1. Aetna considers FDA-approved prosthetic intervertebral discs (e.g., the Charite Artificial Disc, and the ProDisc-L Total Disc Replacement) medically necessary for spinal arthroplasty in skeletally mature persons with symptomatic (e.g., back and/or leg pain) lumbosacral degenerative disc disease confirmed by radiographic studies (e.g., CT, MRI, x-rays) at one level from L3 to S1, and who have failed at least 6 months of conservative management.

2. Aetna considers FDA-approved prosthetic intervertebral discs (e.g., the Prestige Cervical Disc, ProDisc-C Total Disc Replacement, Bryan Cervical Disc) medically necessary for the treatment of skeletally mature persons with symptomatic (e.g., radicular neck and/or arm pain and or functional/neurological deficit) cervical degenerative disc disease or herniated disc at one level from C3 to C7, confirmed by radiographic studies (e.g., CT, MRI, x-rays), and who have failed at least 6 weeks of conservative management.

3. Aetna considers prosthetic intervertebral discs experimental and investigational for persons who have degenerative disk disease at more than one level, and for all other indications.

4. Aetna considers lumbar partial disc prosthetics (e.g., Nubac, DASCOR Disc Arthroplasty System) experimental and investigational because of insufficient evidence of their effectiveness.

5. Aetna considers the use of hybrid fusion with artificial disc replacement experimental and investigational for the management of back pain, spinal disorders, and all other indications.

See also CPB 016 - Back Pain - Invasive Procedures, and CPB 743 - Spinal Surgery: Laminectomy and Fusion.  

Since the 1970s, investigators have been working on developing an artificial prosthetic intervertebral disc (IVD) that can be used to replace degenerated intervertebral discs (Diwan, et al., 1997).  Most of the published clinical evidence for artificial prosthetic intervertebral discs has been of those that replace the entire disc.

The major potential advantage of a prosthetic intervertebral disc over current therapies for degenerated disks (such as spinal fusion or diskectomy) is that the prosthetic intervertebral disk is intended to restore or preserve the natural biomechanics of the intervertebral segment and to reduce further degeneration of adjacent levels.

van Ooij, et al. (2003) reported a series of 27 patients who presented with unsatisfactory results or complications after Charite disc replacement.  Most patients were operated on at the L4 - L5 and/or the L5 - S1 vertebral levels.  The patients were evaluated with plain radiography, some with flexion-extension x-rays, and most of them with computed tomography scans.  The group consisted of 15 women and 12 men.  Their mean age was 40 years (range, 30 - 67 years) at the time of operation.  The patients presented to the investigators a mean of 53 months (range 11 - 127 months) following disc replacement surgery.  In two patients, an early removal of a prosthesis was required and in two patients a late removal.  In 11 patients, a second spinal reconstructive salvage procedure was performed.  Mean follow-up for 26 patients with mid- and long-term evaluation was 91 months (range 15 - 157 months).  Early complications were the following: In one patient, an anterior luxation of the prosthesis after 1 week necessitated removal and cage insertion, which failed to unite.  In another patient with prostheses at L4 - L5 and L5 - S1, the prosthesis at L5 - S1 dislocated anteriorly after 3 months and was removed after 12 months.  Abdominal wall hematoma occurred in four cases.  Retrograde ejaculation with loss of libido was seen in one case and erection weakness in another case.  A temporary benefit was experienced by 12 patients, while 14 patients reported no benefit at all.  Main causes of persistent complaints were degeneration at another level in 14, subsidence of the prosthesis in 16, and facet joint arthrosis in 11.  A combination of pathologies was often present.  Slow anterior migration was present in two cases, with compression on the iliac vessels in one case.  Polyethylene wear was obvious in one patient 12 years after operation.  In eight cases, posterior fusion with pedicle screws was required.  In two cases, the prosthesis was removed and the segment was circumferentially fused.  These procedures resulted in suboptimal long-term results.  In this relatively small group of patients operated on with a Charite disc prosthesis, most problems arose from degeneration of other lumbar discs, facet joint arthrosis at the same or other levels, and subsidence of the prosthesis.

Caspi, et al. (2003) reported results of lumbar disk prosthesis (Charite) after a follow-up period of 48 months.  These investigators found that 80% of patients reported satisfactory to very good results.  Poor results were reported by four patients, one of whom underwent postero-lateral fusion and another is waiting for the same operation.  There were two dislocations of the prosthesis followed by immediate revision surgery. The authors concluded that contraindications for surgery appear to be the principal cause of failure rather than the prosthesis itself.

In a multi-center, prospective, randomized investigational device exemption study of the Charite intervertebral disc, Geisler, et al. (2004) compared the Charite artificial disc with lumbar fusion using the BAK cages in patients with lumbar degenerative disc disease (n = 304).  The authors found that the neurological status was equivalent between the two groups at 6, 12, and 24 months, post-operatively.  They concluded that the Charite intervertebral disc is safe and effective for the treatment of single-level degenerative disc disease, resulting in no higher incidence of neurological complications compared with BAK-assisted fusion, and leading to equivalent or better outcomes (as indicated by visual analog scale and Oswestry Disability Index scores) compared with fusion with those obtained in the control group and those reported in the lumbar fusion literature.  The authors concluded that the findings of this study is promising, but that longer follow-up is needed to determine the durability of the Charite artificial disc and its long-term safety and effectiveness.

The United States Food and Drug Administration (FDA) has approved the Charite Artificial Disc for spinal arthroplasty in skeletally mature patients with degenerative disc disease (DDD) at one level from L4-S1. The indications for the Charite define DDD as discogenic back pain with degeneration of the disc that is confirmed by patient history and radiographic studies. According to the FDA-approved labeling, these DDD patients should have no more than 3 mm of spondylolisthesis at the involved level. The FDA approved labeling states that patients receiving the Charite Artificial Disc should have failed at least six months of conservative treatment prior to implantation of the Charite Artificial Disc.

The Charite Artificial Disc was approved by the FDA based on a clinical trial comparing the device to anterior lumbar interbody fusion (ALIF) with BAK cages filled with iliac crest autograft in subjects with symptomatic single level degenerative disc disease from L4 to S1 who had failed at least 6 months of conservative management.  The purpose of the study was to demonstrate the non-inferiority of the Charite Artificial Disc to an interbody fusion system.  A total of 304 patients were enrolled in the study using a 2:1 (Charite to BAK) randomization scheme.  One-hundred eighty four subjects receiving the Charite Artificial Disc and 81 subjects receiving interbody fusion (controls) completed 24 months follow up.  Safety of the Charite Artificial Disc was assessed by monitoring the intraoperative and postoperative complications, including infection, thrombosis, disc migration, and disc subsidence, as well as reoperation and other adverse events.  Efficacy of the Charite Artificial Disc was assessed primarily by a success criteria comprised of: level of disability (Oswestry Low Back Disability Index (ODI)), neurological assessment (functional status) and information from adverse event data.  To be considered an overall success, a subject must have had: 1) an improvement of at least 25% in the ODI score at 24 months compared to baseline; 2) no device failures requiring revision, reoperation, or removal; 3) absence of major complications, defined as major blood vessel injury, neurological damage, or nerve root injury; and 4) maintenance or improvement in neurological status at 24 months, with no new permanent neurological deficits compared to baseline.  Based on these criteria, the overall success rate was 64% for subjects receiving the Charite Artificial Disc and 57% for control subjects receiving interbody fusion.  The FDA requested that the data be analyzed and reported using an improvement in the Oswestry Disability Index of greater than 15 points at 24 months compared to the score at baseline.  Based on these alternate criteria, the overall success rate for subjects receiving the Charite Artificial Disc was 58%, and the success rate for control subjects was 54%. 

The study sponsor considered the study a success if the overall success rates of the two treatment groups were non-inferior, i.e., the difference in overall success rates (i.e., non-inferiority margin) is no greater than 15%.  However, the FDA requested that the data also be analyzed and reported using a non-inferiority margin of 10%. 

The study demonstrated non-inferiority of the Charite Artificial Disc (within the 90% one-sided confidence interval) to interbody fusion for secondary endpoints, including pain (using a visual analog scale (VAS)), quality of life (Shoft Form-36 Questionnaire), disc height, and device migration.

At 24 months follow-up, subjects receiving the Charite Artificial Disc had 7.5 degrees vertebral range of motion (ROM) at the operative level, compared to 1.1 degrees vertebral ROM for subjects receiving interbody fusion.   The FDA analyzed ROM data versus Overall Success Outcome for all Charite artificial disc subjects with available ROM data at 24 months.  No statistically significant association was found between ROM and success/failure at 24 months.

Because the long-term safety and effectiveness of the Charite Artificial Disc are unknown, the FDA has required the manufacturer to conduct a post-approval study using a maximum of 366 subjects (201 randomized investigational subjects; 67 training investigational subjects; and 98 control subjects).  The manufacturer will be required evaluate subjects on Overall Success and secondary endpoints, and submit annual reports for a total of 5 years post-implantation.    

According to the FDA-approved labeling, the Charite Artificial Disc should not be implanted in patients with the following conditions: osteoporosis; osteopenia; pars defect; bony lumbar stenosis; active systemic infection or infection localized to the site of implantation; allergy or sensitivity to implant materials; and isolated radicular compression syndromes, especially due to disc herniation.

The FDA-approved labeling of the Charite Artificial Disc states that the safety and effectiveness of the device have not been established in patients with the following conditions: pregnancy; morbid obesity; two or more degenerative discs; spondylolisthesis greater than 3 mm; or two or more unstable segments.

Data on the long-term outcomes of the Charite Artificial Disc comes from France, where the artificial disc has been in use for more than a decade.  David (2000) reported in abstract form on a retrospective review of the outcome of 92 patients with chronic low back pain who were implanted with the artificial disc.  The investigators reported “excellent or good” results in 75% of patients after a minimum of 5 years follow up, with no disc space height loss and no loosening or expulsion of the core.  Lemaire, et al., described their 5-year and 10-year results with the Charite Artificial Disc.  In the paper reporting on 10-year results, Lemaire, et al. (2002) reported an excellent or good outcome in 90% of 100 patients with a return to work rate of 91.6%.  In addition, the investigators reported no subluxations or core expulsions, a reoperation rate of 5% and a 2% rate of adjacent-level disc disease.  The mean flexion/extension range of motion was 10.3 degrees, with a mean lateral bending motion of 5.4 degrees.

The National Institute for Clinical Excellence (2004) has concluded: “Current evidence on the safety and efficacy of prosthetic intervertebral disc replacement appears adequate to support the use of this procedure.  However, there is little evidence on outcomes beyond 2-3 years and collection of long-term data is therefore particularly important”.

An assessment by the Ohio Bureau of Workers' Compensation (2005) concluded that the Charite artificial disc can be considered as an alternative to tradition lumbar fusion procedures.

The Ontario Health Technology Advisory Committee of the Ontario Ministry of Health and Long-Term Care (2006) recommended the adoption of lumbar artificial disc replacement according to well defined patient eligibility criteria. The Ontario Health Technology Advisory Committee recommended development of a patient registry to track long-term complications of lumbar artificial disc replacement. Because of the uncertainty in the estimates of benefits, risks and burdens associated with cervical artificial disc replacement, the Ontario Health Technology Advisory Committee did not recommend the use of cervical artificial disc replacement to treat degenerative disc disease of the cervical spine over the use of other alternatives such as spinal fusion.

Tropiano, et al. (2005) presented the clinical and radiographic results assessed 7 to 11 years following a Prodisc total lumbar disc replacement (n = 64 patients who had single or multiple-level implantation of a total lumbar disc replacement).  The mean duration of follow-up was 8.7 years.  Clinical results were evaluated by assessing pre-operative and post-operative lumbar pain, radiculopathy, disability, and modified Stauffer-Coventry scores.  Pre-operative and post-operative radiographs were evaluated as well.  These investigators concluded that the Prodisc lumbar total disc replacement appears to be effective and safe for the treatment of symptomatic degenerative disc disease.  Gender and multi-level surgery did not affect the outcomes, whereas prior lumbar surgery or an age of less than 45 years was associated with slightly worse outcomes.  The authors further stated that longer follow-up of this cohort of patients and randomized trials comparing disc replacement with arthrodesis are needed.

Leivseth, et al. (2006) presented their findings of a longitudinal prospective study on the use of the ProDisc II prosthesis in 41 consecutive disc prosthesis patients, covering a post-operative time period of at least 2 years. They stated that disc replacement in the lumbar spine by a ProDisc II implant failed to restore normal segmental rotational motion in the sagittal plane, specifically at levels L4 - L5 and L5 - S1. As segmental motion of the untreated segments was lower than normal as well, though not quite as conspicuous as that of instrumented segments, adaptation of soft tissue taken place during the pre-operative symptomatic time period is conjectured to cause the observed motion deficit.

On the other hand, findings from other studies indicated that the ProDisc is safe and effective in treating patients with low back pain (LBP).

In a prospective, longitudinal minimum 2-year follow-up study (n = 118), Bertagnoli, et al. (2005) evaluated the safety and effectiveness of the ProDisc implant in patients with disabling single-level discogenic LBP. Patients 18 to 60 years of age with disabling and recalcitrant discogenic LBP with or without radicular pain secondary to single-level discogenic LBP from L3 to S1 were included. Patients were assessed before surgery, and outcome measurements were assessed after surgery at 3, 6, 12, and 24 months. A total of 104 patients (88%) fulfilled all follow-up criteria. The median age of all patients was 47 years (range of 36 to 60 years). Statistical improvements in VAS, Oswestry, and patient satisfaction scores occurred 3 months post-operatively. These improvements were maintained at the 24-month follow-up. Radicular pain also decreased significantly. Full-time and part-time work rates increased from 10 to 35% and 3 to 24%, respectively. No additional fusion surgeries were needed either at the affected or unaffected levels. Radiographical analysis revealed an affected disc height increase from 4 to 13 mm (p < 0.001) and an affected disc motion from 3 to 7 degrees (p < 0.004). The authors concluded that single-level ProDisc lumbar total disc arthroplasty is a safe and effective treatment for debilitating lumbar discogenic LBP. Significant improvements in patient satisfaction as well as disability scores occurred after surgery by 3 months and were maintained at the 2-year follow-up. No device-related complications occurred. Patients with severe to moderate disc height loss as well as those with symptomatic posterior annular defects with minimal disc height loss achieve functional gains and significant pain relief. Careful and appropriate patient selection is essential in ensuring optimal surgical outcomes.

Siepe, et al. (2006) presented their 3-year results with total lumbar disc replacement (TLDR) by means of the ProDisc II with a minimum follow-up of 24 months. They concluded that available data suggest beneficial clinical results of TLDR for the treatment of DDD in a highly selected group of patients. Better functional outcome was obtained in younger patients under 40 years of age and patients with DDD in association with disc herniation. Multi-level disc replacement had significantly higher complication rate and inferior outcome at mid-term follow-up compared with mono-segmental interventions. Thus, only longer follow-up evaluations will demonstrate the real benefit for patients. Results are significantly dependent on pre-operative diagnosis and patient selection, number of replaced segments, and age of patient at the time of operation. The authors stated that because of significantly varying outcomes, indications for disc replacement must be defined precisely.

Schroven and Dorofey (2006) conducted a prospective, non-randomised study on the ProDisc IVD (n = 14) versus anterior lumbar interbody fusion (ALIF, n = 10). In the ProDisc group, the Oswestry Disability Index improved from +/- 38.42 pre-operatively (60 being the worst possible condition) to +/- 15.21 after 6 months, and to +/- 12.5 after 12 months. This was markedly better than the ALIF group, where the corresponding figures were +/- 38, +/- 25 and +/- 21.4. The ProDisc patients also scored better with respect to duration of hospitalization, blood loss and operation time. The complications were comparable in both groups.

Tropiano and colleagues (2006) presented the clinical and radiographical results assessed 7 to 11 years following a ProDisc TLDR. A total of 64 patients had single- or multiple-level implantation of a TLDR between 1990 and 1993. The mean duration of follow-up was 8.7 years. Clinical results were evaluated by assessing pre-operative and post-operative lumbar pain, radiculopathy, disability, and modified Stauffer-Coventry scores. Pre-operative and post-operative radiographs were evaluated as well. Subgroup analysis was performed to determine if gender, an age of less than 45 years, previous surgery, or multi-level surgery had an effect on outcome. At an average of 8.7 years post-operatively, there were significant improvements in the back pain, radiculopathy, disability, and modified Stauffer-Coventry scores. Thirty-three of the 55 patients with sufficient follow-up had an excellent result, 8 had a good result, and 14 had a poor result. Neither gender nor multi-level surgery affected outcome. An age of less than 45 years and prior lumbar surgery had small but significant negative effects on outcome. Radiographs did not demonstrate loosening, migration, or mechanical failure in any patient. Five patients had approach-related complications. These investigators concluded that the ProDisc TLDR appears to be effective and safe for the treatment of symptomatic DDD. Gender and multi-level surgery did not affect the outcomes, whereas prior lumbar surgery or an age of less than 45 years was associated with slightly worse outcomes. The authors noted that longer follow-up of this cohort of patients and randomized studies comparing disc replacement with arthrodesis are needed.

Bertagnoli and colleagues (2006a) conducted a prospective, longitudinal study (n = 20) to evaluate the effectiveness of ProDisc arthroplasty in patients in whom symptomatic adjacent-segment degeneration has developed after remote lumbar fusion. The follow-up period was a minimum of 2 years. Subjects in this study ranged in age from 18 to 67 years. They presented with disabling adjacent-level discogenic LBP with or without L1 - S1 radicular pain. Individuals with radiographic evidence of circumferential spinal stenosis or facet joint degeneration were excluded. Patients were assessed pre-operatively and post-operatively at 3, 6, 12, and 24 months. Eighteen patients (90%) fulfilled all follow-up criteria. The median age of all patients was 50 years. Statistical improvements in VAS, Oswestry Disability Index, and patient satisfaction scores were documented 3 months after arthroplasty. These improvements remained at the 24-month follow-up examinations. Patient satisfaction rates were 86% at 24 months. Radicular pain was also significantly decreased. No additional surgeries were needed at affected or unaffected levels. The authors concluded that analysis of early results indicates that ProDisc lumbar total disc arthroplasty is an effective treatment for symptomatic adjacent-segment lumbar discogenic LBP following remote fusion. Significant improvements in patient satisfaction and disability scores were observed by 3 months post-operatively and were maintained at the 2-year follow-up examination. No device-related complications occurred. Patients should be screened carefully for evidence of facet joint impingement/degeneration, hardware-induced pain, and/or non-union at prior fusion levels before undergoing disc replacement surgery.

The same group of investigators (Bertagnoli, et al., 2006b) also carried out a prospective, longitudinal study to obtain outcome (minimum follow-up period 2 years) regarding the safety and effectiveness of single-level lumbar disc replacement in patients 60 years of age or older. This analysis involved 22 patients in whom the ProDisc was used for total disc arthroplasty. All patients presented with disabling discogenic LBP with or without radicular pain. The involved segments ranged from L2 to S1. Patients in whom there was no evidence of radiographic circumferential spinal stenosis and with minimal or no facet joint degeneration were included. Patients were assessed pre-operatively and outcome was evaluated post-operatively at 3, 6, 12, and 24 months by administration of standardized tests (VAS, ODI, and patient satisfaction). Secondary parameters included analysis of pre- and post-operative radiographic results of disc height at the affected level, adjacent-level disc height and motion, and complications. Twenty-two subjects (100%) fulfilled all follow-up criteria. The median age of all patients was 63 years (range of 61 to 71 years). There were 17 single-level cases, 4 two-level cases, and 1 three-level case. Statistical improvements in VAS, ODI, and patient satisfaction scores were observed at 3 months post-operatively. These improvements were maintained at 24-month follow-up examination. Patient satisfaction rates were 94% at 24 months (compared with 95% reported in a previously reported ProDisc study). Radicular pain also decreased significantly. Patients in whom bone mineral density was decreased underwent same-session vertebroplasty following implantation of the ProDisc device(s). There were 2 cases involving neurological deterioration: unilateral foot drop and loss of proprioception and vibration in 1 patient and unilateral foot drop in another patient. Both deficits occurred in patients in whom there was evidence pre-operatively of circumferential spinal stenosis. There were 2 cases of implant subsidence and no thrombo-embolic phenomena. These researchers concluded that significant improvements in patient satisfaction and ODI scores were observed by 3 months post-operatively and these improvements were maintained at the 2-year follow-up examination. Although the authors' early results indicate that the use of ProDisc lumbar total disc arthroplasty in patients older than 60 years of age reduces chronic LBP and improves clinical functional outcomes, they recommend the judicious use of artificial disc replacement in this age group. Until further findings are reported, the authors cautiously recommend the use of artificial disc replacement in the treatment of chronic discogenic LBP in patients older than age 60 years in whom bone quality is adequate in the absence of circumferential spinal stenosis.

Bertagnoli and associates (2006c) reported that lumbar total disc arthroplasty utilizing the ProDisc prosthesis is equally effective in smokers and non-smokers. These investigators performed a prospective analysis on 104 patients with disabling discogenic LBP treated with single-level lumbar ProDisc total disc arthroplasty. Smokers and non-smokers were evaluated before surgery and after surgery using patient satisfaction, Oswestry, and VAS. Additionally, pre-operative and post-operative neurological, radiographical, and pain medication assessments were performed at similar post-operative intervals. Oswestry, VAS, and patient satisfaction scores revealed statistical improvement beginning 3 months after surgery and were maintained at minimum 2-year follow-up. Patient satisfaction scores were higher in smokers (94%) than in non-smokers (87%) at 2-year follow-up (p = 0.07). Radiographical analysis revealed an affected disc height increase from 4 to 13 mm (p < 0.05) and an affected disc motion from 3 to 7 degrees (p < 0.05). No cases of loosening, dislodgment, mechanical failure, infection, or fusion of the affected segment occurred. The authors concluded that the findings of this study indicate that smokers do equally well as non-smokers when ProDisc artificial disc replacement is used in the treatment of debilitating lumbar spondylosis. Patient outcome and radiographical scores showed significant improvement compared with pre-operative levels.

On August 14, 2006, the FDA approved the ProDisc-L Total Disc Replacement (Synthes Spine, Inc., West Chester, PA) for spinal arthroplasty in patients who meet all of the following criteria:

• Patients are skeletally mature; and
• Patients have DDD at one level in the lumbar spine (from L3 to S1); and
• Patients have no more than Grade 1 spondylolisthesis at the involved level; and
• Patients have had no relief from pain after at least 6 months of non-surgical treatment.

Hannibal, et al. (2007) examined if there is a clinical difference between the 1-level ProDisc patients versus the 2-level ProDisc patients at a minimum of 2-year follow-up. Patients were part of the FDA clinical trial for the Prodisc II versus circumferential fusion study at a single institution. These investigators identified 27 patients who received ProDisc at 1 level and 32 who received it at 2 levels with at least a 2-year follow-up, for a total of 59 patients. Unpaired t tests were performed on the mean results of VAS, ODI, SF-36 Healthy Survey Physical Component Summary, and satisfaction using 10-cm line VAS  to determine a clinical difference, if any, between the 2 populations. While patients receiving ProDisc at 2 levels scored marginally lower in all evaluation indexes, score differences in each category were also found to hold no statistical significance. The authors concluded that this study was unable to identify a statistically significant difference in outcome between 1- and 2-level ProDisc arthroplasty patients in a cohort from a single center. They stated that the equality of clinical effectiveness between 1- and 2-level ProDisc has yet to be determined.

In August 2007, the Centers for Medicare & Medicaid Services (CMS) concluded that lumbar artificial disc replacement (LADR) is not reasonable and necessary for the Medicare population over 60 years of age. CMS announced that Section 150.1 of the Medicare National Coverage Determination (NCD) Manual will be amended to reflect the proposed change from non-coverage for a specific LADR implant to non-coverage for the LADR procedure for the Medicare population over 60 years of age. For Medicare beneficiaries 60 years of age and under, there is no national coverage determination, leaving such determinations to be made on a local basis.

An interventional procedure consultation document prepared for the National Institute for Health and Clinical Excellence (NICE, 2008) included the following provisional recommendations: "[c]urrent evidence on the safety and efficacy of prosthetic intervertebral disc replacement in the lumbar spine is adequate to support the use of this procedure provided that normal arrangements are in place for clinical governance, consent and audit. A multi-disciplinary team with specialist expertise in the treatment of degenerative spine disease should be involved in patient selection for prosthetic intervertebral disc replacement in the lumbar spine.  The procedure should only be carried out in patients for whom conservative treatment options have failed or are contraindicated.  The current evidence is based on studies with maximum follow-up of 13 years.  NICE encourages clinicians to continue to collect and publish data on longer-term outcomes, which should include information about patient selection and the need for further surgery."

Acosta and Ames (2005) noted that cervical disc arthroplasty is a relatively new motion-preserving technique for the treatment of symptomatic DDD of the cervical spine. Unlike anterior discectomy and fusion, cervical disc replacement restores normal motion and a physiologic biomechanical environment to adjacent disc levels, thereby reducing the incidence of adjacent segment disease. To date, cervical disc arthroplasty has been at least as effective as cervical fusion in providing symptomatic relief while lowering peri-operative morbidity, eliminating the need for post-operative external immobilization, and allowing for earlier return to normal function. No significant complications have been associated with this procedure so far. The authors stated that further investigation in the form of large, randomized, prospective studies is needed to ascertain the long-term effectiveness of this procedure as well as to determine the patient populations that may benefit most from cervical disc arthroplasty. This is in agreement with the observations of Pracyk and Traynelis (2005) and Bertagnoli, et al. (2005). Pracyk and Traynelis stated that cervical arthroplasty (by means of devices such as Prestige, Bryan, and ProDisc) is a promising new technology that may improve patient outcome following anterior cervical decompression. Bertagnoli et al noted that long-term follow-up studies are needed before more definitive treatment recommendations can be made regarding cervical disc replacement by means of the ProDisc. Furthermore, in a review on the state of the emerging field of cervical disc replacement, Phillips and Garfin (2005) stated that cervical disc replacement is an innovative technology that preserves motion at the instrumented level/s, and will potentially improve load transfer to the adjacent levels compared with fusion. Clinical reports of success of cervical total disc replacement are encouraging but are also quite preliminary. As the United States investigational device exemption studies are completed, a clearer role for the place of cervical disc replacement in the spine surgeon's armamentarium should emerge.

Traynelis and Treharne (2007) noted that the Prestige artificial cervical disc is a new motion-sparing device designed for use in the cervical spine to treat symptomatic degenerative disc disease in patients who have failed conservative care. It allows for the maintenance of normal cervical spinal motion. Furthermore, this new device does not require bone graft or as long a recovery time as needed for fusion of the joint.

In a prospective, randomized, controlled and double-blinded study, Sekhon and colleagues (2007) compared post-operative imaging characteristics of the four currently available cervical arthroplasty devices (Bryan, Prodisc-C , Prestige LP, and PCM ) at the level of implantation and at adjacent levels. Pre-operative and post-operative magnetic resonance imaging scans of 20 patients who had undergone cervical arthroplasty were evaluated for imaging quality. Five cases each of the four devices were analyzed. Six blinded spinal surgeons scored twice sagittal and axial T2-weighted images using the Jarvik 4-point scale. Statistical analysis was performed comparing quality before surgery and after disc implantation at the operated and adjacent levels and between implant types. Moderate intra-observer and inter-observer reliability was noted. Pre-operative images of patients in all implant groups had high-quality images at operative and adjacent levels. The Bryan and Prestige LP devices allowed satisfactory visualization of the canal, exit foramina, cord, and adjacent levels after arthroplasty. Visualization was significantly impaired in all PCM and Prodisc-C cases at the operated level in both the spinal canal and neural foramina. At the adjacent levels, image quality was statistically poorer in the PCM and Prodisc-C than those of Prestige LP or Bryan. The authors concluded that post-operative visualization of neural structures and adjacent levels after cervical arthroplasty is variable among current available devices. Devices containing non-titanium metals (cobalt-chrome-molybdenum alloys in the PCM and Prodisc-C) prevent accurate post-operative assessment with magnetic resonance imaging at the surgical and adjacent levels. On the other hand, titanium devices, with or without polyethylene (Bryan disc or Prestige LP), allow for satisfactory monitoring of the adjacent and operated levels. This information is crucial for any surgeon who wishes to assess adequacy of neural decompression and where monitoring of adjacent levels is desired.

Mummaneni and associates (2007) reported the results of a prospective randomized multi-center study in which the results of cervical disc arthroplasty with the Prestige ST Cervical Disc System (Medtronic Sofamor Danek) were compared with anterior cervical discectomy and fusion (ACDF).  Patients with symptomatic (neck pain) single-level cervical DDD who failed at least 6 weeks of conservative treatment or had signs of progression or spinal cord/nerve root compression with continued non-operative care were included in the study.  Degenerative disc disease was determined to be present if a herniated disc and/or osteophyte formation were confirmed by history and radiographic studies (e.g., CT, MRI, x-rays).  A total of 541 patients were enrolled at 32 sites and randomly assigned to 1 of 2 treatment groups: (i) 276 patients in the investigational group underwent anterior cervical discectomy and decompression and arthroplasty with the Prestige ST Cervical Disc System; and (ii) 265 patients in the control group underwent decompressive ACDF. A total of 80% of the arthroplasty-treated patients (223 of 276) and 75% of the control patients (198 of 265) completed clinical and radiographical follow-up examinations at routine intervals for 2 years after surgery. Analysis of all currently available post-operative 12- and 24-month data indicated a 2-point greater improvement in the neck disability index score in the investigational group than the control group. The arthroplasty group also had a statistically significant higher rate of neurological success (p = 0.005) as well as a lower rate of secondary revision surgeries (p = 0.0277) and supplemental fixation (p = 0.0031). The mean improvement in the 36-Item Short Form Health Survey Physical Component Summary scores was greater in the investigational group at 12 and 24 months, as was relief of neck pain. The patients in the investigational group returned to work 16 days sooner than those in the control group, and the rate of adjacent-segment re-operation was significantly lower in the investigational group as well (p = 0.0492, log-rank test). The cervical disc implant maintained segmental sagittal angular motion averaging more than 7 degrees. In the investigational group, there were no cases of implant failure or migration. The authors concluded that the Prestige Cervical Disc maintained physiological segmental motion at 24 months after implantation and was associated with improved neurological success, improved clinical outcomes, and a reduced rate of secondary surgeries compared with ACDF.

On July 17, 2007, the FDA approved the Prestige Cervical Disc (Medtronic Sofamor Danek, Memphis, TN) for the treatment of single level cervical degenerative disc disease (C3 to C7). The FDA approval was based on the findings of the study by Mummaneni, et al. (2007). In the approval letter, the FDA stated that Medtronic Sofamor Danek is required to perform a 7-year post-approval study to evaluate the long-term safety and effectiveness of the Prestige Cervical Disc.

Sasso, et al. (2007) evaluated the functional outcome and radiographical results of the Bryan artificial cervical disc replacement for patients with 1-level cervical disc disease. Twelve-month follow-up was available for 110 patients and 24-month follow-up was completed for 99 patients. There were 30 males and 26 females in the Bryan group and 32 males and 27 females in the fusion group. The average age was 43 years (Bryan) and 46 years (fusion). Disability and pain were assessed using the Neck Disability Index (NDI) and the VAS of the neck and of the arm pain. SF-36 outcome measures were obtained including the physical component as well as the mental component scores. Range of motion was determined by independent radiological assessment of flexion-extension radiographs. The average operative time for the control group was 1.1 hours and the Bryan Group 1.7 hours. Average blood loss was 49 ml (control) and 64 ml (Bryan). Average hospital stay was 0.6 days (control) and 0.9 days (Bryan). The mean NDI before surgery was not statistically different between groups: 47 (Bryan) and 49 (control). Twelve-month follow-up NDI is 10 (Bryan) and 18 (control) (p = 0.013). At 2-year follow-up, NDI for the Bryan group is 11 and the control group is 20 (p = 0.005). The mean arm pain VAS before surgery was 70 (Bryan) and 71 (control). At 1-year follow-up, Bryan arm pain VAS was 12 and control 23 (p = 0.031). At 2-year follow-up, the average arm pain VAS for the Bryan group was 14 and control 28 (p = 0.014). The mean neck pain VAS before surgery was 72 (Bryan) and 73 (control); 1-year follow-up scores were 17 (Bryan) and 28 (control) (p = 0.05); 2-year follow-up: 16 (Bryan) and 32 (control) (p = 0.005). SF-36 scores: Physical component -- before surgery Bryan 34 and control 32; at 24 months: Bryan 51 and control 46 (p = 0.009). More motion was retained after surgery in the disc replacement group than the plated group at the index level (p < 0.006 at 3, 6, 12, and 24 months). The disc replacement group retained an average of 7.9 degrees of flexion-extension at 24 months. In contrast, the average range of motion in the fusion group was 0.6 degrees at 24 months. There were 6 additional operations in this series: 4 in the control group and 2 in the investigational group. There were no intra-operative complications, no vascular or neurological complications, no spontaneous fusions, and no device failures or explantations in the Bryan cohort. The authors concluded that the Bryan artificial disc replacement compared favorably to anterior cervical discectomy and fusion for the treatment of patients with 1-level cervical disc disease. At the 2-year follow-up, there are statistically significant differences between the groups with improvements in the NDI, the neck pain and arm pain VAS scores, and the SF-36 physical component score in the Bryan disc population.

In December 2007, the FDA approved the ProDisc-C Total Disc Replacement (Synthes Spine, Inc., West Chester, PA) for use in skeletally mature patients for reconstruction of the disc from C3-C7 following removal of the disc at one level for intractable symptomatic cervical disc disease (SCDD).  The FDA's approval of the ProDisc-C was based upon the results of a clinical trial (non-inferiority) involving 209 patients at 13 clinical sites comparing ProDisc-C to ACDF. Patients with SCDD who failed at least 6 weeks of non-operative treatment or had progressive symptoms or signs of nerve root/spinal cord compression in the face of conservative treatment qualified for the trial.  Intractable SCDD was defined as neck or arm (radicular) pain, and/or a functional/neurological deficit with at least one of the following conditions confirmed by imaging (CT, MRI, or x-rays): (i) herniated nucleus pulposus, (ii) spondylosis (defined by the presence of osteophytes), or (iii) loss of disc height.  Patients were evaluated for pain and disability, neurologic status and range of motion at the index level. Patients were followed for 2 years post surgery. The study data indicated that the ProDisc-C is non-inferior to ACDF.  According to the FDA-approved labeling, the ProDisc-C should not be implanted in patients with an active infection, allergy to any of the device materials, osteoporosis, marked cervical instability, severe spondylosis, clinically compromised vertebral bodies at the level to be treated, and SCDD at more than one level.  The device is implanted via an open anterior approach.

In December 2009, the FDA approved the Bryan Cervical Disc (Medtronic Sofamor Danek, Memphis, TN) for use in skeletally mature patients for reconstruction of the disc from C3-C7 following single-level discectomy for intractable radiculopathy and/or myelopathy.  The FDA's approval of the Bryan Cervical Disc was based upon the results of a clinical trial (non-inferiority) involving 463 patients at 30 clinical sites comparing the Bryan device to ACDF.  Patients with intractable radiculopathy and/or myelopathy resulting in impaired function with at least one clinical neurological sign associated with the cervical level to be treated and who failed at least 6-weeks of conservative treatment qualified for the trial.  Intractable radiculopathy and/or myelopathy was defined as any combination of the following conditions confirmed by imaging (computed tomography, myelography and computed tomography, and/or magnetic resonance imaging): (i) disc herniation with radiculopathy, (ii) spondylotic radiculopathy, (iii) disc herniation with myelopathy, or (iv) spondylotic myelopathy.  Patients were evaluated for pain and disability, and neurological status.  Patients were followed for 2 years post surgery.  The study data indicated that the Bryan Cervical Disc is non-inferior to ACDF.  According to the FDA-approved labeling, the Bryan Cervical Disc should not be implanted in patients with an active infection, allergy to any of the device materials, osteoporosis, moderate to advanced spondylosis, marked cervical instability, significant cervical anatomical deformity or compromised vertebral bodies at the index level, significant kyphotic deformity or significant reversal of lordosis, or symptoms necessitating surgical treatment at more than one cervical level.  The Bryan device is implanted via an open anterior approach.  Because the specific polyurethanes used in the device have not be exhaustively studied for use as sheaths or nuclei in a cervical disc prosthesis, the FDA recommended that the sponsor continue to evaluate explanted devices in a 10 year post-approval study.

An assessment by the BlueCross BlueShield Association Technology Evaluation Center (2009) found that artificial intervertebral disc arthroplasty for the treatment of patients with cervical DDD does not meet its criteria for improving net health outcomes or is as beneficial as ACDF.

A draft assessment by the California Technology Assessment Forum (2009) found insufficient evidence that cervical disc replacement for patients with cervical DDD improves health outcomes over the long term.

Lumbar partial disc replacement is a minimally invasive procedure that replaces only the nucleus pulposus in an attempt to fill the therapy gap between discectomy and fusion.  The procedure targets only the nucleus pulposus as the origin of pain while attempting to restore the biomechanical function of the whole segment.  Careful patient selection is crucial since the prosthetic nucleus is not fixed into position.  An intact annulus and properly functioning endplates must be present.  Exclusion criteria include osteoporosis, endplate problems, posterior element disorder (e.g., stenosis, facit arthritis, isthmic pathologies), and infection tumors.  There are several lumbar partial disc replacement devices currently under investigation. These devices use hydrogel, polymer/synthetic, or mechanical technologies, however, none are commercially available in the United States.  All non-fusion spinal implants are considered Class III medical devices and require Pre-Market Approval (PMA) from the FDA prior to market release in the United States.

Nubac (Pioneer Surgical Technology, Inc., Marquette, MI) is an elastomeric nucleus replacement device composed of polyetheretherketone (PEEK) that is used in partial disc replacement.  The Nubac procedure is intended to conserve most of the annular tissue and to be less invasive than total disc replacment and fusion allowing further treatment options if revision is required.  Alpízar-Aguirre, et al. (2008) reported the results of 10 patients with DDD who underwent discectomy with the Nubac device.  Surgical approach was anterolateral (n = 4), posterior (n = 3) and anterior (n = 3).  After 3-months post-operatively, ODI improved from 58.2% to 24.2% (p < 0.05), VAS improved from 8.1 to 2.5 (p < 0.05), and disc height improved from 9.4 mm to 12.5 mm, but lumbar motion did not improve.  The authors concluded that the Nubac prosthesis improved lumbar discogenic pain in a short time, however, a minimum follow-up of 4 years is needed to make a definite conclusion.  According to a review of nucleus replacement technologies (Coric & Mummaneni, 2008), a challenge of using preformed elastomeric devices is implant extrusion due to their inherently deformable nature.  Other issues include their durability and their effectiveness compared to established alternatives (e.g., laminectomy, percutaneous diskectomy) for lumbar disc herniation. Available published peer reviewed evidence of the Nubac disc prosthesis is of a preliminary nature.  Well controlled clinical studies are necessary to evaluate the effectiveness, safety and durability of results of this device.

The DASCOR (Disc Dynamics Inc., Eden Prairie, MN) is a balloon device that is inserted into the disc space after total nucleus removal.  The balloon is then filled with an injectable polyurethane polymer that conforms to the individual's anatomy  The remaining implant is designed to restore the original disc function and replaces the nucleus.  Ahrens, et al. (2009) reported the results from 2 prospective, non-randomized multi-center European studies on lumbar disc nucleus replacement using the DASCOR disc arthroplasty device for DDD (n = 85).  Data were collected before surgery and after surgery at 6 weeks and at 3, 6, 12, and 24 months.  The clinical outcome measures were obtained from VAS for back pain, ODI, radiographic assessments, and records of analgesic medication use.  Mean VAS and ODI scores improved significantly after 6 weeks and throughout the 2 years.  Radiographic results demonstrated, at a minimum, maintenance of disc height with no device expulsion and, despite Modic-Type 1 changes, no subsidence.  Fourteen patients had serious adverse events including device explants in 7 patients (7 of 85), in which the main complication was resumed back pain after time.  Patients' rate of analgesic medication decreased dramatically over time, with all patients experiencing significant improvements after 3 months and nearly no analgesic medication or narcotic drug use at 2 years.  The authors concluded that these interim outcomes showed significant improvements in mean ODI and VAS scores and suggest that the DASCOR device may be a safe and effective less-invasive surgical option for patients with DDD.

Further clinical investigation with well-designed prospective, randomized trials is needed to determine the efficacy of nucleus replacement in the treatment of lumbar DDD, as well as its ideal indications.

Quan et al (2011) evaluated the long-term outcome of cervical disc arthroplasty.  A total of 21 patients underwent 27 total disc arthroplasties using the Bryan cervical disc after anterior cervical discectomy.  Clinical and radiological data were obtained from the 8-year post-operative review.  Nineteen of 21 patients were able to perform daily activities without limitation; 20 of 21 patients reported fair to excellent outcome according to Odom criteria and 21 of 27 (78 %) operated segments were mobile.  Functional prostheses moved an average of 10.6°, which was similar to the range of movement of the adjacent non-operated segments of the cervical spine.  Heterotopic ossification was evident in 13 of the 27 (48 %) operated segments and restricted movement of the prosthesis in 9 cases.  Five of the 6 patients who received bilevel arthroplasties developed heterotopic ossification.  There was 1 case of posterior migration of the prosthesis, which did not have any clinical repercussion.  No other case showed evidence of migration, subsidence, loosening, or wear.  Radiological evidence of adjacent segment degeneration was observed in 4 patients (19 %); however, each of these patients had pre-existing degenerative disc disease at these levels on pre-operative imaging.  The authors concluded that at 8-year follow-up, the Bryan cervical disc arthroplasty maintains favorable clinical and radiological results, with preservation of movement and satisfactory clinical outcome in the majority of cases.  However, the incidence of heterotopic ossification causing restricted range of movement of the prosthesis appears to increase with time, especially in bilevel procedures.