov FS, et al. Intraoperative identification of recurrent laryngeal nerves in thyroid surgery by electrical stimulation. Folia Med (Plovdiv). 2001;43(4):10-13.
  9. Dionigi G, Donatini G, Boni L, et al. Continuous monitoring of the recurrent laryngeal nerve in thyroid surgery: A critical appraisal. Int J Surg. 2013;11 Suppl 1:S44-S46.
  10. Djohan RS, Rodriguez HE, Connolly MM, et al. Intraoperative monitoring of recurrent laryngeal nerve function. Am Surg. 2000;66(6):595-597.
  11. Gutierrez-Alvarez M, Torres-Ríos JA, Torreblanca-Olascoaga M, et al. Advantages of intraoperative neuromonitoring over direct visualization of the recurrent laryngeal nerve during thyroidectomy. Cureus. 2023;15(8):e43869.
  12. Harrison BJ, Triponez F. Intraoperative adjuncts in surgery for primary hyperparathyroidism. Langenbecks Arch Surg. 2009;394(5):799-809.
  13. Hemmerling TM, Schmidt J, Bosert C, et al. Intraoperative monitoring of the recurrent laryngeal nerve in 151 consecutive patients undergoing thyroid surgery. Anesth Analg. 2001;93(2):396-399.
  14. Hermann M, Hellebart C, Freissmuth M. Neuromonitoring in thyroid surgery: Prospective evaluation of intraoperative electrophysiological responses for the prediction of recurrent laryngeal nerve injury. Ann Surg. 2004;240(1):9-17.
  15. Hillermann CL, Tarpey J, Phillips DE. Laryngeal nerve identification during thyroid surgery -- feasibility of a novel approach. Can J Anaesth. 2003;50(2):189-192.
  16. Horn D, Rotzscher VM. Intraoperative electromyogram monitoring of the recurrent laryngeal nerve: Experience with an intralaryngeal surface electrode. A method to reduce the risk of recurrent laryngeal nerve injury during thyroid surgery. Langenbecks Arch Surg. 1999;384(4):392-395.
  17. Jonas J, Bahr R. Neuromonitoring of the external branch of the superior laryngeal nerve during thyroid surgery. Am J Surg. 2000;179(3):234-236.
  18. Kiviniemi H, Vornanen T, Mäkelä J. Prevention of complications of thyroid and parathyroid surgery. Duodecim. 2010;126(3):269-275.
  19. Mahvi DA, Saadat LV, Knell J, et al. Recurrent nerve injury after total thyroidectomy: Risk factor analysis of a targeted NSQIP data set. Am Surg. 2023;89(5):1396-1404.
  20. Marcus B, Edwards B, Yoo S, et al. Recurrent laryngeal nerve monitoring in thyroid and parathyroid surgery: The University of Michigan experience. Laryngoscope. 2003;113(2):356-361.
  21. Marusch F, Hussock J, Haring G, et al. Influence of muscle relaxation on neuromonitoring of the recurrent laryngeal nerve during thyroid surgery. Br J Anaesth. 2005;94(5):596-600.
  22. National Institute for Health and Clinical Excellence (NICE). Intraoperative nerve monitoring during thyroid surgery. Interventional Procedure Guidance 255. London, UK: NICE; March 2008.
  23. Otto RA, Cochran CS. Sensitivity and specificity of intraoperative recurrent laryngeal nerve stimulation in predicting postoperative nerve paralysis. Ann Otol Rhinol Laryngol. 2002;111(11):1005-1007.
  24. Robertson ML, Steward DL, Gluckman JL, and Welge J. Continuous laryngeal nerve integrity monitoring during thyroidectomy: Does it reduce risk or injury? Otolaryngol Head Neck Surg. 2004;131(5):596-600.
  25. Thomusch O, Sekulla C, Walls G, et al. Intra-operative neuromonitoring of surgery for benign goiter. Am J Surg. 2002;183(6):673-678.
  26. Timon CI, Rafferty M. Nerve monitoring in thyroid surgery: Is it worthwhile? Clin Otolaryngol. 1999;24(6):487-490.
  27. Tomoda C, Hirokawa Y, Uruno T, et al. Sensitivity and specificity of intraoperative recurrent laryngeal nerve stimulation test for predicting vocal cord palsy after thyroid surgery. World J Surg. 2006;30(7):1230-1233.
  28. Tschopp KP, Gottardo C. Comparison of various methods of electromyographic monitoring of the recurrent laryngeal nerve in thyroid surgery. Ann Otol Rhinol Laryngol. 2002;111(9):811-816.
  29. Veetil PP, Puzhakkal S. A comparison of completeness and complication of total thyroidectomy with or without neuromonitoring. Indian J Otolaryngol Head Neck Surg. 2023 ;75(3):1647-1650.
  30. Wang TS, Lyden ML, Sosa JA. Thyroidectomy. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed January 2024.
  31. Wojtczak B, Marciniak D, Kaliszewski K, et al. Proving the superiority of intraoperative recurrent laryngeal nerve monitoring over visualization alone during thyroidectomy. Biomedicines. 2023;11(3):880.

Monitoring of Other Cranial Nerves

  1. Lefaucheur JP, Neves DO, Vial C. Electrophysiological monitoring of cranial motor nerves (V, VII, IX, X, XI, XII). Neurochirurgie. 2009;55(2):136-141.
  2. Schlake HP, Goldbrunner R, Siebert M, et al. Intra-Operative electromyographic monitoring of extra-ocular motor nerves (Nn. III, VI) in skull base surgery. Acta Neurochir (Wien). 2001;143(3):251-261.
  3. Vial Ch, Bouhour F. Electrophysiological examination of the cranial nerves: Technical aspects and practical applications. Rev Med Liege. 2004;59 Suppl 1:82-90.

Monitoring During Spinal Surgery

  1. Beatty RM, McGuire P, Moroney JM, Holladay FP. Continuous intraoperative electromyographic recording during spinal surgery. J Neurosurg. 1995;82(3):401-405.
  2. Bernhardt G, Awiszus F, Meister U, et al. The effect of intraoperative screw monitoring (root monitoring) with the INS-1 System (NUVASIVE) on the radiological outcome of dorsal instrumentation of the lumbar spine. Z Orthop Unfall. 2016;154(3):269-274.
  3. de Blas G, Barrios C, Regidor I, et al. Safe pedicle screw placement in thoracic scoliotic curves using t-EMG: Stimulation threshold variability at concavity and convexity in apex segments. Spine (Phila Pa 1976). 2012;37(6):E387-E395.
  4. Erickson L, Costa V, and McGregor M. Use of intraoperative neurophysiological monitoring during spinal surgery. McGill University Health Centre. Report Number 20. Montreal, QC: McGill University Health Centre; July 7, 2005.
  5. Fehlings MG, Brodke DS, Norvell DC, Dettori JR. The evidence for intraoperative neurophysiological monitoring in spine surgery: Does it make a difference? Spine. 2010;35(9 Suppl):S37-S46.
  6. Finkelstein JA. Can triggered electromyograph thresholds predict safe thoracic pedicle screw placement. Spine. 2003;28(9):960.
  7. Ghatol D, Widrich J. Intraoperative neurophysiological monitoring. In StatPearls [Internet]. Treasure Island, FL: updated August 30, 2022.
  8. Glassman SD, Dimar JR, Puno RM, et al. A prospective analysis of intraoperative electromyographic monitoring of pedicle screw placement with computed tomographic scan confirmation. Spine (Phila Pa 1976). 1995;20:1375-1379.
  9. Gunnarsson T, Krassioukov AV, Sarjeant R, Fehlings MG. Real-time continuous intraoperative electromyographic and somatosensory evoked potential recordings in spinal surgery: Correlation of clinical and electrophysiologic findings in a prospective, consecutive series of 213 cases. Spine. 2004;29(6):677-684.
  10. Holland NR. Intraoperative electromyography during thoracolumbar spinal surgery. Spine. 1998;23(17):1915-1922.
  11. Holland NR. Intraoperative electromyography. J Clin Neurophysiol. 2002;19(5):444-453.
  12. Hussain NS. Analysis of 1014 consecutive operative cases to determine the utility of intraoperative neurophysiological data. Asian J Neurosurg. 2015;10(3):166-172.
  13. Jimenez JC, Sani S, Braverman B, et al. Palsies of the fifth cervical nerve root after cervical decompression: Prevention using continuous intraoperative electromyography monitoring. J Neurosurg Spine. 2005;3(2):92-97.
  14. Kaliya-Perumal AK, Charng JR, Niu CC, et al. Intraoperative electromyographic monitoring to optimize safe lumbar pedicle screw placement - a retrospective analysis. BMC Musculoskelet Disord. 2017;18(1):229.
  15. Krassioukov AV, Sarjeant R, Arkia H, Fehlings MG. Multimodality intraoperative monitoring during complex lumbosacral procedures: Indications, techniques, and long-term follow-up review of 61 consecutive cases. J Neurosurg Spine. 2004;1(3):243-253.
  16. Kundnani VK, Zhu L, Tak H, Wong H. Multimodal intraoperative neuromonitoring in corrective surgery for adolescent idiopathic scoliosis: Evaluation of 354 consecutive cases. Indian J Orthop. 2010;44(1):64-72.
  17. Lee CH, Kim HW, Kim HR, et al. Can triggered electromyography thresholds assure accurate pedicle screw placements? A systematic review and meta-analysis of diagnostic test accuracy. Clin Neurophysiol. 2015;126(10):2019-2025.
  18. Legatt AD, Schroeder CE, Gill B, Goodrich JT. Electrical stimulation and multichannel EMG recording for identification of functional neural tissue during cauda equina surgery. Childs Nerv Syst. 1992;8(4):185-189.
  19. Limbrick DD Jr, Wright NM. Verification of nerve root decompression during minimally-invasive lumbar microdiskectomy: A practical application of surgeon-driven evoked EMG. Minim Invasive Neurosurg. 2005;48(5):273-277.
  20. Maguire J, Wallace S, Madiga R, et al. Evaluation of intrapedicular screw position using intraoperative evoked electromyography. Spine. 1995;20(9):1068-1074.
  21. Mikula AL, Williams SK, Anderson PA. The use of intraoperative triggered electromyography to detect misplaced pedicle screws: A systematic review and meta-analysis. J Neurosurg Spine. 2016;24(4):624-638.
  22. Ovadia D, Korn A, Fishkin M, et al. The contribution of an electronic conductivity device to the safety of pedicle screw insertion in scoliosis surgery. Spine (Phila Pa 1976). 2011;36:E1314-E1321.
  23. Owen JH, Kostuik JP, Gornet M, et al. The use of mechanically elicited electromyograms to protect nerve roots during surgery for spinal degeneration. Spine. 1994;19(15):1704-1710.
  24. Paradiso G, Lee GY, Sarjeant R, et al. Multimodality intraoperative neurophysiologic monitoring findings during surgery for adult tethered cord syndrome: Analysis of a series of 44 patients with long-term follow-up. Spine. 2006;31(18):2095-2102.
  25. Raynor BL, Lenke LG, Kim Y, et al. Can triggered electromyograph thresholds predict safe thoracic pedicle screw placement? Spine. 2002;27(18):2030-2035.
  26. Raynor BL, Padberg AM, Lenke LG, et al. Failure of intraoperative monitoring to detect postoperative neurologic deficits: A 25-year experience in 12,375 spinal surgeries. Spine (Phila Pa 1976). 2016;41(17):1387-1393.
  27. Reidy DP, Houlden D, Nolan PC, et al. Evaluation of electromyographic monitoring during insertion of thoracic pedicle screws. J Bone Joint Surg Br. 2001;83(7):1009-1014.
  28. Resnick D, Choudhri T, Dailey A et al. Guidelines for the performance of fusion procedures for degenerative disease of the lumbar spine. Part 15: Electrophysiological monitoring and lumbar fusion. J Neurosurg Spine. 2005;2(6):725-732.
  29. Scherl SA. Treatment and prognosis of adolescent idiopathic scoliosis. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed June 2012.
  30. Slimp JC. Electrophysiologic intraoperative monitoring for spine procedures. Phys Med Rehabil Clin N Am. 2004;15(1):85-105.
  31. Spitz S, Felbaum D, Aghdam N, Sandhu F. Delayed postoperative C5 root palsy and the use of neurophysiologic monitoring. Eur Spine J. 2015;24(12):2866-2871.
  32. Thirumala PD, Muralidharan A, Loke YK, et al. Value of intraoperative neurophysiological monitoring to reduce neurological complications in patients undergoing anterior cervical spine procedures for cervical spondylotic myelopathy. J Clin Neurosci. 2016;25:27-35.
  33. Weiss DS. Spinal cord and nerve root monitoring during surgical treatment of lumbar stenosis. Clin Orthop Relat Res. 2001;(384):82-100.

Monitoring During Intra-Cranial Tumor Resections

  1. Batchelor T, Curry WT. Clinical manifestations and initial surgical approach to patients with malignant gliomas. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed April 2012.
  2. Grabb PA, Albright AL, Sclabassi RJ, Pollack IF. Continuous intraoperative electromyographic monitoring of cranial nerves during resection of fourth ventricular tumors in children. Neurosurg. 1997;86(1):1-4.
  3. Kombos T, Suess O, Kern BC, et al. Can continuous intraoperative facial electromyography predict facial nerve function following cerebellopontine angle surgery? Neurol Med Chir (Tokyo). 2000;40(10):501-505; discussion 506-507.
  4. Lau C, Teo W-Y. Overview of the management of central nervous system tumors in children. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed April 2012.

Monitoring During Placement of Dorsal Column Stimulator

  1. Mammis A, Mogilner AY. The use of intraoperative electrophysiology for the placement of spinal cord stimulator paddle leads under general anesthesia. Neurosurgery. 2012;70(2 Suppl Operative):230-236.
  2. Shils JL, Arle JE. Intraoperative neurophysiologic methods for spinal cord stimulator placement under general anesthesia. Neuromodulation. 2012;15(6):560-571; discussion 571-572.

EMG Monitoring During Surgical Intervention of the Trigeminal Nerve

  1. Bajwa ZH, Ho CC, Khan SA. Trigeminal neuralgia. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed June 2015.
  2. Brock S, Scaioli V, Ferroli P, Broggi G. Neurovascular decompression in trigeminal neuralgia: Role of intraoperative neurophysiological monitoring in the learning period. Stereotact Funct Neurosurg. 2004;82(5-6):199-206.
  3. Minahan RE, Mandir AS. Neurophysiologic intraoperative monitoring of trigeminal and facial nerves. J Clin Neurophysiol. 2011;28(6):551-565.

EMG Monitoring During Various Indications

  1. Ajiboye RM, Zoller SD, D'Oro A, et al. Utility of intraoperative neuromonitoring for lumbar pedicle screw placement is questionable: A review of 9957 cases. Spine (Phila Pa 1976). 2017;42(13):1006-1010.
  2. Bromberg MB. Brachial plexus syndromes. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed May 2018.
  3. Chou R. Subacute and chronic low back pain: Nonsurgical interventional treatment. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed June 2020; May 2021.
  4. Elangovan C, Singh SP, Gardner P, et al. Intraoperative neurophysiological monitoring during endoscopic endonasal surgery for pediatric skull base tumors. J Neurosurg Pediatr. 2016;17(2):147-155.
  5. Esmail AN, Getz CL, Schwartz DM, et al. Axillary nerve monitoring during arthroscopic shoulder stabilization. Arthroscopy. 2005;21(6):665-671.
  6. Fehlings MG, Brodke DS, Norvell DC, Dettori JR. The evidence for intraoperative neurophysiological monitoring in spine surgery: Does it make a difference? Spine (Phila Pa 1976).. 2010;35(9 Suppl):S37-S46.
  7. Ferreira CJA, Sherer M, Anetakis K, et al. Neurophysiological characteristics of cranial nerves V- and VII-triggered EMG in endoscopic endonasal approach skull base surgery. J Neurol Surg B Skull Base. 2021;82(Suppl 3):e342-e348.
  8. Figueroa D, Calvo R, Vaisman A, et al. Injury to the infrapatellar branch of the saphenous nerve in ACL reconstruction with the hamstrings technique: Clinical and electrophysiological study. Knee. 2008;15(5):360-363.
  9. Friedberg RP. Anterior cruciate ligament injury. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed May 2021.
  10. Goshima K. Overview of thoracic outlet syndromes. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed May 2022.
  11. Isaacson G, Martin WH. First branchial cleft cyst excision with electrophysiological facial nerve localization. Arch Otolaryngol Head Neck Surg. 2000;126(4):513-516.
  12. Klein EA. Radical prostatectomy for localized prostate cancer. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed May 2017.
  13. Margenthaler J. Technique of axillary lymph node dissection. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed May 2021.
  14. Martin GM, Harris I. Total knee arthroplasty. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed May 2020.
  15. Martin SD, Martin TL. Management of rotator cuff tears. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed May 2017.
  16. Niemi-Murola L, Paloheimo M. Feasibility of electromyography (sEMG) in measuring muscular activity during spinal anaesthesia in patients undergoing knee arthroplasty. Acta Anaesthesiol Scand. 2005;49(4):558-562.
  17. Novais EN, Heare T, Kestel L, et al. Multimodal nerve monitoring during periacetabular osteotomy identifies surgical steps associated with risk of injury. Int Orthop. 2017;41(8):1543-1551.
  18. Pring ME, Trousdale RT, Cabanela ME, Harper CM. Intraoperative electromyographic monitoring during periacetabular osteotomy. Clin Orthop Relat Res. 2002;(400):158-164.
  19. Ruschel LG, Aragão A, de Oliveira MF, et al. Correlation of intraoperative neurophysiological parameters and outcomes in patients with intramedullary tumors. Asian J Neurosurg. 2021;16(2):243-248.
  20. Rutkove SB. Overview of lower extremity peripheral nerve syndromes. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed May 2021.
  21. Scibilia A, Terranova C, Rizzo V, et al. Intraoperative neurophysiological mapping and monitoring in spinal tumor surgery: Sirens or indispensable tools? Neurosurg Focus. 2016;41(2):E18.
  22. Shi YB, Binette M, Martin WH, et al. Electrical stimulation for intraoperative evaluation of thoracic pedicle screw placement. Spine (Phila Pa 1976). 2003;28(6):595-601.
  23. Shkarubo AN, Chernov IV, Ogurtsova AA, et al. Cranial nerve monitoring in endoscopic endonasal surgery of skull base tumors (observing of 23 cases). Chin Neurosurg J. 2018;4:38.
  24. Shkarubo AN, Chernov IV, Ogurtsova AA, et al. Neurophysiological identification of cranial nerves during endoscopic endonasal surgery of skull base tumors: Pilot study technical report. World Neurosurg. 2017;98:230-238.
  25. Sierra RJ, Beaule P, Zaltz I, et al. Prevention of nerve injury after periacetabular osteotomy. Clin Orthop Relat Res. 2012;470(8):2209-2219.
  26. Suwanwela NC. Moyamoya disease: Treatment and prognosis. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed May 2019.
  27. Synderman C. Chordoma and chondrosarcoma of the skull base. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed May 2022.
  28. Vivas EX, Carlson ML, Neff BA, et al. Congress of Neurological Surgeons systematic review and evidence-based guidelines on intraoperative cranial nerve monitoring in vestibular schwannoma surgery. Neurosurgery. 2018;82(2):E44-E46.
  29. Wałega P, Romaniszyn M, Wałega M, et al. Intraoperative neuromonitoring of hypogastric plexus branches during surgery for rectal cancer - preliminary report. Pol Przegl Chir. 2017;89(2):69-72.
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EMG Monitoring During Tibial Neurotomy

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Evoked Potential Studies

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  56. Penson DF. Follow-up surveillance after definitive local treatment for prostate cancer. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed January 2022.
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