Lower Limb Prostheses

Number: 0578

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

Policy

Scope of Policy

This Clinical Policy Bulletin addresses lower limb prostheses.

Medical Necessity

Criteria for Lower Limb Prostheses

Aetna considers an orthosis (orthopedic brace) and/or prosthesis medically necessary when:

Care is prescribed by a physician, nurse practitioner, podiatrist or other health professional who is qualified to prescribe orthotics and/or prosthetics according to State law; and
The orthosis or prosthesis will significantly improve or restore physical functions required for mobility related activities of daily living (MRADL's); and
The member’s participating physician or licensed health care practitioner has determined that the orthosis or prosthesis will allow the member to perform ADLs based on physical examination of the member; and
The orthosis or prosthesis is provided within six months of the date of prescription; and
The orthotic or prosthetic services are performed by a duly licensed and/or certified, if applicable, orthotic and/or prosthetic provider. (All services provided must be within the applicable scope of practice for the provider in their licensed jurisdiction where the services are provided); and
The services provided are of the complexity and nature to require being provided by a licensed or certified professional orthotist and/or prosthetist or provided under their direct supervision by a licensed ancillary person as permitted under state laws. (Services may be provided personally by physicians and performed by personnel under their direct supervision as permitted under state laws, as physicians are not licensed as orthotists and/or prosthetists); and
The certified professional orthotist or prosthetist must be in good standing with one or more of the following:
1. American Board for Certification (orthotics, prosthetics, pedorthics) (ABC); or
2. Board of Certification/Accreditation (prosthetics, orthotics) (BOC); or
3. licensed by the state in which services are provided (where legally required).

Aetna considers lower limb prostheses medically necessary for performing normal daily activities when the following criteria are met:

Member is motivated to ambulate; and
Member meets the specific criteria for lower limb prostheses set forth below; and
Member will reach or maintain a defined functional state within a reasonable period of time.

Aetna does not consider a replacement prosthesis medically necessary unless the member's medical needs are not being met by the current prosthetic or it is broken and unrepairable.

Clinical assessments of a member’s rehabilitation potential should be based on the following classification levels.

Table: Classification levels and Clinical assessments of a member’s rehabilitation potential
Levels	Clinical Assessments of Member Rehabilitation Potential
Level 0	Does not have the ability or potential to ambulate or transfer safely with or without assistance and a prosthesis does not enhance their quality of life or mobility.
Level 1	Has the ability or potential to use a prosthesis for transfers or ambulation on level surfaces at fixed cadence. Typical of the limited and unlimited household ambulator.
Level 2	Has the ability or potential for ambulation with the ability to traverse low level environmental barriers such as curbs, stairs or uneven surfaces. Typical of the limited community ambulator.
Level 3	Has the ability or potential for ambulation with variable cadence. Typical of the community ambulator who has the ability to traverse most environmental barriers and may have vocational, therapeutic, or exercise activity that demands prosthetic utilization beyond simple locomotion.
Level 4	Has the ability or potential for prosthetic ambulation that exceeds basic ambulation skills, exhibiting high impact, stress, or energy levels. Typical of the prosthetic demands of the child, active adult, or athlete.

This expectation of functional ability information must be clearly documented and retained in the prosthetist's records. The simple entry of a K modifier in those records is not sufficient. For K3 or above functional levels, there must be documented evaluation from physical therapist to establish functional levels and activities. There must be information about the member’s history and current condition that supports the designation of the functional level by the prosthetist and physical therapist.

Footnote1*Note: Clinical assessments of a member’s rehabilitation potential should be based on the functional classification levels listed in the Appendix.

Medically Necessary Prostheses and Accessories

Aetna considers the following medically necessary:
1. Foot Prosthesis
  1. A solid ankle-cushion heel (SACH) foot for persons whose functional level is 1Footnote1* or above;
  2. An external keel SACH foot or single axis ankle/foot for persons whose functional level is 1Footnote1* or above;
  3. A flexible-keel foot or multi-axial ankle/foot for persons whose functional level is 2Footnote1* or above;
  4. A flex foot system, energy storing foot, multi-axial ankle/foot, dynamic response foot with multi-axial ankle, shank foot system with vertical-loaded pylon or flex-walk system or equal for persons whose functional level is 3Footnote1* or above;
  5. A user-adjustable heel height feature is considered not medically necessary;
  Note: Foot covers (foot shells) are included in the reimbursement for a prosthetic foot component and are not separately payable. Repair or replacement of a foot cover for appearance, comfort, convenience or individual abuse, misuse or neglect is considered not medically necessary. Repair or replacement of a damaged foot cover should be billed using HCPCS repair code L7510. No more than 1 foot cover replacement per prosthetic foot is considered medically necessary once per year.
2. Knee Prosthesis
  1. A fluid or pneumatic knee for persons whose functional level is 3Footnote1* or above;
  2. A single axis constant friction knee and other basic knee systems for persons whose functional level is 1Footnote1* or above;
  3. A high-activity knee control frame for members whose function level is 4Footnote1*;
  4. A fluid, pneumatic, or electronic/microprocessor knee for members with a knee disarticulation amputation, a trans-femoral amputation or a hip disarticulation amputation whose functional level is 3 or above.
3. Ankle Prosthesis
  
  An axial rotation unit for persons whose functional level is 2Footnote1* or above;
  
  Note: Only one axial rotation is considered medically necessary per ankle device/prosthesis.
4. Hip Prosthesis
  
  A pneumatic or hydraulic polycentric hip joint for members whose functional level is 3 or above;
5. Sockets
  1. Two test (diagnostic) sockets for an individual prosthetic; additional documentation of medical necessity is required for more than 2 test sockets;
  2. No more than 2 socket inserts per individual prosthesis at the same time are considered medically necessary;
  3. Socket replacements are considered medically necessary if there is adequate documentation of functional and/or physiological need, including but is not limited to: changes in the residual limb; functional need changes; or irreparable damage or wear/tear due to excessive weight or prosthetic demands of very active amputees.
  Test (diagnostic) sockets for immediate post-surgical or early-fitted prostheses are considered not medically necessary.
  
  Prostheses have no proven value for persons whose potential functional level is 0Footnote1*.
  
  Note: When replacing the socket on an existing prosthesis, socket replacement codes (L5700, L5701, L5702, L5703) should be used as base code. These socket replacement codes should not be used when replacing an entire prosthesis (e.g., a socket with a foot, knee and/or other components that would substantially make an entire prosthesis). Use of socket replacement codes are considered duplicative and not medically necessary when an entire prosthesis, such as feet and knees, are billed with a socket replacement code. When a prosthetic foot, knee or other component is still under warranty a socket replacement should be considered as a first-line treatment. Items billed for replacement that are still under manufacturer warranty are considered not medically necessary. An alignable system is included in a socket replacement and is not separately payable unless a medical need for replacement is documented in the medical records.
6. Accessories
  1. The following are considered medically necessary:
    1. Stump stockings and harnesses (including replacements) when they are essential to the effective use of the artificial limb;
    2. No more than 1 harness/suspension system per limb;
    3. Prosthetic sheaths/socks, including a gel cushion layer (prosthetic gel stockings; 12 in 12 months);
    4. No more than 2 socket inserts per individual prosthesis;
    5. No more than 2 replacement liners per prosthesis in 12 months;
    6. Static compression garments (i.e., shrinkers, stump stockings for edema) for members with:
      1. An amputation of the upper limb between the wrist and shoulder; or
      2. An amputation of the lower limb between the ankle and hip;
    7. No more than 2 static compression garments (i.e., shrinkers, stump stockings for edema) per limb are considered medically necessary every 6 months;
    8. No more than 2 suspension sleeves per limb are considered medically necessary every 6 months;
    9. Custom socket inserts (liners) with clinical documentation by the treating practitioner of atypical amputation and medical necessity.
  2. The following are considered not medically necessary or cosmetic:
    1. A prosthetic donning sleeve is considered not medically necessary;
    2. Passive/restorative devices (such as silicone devices) to make the limb more lifelike are considered cosmetic;
    3. Custom-shaped prosthetic covers are considered cosmetic unless there is medical function and documentation of medical need. Custom-made prosthetic covers are typically made of foam that is cosmetically shaped to the person's limb;
    4. Silver impregnated garments (i.e., shrinkers, socks, sheaths, etc.,) are considered not medically necessary because there is insufficient evidence that silver impregnated garments are superior to standard garments;
    5. Donning tubes or devices for applying compression garment;
    6. A push-button rotation device that allows the user to rotate the prosthesis between the socket and knee/shin/foot region is a considered convenience item (L5926);
    7. Gaitor sealing sleeves are considered a convenience/cosmetic item;
    8. 3-D printed, CAD-CAM, or similar prosthetic covers are considered cosmetic.
7. Microprocessor-Controlled Lower Limb Prostheses
  
  Note: Microprocessor knees, ankles and feet can only be billed with L5999 when Pricing, Data Analysis, and Coding (PDAC) is verified. The use of L5999 for the Otto Bock Genium knee system would be considered incorrect coding (unbundling). The Otto Bock Genium system is not PDAC verified; therefore, it is not a covered item. For additional information on PDAC, see Appendix.
  1. Microprocessor-controlled leg prostheses (“Addition to lower extremity prosthesis, endoskeletal knee-shin system, microprocessor control feature, swing and stance phase, includes electronic sensor(s), any type”) in otherwise healthy, active community ambulating members (functional K level 3Footnote1* or above) with a knee disarticulation amputation or a trans-femoral amputation from a non-vascular cause (usually trauma or tumor) for whom this prosthesis can be fitted and programmed by a qualified prosthetist trained to do so;
  2. A powered flexion-extension assist ("Addition to lower extremity prosthesis, endoskeletal knee-shin system, powered and programmable flexion/extension assist control, includes any type of motor(s)" ) when the member meets all of the criteria below:
    1. Has a microprocessor (swing and stance phase type) controlled (electronic) knee; and
    2. K3 functional level onlyFootnote1*; and
    3. Weight greater than 110 lbs and less than 275 lbs; and
    4. Has a documented comorbidity of the spine and/or sound limb affecting hip extension and/or quadriceps function that impairs K-3 level function with the use of a microprocessor-controlled knee alone; and
    5. Is able to make use of a product that requires daily charging; and
    6. Is able to understand and respond to error alerts and alarms indicating problems with the function of the unit;
    Note: With the exception of items described by specific HCPCS codes, there should be no separate billing and there is no separate payment for a component or feature of a microprocessor controlled knee, including but not limited to real time gait analysis, continuous gait assessment, or electronically controlled static stance regulator.
8. Microprocessor-Controlled Ankle
  1. Microprocessor-controlled ankle-foot prostheses (e.g., PowerFoot BiOM, iWalk, Bedford, MA; Proprio Foot, Ossur, Aliso Viejo, CA) for members whose functional level is 3Footnote1* or above;
  2. Prosthetic shoe for a partial foot amputation when the prosthetic shoe is an integral part of a covered basic lower limb prosthetic device.
9. Protective Outer Surface Covering Systems
  
  Protective outer surface covering systems (L5962, L5964, and L5966) are specialized covers intended to be worn over an existing prosthesis. They are considered medically necessary for members who have special needs for protection against unusually harsh environmental situations where it is necessary to protect the lower limb prosthesis beyond the level of protection that is afforded by covers described by HCPCS codes L5704 - L5707. They are not for cosmetic or convenience reasons, or for everyday usage in a typical environment. Protective outer surface coverings are different from the covering that is already reimbursed as part of the covers described by HCPCS codes L5704 - L5707. When billing for the protective outer surface covering systems (L5962, L5964 and L5966), information regarding the type of protective cover provided (i.e., manufacturer name, make, model or type) must be included in practitioner’s notes in order to ensure correct coding.
Non-Medically Necessary Prostheses

Aetna considers the following not medically necessary:
1. Duplication or upgrade of a functional prosthesis; or
2. Lower limb prosthesis for a functional level of 0; or
3. Otto Bock Kenevo microprocessor-controlled knee for persons whose functional level is 3 or above; or
4. Prosthetic devices or prosthetic components that are primarily for cosmesis; or
5. Prosthetics used for activities other than normal daily living, including, but may not be limited to, those utilized for leisure or sporting activities such as skiing or swimming; or
6. Repair or replacement of a prosthesis for appearance, comfort, convenience or individual abuse, misuse or neglect; or
7. Repair or replacement of parts of a duplicate prosthesis; or
8. Test sockets for an immediate prosthesis; or
9. Water prosthesis (designed to be used for showering, swimming, etc.).

Experimental, Investigational, or Unproven

Aetna considers the following to be experimental, investigational, or unproven because of insufficient published evidence of their safety and effectiveness:
1. Adjustable click prostheses (e.g., Revo, RevoFit, and Boa click systems)
2. Protective cover for microprocessor knees (e.g., C-leg Protector or similar), Bionic Protector for Rheo, UNYQ Prosthetic Covers, Limb-Art Covers (or similar), and 3-D printed covers
3. DAW Sure Stance Knee
4. Endo-skeletal above the knee positioning device that allows 360 degrees of rotation and locks the endo-skeletal prosthetic knee and foot system in a neutral position for ambulation. The predicate product is the Ottobock 4R57 Rotation Adapter (L5926)
5. HiFi Interface System (HiFi Socket)
6. Lower limb prostheses for all other indications
7. Microprocessor-controlled leg prostheses for gait management in spinal cord injury
8. NEURO HiSWING R+
9. Osseointegrated lower limb prosthetic devices (with or without microprocessor-control)
10. Ossur Pivot Foot
11. Ossur Symbiotic Leg
12. Otto Bock Kenevo microprocessor-controlled knee for members with functional level 2 or below
13. Powered ankle (addition, endoskeletal ankle-foot or ankle system, power assist, includes any type motor(s))
14. Robotic lower body exoskeleton suits (e.g., the ReWalk, Argo Medical Technologies Ltd, Marlborough, MA)
15. Walkasins lower extremity sensory prosthesis for improvement of gait and balance function in individuals with peripheral neuropathy who have balance problems.
Cosmetic

Aetna considers the following to be cosmetic:
1. Passive/restorative devices (such as silicone devices) to make the limb more life-like;
2. Custom-shaped prosthetic covers unless there is medical function and documentation of medical need. Custom-made prosthetic covers are typically made of foam that is cosmetically shaped to the person's limb.
Plan Limitations and Exclusions

Evaluation of the member, measurement and/or casting, and fitting/adjustments of the prosthesis are included in the allowance for the prosthesis. There is no separate payment for these services.

There is no separate payment if CAD-CAM technology is used to fabricate a prosthesis. Reimbursement is included in the allowance of the codes for a prosthesis.

Powered base items are those that contain the power source (battery). At the time that a base item is billed, all necessary batteries and/or battery chargers are considered as included in the payment for the powered base item. There is no separate payment for batteries (L7360, L7364, and L7367) and/or battery chargers (L7362, L7366, and L7368) billed concurrently with a powered base item.

Aetna does not consider warranties or guarantees beyond the base warranty included in a device a medical benefit. Additional warranties and guarantees beyond the included base warranty or manufacturer warranty, are considered non-medically necessary convenience items. Items billed for replacement that are still under manufacturer warranty are considered not medically necessary.

A Standard Written Order (SWO) must be communicated to the supplier before a claim is submitted. If the supplier bills for an item addressed in this policy without first receiving a completed SWO, the claim shall be denied as not medically necessary.

Proof of delivery (POD) is a supplier standard and suppliers are required to maintain POD documentation in their files. Proof of delivery documentation must be made available to Aetna upon request. All services that do not have appropriate proof of delivery from the supplier shall be denied as not medically necessary.

Consistent with DME MAC policy:

Treating practitioner means physician (MD or DO) or physician assistant, nurse practitioner, or clinical nurse specialist. A prosthetist, orthotist, orthotic fitter, pedorthotist, physical therapist, or occupational therapist is not considered a treating practitioner.

A new prescription from the treating practitioner is required each time a new device or repair is requisitioned.

There must be sufficient medical information included in the medical record to demonstrate that all applicable coverage criteria are met.

Consistent with DME MAC policy:

Supplier prepared statements and physician attestations by themselves do not provide sufficient documentation of medical necessity, even if signed by the ordering physician.

"Neither a practitioner’s order, nor a supplier-prepared statement, nor a practitioner’s attestation by itself provides sufficient documentation of medical necessity, even though it is signed by the treating practitioner or supplier. There must be information in the member’s medical record that supports the medical necessity for the item and substantiates the information on a supplier-prepared statement or treating practitioner’s attestation (if applicable)."

"Forms are subject to corroboration with information in the medical record."

Records from suppliers or healthcare professionals with a financial interest in the claim outcome are not considered sufficient by themselves for the purpose of determining that an item is reasonable and necessary.

Consistent with DME MAC policy:

A Standard Written Order (SWO) must be communicated to the supplier before a claim is submitted. If the supplier bills for an item addressed in this policy without first receiving a completed SWO, the claim shall be denied as not medically necessary.

The SWO must contain all the following elements:
- - Member's name or Identification Number
  - Order Date
  - General description of the item
    - The description can be either a HCPCS code, a HCPCS code narrative, or a brand name/model number;
    - In addition to the description of the base item, the SWO must include all concurrently ordered options, accessories or additional features that are separately billed or require an upgraded code (list each separately);
    - For supplies - in addition to the description of the base item, the order/prescription must include all concurrently ordered supplies that are separately billed (list each separately)
  - Each item or service requested must individually list the HCPCS code (Procedure code) and Quantity to be dispensed
  - Treating Practitioner Name and National Provider Identifier (NPI)
  - Treating practitioner's signature.
Correct Coding of Endoskeletal Prosthetic Knee-Shin Systems

The endoskeletal prosthetic lower extremity codes (L5312, L5321, L5331, L5341) (Group 1 codes) include reimbursement for a molded prosthetic socket, an endoskeletal single axis knee-shin system and a SACH foot.

The knee-shin systems (L5610, L5611, L5613, L5616, L5810, L5811, L5812, L5814, L5816, L5818, L5822. L5824, L5826, L5828, L5830, L5840) (Group 2 codes) are considered an upgrade to the endoskeletal prosthetic lower extremity (Group 1) codes listed above. The member may qualify for these upgraded knee-shin systems. Qualification is dependent on medical documentation and assigned K-Level modifier (K0-K4). These Group 2 L-codes can fully describe a complete prosthetic knee-shin system commonly referred to as a “base knee code”. The use of two L-codes from this group to fully describe the knee-shin system would be considered incorrect coding (unbundling).

The Group 3 codes (L5925, L5930, L5845, L5848, L5850. L5856, L5857, L5858, L5859) includes a secondary list of L-codes which describe other features and functions not found in the Group 2 “base knee codes”. These addition codes describe additional features and/or functions that do not describe a complete knee-shin system and must be used in combination with an L-code with a base knee-shin system. The use of Group 3 L-codes may also depend on the medical documentation and the assigned K-Level modifier (K0-K4).

HCPCS code L5999 must not be used to bill for features or functions of the knee-shin system included in Group 1, Group 2 or Group 3 code lists. Use of HCPCS code L5999 in this manner will be considered incorrect coding (unbundling).

For information on Pricing, Data Analysis, and Coding (PDAC), see Appendix.
Related Policies

Table:
CPT Codes / HCPCS Codes / ICD-10 Codes
Code	Code Description
Other CPT codes related to the CPB:
27590 - 27596	Amputation, thigh, through femur
HCPCS codes covered if selection criteria are met:
L5000 - L5782, L5785 – L5840, L5842 – L5929, L5931 – L5939, L5941 – L5949, L5951 – L5959, L5961 – L5968, L5970 – L5972, L5974 -L5988	Lower limb prostheses
L5930	Addition, endoskeletal system, high activity knee control frame [covered for members whose functional level is 4]
L5940	Addition, endoskeletal system, below knee, ultra-light material (titanium, carbon fiber or equal) [only covered when ultra-light materials are used in the fabrication of a socket for an endoskeletal prosthesis]
L5950	Addition, endoskeletal system, above knee, ultra-light material (titanium, carbon fiber or equal) [only covered when ultra-light materials are used in the fabrication of a socket for an endoskeletal prosthesis]
L5960	Addition, endoskeletal system, hip disarticulation, ultra-light material (titanium, carbon fiber or equal) [only covered when ultra-light materials are used in the fabrication of a socket for an endoskeletal prosthesis]
L5992	All lower extremity prosthesis, foot shell for modular foot/non-solid ankle cushion heel (sach) replacement only
L5999	Lower extremity prosthesis, not otherwise specified [microprocessor knees, ankles and feet]
L7510, L7520	Repair prosthetic device, labor component, per 15 minutes
L8400, L8410	Prosthetic sheath, below and above knee, each
L8417	Prosthetic sheath/sock, including a gel cushion layer; below knee or above knee, each [12 in 12 months]
L8420, L8430	Prosthetic sheath, below and above knee, each
L8440, L8460	Prosthetic shrinker, below and above knee, each
L8470 - L8485	Prosthetic socks
HCPCS codes not covered for indications listed in the CPB:
Military grade prostheses, osseointegrated lower limb prosthetic devices, ossur pivot foot, Protective cover for microprocessor knees, HiFi Interface System (Hifi Socket) - no specific code
K1007	Bilateral hip, knee, ankle, foot device, powered, includes pelvic component, single or double upright(s), knee joints any type, with or without ankle joints any type, includes all components and accessories, motors, microprocessors, sensors
L2221	Addition to lower extremity orthosis, ankle system, microprocessor-controlled feature plantarflexion and/or dorsiflexion, includes power source
L5783	Addition to lower extremity, user adjustable, mechanical, residual limb volume management system
L5841	Addition, endoskeletal knee-shin system, polycentric, pneumatic swing, and stance phase control
L5969	Addition, endoskeletal ankle-foot or ankle system, power assist, includes any type motor(s)
L5973	Endoskeletal ankle foot system, microprocessor controlled feature, dorsiflexion and/or plantar flexion control, includes power source
L5990	Addition to lower extremity prosthesis, user adjustable heel height
L7360	Six volts battery, each
L7362	Battery charger, six volts, each
L7364	Twelve volts battery, each
L7366	Battery charger, twelve volts, each
L7367	Lithium ion battery, rechargeable, replacement
L7368	Lithium ion battery charger, replacement only
L7600	Prosthetic donning sleeve, any material, each
ICD-10 codes covered if selection criteria are met:
Q72.00 – Q72.93	Reduction defects of lower limb
S88.011A - S88.929S	Traumatic amputation of lower leg
S98.011A - S98.929S	Traumatic amputation of foot
Z89.411 - Z89.9	Acquired absence of lower limb
*Protective outer covering systems*:
HCPCS codes covered if selection criteria are met:
L5704	Custom shaped protective cover, below knee
L5705	Custom shaped protective cover, above knee
L5706	Custom shaped protective cover, knee disarticulation
L5707	Custom shaped protective cover, hip disarticulation
L5962	Addition, endoskeletal system, below knee, flexible protective outer surface covering system
L5964	Addition, endoskeletal system, above knee, flexible protective outer surface covering system
L5966	Addition, endoskeletal system, hip disarticulation, flexible protective outer surface covering system
*Microprocessor-controlled leg prostheses*:
HCPCS codes covered if selection criteria are met:
L5615	Addition, endoskeletal knee-shin system, 4 bar linkage or multiaxial, fluid swing and stance phase control
L5856	Addition to lower extremity prosthesis, endoskeletal knee-shin system, microprocessor control feature, swing and stance phase; includes electronic sensor(s) any type [not covered for gait management in spinal cord injury, for members with functional level 2 or below and persons whose functional level is 3 or above]
L5857	Addition to lower extremity prosthesis, endoskeletal knee-shin system, microprocessor control feature, swing phase only; includes electronic sensor(s), any type [not covered for gait management in spinal cord injury]
L5858	Addition to lower extremity prosthesis, endoskeletal knee-shin system, microprocessor control feature, stance phase only, includes electronic sensor(s) any type [not covered for gait management in spinal cord injury]
L5926	Addition to lower extremity prosthesis, endoskeletal, knee disarticulation, above knee, hip disarticulation, positional rotation unit, any type[Ottobock 4R57 Adapter]
L5973	Endoskeletal ankle foot system, microprocessor controlled feature, dorsiflexion and/or plantar flexion control, includes power source
L7367 - L7368	Lithium ion battery, rechargeable, replacement and ion battery charger
HCPCS codes not covered for indications listed in the CPB:
L5828	Addition, endoskeletal knee-shin system, single axis, fluid swing and stance phase control
L5845	Addition, endoskeletal, knee-shin system, stance flexion feature, adjustable
L5848	Addition to endoskeletal knee-shin system, fluid stance extension, dampening feature, with or without adjustability
ICD-10 codes covered if selection criteria are met:
S88.011A - S88.929S	Traumatic amputation of lower leg
S98.011A - S98.929S	Traumatic amputation of foot at ankle level
Z89.411 - Z89.619	Acquired absence of leg, ankle and foot
ICD-10 codes not covered for indications listed in the CPB:
S12.000A - S12.9xxS S22.000A - S22.089S S32.000A - S32.2xxS	Fracture of vertebral column
S14.0xxA - S14.9xxS S24.0xxA - S24.9xxS S34.01xA - S34.9xxS	Injury of nerves and spinal cord
*Adjustable click systems (e.g., Revo and Boa click systems)*:
HCPCS codes not covered for indications listed in the CPB:
Adjustable click systems (e.g., Revo and Boa click systems) - no specific code:

Background

A prosthesis or prosthetic is an artificial device that replaces a missing body part. Examples of prostheses include eyes, maxillofacial (jaw and face), arms, breasts, ears, legs, hands, and feet.

A lower limb prosthesis is designed to replace portions of the lower extremity to improve function. A prosthetic knee performs several functions: it provides support during the stance phase of ambulation, produces smooth control during the swing phase, and maintains unrestricted motion for sitting and kneeling. The prosthetic knee may have a single axis with a simple hinge and a single pivot point, or it may have a polycentric axis with multiple centers of rotation, which is more similar to the anatomic human knee. Pylons are the connection between the residual limb and the prosthetic joint.

The prosthetic foot also has several basic functions: it provides a stable weight-bearing surface, absorbs shock, replaces lost muscle function and biomechanics of the foot, replicates the anatomic joints of the ankle and foot, and restores appearance.

Multiaxial prosthetic feet permit movements in any direction: plantar flexion, dorsiflexion, inversion, eversion, and a slight amount of rotation around a vertical axis. Multiaxial feet are appropriate for those who ambulate on uneven terrain, such as community ambulators and active adults or athletes.

The solid ankle cushion heel (SACH) consists of a rigid keel covered by semi-noncompressible foam and a synthetic rubber heel wedge. The cushion heel compresses when weight is applied, allowing the forefoot to approach the floor. The amount of simulated plantar flexion depends on the relative softness of the heel material and the weight of the amputee. Because the keel is rigid, the SACH foot does not provide dorsiflexion; this makes its usefulness on uneven surfaces limited.

Conventional lower limb prostheses employ exclusively mechanical control; these may include a pneumatic or hydraulic damping cylinder, which is adjusted by a prosthetist to provide optimum gait parameters at the patient's conventional walking speed. If a patient walks at a different speed, the patient must compensate for the pendulum action of the prosthesis to alter stride length or step rate by tilting the pelvis or by other maneuvers to delay extension to ensure that the foot is in the right place for the next step. These maneuvers lead to an abnormal gait and require extra effort and concentration. Aetna’s policy on standard lower limb prostheses is based on Medicare DME MAC criteria.

The microprocessor-controlled lower limb prosthesis (also known as computerized lower limb prostheses) is relatively new to the United States, although a different brand of microprocessor-controlled lower limb prosthesis has been in use in Europe for many more years. These prostheses employ a microprocessor-controlled knee extension damper, which is designed to detect step time and alter knee extension level to suit walking speed. More advanced microprocessor-controlled lower limb prostheses, such as the C-leg, also have multiple sensors that gather and calculate data on, for example, the amount of vertical load, sagittal plane ankle movement, and specifics of knee joint movement. These prostheses are claimed to be a significant improvement over the conventional mechanically controlled prostheses.

Claimed advantages of the microprocessor-controlled lower limb prostheses include decreased effort involved in walking, improved gait symmetry, increased confidence by the patient in the prosthesis, more natural movement (including on stairs, inclines, and uneven terrain), the perception that participation in activities such as sports is possible, and the avoidance of falls.

Hahn et al. (2022) conducted a systematic review and meta-analysis to update prior evidence on the effectiveness of microprocessor-controlled prosthetic knees (MPKs) for limited community ambulators with transfemoral amputation, defined as Medicare Functional Classification Level 2 (MFCL-2) or equivalent mobility. The authors sought to determine whether MPKs improve safety, functional performance, mobility, and patient-reported outcomes compared with non-microprocessor-controlled prosthetic knees (NMPKs). A comprehensive literature search of multiple databases, including MEDLINE, Cochrane Library, CINAHL, EMBASE, and Google Scholar, was performed through July 2021. Eligible studies included randomized and non-randomized comparative investigations that reported quantitative outcomes for MFCL-2 amputees. Methodological quality was assessed using the American Academy of Orthotists and Prosthetists State of the Science Evidence Report Guidelines, and meta-analyses were conducted when at least three studies reported comparable outcomes. Fifteen publications representing 13 research projects met inclusion criteria, encompassing 2,366 patients overall, including 704 limited community ambulators. Nine studies were rated as having high validity, three as moderate validity, and one as low validity. The review found evidence that MPKs improved safety and mobility relative to NMPKs in limited community ambulators. Meta-analysis demonstrated significant reductions in falls (standardized mean difference [SMD] −0.59; 95% CI, −0.85 to −0.32), fear of falling (SMD 1.20; 95% CI, 0.55 to 1.85), and fall risk as measured by the Timed Up and Go test (SMD −0.45; 95% CI, −0.87 to −0.02). MPKs were also associated with improvements in mobility grade, with approximately 51% of users progressing from MFCL-2 to MFCL-3, as well as improvements in self-selected walking speed (SMD 0.47; 95% CI, 0.14 to 0.81), patient-reported ambulation (mean difference 9.32; 95% CI, 3.61 to 15.02), and prosthetic utility (mean difference 7.76; 95% CI, 2.05 to 13.47). Individual studies additionally reported benefits in stair negotiation, ambulation on slopes and uneven terrain, activities of daily living, confidence, reduced wheelchair dependence, and overall functional performance. Notably, none of the included studies identified a statistically significant outcome favoring NMPKs over MPKs. The authors noted several limitations. Considerable heterogeneity existed across studies in design, patient populations, outcome measures, and reporting methods, which complicated quantitative synthesis and limited exploration of sources of heterogeneity and publication bias. Prosthetic studies are difficult to blind, creating an inherent methodological limitation. Some investigations experienced substantial attrition, particularly among older patients with vascular disease and other comorbidities, which may have affected generalizability. Accommodation and training periods may have been insufficient in certain studies, and not all participants experienced measurable benefits. Differences in outcome reporting prevented inclusion of some potentially informative data in the meta-analysis. In addition to limitations noted by the authors, there are a number of additional limitations. Of the 13 included research projects, three had "moderate" and one had "low" validity ratings, which may introduce bias into the pooled results. The majority of included studies were crossover or pre-post designs rather than randomized controlled trials, which limits the strength of causal inference. The included studies generally had small sample sizes: while 2,366 total patients were described across all studies, only 704 were classified as limited community ambulators (K2), and individual study samples were often quite small. Significant heterogeneity was observed for the fear of falling outcome, suggesting substantial variability across studies in this measure, which weakens confidence in the pooled estimate. While other outcomes showed lower heterogeneity, the diversity of study designs, MPK types, acclimation periods, and outcome measures across studies complicates direct comparison. Acclimation periods varied considerably across studies (from single sessions to several months), which may influence outcomes, particularly for patient-reported measures and functional performance. The included studies varied in amputation etiology (traumatic vs. dysvascular), age, and comorbidity burden, all of which may influence responsiveness to MPK intervention. The review authors were affiliated with a prosthetic knee manufacturer. Three of the coauthors disclosed that they were full time employees of Ottobock, the manufacturer of several microprocessor-controlled knees. The fourth coauthor was full-time employee of a consulting firm contracted by Ottobock as a statistical consultant overseeing the analysis.

Wurdeman et al. (2026) conducted the ASCENT K2 randomized controlled trial to evaluate whether microprocessor knees (MPKs) improve clinical outcomes compared with non-microprocessor knees (NMPKs) in adults aged 65 years or older with unilateral above-knee amputation who were classified as Medicare K2 limited community ambulators. The study enrolled 107 participants from across the United States and randomly assigned them to receive either an MPK (n=54) or continue using an NMPK (n=53) for 12 months. The primary outcome was activity avoidance due to fear of falling, measured by the Fear of Falling Avoidance Behavior Questionnaire (FFABQ). Secondary outcomes included falls, near-falls, health-related quality of life, balance confidence, mobility measures, and adverse events. Participants were followed biweekly to collect fall and near-fall data, and both intention-to-treat and per-protocol analyses were performed. The study found that participants using MPKs experienced significantly greater improvements than those using NMPKs. Activity avoidance due to fear of falling improved significantly in the MPK group but not in the NMPK group. The MPK group also reported significantly fewer falls, near-falls, and total fall events during the 12-month observation period. In addition, MPK users demonstrated significant improvements in performance-based mobility measures, including the Timed Up and Go test, 10-meter walk test, and 2-minute walk test, while maintaining health-related quality of life. In contrast, participants using NMPKs experienced a significant decline in EQ-5D-5L quality-of-life scores. The findings suggested that MPKs provide meaningful benefits in safety, mobility, and preservation of quality of life among older, lower-functioning prosthesis users. Several limitations were acknowledged. The study was conducted across multiple clinical sites, introducing potential variability in prosthetic fitting and clinical practice. The strict inclusion and exclusion criteria may limit generalizability to broader amputee populations. Lack of blinding was unavoidable because MPKs require charging, which could have introduced bias. Some control-group participants obtained MPKs outside the study, affecting internal validity. Missing data required imputation, and participant withdrawals and deaths may have diluted treatment effects. Additionally, fall outcomes lacked a pre-intervention baseline observation period, necessitating between-group comparisons rather than within-subject longitudinal analyses for fall events. The authors also noted that the frequency of follow-up contacts may have influenced participant behavior through a Hawthorne effect. Additionally, there are other limitations. Given the nature of the intervention (MPK vs. NMPK), participants and clinicians were not be blinded to group assignment. This introduces potential performance and detection bias, particularly for self-reported outcomes like the FFABQ and HR-QoL measures, where knowledge of receiving the "advanced" device may inflate perceived benefit. While 107 participants makes this one of the larger RCTs in this population, the sample remains relatively modest for detecting differences across subgroups (e.g., by amputation etiology, comorbidity burden, or baseline mobility level). Subgroup analyses would be underpowered. The study focused exclusively on unilateral above-knee amputees over age 65 classified as K2 ambulators, with the vast majority having diabetes/dysvascular etiology (47/54 MPK, 44/53 NMPK). Results may not generalize to younger K2 users, bilateral amputees, or those with traumatic etiologies. Only K2-level ambulators were included. Whether these findings extend to K1 (household) ambulators or those transitioning between functional levels is unknown. The primary outcome, FFABQ, is a patient-reported measure of avoidance behavior due to fear of falling, which is inherently subjective and susceptible to expectation bias, especially in an unblinded trial. Falls and near-falls were likely captured via self-report (e.g., diaries or recall), which is subject to recall bias and may undercount events, particularly near-falls. The 12 months follow-up may be insufficient to assess long-term durability of benefits, device maintenance burden, or whether initial improvements plateau or diminish over time. At the start of the observation period, participants received 1 to 4 training sessions on their assigned knee (MPK or NMPK), with the number of sessions varying according to the participant's comfort level with the device. However, the investigators did not specify a fixed accommodation period before outcome measurement. Differential attention during training for MPK versus NMPK could introduce co-intervention bias. The study does not address the economic implications of MPK use, which is an important consideration given the substantially higher cost of MPKs. As only one MPK model was used, results may not be generalizable across all commercially available MPKs, which vary in features and control algorithms. Two coauthors were employees of Ottobock, the manufacturer of the microprocessor knee (Kenevo) used as the intervention device in the trial. Although the study reported that no external funding was received, the acknowledgments section states that Ottobock donated microprocessor knees to participants who withdrew from the study.

A VA/DoD Clinical Practice Guideline for Rehabilitation of Lower Limb Amputation includes a weak recommendation for MPKs over non-MPKs for most ambulatory patients, not limited to community ambulators (Stuart, et al., 2024).

The Otto Bock C-leg was cleared by the Food and Drug Administration (FDA) based on a 510(k) application; FDA clearance was based on the Otto Bock C-leg's substantial equivalence to a predicate device that was on the market prior to the date of enactment of the 1976 Medical Device Amendments to the Food, Drug, and Cosmetic Act.

A number of systematic evidence reviews have identified limitations in current literature on microprocessor-controlled knees. The majority of this literature evaluates intermediate outcomes, although some studies have focused on actual functional outcomes. However, the bulk of all of these studies show improvement in outcomes when the microprocessor-controlled knee is used compared to a more traditional non-microprocessor-controlled knee.

The first systematic evidence review of microprocessor-controlled knees was prepared by the Department of Veterans Affairs Technology Assessment Program (VA TAP) (MDRC, 2000). The VA TAP assessment reviewed the evidence supporting the use of computerized lower limb prostheses such as the Otto Bock C-leg and the Intelligent Prosthesis, a microprocessor-controlled lower limb prosthesis that is slightly different from the Otto Bock C-leg (MDRC, 2000). The VA TAP found, upon review of published studies, that users' perceptions of the microprocessor-controlled prosthesis are favorable. They also found that, although the energy requirements for ambulation (compared to requirements for conventional prostheses) are decreased at walking speeds slower or faster than the amputee's customary speed, energy requirements are not significantly different at customary speeds. The VA TAP found that the reported results on the ability to negotiate uneven terrain, stairs, or inclines are "mixed."

At that time, the VA TAP found the evidence of effectiveness of the microprocessor-controlled lower limb prostheses (Intelligent Prosthesis, Otto Bock C-leg) to be limited (MDRC, 2000). Regarding the evidence of effectiveness, the report drew the following conclusions: “The published research is a small body of work. Less than 3% of the published and indexed articles represent structured research, with the larger fraction of published articles being purely descriptive or frankly promotional. Most of the available structured research is based on a slightly different microprocessor-controlled prosthesis (the [Endolite] Intelligent Prosthesis (IP), Blatchford, United Kingdom). The IP is associated with many of the same potential benefits as the C-leg.”

The VA TAP reported (MDRC, 2000): “Published studies have enrolled highly selected samples of amputees who do not have additional medical problems, whose amputations were secondary to trauma or congenital defects, and who are fit and active. These and similar characteristics have been shown to be independently predictive of successful rehabilitation or return to normal living after amputation, and may confound the results of the non-randomized, uncontrolled microprocessor-controlled prosthesis studies that have been published to date.”

Results in the highly selected patients who have participated in the available published studies may not be directly transferable to VA amputees, who are likely to have multiple additional medical problems and amputations secondary to vascular disease.
The selective inclusion for research patients noted above undoubtedly introduce bias into study results, precluding definitive attribution of improvements in gait, energy expenditure, etc., to the computerized prosthesis."

An assessment conducted by the Washington State Department of Labor and Industries (2002) concluded "[d]ue to the small number of studies and study participants, evidence of the broad effectiveness of microprocessor-controlled prosthetic knees remains inconclusive."

An evidence review prepared by the Evidence-Based Group of the Workers Compensation Board of British Columbia (Martin, 2003) concluded that, "[t]o date, the published research on computerized knee prostheses is very limited. Less than 3% of published and indexed research represents structured research. Most published articles are purely descriptive or promotional in nature." The evidence review noted: “Published studies enrolled highly selected samples of amputees who did not have additional medical problems and who were fit and active. These characteristics have been shown to be independently predictive of successful rehabilitation or return to ‘normal’ living after amputation. Thus, these variables are most likely to confound the results of the non-randomized, uncontrolled studies on microprocessor-controlled knee prostheses that have been published to date.” The evidence review concluded that, "[a]t present, the small number of studies on computerized knee prostheses does not conclusively show the effectiveness of the prostheses" in reducing energy expenditure, particularly in normal speed walking, improving the ability to walk on uneven terrain, improving the ability to climb and descend stairs, and increasing walking distance.

Additional studies have been published since these technology assessments were released. Although each of these studies has flaws, the bulk of the studies show improvement in outcomes when the microprocessor-controlled knee is used compared to a standard hydraulic knee. Similar to previously published studies, Stinus (2000) authored an uncontrolled descriptive study involving a selected group of 15 patients, reporting on their subjective assessments of the microprocessor-controlled lower limb prosthesis compared with previously fitted mechanically controlled prosthetic knee joints. This study did not include objective assessments of improvements in function and reductions in disability compared with conventional prostheses. Schmalz et al. (2002) reported on the results of a randomized controlled clinical study comparing conventional hydraulic knees with electronically controlled knee joints during walking on a treadmill. The investigators reported reductions in oxygen consumption in persons with electronically controlled knees compared to patients with conventional hydraulic knees when walking at speeds other than the amputee’s customary walking speeds. This study, however, did not assess differences in function between these groups. Similarly, a study by Chin et al. (2003) of 8 traumatic amputees fitted with an Intelligent Prosthesis compared to 14 normal non-amputee controls reported a 24% greater energy expenditure compared to controls walking at equal speeds. However, this study did not assess reductions in disability and improvements in function with the Intelligent Prosthesis.

In a subsequent study, Chin et al. (2005) reported on changes in oxygen consumption of 3 amputees after the prescription of a microprocessor-controlled prosthesis. The change in energy expenditures reported was highly variable among subjects, with one subject reporting minor reductions in oxygen consumption of 4.9%, 11.6%, and 105%, another reporting changes in energy expenditures of 10.3%, 14.9%, and 23.3% depending upon speed, and the third subject reporting larger changes in energy expenditures (39.6%, 24.6%, and 23.3%). The study provided no details about how these cases were selected. Thus, one is not able to determine whether one can generalize from this selected set of individual cases to other amputees. The study suffers from the same flaws as the previous study by the same investigator group; it does not represent a stronger study, in terms of design, than previously published studies. The study by Chin et al. (2005) is a pre-/post-study without concurrent controls; other factors may have accounted for changes in energy expenditures after the prescription of the microprocessor-controlled prosthesis, including the training program and practice subjects received to improve their ability to walk with a microprocessor-controlled prosthesis before their energy expenditures were re-assessed. The study by Chin et al. also suffered from the limitations of his previous study in that it assessed differences in oxygen consumption, an intermediate endpoint, and did not assess clinically relevant endpoints of reductions in disability and improvement in function.

A study by Johansson et al. (2005) compared the magnetorheological-based Ossur Rheo prosthesis to the hydraulic-based Otto-Bock C-Leg microprocessor-controlled prosthesis and a standard hydraulic-based (Mauch) prosthesis. The study found no statistically significant difference between the C-Leg microprocessor-controlled prosthesis and a standard hydraulic (Mauch) prosthesis in metabolic expenditure (as measured by oxygen consumption) with walking, the primary study endpoint. The investigators (from a group headed by an inventor and patent-holder of the Ossur Rheo microprocessor-controlled leg prosthesis) reported a 5% lower average metabolic consumption with walking using the Ossur Rheo prosthesis and a 2% lower average metabolic consumption with walking using the C-Leg microprocessor-controlled prosthesis compared to a standard hydraulic (Mauch) prosthesis; the latter difference did not achieve statistical significance. There is also a question about the clinical significance of such small differences in metabolic consumption, especially among the younger active amputees for whom microprocessor-controlled prostheses are most commonly prescribed.

The study by Johansson et al. (2005) also evaluated differences in kinetics, kinematics, and electromyographic data between the C-Leg, the Ossur Rheo prosthesis, and standard hydraulic prostheses in walking sessions performed in the laboratory. However, the study fails to show how any identified differences in these intermediate outcomes, while statistically significant, translated into tangible, clinically significant reductions in disability and improvements in function. The small size of the study (n = 8) may limit one's ability to generalize its findings to other amputees. Observed differences between microprocessor-controlled prostheses and the standard hydraulic-based Mauch prosthesis may be due, in part, to the fact that half of the study subjects had been using microprocessor-controlled prostheses as their usual prosthesis prior to study initiation, and only one study subject used the Mauch hydraulic prosthesis as her usual prosthesis prior to study initiation. In addition, laboratory-based evaluation of prostheses and their components may not necessarily reflect the characteristics of the prostheses when used outside of the clinical setting (in real-life situations) and in subjects with more experience with the use of these particular prosthetics.

A study by Datta et al. (2005) comparing the Intelligent Prosthesis microprocessor-controlled prosthesis to conventional pneumatic leg prostheses in 10 amputees found no significant difference in metabolic expenditures (oxygen consumption) at average walking speeds. The study also found no significant differences in temporal and spatial parameters of gait between the two types of knee joints, nor any significant differences in gait by observational video analysis. The study found statistically significantly lower energy expenditures using the Intelligent Prosthesis (0.30 ml/kg·m) compared to the standard pneumatic prosthesis (0.33 ml/kg·m) only when subjects walked at about half normal speed. However, the clinical significance of this degree of difference in metabolic expenditure, which is only manifest at slow walking speeds, is in question, especially for younger, healthy subjects.

A study by Swanson et al. (2005) evaluated body image and function in 8 amputees using the Otto-Bock C-Leg. However, the study did not include a comparison group of individuals using a standard hydraulic-based prosthesis. Thus, no conclusions can be drawn regarding differences in body image and function levels of individuals using the C-Leg and individuals using a standard hydraulic-based prosthesis.

In a randomized controlled cross-over study comparing the C-Leg to a standard mechanical knee (Mauch SNS knee), Orendurff et al. (2006) found that, at measured walking speeds, the C-Leg did not significantly improve gait efficiency in trans-femoral (TF) amputees. Eight TF amputees were randomized to the Mauch SNS knee and the C-Leg microprocessor-controlled knee. The subjects were given a 3-month acclimation period in each knee. Then, their net oxygen cost (mL/kg/m) was measured while they walked overground at four speeds in random order: 0.8 m/s, 1.0 m/s, 1.3 m/s, and self-selected walking speed (SSWS). The C-Leg caused small reductions in net oxygen cost that were not statistically significant compared with the Mauch SNS at any of the walking speeds (p > 0.190). Subjects chose higher SSWSs with the C-Leg compared with the Mauch SNS (mean ± standard deviation = 1.31 ± 0.12 m/s versus 1.21 ± 0.10 m/s, respectively, p = 0.046) but did not incur higher oxygen costs (p = 0.270), which suggests greater efficiency only at their SSWS.

A randomized cross-over study by Segal et al. (2006) comparing the C-Leg to a standard mechanical knee (Mauch SNS knee) found no significant differences in gait biomechanics. After subjects had a 3-month acclimation period with each prosthetic knee, typical gait biomechanical data were collected in a gait laboratory. The investigators reported that, at a controlled walking speed (CWS), peak swing phase knee-flexion angle decreased for the C-Leg group compared with the Mauch SNS group (55.2° ± 6.5° versus 64.41° ± 5.8°, respectively; p = 0.005); the C-Leg group was similar to control subjects' peak swing knee-flexion angle (56.0° ± 3.4°). Stance knee-flexion moment increased for the C-Leg group compared with the Mauch SNS group (0.142 ± 0.05 versus 0.067 ± 0.07 N²m, respectively; p = 0.01), but remained significantly reduced compared with control subjects (0.477 ± 0.1 N²m). Prosthetic limb step length at CWS was less for the C-Leg group compared with the Mauch SNS group (0.66 ± 0.04 versus 0.70 ± 0.06 m, respectively; p = 0.005), which resulted in increased symmetry between limbs for the C-Leg group. Subjects also walked faster with the C-Leg versus the Mauch SNS (1.30 ± 0.1 versus 1.21 ± 0.1 m/s, respectively; p = 0.004). The C-Leg prosthetic limb vertical ground reaction force decreased compared with the Mauch SNS (96.3 ± 4.7 versus 100.3 ± 7.5% body weight, respectively; p = 0.0092). The investigators concluded: "Our study demonstrated minimal differences between the gait biomechanics of subjects walking with the C-Leg compared with the Mauch SNS, a non-computerized prosthetic knee, during constant speed ambulation at approximately TF amputee SSWS."

Klute et al. (2006) found that a microprocessor-controlled knee had no effect on amputees' functional level compared to mechanical knees. To investigate the effect of prosthetic interventions on the functional mobility of lower-extremity amputees, the investigators conducted a cross-over study involving 5 TF amputees comparing a microprocessor-controlled knee (C-Leg) to a non-microprocessor-controlled knee (Mauch SNS). The investigators reported that knee type had no effect on the daily activity level or duration for TF amputees.

A study by Seymour et al. (2007) (n = 13) comparing the C-Leg to various non-microprocessor-controlled knees reported decreased oxygen consumption with the C-Leg. However, this study is of weaker design than the studies by Orendurff et al. (2006) and Segal et al. (2006) described above, in that it was a simple pre-post study, which is of weaker design than a randomized controlled clinical trial. Another recently reported study comparing functional performance of microprocessor-controlled and mechanical knees is also of weaker design (Hafner et al., 2007) (n = 21).

There is limited evidence for the use of microprocessor-controlled knees in patients with unilateral hip disarticulation. Chin et al. (2005) compared the energy expenditure during walking in 3 patients, aged between 51 and 55 years, with unilateral disarticulation of the hip when using the mechanical-controlled stance-phase control knee (Otto Bock 3R15) and the microprocessor-controlled pneumatic swing-phase control knee (Intelligent Prosthesis, IP). All had an endoskeletal hip disarticulation prosthesis with an Otto Bock 7E7 hip and a single-axis foot. The energy expenditure was measured when walking at speeds of 30, 50, and 70 m/min. Two patients showed a decreased uptake of oxygen (energy expenditure per unit time, ml/kg/min) of between 10.3% and 39.6% when using the IP compared with the Otto Bock 3R15 at the same speeds. One did not show any significant difference in the uptake of oxygen at 30 m/min, but at 50 and 70 m/min, a decrease in uptake of between 10.5% and 11.6% was found when using the IP. The use of the IP decreased the energy expenditure of walking in these patients.

The California Technology Assessment Forum (CTAF, 2007) recommended the use of a C-Leg microprocessor-controlled prosthetic knee in otherwise healthy, active K3-K4 community ambulating adults with a trans-femoral amputation from a non-vascular cause (usually trauma or tumor) for whom this prosthesis can be fit and programmed by a qualified prosthetist trained to do so. (Note: Medicare level K3 refers to unlimited community ambulator, while level K4 refers to an active adult or athlete who has the need to function at a K3 level in daily activities.)

A technology assessment of microprocessor-controlled prosthetic knees prepared by the CTAF (2007) noted that the majority of available literature evaluated intermediate outcomes; however, three studies were identified that focused on actual functional outcomes. The CTAF assessment found that the bulk of all of these studies show improvement in outcomes when the microprocessor-controlled knee is used compared to a more traditional non-microprocessor-controlled (NMC) knee. The CTAF assessment reported: "While it is unclear how some of the intermediate outcomes impact clinical or functional outcomes, the functional outcomes of improved gait biomechanics, improved balance, fewer falls, improved performance on an obstacle course, and going down stairs and hills, as well as fewer self-reported falls, have obvious benefits for the prosthetic users. While none of the studies is without flaws, the bulk of the evidence is in favor of the studied microprocessor-controlled prosthetic knees for the populations enrolled." The CTAF assessment concluded that it appears that healthy, active adults with a trans-femoral amputation for a non-vascular cause (usually trauma or tumor) derive functional benefit from wearing a microprocessor-controlled knee.

According to the CTAF assessment, there are questions remaining about microprocessor-controlled prosthetic knees (CTAF, 2007). The CTAF assessment notes that many of the studies attempted to enroll more individuals, but some of their enrollees either could not be fit with the prosthesis or could not adapt to it. It is unclear whether there are particular predictors of who these people might be – is it something to do with the interface between stump and socket, or are there other important predictors? The CTAF assessment also observed that all of the studies were of individuals who were long-term users of an NMC previously; is there a population that should be offered a microprocessor-controlled prosthetic knee as their initial prosthesis? The CTAF assessment commented that most of the studies enrolled active adults, and only a few enrolled moderately active or older dysvascular adults – is there a group of moderately active adults whose activity level would improve even more with this technology? "Perhaps these researchers would have observed even greater differences if they had studied somewhat less active individuals with the potential for enhanced mobility with a more responsive prosthesis."

The Proprio Foot (Ossur, Alsio Viejo, CA) is a microprocessor-controlled prosthetic ankle-foot system for lower-extremity amputees. It is designed to adjust to uneven ground, ramps, stairs, and other environmental obstacles. It consists of 4 parts:

an energy storing prosthetic foot,
a battery-powered prosthetic ankle that dorsiflexes and plantarflexes during swing phase,
a microprocessor that controls dorsiflexion and plantarflexion in real time and in response to changes in the underlying terrain by sampling ankle position more than 1,000 times per second, and
a lithium-ion battery and charger.

Its Terrain Logic software permits the adjustment to surface gradients of up to 20 degrees.

Published evidence on microprocessor-controlled ankle-foot orthoses is limited to small studies examining the short-term effects on kinematic parameters, which are considered short-term surrogate outcomes (Fradet et al., 2010; Alimusaj et al., 2009; and Wolf et al., 2009). However, there is a lack of data on other relevant aspects of ambulation (e.g., daily step frequency, estimated step distance, stopping and standing safely, adaptation to different walking speeds, and fall frequency). In addition, there is a lack of reliable published evidence of the impact of microprocessor-controlled ankle-foot prostheses compared to standard ankle-foot prostheses on other relevant outcomes, including energy expenditure, cognitive requirements of ambulation, and patient-centered outcomes (quality of life, impact on activities of daily living, work, and work performance).

A systematic evidence review prepared for the Washington State Health Technology Advisory Committee (Henrickso et al., 2011) found no studies of the Proprio Foot or other microprocessor-controlled foot devices that met inclusion criteria for the systematic evidence review. The review stated that "[t]here is insufficient evidence to evaluate the comparative effectiveness, safety, or cost-effectiveness of microprocessor-controlled foot devices."

Bellmann et al. (2012) examined the immediate biomechanical effects after the transition to a new microprocessor-controlled prosthetic knee joint. Subjects were men (n = 11; mean age ± SD, 36.7 ± 10.2 years; Medicare functional classification level, 3 to 4) with unilateral transfemoral (TF) amputation. Two microprocessor-controlled prosthetic knee joints, the C-Leg and a new prosthetic knee joint, Genium, were used in this study. Main outcome measures included static prosthetic alignment, time-distance parameters, kinematic and kinetic parameters, and center of pressure. After a half-day training and an additional half-day accommodation, improved biomechanical outcomes were demonstrated by the Genium: lower ground reaction forces at weight acceptance during level walking at various velocities, increased swing phase flexion angles during walking on a ramp, and level walking with small steps. Maximum knee flexion angle during the swing phase at various velocities was nearly equal for Genium. Step-over-step stair ascent with the Genium knee was more physiologic, as demonstrated by a more equal load distribution between the prosthetic and contralateral sides and a more natural gait pattern. When descending stairs and ramps, knee flexion moments with the Genium tended to increase. During quiet stance on a decline, subjects using Genium accepted higher loading of the prosthetic side knee joint, thus reducing same-side hip joint loading as well as postural sway. The authors concluded that, in comparison to the C-Leg, the Genium demonstrated immediate biomechanical advantages during various daily ambulatory activities, which may lead to an increase in the range and diversity of activity of people with above-knee amputations. Results showed that the use of the Genium facilitated more natural gait biomechanics and load distribution throughout the affected and sound musculoskeletal structure. This was observed during quiet stance on a decline, walking on level ground, and walking up and down ramps and stairs.

Bellmann et al. (2012) reported a biomechanical study to assess objective gait measurements and calculate joint kinematics and kinetics as subjects ascended stairs. The investigators stated that results demonstrated that climbing stairs step over step is more biomechanically efficient for an amputee using the Genium prosthetic knee than the previously possible conventional method, where the extended prosthesis is trailed as the amputee executes one or two steps at a time. The investigators explained that there is a natural amount of stress on the residual musculoskeletal system, and it has been shown that the healthy contralateral side supports the movements of the amputated side. The mechanical power that the healthy contralateral knee joint needs to generate during the extension phase is also reduced. Similarly, there is near-normal loading of the hip joint on the amputated side.

Highsmith et al. (2016) conducted a study to determine if laboratory-determined benefits of Genium are detectable using common clinical assessments and if there are economic benefits associated with its use. This study utilized a randomized AB crossover design with a 60-day follow-up, including cost-effectiveness analysis. Twenty transfemoral amputee (TFA) patients tested both knees in mobility and preference measures. Incremental cost-effectiveness ratios (ICER) were calculated based on performance measures. Stair Assessment Index scores improved with Genium. Mean stair completion times and descent stepping rates were not different between knees. Stair ascent stepping rate for the C-Leg was greater compared with Genium (p = 0.04). Genium use decreased Four Square Step Test completion time and increased functional level and step activity (p ≤ 0.05). Further, Genium use improved (p ≤ 0.05) function and safety in 3 out of 5 Activities of Daily Living (ADL) survey domains. Finally, more subjects preferred Genium following testing. Functional measures were used to calculate ICERs. ICER values for Genium fall within established likely-to-accept value ranges. The authors concluded that, compared with C-Leg, Genium use improved stair walking performance, multi-directional stepping, functional level, and perceived function. In this group of community ambulators with TFA, Genium was preferred, and while more costly, it may be worth funding due to significant improvements in functional performance with ADLs.

Kannenberg et al. (2013) conducted a study with 10 unilateral transfemoral amputees (Medicare Functional Classification level 3 and 4) to investigate whether the Genium Knee is able to further improve the perceived safety and difficulty of 45 activities of daily living compared with the C-Leg. Results show that after 3 months of Genium use, it could be shown that perceived safety improved in 27 activities (60%) and perceived difficulty improved in 24 activities (53%). Improvements were seen in the categories of Family and Social Life as well as Mobility and Transportation. The authors concluded that these findings create the basis for further improvement of independence and participation of amputees in family, business, and social life by using the Genium Bionic Prosthetic Knee.

The Prosthesis Evaluation Questionnaire (PEQ) evaluates prosthetic-related function and quality of life. The PEQ has been used in microprocessor knee literature to compare perceptive responses between C-Leg and non-microprocessor-controlled knee mechanisms. Highsmith et al. (2014) studied perceived differences in prosthetic function and quality of life following accommodation with a Genium compared with a C-Leg. Twenty people with TFA participated in this randomized crossover study. C-Leg users randomized to test first with their own C-Leg or a Genium then crossed over into the other condition for repeated testing. Non-knee prosthetic attributes were held constant. Participants completed the PEQ for each knee condition to compare perceived differences in prosthetic function and quality of life. Genium use resulted in significant improvements (p ≤ 0.05) in the following scales: Perceived Response, Social Burden, Utility, and Well-Being, as well as in individual items related to improved standing comfort, satisfaction with walking ability, and improved gait in tight spaces, hills, and slippery surfaces (p < 0.025). As a result of using the Genium, patients perceive improvements in prosthetic-related quality of life and function. Further, patients perceive improvements in very specific mobility functions related to ambulation in complex settings.

Highsmith et al. (2016) conducted a study using a randomized experimental crossover of TFA patients using Genium and C-Leg microprocessor knees (MPKs) (n = 20). Biomechanical gait analysis by 3D motion tracking with floor-mounted force plates of TFA patients ambulating at different speeds on 5° ramps was completed. Knee moment differences of angle (DoA) were significantly different between MPK conditions in the slow and fast uphill as well as the slow and self-selected downhill conditions. In a sample of high-functioning TFA patients, Genium knee system accommodation and use improved knee moment symmetry in slow-speed walking up and down a five-degree ramp compared with C-Leg. Additionally, the Genium improved knee moment symmetry when walking downhill at a comfortable speed. These results likely have applications in other patients who could benefit from more consistent knee function, such as older patients and others who have slower walking speeds.

Lura et al. (2015) used a randomized experimental crossover of persons with transfemoral amputation using the Genium and C-Leg microprocessor knees (n = 25), with an observational sample of non-amputee controls (n = 5). Gait analysis by 3D motion tracking of subjects ambulating at different speeds on level ground and on 5° and 10° ramps was completed. The investigators found that the use of the Genium resulted in a significant increase in peak knee flexion for swing (5°, p < 0.01, d = 0.34) and stance (2°, p < 0.01, d = 0.19) phases relative to C-Leg use. There was a high degree of variability between subjects, and significant differences still remain between the Genium group and the control group's knee flexion angles for most speeds and slopes. The investigators concluded that the Genium knee generally increases flexion in swing and stance, potentially decreasing the level of impairment for persons with transfemoral amputation. The investigators stated that this study demonstrates functional differences between the C-Leg and Genium knees to help prosthetists determine if the Genium will provide functional benefits to individual patients.

Highsmith et al. (2014) conducted a project to determine if walking speed increases and if ambulatory-related exertion decreases in transfemoral amputees (TFAs) using the novel Genium microprocessor knee. A second purpose was to determine if directional and postural control improves with the Genium knee. Twenty-five (n = 25) subjects consented to participate in the study; 20 subjects had unilateral TFA, and 5 non-amputees served as controls. A randomized A–B crossover design was used. Gait speed increases in TFAs were not observed in preliminary analyses. However, gait biomechanical improvements, such as swing phase knee flexion angle consistency, were reported. Such improvements may be perceptible to the user in short and mid-distance walking tests. Significant differences were observed between TFAs and controls for walking test times, but no differences were found between knee systems. A trend of decreased perceived exertion was observed with Genium compared with C-Leg, but differences did not reach significance. Controls consistently rated greater exertion during walking, possibly as a result of walking faster. TFAs show considerable impairment compared to controls in directional control, and the Genium tends to improve rearward-directed control. The C-Leg significantly improves control over the prosthetic forefoot. Postural control was not different between the two knee systems. During short to medium distances, the Genium sustains walking speed improvements realized by the C-Leg but at potentially decreased levels of perceived exertion. However, C-Leg use results in improved anterolateral directional control compared with Genium, likely due to its toe load requirement. Conversely, Genium use tended to improve control in rearward directions.

Powered prosthetic devices, which utilize signals from muscle activity in the remaining limb to bend and straighten the device, are being researched. These devices use sensors and electronics to process data and control movement and power of the knee. Examples of these devices include the Power Knee (Ossur, Foothill Ranch, CA). According to the manufacturer, the Power Knee is the first motorized prosthetic knee available for TF amputees weighing up to 275 pounds. It is designed for use by functional level K3 individuals with a documented co-morbidity in their sound limb or spine and by bilateral amputees. The knee houses an electro-mechanical actuator that actively initiates and controls all aspects of the user's gait. It also provides powered knee flexion and extension under full user load. The motor initiates appropriate movement and function based on data collected through accelerometers, gyroscopes, a torque sensor, and a load sensor. When users walk with the Power Knee, the device samples knee position and loads at the rate of 1,000 times per second to provide appropriate power for the user in all three phases of the extension portion of the gait cycle. At heel strike, the motor permits and encourages active stance flexion, functioning to replace foot/ankle, knee, and hip muscles. This allows a flexion moment that more accurately replicates able-bodied gait while simultaneously providing full support and stability for users. The motor-controlled knee flexion at heel strike also reduces the impact on users, permitting a smoother transition from the sound side to the prosthetic side, facilitating a more symmetrical gait. When users walk down declines and stairs, the Power Knee allows leg-over-leg descent. When users stand still, it permits them to stand with the prosthetic knee flexed, as the electro-mechanical motor actively supports the user's weight. The Power Knee’s motor actively extends the knee from a flexed (seated) position into an extended (standing) one. The motor provides an affirmative, dynamic response that resists gravity, lifting the user up. Upon initial use, a practitioner must program and align the knee. Once programming and alignment are complete, the user needs only to press the power button to use the device. The user must also charge the lithium-polymer batteries that power the device. A 3.5-hour charge is recommended to ensure maximum battery life. On a full charge, battery life is up to 12 hours, depending on the user's activities. Each Power Knee comes with two batteries.

The BiOM is a below-knee robotic prosthesis designed for use by individuals with lower extremity amputation. This prosthesis, which includes the foot, ankle, and lower calf, uses robotics to replicate the calf muscles and Achilles tendon. With each step, the BiOM provides a powered push-off that propels the wearer forward. Powered plantar flexion enables the prosthesis to normalize the gait and metabolic demands to those of non-amputees. With its bionic functionality, this prosthesis can resolve clinical issues faced by amputees, including tiredness, slowness, and a feeling of being unstable on their feet. The robotic muscle power provided by the BiOM during toe-off requires less energy from the user. It also provides more power when the user walks faster and less when the user walks slower, which produces a natural gait at variable speeds. Users are able to negotiate stairs and inclines with increased confidence and stability due to improved articulation and the design’s ability to mechanically yield and conform.

Mancinelli et al. (2011) stated that passive-elastic foot prostheses cannot produce power. Consequently, passive-elastic foot prostheses are limited in their ability to enable a biologically realistic gait pattern in transtibial amputees. This shortcoming results in difficulties in balance and walking and leads to high levels of oxygen consumption during locomotion. A powered prosthesis has the potential for overcoming these problems and allowing transtibial amputees to achieve a biologically realistic gait pattern. In this study, these researchers compared the effects of the Ceterus by Ossur, a traditional passive-elastic prosthesis, with those of the PowerFoot Biom (iWalk, Cambridge, MA), a recently developed powered prosthesis. Gait biomechanics and metabolic cost were compared in a group of 5 transtibial amputees during level-ground walking. The results provided preliminary evidence that the use of a powered prosthesis leads to a decrease in the level of oxygen consumption during ambulation due to improvements in ankle kinematics and kinetics, primarily during late stance. An average decrease in oxygen consumption of 8.4% was observed during the study when subjects used the PowerFoot compared to the Ceterus. An average increase of 54% was observed in the peak ankle power generation during late stance. The authors concluded that these findings suggested that powered prostheses have the potential for significantly improving ambulation in transtibial amputees.

Aldridge and colleagues (2012) noted that during stair ascent (STA) persons with transtibial amputation (TTA) typically adopt a hip strategy to compensate for the limited ankle motion and joint power that is characteristic of conventional energy storing and returning (ESR) prosthetic feet. The purpose of this investigation was to determine if providing ankle power via a powered prosthetic device (BiOM) normalized STA kinematics and kinetics. A total of 11 individuals with TTA participated in 2 STA gait analysis sessions:

using an ESR foot, and
using the BiOM.

Eleven height- and weight-matched able-bodied controls (CONT) were also assessed. Lower extremity peak kinematic and kinetic values were calculated at a self-selected and controlled cadence (80 steps/min). Increased prosthetic limb peak ankle plantar flexion and push-up power were observed while using the BiOM compared to the ESR. Peak ankle power was not significantly different between the BiOM and CONT, indicating normalization of ankle power generation. However, peak ankle plantar flexion was significantly lower than CONT. Limb asymmetries, including greater prosthetic limb hip flexion and power during stance, and decreased prosthetic limb knee power during stance, were observed in the BiOM and ESR conditions. The authors concluded that these findings suggested that the BiOM successfully increased ankle motion and restored ankle power during stair ascent (STA). These differences did not, however, reduce the use of a hip strategy while ascending stairs. They stated that additional device-specific training may be necessary to utilize the full benefits of the device.

However, due to the small sample sizes in these studies, it is unclear if these preliminary findings would be observed in the general transtibial amputee (TTA) population. Further investigation is needed to establish a meaningful clinical outcome benefit of the iWalk BiOM prosthetic foot over the conventional ankle-foot prosthesis. Furthermore, the Washington State Health Care Authority (2011) does not cover microprocessor-controlled lower limb prostheses for the feet and ankle (e.g., the iWalk PowerFoot BiOM).

Wearable robotic exoskeletons have been developed to reportedly help individuals ambulate despite partial or complete paraplegia. The devices include fitted braces for the legs and upper body with motorized hip and knee joints, a backpack containing a computer and rechargeable batteries, an array of upper body motion sensors, and a computer-based wireless control system worn on the individual’s wrist. Crutches are also used to provide the user with additional stability when walking, standing, or rising from a chair. Typically, these devices are indicated for use by people with paraplegia due to spinal cord injuries at levels T7 to L5 when accompanied by a specially trained caregiver, and for individuals with spinal cord injuries at levels T4 to T6, where the device is limited to use in rehabilitation institutions. Examples of devices include, but may not be limited to, the following: ESKO GT system (for use only in rehabilitation institutions), Indego powered exoskeleton, and ReWalk personal system. Generally, the use of these devices requires that individuals are able to stand using an assistive device (e.g., standing frame) and that their hands and shoulders are able to support crutches or a walker.

Federici et al. (2015) reviewed the clinical effectiveness of various types of active, powered, wearable lower limb exoskeletons for the rehabilitation of gait disorders in paraplegic patients resulting from central nervous system lesions caused by, for example, spinal cord injuries (SCIs) or cerebrovascular accidents (CVAs). The most commonly studied exoskeletons were the HAL, ReWalk, and the Vanderbilt lower limb exoskeleton. Studies of exoskeleton use in neurorehabilitation contexts have mostly evaluated the safety of the devices, the physical and cognitive effort required to use them, how easy it is to learn to use them, and how effectively they enhance patients’ gait. The studies confirmed that the HAL, Tibion Bionic Technologies, and Ekso devices were safe to use in controlled environments and with the assistance of expert professionals (i.e., physiotherapists). The authors found no studies evaluating the effectiveness of exoskeletons outside laboratory or clinical settings, and hence no evidence of their effectiveness in everyday living environments, for example, for walking on rough surfaces such as a sidewalk or a staircase with uneven steps. The authors noted that there is a dearth of experimental evidence demonstrating that exoskeletons are more effective than other rehabilitative techniques and technologies. They also noted that none of the publications reviewed analyzed users’ experiences with an exoskeleton in activities of daily living.

Louie et al. (2015) systematically reviewed the literature to determine the gait speed attained by individuals with SCI when using a powered exoskeleton to walk, factors influencing this speed, and characteristics of studies involving a powered exoskeleton (e.g., inclusion criteria, screening, and training processes). A systematic search in computerized databases was conducted to identify articles that reported on walking outcomes when using a powered exoskeleton. Individual gait speed data from each study was extracted. Pearson correlations were performed between gait speed and

age,
years post-injury,
injury level, and
number of training sessions.

Fifteen articles met inclusion criteria, 14 of which investigated the powered exoskeleton as an assistive device for non-ambulatory individuals and one which used it as a training intervention for ambulatory individuals with SCI. The mean gait speed attained by non-ambulatory participants (n = 84) while wearing a powered exoskeleton was 0.26 m/s, with the majority having a thoracic-level motor-complete injury. Twelve articles reported individual data for the non-ambulatory participants, from which a positive correlation was found between gait speed and

age (r = 0.27, 95% CI: 0.02 to 0.48, p = 0.03, 63 participants),
injury level (r = 0.27, 95% CI: 0.02 to 0.48, p = 0.03, 63 participants), and
training sessions (r = 0.41, 95% CI: 0.16 to 0.61, p = 0.002, 55 participants).

The authors stated that this systematic review has some limitations. The level of evidence in the current literature is limited to studies with a small number of participants. In addition, a true control group (without a device to walk) is not relevant as most participants would not have been able to walk without the exoskeleton; however, future studies could compare different orthotic, FES, or exoskeleton systems. There was heterogeneity in the study characteristics (device, control of stepping, training duration, outcome measurement), which made it challenging to compare results and reduces the ability to generalize results. However, the authors attempted to overcome this by aggregating participant data to allow statistical analysis to explore correlations between participant characteristics and outcomes. The authors stated that, in the future, it would be useful for studies to report on the exact intensity of training, using such measures as number of steps or walking time.

Lajeunesse et al. (2016) stated that rehabilitation professionals have little information concerning lower limb exoskeletons for people with paraplegia.This study has 4 objectives:

outline the characteristics of the exoskeletons' design and their usefulness evidence as assistive mobility devices in the community for the ReWalk, Mina, Indego, Ekso (previously known as the eLEGS) and Rex;
document functional mobility outcomes of using these exoskeletons;
document secondary skills and benefits achieved with these exoskeletons, safety, user satisfaction and applicability in the community; and
establish level of scientific evidence of the selected studies.

These researchers performed a systematic review of the literature (January 2004 to April 2014) using the databases PubMed, CINAHL and Embase and groups of keywords associated with "exoskeleton", "lower limb" and "paraplegia". A total of 7 articles were selected. Exoskeleton use is effective for walking in a laboratory but there are no training protocols to modify identified outcomes over the term usage (ReWalk: 3 months, Mina: 2 months and Indego: 1 session). Levels of evidence of selected papers are low. The authors concluded that the applicability and effectiveness of lower limb exoskeletons as assistive devices in the community have not been demonstrated. They stated that more research is needed on walking performance with these exoskeletons compared to other mobility devices and other training contexts in the community. Characteristics of the exoskeletons' design and their usefulness evidence as assistive mobility devices in the community were addressed for the Rewalk, Mina, Indego, Ekso and Rex; ReWalk, Indego and Mina lower limb exoskeletons were effective for walking in a laboratory for individuals with complete lower-level SCI. The ReWalk has the best results for walking, with a maximum speed of 0.51 m/s after 45 sessions lasting 60 to 120 mins; it is comparable to the average speed per day or per week in a manual wheelchair. The level of scientific evidence is low. These investigators stated that further studies are needed to provide more information about performance over the longer term when walking with an exoskeleton, compared to wheelchair mobility, the user's usual locomotion, the use of different exoskeletons or the training context in which the exoskeleton is used.

An industry-funded consulting firm published a systematic evidence review (Miller et al., 2016) that included a total of 14 studies (8 ReWalk, 3 Ekso, 2 Indego, and 1 unspecified exoskeleton) representing 111 patients included in the analysis. Training programs were typically conducted three times per week, lasting 60 to 120 minutes per session, for 1 to 24 weeks. Ten studies utilized flat indoor surfaces for training, while 4 studies incorporated complex training, including walking outdoors, navigating obstacles, climbing and descending stairs, and performing activities of daily living. Following the exoskeleton training program, 76% of patients were able to ambulate with no physical assistance. The weighted mean distance for the 6-minute walk test was 98 meters. The physiological demand of powered exoskeleton-assisted walking was 3.3 metabolic equivalents, and the rating of perceived exertion was 10 on the Borg 6 to 20 scale, comparable to self-reported exertion of an able-bodied person walking at 3 miles per hour. Improvements in spasticity and bowel movement regularity were reported in 38% and 61% of patients, respectively. No serious adverse events occurred. The incidence of falls at any time during training was 4.4%, all occurring while tethered using a first-generation exoskeleton, and none resulting in injury. The incidence of bone fractures during training was 3.4%. The authors asserted that these risks have since been mitigated with newer generation exoskeletons and refinements to patient eligibility criteria. The authors noted that, as with any meta-analysis, interpretation of outcomes may be confounded by issues related to individual study designs and by issues inherent in the analysis of summary data. There was considerable variation in the consistency of outcome reporting among studies. The development of minimum reporting standards for powered exoskeleton clinical trials is recommended to facilitate comparisons among studies. Additionally, the number of studies limited the ability to explore sources of heterogeneity such as age, level of injury, and duration of injury.

This analysis was funded by ReWalk, and the authors are from "Miller Scientific Consulting." The meta-analysis combined results using a variety of exoskeleton devices, subject characteristics, and settings, and reported “considerable variation in outcome reporting among studies” and substantial heterogeneity among most study outcomes. A major drawback of this meta-analysis was a lack of critical assessment of the quality of the studies included in the analysis.

The ReWalk exoskeleton (Argo Medical Technologies Ltd, Marlborough, MA) is designed for persons with a spinal cord injury (SCI) who retain upper-limb strength and mobility to manage stabilizing crutches. It is worn outside clothing and weighs 44 pounds. It consists of an upper-body harness, lower-limb braces, motorized joints, ground-force sensors, a tilt sensor, a locomotion-mode selector, and a backpack carrying a computerized controller and rechargeable battery. The device is strapped to the user at the waist, alongside each lower limb, and at the feet. Ordinary crutches help maintain stability. The ReWalk exoskeleton comes in 2 sizes:

one that fits persons 5 feet 3inches to 5 feet 9 inches in height, and
one that accommodates persons up to 6 feet 3 inches.

The ReWalk can be worn by individuals weighing up to 220 pounds. Two types of the ReWalk exoskeletons are available:

the institutional version, the ReWalk-I, which is designed for rehabilitation centers and physician private practices, and
a personal version, the ReWalk-P, which is designed for an individual’s sole use.

According to the product labeling, the ReWalk is currently indicated for use only with supervision of a specialty-trained companion.

The ReWalk system comprises a set of computer-controlled, motorized leg braces that restore the ability to walk with crutches to patients with paraplegia who retain the ability to use their hands and shoulders for walking with crutches and who have good bone density and cardiovascular health (ECRI, 2013). The wearable support system uses an array of sensors and proprietary computer algorithms to analyze body movements and manipulate the motorized leg braces to help users maintain proper gait using crutches for walking, climbing stairs, and other movements. The onboard computer, sensor array, and rechargeable batteries that power the wearable exoskeleton are contained in a backpack that users wear in addition to the leg braces.

In a pilot study, Zeilig et al. (2012) evaluated the safety and tolerance of the ReWalk exoskeleton ambulation system in people with spinal cord injury (SCI). Measures of functional ambulation were assessed and correlated to neurological spinal cord level, age, and duration since injury. A total of 6 volunteer participants were recruited from a follow-up outpatient clinic. Safety was assessed concerning falls, skin condition, spine and joint status, blood pressure, pulse, and electrocardiography (ECG). Pain and fatigue were graded by participants using a visual analog scale pre- and post-training. Participants completed a 10-statement questionnaire regarding safety, comfort, and secondary medical effects. After being able to walk 100 meters, timed up and go, distance walked in 6 minutes, and a 10-meter timed walk were measured. There were no adverse safety events. The use of the system was generally well-tolerated, with no increase in pain and a moderate level of fatigue after use. Individuals with a lower level of SCI performed walking more efficiently. The authors concluded that volunteer participants were able to ambulate with the ReWalk for a distance of 100 meters, with no adverse effects during the course of an average of 13 to 14 training sessions. The participants were generally positive regarding the use of the system. Moreover, the authors stated that the potential benefits of the ReWalk include improved functional mobility, cardiovascular and respiratory status, bone metabolism, and bowel and bladder function, as well as a reduction in spasticity and neuropathic pain, but efficacy still needs to be demonstrated in a larger study. Additionally, these researchers noted that this study did not include any female subjects, individuals with tetraplegia, children, or older adults; future large-scale inclusive studies are needed.

In an open, non-comparative, non-randomized study, Esquenazi et al. (2012) evaluated the safety and performance of ReWalk in enabling people with paraplegia due to SCI to carry out routine ambulatory functions. All 12 subjects completed the active intervention; 3 remained in long-term follow-up. After training, all subjects were able to independently transfer and walk without human assistance while using the ReWalk for at least 50 to 100 meters continuously, for a period of at least 5 to 10 minutes, with velocities ranging from 0.03 to 0.45 m/sec (mean of 0.25 m/sec). Excluding 2 subjects with considerably reduced walking abilities, average distances and velocities improved significantly. Some subjects reported improvements in pain, bowel and bladder function, and spasticity during the trial. All subjects had strong positive comments regarding the emotional and psychosocial benefits of using ReWalk. The authors concluded that the ReWalk holds considerable potential as a safe ambulatory powered orthosis for motor-complete thoracic-level SCI patients. Most subjects achieved a level of walking proficiency close to that needed for limited community ambulation. A high degree of performance variability was observed across individuals. Some of this variability was explained by the level of injury, but other factors have not been completely identified. The authors stated that further development and application of this rehabilitation tool to other diagnoses are expected in the future.

Spungen et al. (2013) reported on a single-group, pre/post intervention pilot study to determine the number of sessions and level of assistance needed to execute standing, walking, and stair climbing skills with the ReWalk powered exoskeleton. Seven persons with motor-complete paraplegia were studied over an average of 45 ± 20 sessions. Sessions consisted of 1 to 2 hours of standing and overground ambulation for 3 sessions per week. All 7 participants learned to perform sit-to-stand, stand-to-sit, and to walk 50 to 166 meters in 6 minutes with none (n=4) to varying levels (n=3) of assistance. Four of the 7 participants learned to ascend and descend five or more stairs with assistance, and these 4 also achieved some outdoor-specific walking skills. No relationship with the achievement of exoskeletal-assisted mobility skills was found with the duration or level of SCI; however, the participant with the highest cord lesion (thoracic level 1) did require the most assistance. The authors concluded that these preliminary results suggest that exoskeletal-assisted walking and other mobility skills can be performed independently by persons with motor-complete SCI.

Fineberg et al. (2013) conducted a study using vertical ground reaction force (vGRF) to show the magnitude and pattern of mechanical loading in persons with spinal cord injury (SCI) during powered exoskeleton-assisted walking with ReWalk. The authors conducted a cross-sectional study to analyze vGRF during powered exoskeleton-assisted walking compared with vGRF of able-bodied gait. Six persons with thoracic motor-complete SCI (T1-T11 AIS A/B) and three age-, height-, weight-, and gender-matched able-bodied volunteers participated. SCI participants were trained to ambulate over ground using a ReWalk. vGRF was recorded using the F-Scan system (TekScan, Boston, MA, USA). Peak stance average (PSA) was computed from vGRF and normalized across all participants by percent body weight. Peak vGRF was determined for heel strike, mid-stance, and toe-off. Relative linear impulse and harmonic analysis provided quantitative support for the analysis of powered exoskeletal gait. The investigators reported that participants with motor-complete SCI, ambulating independently with a ReWalk, demonstrated mechanical loading magnitudes and patterns similar to able-bodied gait. Harmonic analysis of the PSA profile by Fourier transform contrasted the frequency of stance phase gait components between able-bodied and powered exoskeleton-assisted walking.

Asselin et al. (2015) reported on heart rate and oxygen demand of powered exoskeleton-assisted walking in persons with paraplegia. As part of an ongoing clinical study, eight non-ambulatory persons with paraplegia were trained to ambulate with a ReWalk powered exoskeleton. Measurements of oxygen uptake (VO2) and heart rate (HR) were recorded for 6 minutes each during each maneuver while sitting, standing, and walking. The average value of VO2 during walking (11.2 ± 1.7 ml/kg/min) was significantly higher than those for sitting and standing (3.5 ± 0.4 and 4.3 ± 0.9 ml/kg/min, respectively; p < 0.001). The HR response during walking was significantly greater than that of either sitting or standing (118 ± 21 versus 70 ± 10 and 81 ± 12 beats per minute, respectively: p < 0.001). The authors stated that these findings suggest that routine use of this device to increase activity expenditure may be expected to have positive cardiopulmonary and metabolic benefits, although the results of this study did not address long-term changes in oxygen demand with habitual use.

White et al. (2015) examined short-term changes in patients’ joint range of motion as a consequence of one week of intensive powered exoskeleton training as part of a physiotherapy program. Sixteen participants aged 21-69 years with spinal cord injury between C3 and T12 (ASIA Impairment Scale A-D) visited the therapy center. Passive range of motion of ankle dorsiflexion, hip extension, and shoulder internal rotation and extension was measured using goniometry. Participants then undertook the training program, which included the use of parallel bars, crutches, different surfaces, and stairs/sitting/standing/walking. The program was supplemented by the use of functional electrical stimulation, far-infrared heat therapy, and physiotherapy for exercise preparation. After five days, range of motion was re-measured. Paired t-tests were run on bilaterally averaged pre- and post-ranges of motion, with an accepted significance value of p≤0.05. Mean dorsiflexion increased from 1.7° (plantigrade = 0) to 6.9° (t(11) = -6.3; p < 0.001). Mean hip extension increased from 8.2° to 14.1° (t(13) = -3.5; p = 0.017). There were no significant changes to shoulder extension (pre-64.7, post-66.7°, n = 9) or shoulder internal rotation (pre-74.3, post-78.9°, n = 11). The authors concluded that, although this was a pilot study and lacked a control condition, the addition of ReWalk technology was novel as part of a physiotherapy program. The authors stated that participation in the training program appeared to result in significant increases in ankle dorsiflexion and hip extension, which may be beneficial for all types of ongoing upright weight-bearing therapy in this population.

Yang et al. (2015) sought to evaluate exoskeletal-assisted walking (EAW) velocity, number of sessions, and level of assistance (LOA) and the relationships among them. The secondary aims were to report on safety and the qualitative analysis of gait and posture during EAW in a hospital setting. Twelve individuals with SCI ≥ 1.5 years who were wheelchair users participated. They wore a powered exoskeleton (ReWalk; ReWalk Robotics, Inc., Marlborough, MA) with Lofstrand crutches to complete 10-meter (10 MWT) and 6-minute (6MWT) walk tests. LOA was defined as modified independence (MI), supervision (S), minimal assistance (Min), and moderate assistance (Mod). Best effort EAW velocity, LOA, and observational gait analysis were recorded. Seven of 12 participants ambulated ≥ 0.40 m/s. Five participants walked with MI, 3 with S, 3 with Min, and 1 with Mod. Significant inverse relationships were noted between LOA and EAW velocity for both 6 MWT (Z value = 2.63, Rho = 0.79, p = .0086) and 10 MWT (Z value = 2.62, Rho = 0.79, p = .0088). There were 13 episodes of mild skin abrasions. MI and S groups ambulated with a 2-point alternating crutch pattern, whereas the Min and Mod groups favored a 3-point crutch gait. The authors concluded that the ReWalk is a safe device for in-hospital ambulation.

Talaty et al. (2013) reported preliminary analysis of how walking kinematics differed across 12 subjects using the ReWalk. All subjects met basic criteria to be able to use the ReWalk, including sufficient bone mineral density, leg passive range of motion, strength, body size, and weight limits. All subjects received approximately the same number of training sessions. However, there was a wide distribution in walking ability. Walking velocities ranged from under 0.1 m/s to approximately 0.5 m/s. The authors stated that this variability was not completely explained by injury level. The remaining sources of that variability are not clear at present.

Raab et al. (2016) reported on a single case study investigating to what extent the quality of life (QOL) of patients with spinal cord injury can be influenced by training with an exoskeleton. The study was carried out at a hospital for neurological rehabilitation in Germany. One patient (male, 22 years), initially unable to walk independently after traumatic spinal cord injury with a neurological level of Th11 (ASIA Impairment Scale C), was recruited for this study 1 year after injury. The progress of the first 6 months of ReWalk training was documented, and as a primary outcome measure, QOL was measured with the SF-36 questionnaire. Secondary outcome measures included the ASIA scale, Berg Balance Scale, and Dynamic Gait Index. The authors reported that, at the end of the study period, the patient was able to walk independently supervised by one person. QOL, mobility, risk of falling, motor skills, and control of bladder and bowel functions were improved. A positive effect of robot-assisted gait training on various areas of QOL was shown. The authors stated that subsequent studies should aim to verify this effect through a higher number of patients and across different injury levels.

Benson et al. (2016) conducted a longitudinal, prospective, self-controlled study to assess the feasibility of conducting a well-powered trial evaluating the neurological and functional effects of using an exoskeleton in individuals with chronic motor complete or incomplete spinal cord injury at a UK specialist spinal cord injuries center. Enrolled subjects were assigned to 20 ReWalk exoskeleton training sessions over a 10-week training period. Feasibility measures, clinical and mobility outcome measures, and measures appraising subjects' disability and attitude towards assistive technology were assessed before, during, and after the study. Descriptive statistics were applied. Out of 60 candidates, 10 (17%) were enrolled, and 5 (8%) completed the training program. Primary reasons for not enrolling were ineligibility (n = 24, 40%) and limited interest in engaging in a 10-week training program (n = 16, 27%); 5 out of 10 enrolled subjects experienced grade I/II skin aberrations. While walking speeds were higher and walking distances were longer in all exoskeleton users compared with non-use, the exoskeleton did not generally meet subjects' high expectations in terms of perceived benefits. The authors concluded that conducting a controlled trial evaluating the benefits of using exoskeletons that require a lengthy user commitment to training for individuals with chronic motor complete or incomplete spinal cord injury comes with considerable feasibility challenges. Vigilance is required for preventing and detecting medical complications in spinal cord injury exoskeleton users.

Lonini et al. (2016) noted that clinical scores for evaluating walking skills with lower limb exoskeletons are often based on a single variable, such as distance walked or speed, even in cases where a host of features are measured. In a pilot study, these researchers ascertained how to combine multiple features such that the resulting score has high discriminatory power, particularly with few patients. A new score is introduced that allows quantifying the walking ability of patients with SCI when using a powered exoskeleton. A total of 4 SCI patients were trained to walk over ground with the ReWalk exoskeleton. Body accelerations during the use of the device were recorded by a wearable accelerometer, and 4 features to evaluate walking skills were computed. The new score is the Gaussian naive Bayes surprise, which evaluates patients relative to the features' distribution measured in 7 expert users of the ReWalk. These investigators compared their score based on all the features with a standard outcome measure, which is based on the number of steps only. All 4 patients improved over the course of training, as their scores trended towards the expert users' scores. The combined score (Gaussian naive surprise) was considerably more discriminative than the one using only walked distance (steps). At the end of training, 3 out of 4 patients were significantly different from the experts, according to the combined score (p < 0.001, Wilcoxon Signed-Rank Test). In contrast, all but 1 patient were scored as experts when the number of steps was the only feature. The authors concluded that integrating multiple features could provide a more robust metric to measure patients' skills while they learn to walk with a robotic exoskeleton; testing this approach with other features and more subjects remains as future work.

Khan et al. (2019) reported on a study where participants with chronic (> 1 year) motor complete or incomplete spinal cord injury, who were primarily wheelchair users, were trained to walk in the ReWalk powered exoskeleton for 12 weeks. Measures were taken before, during, immediately after, and 2-3 months after training. Measures included walking progression, sitting balance, skin sensation, spasticity, and strength of the corticospinal tracts. Twelve participants were enrolled, with 10 completing training. The investigators reported that the progression in training required about 45 sessions to reach 80% of final performance in training. By the end of training, participants walked at speeds of 0.28-0.60 meters per second and distances of 0.74-1.97 km in 1 hour. The effort of walking was about 3.3 times that for manual wheelchair propulsion. One non-walker with an incomplete injury became a walker without the ReWalk after training. The investigators reported that sitting balance was improved in some, as seen from the limits of stability and sway speed. Neuropathic pain showed no long-term changes. Change in spasticity was mixed, with suggestions of differences between those with high versus low spasticity prior to training. The strength of motor pathways from the brain to back extensor muscles remained unchanged. Minor adverse events were encountered by the participants and trainer (skin abrasions, non-injurious falls). The majority of participants could walk on uneven surfaces outdoors. Some limitations were encountered in home-like environments.

Manns et al. (2019) evaluated the expectations and experiences of persons with spinal cord injury training with the ReWalk exoskeleton. A qualitative research design with individual interviews was used. Eleven participants with spinal cord injury, taking part in 12 weeks of 4 times weekly training using the ReWalk, were interviewed before, immediately after, and 2 months after training. Interviews were audio recorded and transcribed verbatim. A six-stage approach to thematic analysis was used. The investigators found that the theme consistently expressed was that the exoskeleton allowed participants to do everyday activities like everyone else, such as looking people in the eye or walking outside. Their experiences were captured in three categories: 1) learning, a description of both expectations for learning and perspectives on how learning occurred; 2) changing, perspectives on perceived changes with training; and 3) contributing, which captured participant perspectives on contributing to research, including providing direct feedback regarding the exoskeleton (i.e., what worked and what could be changed).

Guanziroli et al. (2019) assessed whether the walking ability of motor-complete spinal cord injury (SCI) patients at thoracic or lower levels, using a wearable powered exoskeleton (ReWalk), can be influenced by different exoskeleton software control. Fifteen chronic SCI patients (4 females and 11 males) were recruited and divided into two groups: group 1, trained with the first software generation of ReWalk, and group 2, trained with the second software generation, a software upgrade of the previous version. Subjects were trained during three 60-minute sessions a week for at least eight weeks using ReWalk, a wearable lower limb powered exoskeleton that allows thoracic or lower-level motor-complete individuals with SCI to walk, stand, sit, and climb/descend stairs. Outcome measures collected at the end of the training period while wearing the exoskeleton included the 6-minute Walking Test, 10-meter Walking Test, and the time necessary to transition from sitting to standing and start walking (STS-time). For each group, Pearson Coefficient was calculated to explore correlations between the subjects' characteristics and gait performance reached at the end of the training period. Group 1 showed a correlation between performances and weight, height, and neurological lesion level, while group 2 showed no correlation between performances and weight and height, but correlation only with neurological lesion level. Group 2 covered more distance in 6 minutes (+124.52%) and required less time (-70.34%) to perform the 10-meter Walking Test and to STS-time (-38.25%) compared to group 1.

Muijzer-Witteveen et al. (2018) examined which information would be most important to receive while using an exoskeleton and how this feedback should be provided. To investigate the preferences of users of an exoskeleton, a questionnaire was filled out by 10 subjects with spinal cord injury (SCI) who underwent a training program with a commercial exoskeleton (ReWalk). The questionnaire consisted of questions about the use of the exoskeleton to identify which information was missing and which instructions from therapists were needed to control the exoskeleton. The second part of the questionnaire focused on the possibilities of sensory feedback, investigating preferences for stimulation methods (auditory, vibrotactile, or visual) and feedback timing (discrete or continuous). Furthermore, six options for feedback parameters (step initiation, continuous and discrete gait phases, foot position, and mediolateral and anteroposterior weight shift) were proposed, and respondents were asked to indicate their preferences. Three feedback parameters (feedback about mediolateral and anteroposterior weight shift and feedback about step initiation) were considered possibly helpful by the respondents. Additionally, there were slight preferences for the use of vibrotactile feedback (over auditory and visual) and discrete feedback (over continuous).

van Dijsseldonk et al. (2017) sought to develop and test the hierarchy and reliability of a framework for measuring progress in the ability to perform basic and advanced skills. Twelve participants with paraplegia were given twenty-four training sessions over 8 weeks with the ReWalk exoskeleton. During the 2nd, 4th, and 6th training weeks, the Intermediate-skills-test was performed, consisting of 27 skills measured in a hierarchical order of difficulty until two skills were not achieved. When participants could walk independently, the Final-skills-test, consisting of 20 skills, was performed in the last training session. Each skill was performed at least two times with a maximum of three attempts. As a reliability measure, consistency was used, defined as the number of skills performed the same in the first two attempts relative to the total number. Ten participants completed the training program. Their number of achieved intermediate skills was significantly different between measurements (XF2(2) = 12.36, p = 0.001). Post-hoc analysis revealed a significant increase in the median achieved intermediate skills from 4 [1-7] at the first to 10.5 [5-26] at the third Intermediate-skills-test. The rate of participants who achieved the intermediate skills decreased, and the coefficient of reproducibility was 0.98. Eight participants met the criteria to perform the Final-skills-test. Their median number of successfully performed final skills was 16.5 [13-20] and 17 [14-19] skills in the first and second attempts, respectively. The overall consistency of >70% was achieved in the Intermediate-skills-test (73%) and the Final-skills-test (81%). Eight out of twelve participants experienced skin damage during training, with four participants missing training sessions as a result. The framework proposed in this study measured progress in performing basic and advanced exoskeleton skills during a training program. The investigators concluded that the hierarchical ordered skills-test could discriminate across participants' skill levels, and the overall consistency was considered acceptable.

Fritz et al. (2019) provided an overview of the features and limitations of four robotic exoskeleton products (EKSO Bionics, ReWalk, Rex Bionics, and Indego) currently being used in rehabilitation settings in the United States. The authors stated that available devices appear to be better suited for rehabilitation settings than for home use. Issues such as device weight, the need for upper extremity supports, supervision requirements, and a limited range of movements all limit functionality and restrict opportunities for using such devices in real-world contexts. Designing the next generation of exoskeletons to be more useful in everyday life will require further collaboration among engineers, clinicians, and patients. The authors stated that further development of exoskeleton technologies is warranted to improve the devices for real-world use.

He et al. (2017) noted that in 2014, the US Food and Drug Administration approved the marketing of the ReWalk Personal Exoskeleton as a class II medical device with special controls. Since then, Indego and Ekso have also received regulatory approval. With similar trends worldwide, this industry is likely to grow rapidly. However, the regulatory science of powered exoskeletons is still developing. The type and extent of probable risks associated with these devices are yet to be fully understood, and industry standards are still being developed. To address this gap, the Manufacturer and User Facility Device Experience, ClinicalTrials.gov, and PubMed databases were searched for reports of adverse events and inclusion and exclusion criteria involving the use of lower limb powered exoskeletons. Current inclusion and exclusion criteria, which can determine probable risks, were found to be diverse. Reported adverse events and identified risks of current devices are also wide-ranging. In light of these findings, the authors compared current regulations, standards, and regulatory procedures for medical device applications in the USA, Europe, and Japan. The authors stated that there is a need to raise awareness of probable risks associated with the use of powered exoskeletons and to develop adequate countermeasures, standards, and regulations for these human-machine systems. With appropriate risk mitigation strategies, adequate standards, comprehensive reporting of adverse events, and regulatory oversight, powered exoskeletons may one day allow individuals with gait disabilities to safely and independently ambulate.

The Ekso (formerly eLegs) system is another powered exoskeleton device for patients with paraplegia or lower-extremity paresis due to neurologic conditions, including spinal cord injuries, multiple sclerosis, amyotrophic lateral sclerosis, or Guillain-Barré syndrome (ECRI, 2013). It incorporates technology similar to that of the ReWalk system. The 45 lb Ekso system is based on the Human Universal Load Carrier that the U.S. military uses; it is a motorized exoskeleton designed to allow users to carry up to 200 lb continuously for several hours over any terrain. The manufacturer states that transfer to and from a patient’s wheelchair and the powered exoskeleton device takes less than 5 minutes and that the user requires little to no assistance. The company estimates the battery life for this device to be 3 hours.

The Ekso robotic exoskeleton is a motorized orthosis device for use in rehabilitation activities for people who have weak or paralyzed legs and sufficient arm strength to use crutches (NICE, 2017). It is intended to help people relearn to stand and walk. The innovative aspect of the Ekso GT robotic exoskeleton is the SmartAssist software incorporated into the device (NICE, 2017). This allows physiotherapists to set the power for each leg independently to best suit the user. Multiple patients can use each Ekso robotic exoskeleton, with it being adapted to their specific needs. The intended place in therapy would be instead of, or in addition to, existing rehabilitation activities, including physiotherapy, exercise, strength training, walking therapies with or without support, and functional electrical stimulation.

A MedTech Innovation Briefing (NICE, 2017) stated that the key points from the evidence summarized in this briefing are from one systematic review and five case series, involving a total of 41 patients in a rehabilitation setting. After using Ekso, these patients were able to walk without assistance from physiotherapists, and their walking speed and distance increased. No serious adverse events were reported. The briefing stated that key uncertainties around the evidence are that the included studies were small and non-comparative. The briefing also noted that the resource impact is currently unclear due to a lack of evidence.

Kolakowsky-Hayner et al. conducted a prospective pilot study in a spinal cord injury rehabilitation center outpatient gym to evaluate the feasibility and safety of Ekso to aid ambulation in individuals with SCI. Eight individuals, at least 18 years of age, with complete T1 SCI or below, within 2 years of injury, completed initial inpatient rehabilitation. All participants signed informed consent, had been cleared from requiring spinal orthoses, met inclusion criteria, and were pre-screened based on device requirements and medical stability. The subjects received six weekly sessions with graduated time and less assistance in the Ekso device. Outcome measures included skin evaluation, blood pressure, pain level, spasticity, time and level of assistance needed to transfer into and don the device; time ambulating; time up in the device; assistive devices used during ambulation; step length; distance walked; level of assistance during use; losses of balance; number of falls; and level of assistance needed to doff and transfer out of the device. The investigators reported no major skin effects, minimal pain reports, no known fractures, swelling, or other adverse events. The level of assistance ranged from dependent to moderately independent, with an average setup time of 18.13 minutes, and losses of balance and falls were infrequent. The investigators concluded that bionic exoskeletons such as Ekso are safe for those with complete thoracic SCI in a controlled environment, in the presence of experts, and may eventually enhance mobility in those without volitional lower extremity function. There appears to be a training effect in the device, but further trials are needed. The investigators stated that future studies of bionic exoskeletons as gait training devices are warranted, and that future studies of bionic exoskeletons as a clinical tool to alleviate secondary complications should be considered.

Kozlowski et al. (2015) sought to quantify the time and effort required by persons with SCI to learn to use the Ekso exoskeleton for assisted walking. A convenience sample was enrolled to learn to use the first-generation Ekso powered exoskeleton to walk. Participants were given up to 24 weekly sessions of instruction. Data were collected on assistance level, walking distance and speed, heart rate, perceived exertion, and adverse events. Time and effort were quantified by the number of sessions required for participants to stand up, walk for 30 minutes, and sit down, initially with minimal and subsequently with contact guard assistance. Of 22 enrolled participants, 9 screen-failed, and 7 had complete data. All of these 7 were men; 2 had tetraplegia and 5 had motor-complete injuries. Of these, 5 participants could stand, walk, and sit with contact guard or close supervision assistance, and 2 required minimal to moderate assistance. Walk times ranged from 28 to 94 minutes, with average speeds ranging from 0.11 to 0.21 m/s. For all participants, heart rate changes and reported perceived exertion were consistent with light to moderate exercise.

In a case series from an academic research center, Kressler et al. (2014) explored responses to overground bionic ambulation (OBA) training with the Ekso exoskeleton three days per week for 6 weeks from an interdisciplinary perspective, including key components of neuromuscular activation, exercise conditioning, mobility capacity, and neuropathic pain. Persons (n = 3; 2 men, 1 woman) aged 26 to 38 years with complete spinal cord injury (SCI) (American Spinal Injury Association Impairment Scale grade A) between the levels of T1 and T10 for 1 year or longer participated. To obtain a comprehensive understanding of responses to OBA, an array of measures were obtained while walking in the device, including walking speeds and distances, energy expenditure, exercise conditioning effects, and neuromuscular and cortical activity patterns. Changes in spasticity and pain severity related to OBA use were also assessed. With training, participants were able to achieve walking speeds and distances in the OBA device similar to those observed in persons with motor-incomplete SCI (10-m walk speed, 0.11 to 0.33 m/s; 2-min walk distance, 11 to 33 m). The energy expenditure required for OBA was similar to walking in persons without disability (i.e., 25% to 41% of peak oxygen consumption). Subjects with lower soleus reflex excitability walked longer during training, but there was no change in the level or amount of muscle activity with training. There was no change in cortical activity patterns. Exercise conditioning effects were small or nonexistent. However, all participants reported an average reduction in pain severity over the study period, ranging between 1.3 and 1.7 on a 0-to-6 numeric rating scale. The authors concluded that OBA training improved mobility in the OBA device without significant changes in exercise conditioning or in neuromuscular or cortical activity. However, pain severity was reduced, and no severe adverse events were encountered during training. OBA therefore opens the possibility to reduce the common consequences of chronic, complete SCI, such as reduced functional mobility and neuropathic pain.

Giulia et al. (2016) investigated the acceptability of overground robot-assisted walking and its effect on pain and spasticity. Twenty-one SCI persons participated in a single walking session assisted by a powered robotic exoskeleton. Pain assessed using a Numeric Rating Scale (NRS) and muscle spasticity, assessed as subjective perception using an NRS scale and as objective assessment using the Modified Ashworth scale and the Penn scale, were evaluated before and after the walking experience. Positive and negative sensations were investigated using a questionnaire. The patient’s global impression of change (PGIC) scale was administrated as well. After the walking session, a significant decrease in the muscle spasticity and pain intensity was observed. The SCI persons recruited in this study reported

a global change after the walking session,
high scores on the positive and
low scores on the negative sensations, thus indicating a good acceptability of the robot-assisted walking.

In contrast to other exoskeletons, HAL (hybrid assistive limb) exoskeleton (Cyberdyne Inc., Japan) offers the possibility of monitoring muscle contractions via surface EMG-electrodes at the extensor-flexor muscle region of the lower extremities (Sczensy-Kaiser et al., 2015). This allows for voluntary machine-supported motion using minimal signals recorded from hip and knee flexors and extensors.

Nilsson et al. (2014) investigated the safety and feasibility of the Hybrid Assistive Limb (HAL) exoskeleton for intensive gait training as part of a regular inpatient rehabilitation program for hemiparetic patients with severely impaired gait early after stroke. Eligible patients were those within 7 weeks post-hemiparetic stroke. Training with HAL was performed 5 days per week using either the autonomous or voluntary control mode offered by the system. The study protocol covered safety and feasibility issues, as well as aspects of motor function, gait performance according to the 10 Meter Walking Test (10MWT), Functional Ambulation Categories (FAC), and activity performance. Eight patients completed the study, with a median time from stroke to inclusion of 35 days (range of 6 to 46). Training began with the autonomous HAL mode for all participants and later switched to the voluntary mode for all but one, requiring one or two physiotherapists. The number of training sessions ranged from 6 to 31 (median 17), with walking time per session around 25 minutes. The training was well tolerated, and no serious adverse events occurred. All patients improved their walking ability during the training period, as reflected by the 10MWT (from a median of 111.5 to 40 seconds) and the FAC (from a median score of 0 to 1.5).

Sczesny-Kaiser et al. (2015) sought to assess whether robotic-assisted bodyweight supported treadmill training (BWSTT) with the HAL exoskeleton affects cortical excitability in the primary somatosensory cortex (S1) in SCI patients, as measured by paired-pulse somatosensory evoked potentials (ppSEP) stimulated above the level of injury. Eleven SCI patients participated in HAL-assisted BWSTT for 3 months. Pulse paired stimulation techniques of somatosensory evoked potentials (PpSEP) were conducted before and after this training period, where amplitude ratios (SEP amplitude following double pulses - SEP amplitude following single pulses) were assessed and compared to eleven healthy control subjects. To assess improvement in walking function, the investigators used the 10-m walk test, timed-up-and-go test, the 6-min walk test, and the lower extremity motor score. PpSEPs were significantly increased in SCI patients compared to controls at baseline. Following training, ppSEPs increased from baseline and no longer significantly differed from controls. Walking parameters also showed significant improvements, yet there was no significant correlation between ppSEP measures and walking parameters. The investigators concluded that robotic-assisted BWSTT with HAL in SCI patients is capable of inducing cortical plasticity following highly repetitive, active locomotive use of paretic legs. While there was no significant correlation of excitability with walking parameters, brain areas other than S1 might reflect improvement in walking functions. The investigators posited that EEG and neuroimaging studies may provide further information about supraspinal plastic processes and foci in SCI rehabilitation.

In a pilot study, Aach et al. (2014) examined whether locomotor training with the HAL exoskeleton is safe and can increase functional mobility in chronic paraplegic patients after SCI. This trial was a single-case experimental A-B (pre-post) design study with repeated assessments of the same patients. The subjects performed 90 days (5 times per week) of HAL exoskeleton body weight supported treadmill training with variable gait speed and body weight support. A total of 8 patients with chronic SCI classified by the American Spinal Injury Association (ASIA) Impairment Scale (AIS) participated: ASIA A (zones of partial preservation [ZPP] L3 to S1), n = 4; ASIA B (with motor ZPP L3 to S1), n = 1; and ASIA C/D, n = 3, who received full rehabilitation in the acute and sub-acute phases of SCI. Functional measures included treadmill-associated walking distance, speed, and time, with additional analysis of functional improvements using the 10-m walk test (10MWT), timed-up-and-go test (TUG), 6-minute walk test (6MWT), and the walking index for SCI II (WISCI II) score. Secondary physiologic measures included the AIS with the lower extremity motor score (LEMS), spinal spasticity (Ashworth scale), and lower extremity circumferences. Subjects performed standardized functional testing before and after the 90 days of intervention. Highly significant improvements in HAL-associated walking time, distance, and speed were noted. Furthermore, significant improvements were especially shown in functional abilities without the exoskeleton for over-ground walking, as obtained in the 6MWT, TUG test, and 10MWT, including an increase in the WISCI II score for 3 patients. Muscle strength (LEMS) increased in all patients, accompanied by a gain in lower limb circumferences. A conversion in the AIS was noted in 1 patient (from ASIA B to ASIA C), and 1 patient reported a decrease in spinal spasticity. The authors concluded that HAL exoskeleton training resulted in improved over-ground walking and suggested a beneficial effect on ambulatory mobility. However, they stated that evaluation in larger clinical trials is needed.

Chihara et al. (2016) investigated factors predicting the effects of HAL in 15 patients with central nervous system injury, primarily due to stroke, who underwent training using HAL during the acute phase. Patients were classified as either “with HAL suitability” or “without HAL suitability” based on scores from 10-m walking speed, gait, satisfaction, and pain. In both groups, Brunnstrom stage before HAL intervention, Fugl-Meyer assessment (FMA), stroke impairment assessment set (SIAS), and functional independence measure (FIM) were evaluated. Although motor function items did not differ significantly, FIM cognitive function items (p = 0.036), visuospatial perception items on SIAS (p = 0.0277), and pain items on SIAS (p = 0.0122) differed significantly between groups. The authors stated that these results indicated that training using HAL does not involve pain in patients with central nervous system injury during the acute phase and exhibits positive effects in patients without pain and with high communication ability and visuospatial perception function.

Wall et al. (2015) reviewed the literature on clinical applications of the HAL system for gait training. A systematic literature search was conducted using Web of Science, PubMed, CINAHL, and clinicaltrials.gov, with additional searches made using reference lists in identified reports. Abstracts were screened, relevant articles were reviewed, and subject to quality assessment. Out of 37 studies, 7 studies fulfilled inclusion criteria. Six studies were single-group studies, and 1 was an explorative randomized controlled trial. In total, these studies involved 140 participants, of whom 118 completed the interventions and 107 used HAL for gait training. Five studies concerned gait training after stroke, 1 after spinal cord injury (SCI), and 1 study after stroke, SCI, or other diseases affecting walking ability. Minor and transient side effects occurred, but no serious adverse events were reported in the studies. Beneficial effects on gait function variables and independence in walking were observed. The accumulated findings demonstrate that the HAL system is feasible when used for gait training of patients with lower extremity paresis in a professional setting. Beneficial effects on gait function and independence in walking were observed, but the data do not allow for definitive conclusions. The investigators stated that further controlled studies are recommended.

Swank et al. (2020) sought to compare temporospatial, kinematic, and muscle activity gait characteristics before and after a single EKSO session and examine kinematic symmetry between involved and uninvolved limbs. Participants post-stroke walked under two conditions: pre-EKSO and immediately post-EKSO. A 10-camera motion capture system synchronized with 6 force plates was used to obtain temporospatial and kinematic gait characteristics from 5 walking trials of 9 meters at a self-selected speed. Surface EMG activity was obtained from bilateral gluteus medius, rectus femoris, medial hamstrings, tibialis anterior, and soleus muscles. Wilcoxon Signed Rank tests were used to analyze differences pre- and post-EKSO. The single EKSO session consisted of 22.3±6.8 minutes total time (walk time=7.2±1.5 minutes) with 250±40 steps. Six ambulatory adults (Functional Ambulation Category, range=4-5) with chronic stroke (4.5±1.9 years post-stroke) participated. No significant differences were observed for temporospatial gait characteristics. Muscle activity was significantly less post-EKSO in the involved leg rectus femoris during the swing phase (p=0.028). Ankle dorsiflexion range of motion on the involved leg post-EKSO was significantly less during the stance phase (p=0.046). Differences between involved and uninvolved joint range of motion symmetry were found pre-EKSO but not post-EKSO in swing phase hip flexion and stance phase knee flexion and knee extension. The investigators concluded that EKSO training appears capable of altering gait in people with chronic stroke and is a viable intervention to reduce gait dysfunction post-stroke.

Rojek et al. (2020) sought to evaluate the effects of EKSO GT exoskeleton-assisted gait training on balance, load distribution, and functional status of patients after ischemic stroke. Study outcomes were based on 44 patients aged 55-85 years after ischemic stroke who were previously randomly assigned into two groups: experimental (with EKSO GT rehabilitation) and control (with classical rehabilitation). At baseline and after 4 weeks of treatment, the patients were evaluated on balance, load distribution, and functional status using a stabilometric platform, the Barthel Index, and the Rivermead Mobility Index. In the experimental group, balance improved regarding the variables describing sway area as ellipse major and minor axes. In the control group, improvement was noted in sway velocity. After therapy, total load distribution on feet in both groups showed a small and insignificant tendency toward reduction in the amount of uninvolved limb loading. In the control group, significant load transfer from the backfoot to the forefoot was noted. Both forms of rehabilitation caused significant changes in functional status. The investigators concluded that both training with the EKSO GT exoskeleton and classical physiotherapy lead to functional improvement of patients after ischemic stroke. However, in the experimental group, improvement was observed in a larger number of categories, suggesting a potentially greater impact of treatment with the exoskeleton on functional status. Additionally, both forms of rehabilitation caused significant changes in balance, but the investigators noted some trends indicating that treatment with the exoskeleton may be more beneficial for some patients. The load transfer from the backfoot to the forefoot observed in the control group was an unfavorable phenomenon. The investigators suggested that the EKSO GT exoskeleton may be a promising tool in the rehabilitation of patients after stroke.

Swank et al. (2019) examined whether wearing a robotic exoskeleton affects temporospatial parameters, kinematics, and muscle activity during gait. The study was completed by 15 healthy adults (mean age 26.2 [SD 8.3] years; 6 males, 9 females). Each participant performed walking under two conditions: with and without wearing a robotic exoskeleton (EKSO). A 10-camera motion analysis system synchronized with 6 force plates and a surface electromyography (EMG) system captured temporospatial and kinematic gait parameters and lower extremity muscle activity. For each condition, data for 5 walking trials were collected and included for analysis. Differences were observed between the two conditions in temporospatial gait parameters of speed, stride length, and double-limb support time. When wearing EKSO, hip and ankle range of motion (ROM) were reduced, and knee ROM increased during the stance phase. However, during the swing phase, knee and ankle ROM were reduced when wearing the exoskeleton. When wearing EKSO, EMG activity decreased bilaterally in the stance phase for all muscle groups of the lower extremities and in the swing phase for the distal muscle groups (tibialis anterior and soleus) as well as the left medial hamstrings. The investigators concluded that wearing EKSO altered temporospatial gait parameters, lower extremity kinematics, and muscle activity during gait in healthy adults. EKSO appears to promote a type of gait that is disparate from normal gait in first-time users. The investigators stated that more research is needed to determine the impact of gait training with EKSO in people with gait impairments.

Swank et al. (2010) sought to determine the feasibility of integrating the Ekso Gait Training device into inpatient rehabilitation in a neurologic population. The study included a longitudinal cohort design and convenience sample involving physical therapists trained to use the Ekso Bionics Ekso GT robotic exoskeleton or inpatients with stroke or SCI. Therapists completed a focus group and survey at baseline and 6 months after initial Ekso training. Patients completed a survey indicating their satisfaction with using the Ekso. Twenty-five patients used the Ekso an average of 4.5 sessions during their 38.5-day rehabilitation stay. Survey and focus group feedback revealed that therapists encountered measurement difficulties with the Ekso and limited treatment time, which influenced the effectiveness of usage. After 6 months, therapists reported an improvement in feasibility. Patients tolerated Ekso sessions well, without any complications or adverse incidents, and reported improved mobility post-session. The investigators concluded that integrating Ekso gait training into clinical practice was not seamless but appears feasible. Barriers were addressed within the rehabilitation team and received administrative support in a process lasting several months. Patients enjoyed walking in Ekso and felt secure within the device.

Poritz et al. (2020) reported on the results of a robotic exoskeleton user satisfaction questionnaire completed by participants utilizing two robotic exoskeletons. Seven individuals with physical disabilities engaged in two exoskeleton-assisted training phases with the REX and the Ekso 1.1 (Ekso), after which they completed a user satisfaction questionnaire. The questionnaire consisted of structured items with a Likert scale, which were averaged and compared, as well as free response questions, which were interpreted thematically. Participants reported some differences in user satisfaction between the two exoskeletons. They indicated higher satisfaction with transferring in and out of the REX and with its appearance, and higher satisfaction with the transportability of the Ekso. Expectations for exoskeleton use were relatively similar for the two devices, with some exceptions. While participants indicated that many changes should be made to both exoskeletons, they reported that some were more necessary for the REX and others were more necessary for the Ekso. Participants reported that they would be somewhat likely to use both exoskeletons at home and in the community if they were available.

Gorman et al. (2019) reported on a randomized dual-center controlled clinical trial to determine and compare the cardiorespiratory impact of 3 months of aquatic and robotic therapy for individuals with chronic motor incomplete spinal cord injury (CMISCI). Thirty-one individuals at two rehabilitation specialty hospitals with CMISCI and neurological levels between C2-T12, at least 1 year post-injury, were randomized to either aquatic or robotic treadmill therapy for 36 sessions. Customized sessions lasted 40-45 minutes at 65-75% heart rate reserve intensity, with peak oxygen consumption (peak VO2) measured during arm ergometry at baseline and post-intervention. Additional peak robotic treadmill VO2 assessments were obtained before and after training for participants randomized to the robotic intervention. Peak VO2 measured with arm ergometry was not significantly different with either aquatic intervention (8.1%, p = 0.14, n = 15) or robotic intervention (-0.7%, p = 0.31, n = 17). Peak VO2 measured with robotic treadmill ergometry demonstrated a statistical improvement (14.7%, p = 0.03, n = 17, two-tailed t-test) across the robotic intervention. Comparison between the two interventions demonstrated a trend favoring aquatic therapy for improving arm ergometry peak VO2 (ANOVA, p = 0.063). The authors concluded that neither 3-month exercise intervention statistically improved arm cycle ergometry peak VO2, the study's cardiorespiratory surrogate marker, although percent improvement was greater in the aquatic exercise condition. Robotic ergometry peak VO2 did improve for the robotic intervention, confirming previous work. These results suggest that either intervention may hold utility in improving cardiorespiratory fitness in CMISCI, but the peak VO2 measurement technique appears critical in detecting effects.

Alamro et al. (2018) conducted a study to characterize and compare the activation of trunk muscles during walking with two robotic gait training devices (Ekso and Lokomat) in people with high thoracic motor-complete SCI. Participants with chronic motor-complete paraplegia performed 3 speed-matched walking conditions: Lokomat-assisted walking, Ekso-assisted walking overground, and Ekso-assisted walking on a treadmill. Surface electromyography (EMG) signals were recorded bilaterally from the rectus abdominis (RA), external oblique (EO), and erector spinae (ES) muscles. Greater recruitment of trunk muscle EMG was elicited with Ekso-assisted walking compared to Lokomat. Similar levels of trunk EMG activation were observed between Ekso overground and Ekso on the treadmill, indicating that differences between Ekso and Lokomat could not be attributed to the use of a hand-held gait aid. The level of trunk EMG activation during Lokomat walking was not different from that recorded during quiescent supine lying.

Baunsgaard et al. (2018) conducted a prospective, observational multicenter study to explore changes in pain, spasticity, range of motion, activities of daily living, bowel and lower urinary tract function, and quality of life of individuals with spinal cord injury following robotic exoskeleton gait training. Subjects underwent three training sessions per week for 8 weeks using an Ekso GT robotic exoskeleton. Included were individuals with recent (<1 year) or chronic (>1 year) injury, paraplegia, and tetraplegia, complete and incomplete injury, men and women. Fifty-two participants completed the training protocol. Pain was reported by 52% of participants during the week prior to training and 17% during training, but no change occurred longitudinally. Spasticity decreased after a training session compared with before the training session (p < 0.001), but not longitudinally. Chronically injured participants increased their Spinal Cord Independence Measure (SCIM III) from 73 to 74 (p = 0.008) and improved life satisfaction (p = 0.036) over 8 weeks of training. Recently injured participants increased SCIM III from 62 to 70 (p < 0.001), but no significant change occurred in life satisfaction. Range of motion, bowel, and lower urinary function did not change over time.

Gorgey et al. (2017) studied whether the use of a powered exoskeleton can improve parameters of physical activity as determined by walking time, stand-up time, and number of steps in persons with spinal cord injury (SCI). Three men with complete (1 C5 AIS A and 2 T4 AIS A) and one man with incomplete (C5 AIS D) SCI participated in a clinical rehabilitation program. In the training program, the participants walked once weekly using a powered exoskeleton (Ekso) for approximately 1 hour over the course of 10 to 15 weeks. Walking time, stand-up time, ratio of walking to stand-up time, and number of steps were determined. Oxygen uptake (L/min), energy expenditure, and body composition were measured in one participant after training. Over the course of 10 to 15 weeks, the maximum walking time increased from 12 to 57 minutes, and the number of steps increased from 59 to 2,284 steps. At the end of the training, the 4 participants were able to exercise for 26 to 59 minutes. For one participant, oxygen uptake increased from 0.27 L/min during rest to 0.55 L/min during walking. Maximum walking speed was 0.24 m/s, and delta energy expenditure increased by 1.4 kcal/min during walking. Body composition showed a modest decrease in absolute fat mass in one participant.

Baunsgaard et al. (2018) conducted a prospective pre-post study at nine European rehabilitation centers to assess the safety, feasibility, training characteristics, and changes in gait function for persons with spinal cord injury (SCI) using the robotic exoskeletons from Ekso Bionics. Subjects underwent robotic exoskeleton gait training three times weekly over 8 weeks. Time upright, time walking, and steps in the device (training characteristics) were recorded longitudinally. Gait and neurological function were measured by the 10 Meter Walk Test (10 MWT), Timed Up and Go (TUG), Berg Balance Scale (BBS), Walking Index for Spinal Cord Injury (WISCI) II, and Lower Extremity Motor Score (LEMS). Fifty-two participants completed the training protocol. The subjects' median age was 35.8 years (inter-quartile range [IQR] 27.5-52.5), and included 36 men and 16 women, with neurological levels of injury at C1-L2 and severity AIS A-D (American Spinal Injury Association Impairment Scale). The time since injury (TSI) was less than 1 year in 25 subjects and greater than 1 year in 27 subjects. No serious adverse events occurred. Three participants dropped out following ankle swelling (overuse injury). Four participants sustained a Category II pressure ulcer at contact points with the device but completed the study, and skin normalized. Training characteristics increased significantly for all subgroups. The number of participants with TSI < 1 year and gait function increased from 20% to 56% (P = 0.004), and 10MWT, TUG, BBS, and LEMS results improved (P < 0.05). The number of participants with TSI > 1 year and gait function increased from 41% to 44%, and TUG and BBS results improved (P < 0.05).

The Indego exoskeleton (Parker Hannifin Corporation, Macedonia, OH) incorporates four motors for powered movement of bilateral hip and knee joints in the sagittal plane, in addition to built-in ankle-foot orthoses (AFOs) at both ankle joints to provide ankle stability and transfer the weight of the exoskeleton to the ground.

Hartigan et al. (2015) conducted a study to evaluate mobility outcomes for individuals with SCI after 5 gait-training sessions with the Indego powered exoskeleton, with a primary goal of characterizing the ease of learning and usability of the system. Sixteen subjects with SCI were enrolled in a pilot clinical trial at Shepherd Center, Atlanta, Georgia, with injury levels ranging from C5 complete to L1 incomplete. An investigational Indego exoskeleton research kit was evaluated for ease of use and efficacy in providing legged mobility. Outcome measures of the study included the 10-meter walk test (10MWT) and the 6-minute walk test (6MWT), as well as measures of independence including donning and doffing times and the ability to walk on various surfaces. At the end of 5 sessions (1.5 hours per session), average walking speed was 0.22 m/s for persons with C5-6 motor complete tetraplegia, 0.26 m/s for T1-8 motor complete paraplegia, and 0.45 m/s for T9-L1 paraplegia. Distances covered in 6 minutes averaged 64 meters for those with C5-6, 74 meters for T1-8, and 121 meters for T9-L1. Additionally, all participants were able to walk on both indoor and outdoor surfaces.

Evans et al. (2015) conducted a pilot study to evaluate the acute cardiorespiratory and metabolic responses associated with Indego exoskeleton-assisted walking overground and to determine the degree to which these responses change at differing walking speeds. Five subjects (4 male, 1 female) with chronic SCI (AIS A) volunteered for the study. Expired gases were collected during maximal graded exercise testing and two 6-minute bouts of exoskeleton-assisted walking overground. Outcome measures included peak oxygen consumption (VO2peak), average oxygen consumption (VO2avg), peak heart rate (HRpeak), walking economy, metabolic equivalent of tasks for SCI (METssci), walk speed, and walk distance. Significant differences were observed between walk-1 and walk-2 for walk speed, total walk distance, VO2avg, and METssci. Exoskeleton-assisted walking resulted in a % VO2peak range of 51.5% to 63.2%. The metabolic cost of exoskeleton-assisted walking ranged from 3.5 to 4.3 METssci.

Tefertiller et al. (2018) assessed the safety and mobility outcomes utilizing the Indego powered exoskeleton in indoor and outdoor walking conditions with individuals previously diagnosed with a spinal cord injury (SCI). The investigators conducted a multicenter prospective observational cohort study in outpatient clinics associated with 5 rehabilitation hospitals. A convenience sample of nonambulatory individuals with SCI (N = 32) completed an 8-week training protocol consisting of walking training 3 times per week utilizing the Indego powered exoskeleton in indoor and outdoor conditions. Participants were also trained in donning and doffing the exoskeleton during each session. Safety measures such as adverse events (AEs) were monitored and reported. Time and independence with donning and doffing the exoskeleton, as well as walking outcomes including the 10-meter walk test (10MWT), 6-minute walk test (6MWT), Timed Up & Go test (TUG), and 600-meter walk test, were evaluated from midpoint to final evaluations. All 32 participants completed the training protocol with limited device-related AEs, which resulted in no interruption in training. The investigators reported that the majority of participants in this trial were able to don and doff the Indego independently. Final walking speed ranged from 0.19 to 0.55 m/s. Final average indoor and outdoor walking speeds among all participants were 0.37 m/s (SD = 0.08, 0.09, respectively) after 8 weeks of training. Significant (p < .05) improvements were noted between midpoint and final gait speeds in both indoor and outdoor conditions. Average walking endurance also improved among participants after training.

Takahashi et al. (2015) stated that in persons post-stroke, diminished ankle joint function can contribute to inadequate gait propulsion. To target paretic ankle impairments, these researchers developed a neuromechanics-based powered ankle exoskeleton. Specifically, this exoskeleton supplies plantar-flexion assistance that is proportional to the user's paretic soleus electromyography (EMG) amplitude only during a phase of gait when the stance limb is subjected to an anteriorly directed ground reaction force (GRF). In a feasibility study, these investigators examined the short-term effects of the powered ankle exoskeleton on the mechanics and energetics of gait. Investigators fabricated a lightweight ankle exoskeleton for each individual’s paretic limb. A total of 5 subjects with stroke walked with a powered ankle exoskeleton on the paretic limb for 3 sessions (5 minutes each session). They analyzed the peak paretic ankle plantar-flexion moment, paretic ankle positive work, symmetry of GRF propulsion impulse, and net metabolic power. The exoskeleton increased the paretic plantar-flexion moment by 16% during the powered walking trials relative to the unassisted walking condition (p < 0.05). Despite this enhanced paretic ankle moment, there was no significant increase in paretic ankle positive work or changes in any other mechanical variables with the powered assistance. The exoskeleton assistance appeared to reduce the net metabolic power gradually with each 5-minute repetition, though no statistical significance was found. In 3 of the subjects, the paretic soleus activation during the propulsion phase of stance was reduced during the powered assistance compared to unassisted walking (35% reduction in the integrated EMG amplitude during the 3rd powered session). The authors concluded that the findings of this feasibility study demonstrated that the exoskeleton can enhance paretic ankle moment. Moreover, they stated that future studies with a greater sample size and prolonged sessions are needed to evaluate the effects of the powered ankle exoskeleton on overall gait outcomes in persons post-stroke.

Wilcox et al. (2016) examined peak interaction forces and electromyography (EMG) analysis to determine whether these interaction forces are due to the muscular activity of the participant or the movement of the REX Personal (Rex Bionics, New Zealand) exoskeleton itself. Interestingly, the authors found that peak forces preceded peak EMG activity. This study did not find a significant correlation between EMG activity and force data, indicating that the interaction forces can largely be attributed to the movement of the exoskeleton itself. However, the authors reported significantly higher correlation coefficients in muscle/force pairs located at the anterior aspect of the right leg. In their previous research, they had shown peak interaction forces at the same locations, suggesting that the muscular activity of the participant makes a more significant contribution to the interaction forces at these locations.

Birch et al. (2017) reported interim results of the RAPPER II study, which investigated the feasibility, safety, and acceptability of using the REX self-stabilizing robotic exoskeleton in people with spinal cord injury (SCI) who are obligatory wheelchair users. Feasibility was assessed by the completion of transfer into the REX device, competency in achieving autonomous control, and completion of upper body exercise in an upright position in the REX device. Safety was measured by the occurrence of serious adverse events, while device acceptability was assessed with a user questionnaire. RAPPER II is a prospective, multi-center, open-label, non-randomized, non-comparative cohort study involving people with SCI recruited from neurological rehabilitation centers in the United Kingdom, Australia, and New Zealand. This report was the planned interim report of the first 20 participants. Each participant completed a transfer into the REX, was trained to achieve machine control, and completed Timed Up and Go (TUG) tests as well as upper body exercises in standing during a single first-time session. The time to achieve each task and the amount of assistance required were recorded. After finishing the trial tasks, a User Experience questionnaire exploring device acceptability was completed. All participants could transfer into the REX, with a mean transfer time of 439 seconds. Nineteen completed the exercise regime, and eighteen achieved autonomous control of the REX, with 17 needing either no assistance or the help of just one therapist. Eighteen participants completed at least one TUG test in a mean time of 313 seconds, with 15 requiring assistance from just one therapist. The questionnaire demonstrated high levels of acceptability among users, and there were no serious adverse events.

Arazpour et al. (2013) analyzed energy expenditure during walking with mechanical orthoses (hip knee ankle foot orthosis [HKAFO] and the isocentric reciprocating gait orthosis [IRGO]) compared with a new powered gait orthosis (PGO) in patients with SCI. Five patients with SCI who were experienced users of HKAFOs participated in this study. Subjects were fitted with an IRGO and PGO and underwent a specific gait training program. Patients walked along a flat walkway using the three types of orthosis at their self-selected walking speed. A stopwatch and a polar heart rate monitor were used to measure walking speed and heart rate. The authors reported that walking speed, distance walked, and the physiological cost index (PCI) all improved with both the new PGO and the IRGO compared with the HKAFO.

Gholizadeh et al. (2014a) noted that several prosthetic suspension systems are available for trans-tibial amputees. Consideration of an appropriate suspension system can ensure that the amputee's functional needs are satisfied. The higher the insight into suspension systems, the easier it would be for prosthetists to make selections. These investigators attempted to find scientific evidence pertaining to various trans-tibial suspension systems to provide selection criteria for clinicians. Databases of PubMed, Web of Science, and ScienceDirect were explored to find related articles. Search terms included "Transtibial prosthesis," "prosthetic suspension," "lower limb prosthesis," "below-knee prosthesis," "prosthetic liner," "transtibial," and "prosthetic socket." Two reviewers separately examined the papers. Study design (case series of 5 or more subjects, retrospective or prospective), research instrument, sampling method, outcome measures, and protocols were reviewed. Based on the selection criteria, 22 articles (15 prospective studies and 7 surveys) remained. Sweat control was found to be a major concern with the available suspension liners. Donning and doffing procedures for soft liners were also problematic for some users, particularly those with upper limb weakness. Moreover, the total surface bearing (TSB) socket with pin/lock system is favored by the majority of amputees. The authors concluded that no clinical evidence was available to suggest what kind of suspension system could serve as a "standard" system for all trans-tibial amputees. However, among various suspension systems for trans-tibial amputees, the Iceross system was favored by the majority of users in terms of function and comfort.

Gholizadeh et al. (2014b) examined the scientific evidence pertaining to various trans-femoral suspension systems to provide selection criteria for clinicians. Databases of PubMed, Web of Science, and ScienceDirect were explored. The following key words, as well as their combinations and synonyms, were used for the search: transfemoral prosthesis, prosthetic suspension, lower limb prosthesis, above-knee prosthesis, prosthetic liner, transfemoral, and prosthetic socket. The study design, research instrument, sampling method, outcome measures, and protocols of articles were reviewed. Based on the selection criteria, a total of 16 articles (11 prospective studies and 5 surveys) were reviewed. The main causes of reluctance to prosthesis, aside from energy expenditure, were socket-related problems such as discomfort, perspiration, and skin issues. Osseo-integration was a suspension option, yet it is rarely applied due to several drawbacks, such as an extended rehabilitation process, risk of fracture, infection, and excessive cost. The authors concluded that no clinical evidence was found to suggest a "standard" system of suspension and socket design for all trans-femoral amputees. However, among various suspension systems for trans-femoral amputees, the soft insert or double socket was favored by most users in terms of function and comfort.

According to the Ottobock website, the C-Leg Protector 4X160 represents the modern solution for C-Leg and C-Leg compact wearers. The C-Leg Protector covers and protects the joints of the C-Leg Product Line, including the tube adapter, and provides a cosmetic contour in the calf area. The manufacturer states that the result is an attractive appearance without any functional restrictions. The website states that the C-Leg Protector can be used on either side and is quick and easy to adjust. According to the manufacturer, during everyday use, the patient can put it on, take it off, and clean it easily if needed.

The Ossur Symbiotic Leg (Ossur Americas, Foothill Ranch, CA), a microprocessor knee/foot unit, combines the capabilities of the bionic products, RHEO KNEE and PROPRIO FOOT, into a single integrated unit offering functionality for transfemoral (above-knee) amputees. The prosthesis was designed to enable users to experience confident mobility on all terrains without gait deviations or compensations. This new product, which is the first of its kind in the market, has been in user testing for over a year and will be available on a limited basis in late 2011.

Alimusaj et al. (2009) stated that conventional prosthetic feet cannot adapt to specific conditions such as walking on stairs or ramps. Amputees are therefore forced to compensate for their prosthetic deficits by modifying the kinematics and kinetics of their lower limbs. The Proprio-Foot (Ossur) intends to reduce these compensation mechanisms by automatically increasing dorsiflexion during stair ambulation, thanks to an adaptive microprocessor-controlled ankle. These investigators analyzed the biomechanical effects of the dorsiflexion adaptation in trans-tibial (TT) amputees during stair ambulation. A total of 16 TT amputees and 16 healthy controls underwent conventional 3D gait analysis. Kinematics and kinetics of the lower limbs were compared during stair ascent and descent performed by patients with the prosthetic foot set to a neutral ankle angle and with an adapted dorsiflexion ankle angle of 4 degrees. Norm distance, as well as minimum and maximum values of sagittal kinematics and kinetics, were calculated for comparisons between patients and control subjects. For both stair ascent and descent, an improvement in knee kinematics and kinetics could particularly be noticed on the involved side, with an increase in knee flexion and an increase in knee moment during stance. The authors concluded that despite its additional weight compared to a conventional prosthetic ankle, the Proprio-Foot should be beneficial to active TT amputees whose knee musculature strength does not constitute a handicap.

Wolf et al. (2009) stated that technological advances in developing highly functional prostheses are promising for very active patients, but it is unknown whether they cause an increase in biomechanical load along with possibly negative consequences for pressure conditions in the socket. Therefore, this study monitored the socket pressure at specific locations of the stump when using a microprocessor-controlled adaptive prosthetic ankle under different walking conditions. A total of 12 unilateral TT amputees (TTAs) between 43 and 59 years of age were provided with the Proprio-Foot (Ossur) and underwent an instrumented 3D gait analysis in level, stair, and incline walking, including synchronous data capturing of socket pressure. Peak pressures and pressure time integrals (PTI) at three different locations were compared for five walking conditions with and without using the device's ankle adaptation mode. The highest peak pressures of 2.4 kPa/kg were found for incline ascent at the calf muscle compared to 2.1 kPa/kg in level walking, with large inter-individual variance. In stair ascent, a strong correlation was found between maximum knee moment and socket pressure. The most significant pressure changes relative to level walking were seen in ramp descent anteriorly towards the stump end, with PTI values being almost twice as high as those in level walking. Adapting the angle of the prosthesis on stairs and ramps modified the pressure data such that they were closer to those in level walking. The authors concluded that pressure at the stump depended on the knee moments involved in each walking condition. Adapting the prosthetic ankle angle is a valuable means of modifying joint kinetics and thereby the pressure distribution at the stump. However, large inter-individual differences in local pressures underline the importance of individual socket fitting.

Fradet et al. (2010) noted that the fixed neutral position of conventional prosthetic feet causes difficulties for TTAs when walking on ramps. New microprocessor-controlled prosthetic ankles, such as the Proprio-Foot (Ossur), aim to reduce these difficulties by modifying the prosthetic ankle angle according to the gait condition. These researchers evaluated the biomechanical effects of adaptation of the prosthetic ankle on ramp ambulation in TTAs. A total of 16 TTAs and 16 controls underwent a conventional 3D gait analysis while walking up and down a ramp. Trans-tibial amputees walked with the prosthetic foot set to a neutral mode angle and set to the adapted mode. Norm distance, sagittal kinematics, and kinetics were calculated for comparisons between TTAs and controls. During ramp ascent, the dorsiflexion brought about by the adapted prosthetic ankle reduced the increased knee extension noted on the TTAs' involved side and the increased plantar-flexion on their sound side. During ramp descent, the plantar-flexion of the adapted mode increased the adaptation mechanisms observed in TTAs. The authors concluded that these findings suggested that the adapted mode leads to more physiologic kinematics and kinetics in the lower limbs in TTAs during ramp ascent but not during ramp descent. However, in the adapted mode, patients reported feeling safer during ramp descent, indicating that there might be other safety-related measures, such as toe clearance or coefficient of friction, influencing this perception. (This study appeared to have the same subjects [n = 16] and controls [n = 16] as the 2009 study by Alimusaj et al.; Fradet was the second author in that study.)

In an unpublished study, Ludviksdottir (2012) evaluated the effect on mobility and safety for lower limb amputees (LLA; n = 8) when changing from a carbon fiber prosthetic foot to a bionic foot. Results suggested that user mobility improves when using the bionic foot, and subjects experienced fewer falls and stumbles. The authors concluded that despite the limitation of the study, which is a small sample size (n = 8) and mixing above-knee and below-knee amputees, the results indicated that improvements in perceived mobility and reduced risk of falling while using the bionic foot may relate to the intelligent functions offered by the bionic foot, particularly the toe-lift in swing and terrain adaptation functions, which are not offered by mechanical prosthetic feet. They stated that to confirm these preliminary findings, a larger study is needed.

Rosenblatt et al. (2014) stated that people with amputation are at increased risk of falling compared with age-matched, non-disabled individuals. This may partly reflect amputation-related changes to minimum toe clearance (MTC) that could increase the incidence of trips and fall risk. This study determined the contribution of a dorsiflexing prosthesis to MTC. These researchers hypothesized that regardless of speed or incline, the active dorsiflexion qualities of the ProprioFoot would significantly increase MTC and decrease the likelihood of tripping. A total of 8 TTAs walked on a treadmill with their current foot at 2 grades and 3 velocities, then repeated the protocol after 4 weeks of accommodation with the ProprioFoot. A mixed-model, repeated-measures analysis of variance was used to compare MTC. Curves representing the likelihood of tripping were derived from the MTC distributions, and a multiple regression was used to determine the relative contributions of hip, knee, and ankle angles to MTC. Regardless of condition, MTC was approximately 70% larger with the ProprioFoot (p < 0.001), and the likelihood of tripping was reduced. Regression analysis revealed that MTC with the ProprioFoot was sensitive to all three angles, with sensitivity of hip and ankle being greater. The authors concluded that the ProprioFoot may increase user safety by decreasing the likelihood of tripping and thus the subsequent likelihood of a fall.

Rosenblatt et al. (2017) noted that individuals with trans-tibial amputation (TTA) are at increased risk of falling. The absence of an ankle joint and the associated musculature in these individuals can reduce clearance between the prosthetic foot and ground during the swing phase of gait, which may increase the risk of stumbling and, in turn, falling. In a prospective cohort study, these researchers attempted to associate minimum toe clearance (MTC; defined as a local minimum of the vertical displacement of the toe from toe-off to heel-strike relative to its position during mid-stance) during gait in the laboratory with community-based, trip-related stumbles by individuals with TTA using conventional feet. Participants completed electronic surveys to prospectively report stumbles and falls for 1 year thereafter. A volunteer sample of 8 unilateral, trans-tibial amputees who were K3- or K4-level ambulators and current patients at a local prosthetic clinic participated in this study. All participants completed the entire 1-year follow-up study. Prosthetic-side MTC while walking on a level treadmill at self-selected velocity (SSV) and self-reported trip-related stumbles in the community were recorded. Prosthetic-side MTC was more than 50% lower for participants who reported one or more trip-related stumbles on that side compared with participants who reported zero trip-related stumbles on the prosthetic side (MTC = 12.3 ± 0.8 mm versus 25.6 ± 5.4 mm, respectively; p = 0.036). The authors concluded that this was the first study relating laboratory-based measures to prospective stumbles by prosthesis users. The results suggested that prosthesis users with low MTC may be at increased risk of experiencing a trip-related stumble in the community. They stated that these preliminary findings justified the need for a larger study to relate MTC and the causes of community-based stumbles and falls by individuals with TTA.

This study had several drawbacks:

given the small sample size (n = 8), the study may be under-powered to detect a relationship between prosthetic-side MTC and any-cause stumbles, although, as discussed, these results were expected and logical. To minimize the influence of small sample size, these researchers included data from 2 participants (P7 and P14) who did not walk on a treadmill at 0% grade and at SSV. However, inclusion was justified, and given the large effect size, even excluding these subjects would not result in p > 0.05,
based on the definition, self-report of stumbles may be more subjective than that of falls, which may explain the high inter-subject variability in this measure (e.g., the high number of stumbles reported by participant P7 may reflect individual hyper-vigilance with regard to balance loss. This subject may have reported events that other participants ignored or deemed unimportant to report. Increasing sample size would reduce this variability, and
the results of this study were limited to subjects who were 30 years of age and older and may not generalize to younger prosthesis users.

Powered Lower Limb Prosthesis

Carey et al. (2015) stated that the choice of a myoelectric or body-powered upper-limb prosthesis can be determined using factors including control, function, feedback, cosmesis, and rejection. Although body-powered and myoelectric control strategies offer unique functions, many prosthesis users must choose one. These investigators performed a systematic review to determine differences between myoelectric and body-powered prostheses to inform evidence-based clinical practice regarding prescription of these devices and training of users. A search of 9 databases identified 462 unique publications. A total of 31 of them were included and 11 empirical evidence statements were developed. Conflicting evidence has been found in terms of the relative functional performance of body-powered and myoelectric prostheses. Body-powered prostheses have been shown to have advantages in durability, training time, frequency of adjustment, maintenance, and feedback; however, they could still benefit from improvements of control. Myoelectric prostheses have been shown to improve cosmesis and phantom-limb pain and are more accepted for light-intensity work. The authors concluded that current evidence is insufficient to conclude that either system provides a significant general advantage. Prosthetic selection should be based on a patient's individual needs and include personal preferences, prosthetic experience, and functional needs. This work demonstrated that there is a lack of empirical evidence regarding functional differences in upper-limb prostheses.

Proprio Foot

Gailey et al. (2012) examined the application of outcome measures to determine changes in function caused by standardized functional prosthetic gait training and the use of four different prosthetic feet in people with unilateral trans-tibial limb loss. The study utilized two self-report measures (Prosthetic Evaluation Questionnaire-Mobility Scale [PEQ-13] and Locomotor Capabilities Index [LCI]) and three performance-based measures (Amputee Mobility Predictor with a prosthesis [AMPPRO], 6-minute walk test [6MWT], and step activity monitor [SAM]). A total of 10 individuals with unilateral trans-tibial limb loss participated, with 5 having peripheral vascular disease (PVD) and 5 without PVD. Subjects were tested at baseline and after receiving training with their existing prosthesis and with the study socket and four prosthetic feet: SACH (solid ankle cushion heel), SAFE (stationary attachment flexible endoskeletal), Talux, and Proprio Feet, over a period of 8 to 10 weeks. Training was administered between testing sessions. No differences were detected by the PEQ-13, LCI, 6MWT, or SAM following training and after fitting with the test feet. However, the AMPPRO demonstrated differences following training with the existing prosthesis in the PVD group and between selected feet from baseline testing (p ≤ 0.05). Significant differences were found between the PVD and non-PVD groups (p ≤ 0.05) in the AMPPRO and 6MWT when using the Proprio Foot. Self-report measures were unable to detect differences between prosthetic feet.

The authors noted that drawbacks related to this study were similar to those found in many studies examining prosthetic components. For example, the small sample size (n = 10) was not due to recruitment issues but rather to the cost and time constraints associated with training each subject, fabricating the sockets, maintaining the prostheses, and purchasing the prosthetic feet and other related components. A larger study population would certainly increase the power of this study and enhance confidence in the results. Additionally, alternative prosthetic foot designs might yield different results than those feet selected in this trial; due to the previously mentioned constraints, this study was limited to four feet. The investigators expressed hope that this article would motivate further research to examine the use of these and other self-report and performance-based outcome measures in a larger sample of individuals functioning at all levels, particularly at the lower levels. Furthermore, the researchers did not evaluate the value of the prosthetic socket and suspension system, which should be incorporated into future studies. Lastly, using instrumented functional gait analysis, such as force distribution, stride length, and step width, could provide objective findings to determine potential differences among various prosthetic feet.

Delussu and colleagues (2013) determined the energy cost of walking (ECW) of a bionic foot (Proprio-Foot) during ambulation on floor and on treadmill (at different slopes) compared to walking with a dynamic carbon fiber foot (DCF). These researchers evaluated trans-tibial amputees (TTAs) perceived mobility with the prosthesis and their walking ability on stairs and ramps. The ECW tests were conducted on a regular floor surface and on treadmill with -5%, 0% and 12% slopes. In all conditions, TTAs were asked to walk at their own self-selected speed. Metabolic and cardiac data were collected using a portable gas analyzer. Tests were carried out at 6 data collection points:

with a standard suction system (SSS) and the DCF;
with the DCF after 7 weeks of using a hypobaric suspension system (HSS) with the DCF;
after 1 hour of Proprio-Foot use together with the HSS; and 3 more testing sessions were carried out at 30-day intervals, i.e., after 30, 60 and 90 days of Proprio-Foot use together with the HSS; TTAs perceived mobility using the prosthesis and walking ability on stairs and ramps were assessed.

A total of 10 TTAs completed the measurements; ECW with the Proprio-Foot obtained in the final floor-walking test was significantly lower than ECW with the DCF (p = 0.002). No significant improvements were observed for perceived mobility or walking ability. The authors concluded that these findings suggested that use of the Proprio-Foot can lower the ECW for TTAs in spite of its added weight compared to DCF. Moreover, they stated that further studies are needed to investigate ECW, quality of life (QOL), perceived mobility and motor capability in older and/or less active TTAs.

This study had several drawbacks. First, small sample size (n = 10). Second, the authors were aware that to achieve the secondary aim, i.e., to compare the effects of the Proprio Foot on ECW with those of the DCF, the same data collection should had been carried out in TTAs using the Proprio-Foot1 in association with their usual standard suction socket. Finally, the subjects included TTAs with high functional status who had a young mean age. Thus, the results could not be generalized across a wider population.

Agrawal et al. (2013) stated that, unlike the stance-phase dorsiflexion of conventional prosthetic feet, the microprocessor-controlled Proprio Foot allows for swing-phase dorsiflexion on stairs. The researchers compared Symmetry in External Work (SEW) between a microprocessor-controlled foot and conventional prosthetic feet in two groups with unilateral trans-tibial amputation (TTA) classified as Medicare Functional Classification Levels K-Level-2 and K-Level-3 during stair ascent and descent. A total of 10 subjects were evaluated while wearing three conventional prosthetic feet—solid ankle cushion heel (SACH), stationary attachment flexible endoskeleton (SAFE), and Talux—and the Proprio Foot using a study socket, with a 10- to 14-day accommodation period for each foot. Ground reaction forces (GRFs) were collected using F-scan sensors during stair ascent and descent. The SEW between the intact and amputated limbs was calculated for each foot. During stair ascent, the Proprio Foot resulted in higher inter-limb symmetry than conventional prosthetic feet, with significant differences between the Proprio Foot and SACH/SAFE feet. The swing-phase dorsiflexion appeared to promote greater inter-limb symmetry by facilitating forward motion of the body, resulting in a heel-to-toe center of pressure trajectory. During stair descent, all feet exhibited low symmetry without significant differences between them. The movement strategy used when descending stairs, which involved rolling over the edge of a step, had a greater influence on symmetry than the dorsiflexion features of the prosthetic feet. The authors concluded that individuals with unilateral TTA who function at either K-Level-2 or K-Level-3 and regularly negotiate stairs in their home, community, or work environment may benefit from using the Proprio Foot or other microprocessor-controlled feet that allow active dorsiflexion during swing.

The authors acknowledged several drawbacks in this study. The altered strategies employed by subjects while descending stairs suggested potential limitations in work calculation for this task due to the shortcomings of current in-sole sensor technology. Since the F-scan sensors could only measure the normal forces applied to the sensor, the movement of the prosthetic foot over the edge of the step may have resulted in GRFs with a substantial shear component. Therefore, the SEW results during stair descent should be interpreted and weighed appropriately. The strategy of rolling over the edge of the step during descent presented a significant challenge in measuring GRFs with commercially available instrumentation. However, despite some error, the SEW measure was able to quantify the asymmetry apparent during stair descent. An advantage of determining inter-limb symmetry with measures like SEW—compared to comparing movement kinetics in subjects without amputation—was the ability to quantify the similarity in strategies used by the intact and prosthetic limbs to move the body during stair negotiation. The absence of motion-capture data restricted the ability to determine joint kinematics, limiting the discussion to clinical observations and findings published in the literature. All prosthetic fitting and alignment procedures were performed by the same board-certified prosthetist using standard protocols as stated in the manufacturer’s technical manual. At the time of data collection, there were no commercially available, reliable, and valid devices that could quantify the dynamic alignment of a prosthetic foot.

Struchkov and Buckley (2016) noted that walking down slopes and/or over uneven terrain is problematic for unilateral TTAs. Accordingly, “ankle” devices have been added to some dynamic-response feet. This study examined whether the use of a microprocessor-controlled (MPC) passive-articulating hydraulic ankle-foot device improved the gait biomechanics of ramp descent compared to conventional ankle-foot mechanisms. A total of 9 active unilateral TTAs repeatedly walked down a 5° ramp, using a hydraulic ankle-foot with the microprocessor active or inactive, or using a comparable foot with a rubber ball-joint (elastic) “ankle” device. When inactive, the hydraulic unit's resistances were set to those deemed optimal for level-ground walking, and when active, the plantar- and dorsi-flexion resistances switched to a ramp-descent mode. Residual limb kinematics, joint moments/powers, and prosthetic foot power absorption/return were compared across ankle types using ANOVA. Foot-flat was attained fastest with the elastic foot and second fastest with the active hydraulic foot (p < 0.001). Prosthetic shank single-support mean rotation velocity (p = 0.006), as well as flexion (p < 0.001) and negative work done at the residual knee (p = 0.08), were reduced, while negative work done by the ankle-foot increased (p < 0.001) when using the active hydraulic compared to the other two ankle types. The authors concluded that the greater negative “ankle” work done when using the active hydraulic compared to the other two ankle types explained the corresponding reduction in flexion and negative work at the residual knee. They suggested that the use of a microprocessor-controlled hydraulic foot would reduce the biomechanical compensations required to walk down slopes.

The authors acknowledged several drawbacks in this study. First, with only one force platform within the ramp system, only trials where the prosthetic limb landed on the force platform were undertaken. Expanding the protocol to include trials in which the intact limb landed on the platform would have increased the likelihood of participants becoming fatigued. The researchers chose to remotely “trigger” the MPC foot into its “ramp descent” mode using a Bluetooth connection to the device. Although this does not reflect real-world usage, the investigators felt it was more important to assess the effects of the hydraulic resistance alterations associated with the device's “ramp descent” mode rather than to test when switching to this mode occurred. Second, all participants were familiarized with either an Elan or Echelon VT foot, both of which were hydraulic ankle-foot devices. Although the investigators found that the type of habitual foot participants used had minimal effect on results, having only 20 minutes to become familiar with the non-hydraulic Epirus foot may mean that familiarity is a confounding factor. The relatively short familiarization period may explain why certain parameters investigated returned relatively high group standard deviation values. Finally, there was no comparison of ramp descent with a non-articulating (rigid ankle) prosthetic ankle-foot. This was because it was felt that adding a fourth foot condition would be problematic due to potential fatigue issues for participants and/or that the biomechanical compensation required when using such feet might have “carry-over” effects to the other foot conditions, especially since all participants habitually used an articulating ankle-foot device.

Pro-Flex Foot

Childers and Takahashi (2018) stated that prosthetic feet are designed to store energy during early stance and then release a portion of that energy during late stance. The usefulness of providing more energy return depends on whether that energy transfers up the lower limb to aid in whole-body propulsion. These researchers examined how increasing prosthetic foot energy return affected walking mechanics across various slopes. A total of 5 individuals with unilateral trans-tibial amputation (TTA) walked on an instrumented treadmill at 1.1 m/s under three conditions (level ground, +7.5°, −7.5°) while wearing a prosthetic foot with a novel linkage system and a traditional energy storage and return foot. The novel foot (NF) demonstrated a greater range of motion (ROM; p = 0.0012) and returned more energy (p = 0.023) compared to the traditional foot. The increased energy correlated with an increase in center of mass (CoM) energy change during propulsion from the prosthetic limb (p = 0.012), and the increased prosthetic limb propulsion correlated to a decrease in CoM energy change (i.e., collision) on the sound limb (p < 0.001). The authors concluded that these findings showed that the NF was able to return more energy than a traditional prosthetic foot and that this additional energy was used to increase whole-body propulsion. They stated that the novel linkage system in the Pro-Flex foot allowed it to have more ROM and better conform to different slopes. The Pro-Flex foot leveraged its additional ROM to absorb and return more energy than the more traditional Vari-Flex foot. The additional energy return from the Pro-Flex foot translated up the kinematic chain to affect the whole body CoM in such a way that it enabled more energy for propulsion than the Vari-Flex foot. There was a significant inverse relationship between increasing CoM energy change during propulsion from the amputated limb and negative work absorbed by the sound limb during collision with the Pro-Flex foot, providing some support that the Pro-Flex foot has promise to reduce sound limb loading. However, there were no other differences in variables that correlated with reducing the risk of developing knee osteoarthritis, most likely due to the low sample size and low statistical power.

Heitzmann et al. (2018) noted that individuals with TTA showed greater peak prosthetic ankle power (push-off) when using energy-storing and returning (ESAR) prosthetic feet compared to solid-ankle cushion-heel feet. ESAR feet further contribute to the users' body support and thus limit prosthetic ankle motion. To improve ankle motion, articulating prosthetic feet have been introduced; however, these may diminish push-off. The investigators examined whether a novel prosthetic foot, featuring a serial layout of carbon fiber leaf springs connected by a multi-center joint construction, has advantages in kinematics and kinetics over a conventional ESAR prosthetic foot. A total of 11 individuals with unilateral TTA were fitted with the novel foot (NF) and a conventional ESAR foot (CF) and underwent 3-D gait analysis. As an additional power estimate of the prosthetic ankle, a unified, deformable segment (UD) model approach was applied; 11 matched individuals without impairments served as a reference. The NF showed an effective prosthetic ankle ROM that was closer to a physiologic ankle ROM, measuring 31.6° compared to 15.2° with the CF (CF versus NF, p = 0.003; NF versus reference, p = 0.171) without reducing the maximum prosthetic ankle joint moment. Furthermore, the NF exhibited a significant increase in prosthetic ankle power (NF 2.89 W/kg versus CF 1.48 W/kg; CF versus NF, p < 0.001) and a reduction of 19% in the peak knee varus moment and 13% in vertical ground reaction forces on the sound side for the NF compared to the CF. The authors concluded that the NF demonstrated that serial carbon fiber leaf springs connected by a multi-center joint construction provided a larger ankle joint ROM and higher ankle power than a conventional carbon fiber structure alone. Consequently, load was taken off the contralateral limb, as evidenced by the decrease in vertical ground reaction forces and peak knee varus moment.

The authors acknowledged several drawbacks in this study. The different accommodation times of 2 weeks for the CF and only 30 to 45 minutes for the re-fitted NF may have affected the results. As the NF was a pilot production product, the researchers had no prior experience with it and decided to conduct initial trials in a controlled environment, thus foregoing a 2-week accommodation period. However, they believed that a satisfactory accommodation period for the NF was provided, as subjects could get accustomed to it in various terrains. Another potential drawback was the fixed order of measurements (NF first; CF second), which may have introduced bias. This measurement order was chosen for practical reasons to increase the feasibility of the study and to avoid the need for removing and replacing markers between experimental conditions. Individuals with TTA walked slightly, but significantly slower with the NF (0.06 m/s) compared to the CF, and differences in kinetics may thus be attributed to speed as a confounding factor. Since a violation of normal distribution could occasionally be accepted in parametric tests, the authors retrospectively compared kinetics using a multivariate analysis of covariance (MANCOVA), with speed as a covariate. This retrospective analysis confirmed the results of the original non-parametric statistical analysis (peak dorsiflexion power conventional model NF 2.89 ± 0.90, CF 1.48 ± 0.35 W/kg, p < 0.001; UD model NF 2.77 ± 0.70, CF 2.12 ± 0.49 W/kg, p = 0.002). Thus, the researchers were confident that the differences in kinetics reflected the effects of the feet rather than differences in walking speed.

Osseointegrated Lower Limb Prosthetic Devices

Jonsson et al. (2011) noted that the osseointegration (OI) program for upper extremity amputation began in Sweden in 1990, when a titanium fixture was first implanted into a thumb. This method has since been applied to trans-humeral and below-elbow amputations. The treatment involves two surgical procedures: the first involves surgically attaching a titanium fixture to the skeleton, and the second, occurring six months later, involves placing a skin-penetrating abutment to which the prosthesis is attached. The researchers described the OI procedure concerning surgery, prosthetics, and rehabilitation. Patients with short stumps and previous issues with prosthetic fitting were selected for the program. From 1990 to April 2010, a total of 37 upper limb cases were treated and fitted with prostheses: 10 thumbs, 1 partial hand, 10 trans-radial, and 16 trans-humeral amputations. Of these, 7 patients were not prosthetic users. Patients reported improvements in function and quality of life (QOL) since undergoing OI. The authors concluded that OI represents an important platform for current and future prosthetic technology, as it improves the prosthetic situation through stable fixation, freedom of motion, and enhanced functionality. They also stated that further reports on complications and outcome data, including QOL assessments, would enhance the clinical relevance of this new treatment concept.

Hebert et al. (2017) noted that traditional socket prostheses are not a viable option for all lower-limb prosthetic users due to discomfort, pain in the residual limb, and fit-related issues, which negatively impact QOL and mobility. Osseointegrated or bone-anchored prosthetic implants have evolved over the last 20 years as a promising alternative for patients experiencing significant issues with socket prostheses. The investigators reviewed the literature to identify studies focusing on the evolution, clinical outcomes, success rates, and complications of osseointegrated lower-limb prostheses. Studies were summarized according to implant type, amputation level, and study characteristics, with a rating of the Level of Evidence. Information on patient selection criteria, outcomes, and complications was extracted. A total of 14 articles (with Level II, III, or IV evidence) met the inclusion criteria. Infection and soft-tissue irritation at the stoma were the most common complications. It was evident that over the years, changes in implant design, surgical technique, peri-operative and post-operative care, and rehabilitation protocols have resulted in improvements in functional outcomes and health-related QOL, as well as a reduction in complication rates. The authors concluded that osseointegration has become an established therapeutic option for a selected group of patients with limb amputation who do not tolerate traditional socket fittings. There is sufficient evidence to inform patients about the possible risks and complications compared to the benefits. They stated that osseointegration could provide substantial benefits to function and QOL for appropriate patients who accept the documented risks. They also noted that, as with any new technology, ongoing incremental iterations to optimize outcomes are expected during this clinical evolutionary phase. Adopting a standard classification system for tracking outcomes and complications would greatly assist in ongoing and future evaluations of implant techniques. Level of Evidence = IV.

Ontario Health’s technology assessment on “Osseointegrated prosthetic implants for people with lower-limb amputation” (2019) noted that osseointegrated prosthetic implants are biocompatible metal devices inserted into the residual bone to integrate with the bone and attach to the external prosthesis, eliminating the need for socket prostheses and the associated problems. The investigators conducted a health technology assessment of osseointegrated prosthetic implants compared with conventional socket prostheses for individuals with lower-limb amputation who experienced chronic issues with their prosthetic socket, leading to prosthesis intolerance and reduced mobility. The analysis included an evaluation of safety, effectiveness, cost-effectiveness, the budget impact of publicly funding osseointegrated prosthetic implants, as well as patient preferences and values. They performed a systematic literature search of the clinical evidence on the safety and effectiveness of the latest iterations of three implant systems: the Osseointegrated Prostheses for the Rehabilitation of Amputees (OPRA) Implant System, the Endo-Exo-Femur-Prosthesis, and the Osseointegration Group of Australia–Osseointegration Prosthetic Limb (OGAP-OPL). They examined the risk of bias in individual studies and determined the quality of the body of evidence according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) Working Group criteria. They also conducted a systematic economic literature search and performed a cost-utility analysis with a lifetime horizon from a public payer perspective. Furthermore, the investigators analyzed the net budget impact of publicly funding osseointegrated prosthetic implants in Ontario. To contextualize the potential value of osseointegrated prosthetic implants, they spoke with individuals with lower-limb amputations. A total of 9 studies were included in the clinical evidence review, all involving patients with above-the-knee amputation who underwent two-stage surgery and mostly had short-term follow-up. With osseointegrated prosthetic implants, scores for functional outcomes improved significantly as measured by the 6-Minute Walk Test (6MWT), Timed Up and Go (TUG) test, and Questionnaire for Persons with a Transfemoral Amputation (Q-TFA). The scores for QOL measured by the SF-36 showed significant improvement in the physical component summary but a non-significant decline in the mental component summary. The most frequently observed adverse event (AE) was superficial infection, occurring in about 50% of patients in some studies. Deep or bone infection was a serious AE, with variable rates among the studies depending on the length of follow-up. Treatment of deep or bone infection required long-term antibiotic use, surgical debridement, revision surgery, and, in some cases, implant extraction. Other AEs included femoral bone fracture, implant breakage, issues with extra-medullary parts requiring replacement, and implant removal. The examination of the quality of the clinical evidence according to the GRADE criteria found low certainty regarding improvement in functional outcomes, low certainty for QOL, and high certainty of an increase in AEs; all findings compared receiving an osseointegrated prosthetic implant versus not receiving one. In the economic model, osseointegrated prosthetic implants were found to be more effective and more expensive than remaining users of an uncomfortable socket prosthesis. The best estimate of the incremental cost-effectiveness ratio (ICER) for osseointegration compared with an uncomfortable socket was $94,987 per quality-adjusted life-year (QALY) gained. The probability of osseointegration being cost-effective was 54.2% at a willingness-to-pay value of $100,000 per QALY gained. The annual net budget impact of publicly funding osseointegrated prosthetic implants in Ontario over the next five years, for a small population of eligible candidates, would range from $1.5 million in year 1 to $0.6 million in year 5, for a total of $5.3 million over five years. The investigators interviewed 13 individuals with lower-limb amputation; 9 had experience with both a conventional socket prosthesis and an osseointegrated prosthetic implant, 3 had experience with a conventional socket prosthesis only, and 1 had only recently undergone amputation and had not yet chosen a prosthesis. Individuals who received an osseointegrated prosthetic implant reported better mobility and QOL than before receiving the implant but expressed concerns regarding the ongoing risk of infection and potential problems with implant maintenance. Individuals using a conventional socket prosthesis cited cost as the only factor preventing them from undergoing an osseointegration procedure. The authors concluded that in the studies included in the clinical evidence review, most individuals who received osseointegrated prosthetic implants were followed for only a few years. Studies showed that functional outcomes and physical ability improved with osseointegrated prosthetic implants (GRADE: Low), but there was uncertainty regarding the impact of these implants on emotional health (GRADE: Low). Osseointegrated prosthetic implants can lead to serious AEs such as bone infection and fracture in some patients, which may require additional surgeries (GRADE: High). The reference case of the primary economic evaluation represented a conservative estimate of cost-effectiveness and found that osseointegration may be cost-effective, but there is a large degree of uncertainty given parameter uncertainty and the need to use proxy costs. Scenario analyses examined potential variations in approaches to modeling and parameter selection. Qualitative interviews with individuals with lower-limb amputation and caregivers underscored the challenges of conventional socket prostheses, but cost remains an important barrier to pursuing osseointegrated prosthetic implantation.

Diaz-Balzani et al. (2020) stated that the conventional use of custom-designed prosthetic sockets is affected by discomfort related to well-known problems such as sweating, sores or skin irritation, excessive weight and harness, and impaired body image, leading to a high rate of abandonment. Osseointegrated prosthetic implants for limb amputation are progressively evolving to overcome the limitations of sockets. The researchers conducted a systematic review of the use, safety in terms of infection rates and complications, and reported outcomes of upper and lower limb osseointegrated prosthetic implants. A systematic search was performed for studies examining outcomes of the osseointegration technique in upper and lower limb amputees according to PRISMA guidelines, using a PRISMA checklist and algorithm. The MINORS score was used for methodological assessment. A total of 17 articles about the treatment of patients with upper or lower limb amputation using an osseointegrated prosthesis were included. The overall rate of infections was 32%. All clinical outcomes reported were related to lower limb amputations, and no clinical data for upper limb cases were found. The post-operative mean values of the Mental Component Summary (MCS) and Physical Component Summary (PCS) of the SF-36 and Q-TFA were 55.1, 45.4, and 73.8, respectively, while the 6MWT and TUG test scored average values of 388 meters and 11.5 seconds, respectively. The MINORS score ranged from 5 to 13, with a median of 11 (IQR, 9 to 11). Osseointegration was associated with a high rate of post-operative complications, but significant improvements in clinical outcomes compared to pre-operative times were observed. The authors concluded that available evidence was limited but suggested good clinical outcomes and significant survivorship of the implants. Moreover, they stated that further clinical studies are needed to establish which type of implant is associated with higher clinical performance and lower rates of post-operative complications and infections.

Safari (2020) noted that the human-prosthesis interface is one of the most complicated challenges facing the field of prosthetics, despite substantial investments in research and development by researchers and clinicians worldwide. The journal of the International Society for Prosthetics and Orthotics, Prosthetics and Orthotics International, has contributed significantly to the growing body of knowledge on this topic. In celebrating the 50th anniversary of the International Society for Prosthetics and Orthotics, this narrative review aimed to examine how human-prosthesis interfaces have changed over the past 50 years; how research has contributed to an understanding of interface mechanics; how clinical practice has been informed as a result; and what potential future directions may be. Studies reporting on the comparison, design, manufacturing, and evaluation of lower limb prosthetic sockets and osseointegration were considered. This review demonstrated that, over the last five decades, clinical research has improved the understanding of socket designs and their effects; however, high-quality research is still needed. In particular, there have been advances in the development of volume and thermal control mechanisms, with a few designs having the potential for clinical application. Similarly, advances in sensing technology, soft tissue quantification techniques, computing technology, and additive manufacturing are moving towards enabling automated, data-driven manufacturing of sockets. For individuals unable to use a prosthetic socket, osseointegration provides a functional solution not available 50 years ago. Furthermore, osseointegration has the potential to facilitate neuromuscular integration. Despite these advances, further improvements in the mechanical features of implants, as well as infection control and prevention, are needed.

Pitkin and Frossard (2021) noted that osseointegrated implants for direct skeletal attachment of transtibial prostheses carry risks that are yet to be fully resolved, such as early loosening, mechanical failure of percutaneous and medullary parts of the implant, peri-prosthetic issues, and infections. Under-loading could lead to early loosening and infection, while over-loading might compromise the bone-implant interface; thus, a Goldilocks loading regimen applied by transtibial bone-anchored prostheses is critical for the safe and efficient development of osseointegration (OI) around the implant during rehabilitation and beyond. The researchers hypothesized that Goldilocks loading could be achieved when ambulating with an anthropomorphic prosthetic ankle showing a moment-angle relationship similar to that of a sound ankle. Quantitative characteristics of the moment-angle curve of the sound ankle during the dorsiflexion phase of free-paced walking were extracted for four able-bodied subjects (experiment 1). A slope of the moment-angle curve (stiffness) was calculated twice: for the first half and for the second half of the moment-angle curve. The difference in stiffnesses (those in the second half minus those in the first half) was termed the index of anthropomorphicity (IA). By definition, a positive IA was associated with a concave shape of the moment-angle curve, while a negative IA was associated with a convex shape. In experiment 2, the same recordings and calculations were carried out for three subjects fitted with transtibial osseointegrated fixation while walking with their usual feet and the Free-Flow Foot (Ohio Willow Wood). The Free-Flow Foot was selected for its anthropomorphicity demonstrated in previous studies with amputees using traditional socket attachment. The IA was 5.88 ± 0.93 for the able-bodied subjects, indicating that the stiffness during the first part of the dorsiflexion phase was substantially less than during the second part, as the calf muscles resisted angulation in the ankle significantly less than during the second part of the dorsiflexion phase. For amputees fitted with the Free-Flow Foot, IA was 2.68 ± 1.09, while it was −2.97 ± 2.37 for the same amputees fitted with their usual feet. The authors concluded that IA, while of different magnitudes, were positive in both the control able-bodied group and the amputee group wearing the Free-Flow Foot, which was qualitatively associated with a concave shape of their moment-angle curves. The three usual feet worn by the subjects were classified as non-anthropomorphic, as their individual moment-angle curves were convex, resulting in negative IAs. Furthermore, this study showed that a foot with anthropomorphic characteristics tended to decrease maximal loads at the bone-implant interface compared to non-anthropomorphic feet, potentially minimizing the risks to compromise the integrity of this interface. The researchers stated that this study should be considered a stepping stone for manufacturers of components, prosthetic care providers, and decision-makers developing international standards and guidelines toward better evidence-based prescriptions of safe prosthetic components for the growing population of individuals with transtibial amputation fitted with osseointegrated fixation worldwide. They suggested that future longitudinal studies should compare ankle stiffness with various prosthetic constructs (e.g., components, alignment) for a larger cohort of individuals fitted with a transtibial prosthesis. This could provide a better understanding of intra- and inter-variability inherent to the design of components and daily activities. Subsequent cross-sectional studies could establish a link between ankle stiffness outcomes and additional 3D biomechanical (e.g., dynamics, kinematics, joint work, and power), physiological (e.g., EMG of residual muscles, metabolic energy consumption, development of OI, and skin damage), and subject experience (e.g., PEQm, TAPES-M) information.

The authors acknowledged that this study presented the typical drawbacks of a retrospective preliminary study comparing kinematic and kinetic data collected with two small and unrelated series. As these investigators reported (Frossard et al., 2019), the interpretation of differences in stiffness outcomes between prostheses was limited mainly due to unknown effects of confounders (e.g., individual length of the residual limb, distal position of the transducer, short acclimation with the Free-Flow Foot, foot size, and footwear). Unknown differences in spatiotemporal gait characteristics (e.g., walking speed, walking base, step, and stride length), kinematics (e.g., trunk bending, knee flexion, and hip range of movement), and kinetics (e.g., knee and hip joint power) also limited the comparison. Furthermore, the comparison of stiffness between series of able-bodied individuals and those with transtibial amputation was constrained by discrepancies in measurements of ankle angle during dorsiflexion (e.g., automated 3D Vicon motion capture versus manual 2D Kinovea movement analysis) and bending moment (e.g., inverse dynamics using fixed force plates versus direct measurement using a wearable load cell).

Donnelley et al. (2021) synthesized existing literature on the cost-effectiveness of prosthetic interventions and examined their applicability to low- and middle-income country (LMIC) settings. The investigators conducted a systematic literature review using subject headings including "prosthetics," "amputation," and "cost analysis" with PubMed, Embase, and Web of Science search engines, yielding 1,194 articles. An additional 22 articles were identified via backward citation searching, resulting in a total of 1,144 after duplicate removal. The search was last conducted in May 2019. Studies were included if they conducted an economic analysis of an upper or lower extremity prosthetic device. Studies were excluded if (i) the full text was unavailable in English; (ii) the study was a systematic review or meta-analysis; or (iii) the study did not have a prosthetic comparison group. Using DistillerSR software, two authors independently conducted title and abstract screening, while one author conducted full-text screening. The proportion of initially identified studies that met the final inclusion criteria was 1% (12 of 1,144). Data were dually extracted by two authors and reviewed by three additional authors. All included studies (n = 12) examined lower extremity amputations comparing advanced technology. No studies were conducted in LMICs. Comparable data between studies demonstrated (i) the cost-effectiveness of microprocessor-controlled knees over non-microprocessor-controlled knees for trans-femoral (TF) amputation in high-income settings; (ii) equivocal findings regarding osseointegrated versus socket-suspended prostheses; and (iii) increased costs for ICEX and modular socket systems over patellar tendon-bearing socket systems with no functional improvement. The authors concluded that there are few prosthetic cost analyses in the literature; additional analyses are needed to determine the direct and indirect costs associated with prosthetic acquisition, fitting, and maintenance; the costs of amputee rehabilitation; and long-term economic and quality-of-life (QOL) benefits. Such studies may guide future prosthetic and rehabilitative care, especially in resource-austere settings where prosthetic needs are greatest.

Akhtar et al. (2021) noted that the management of peripheral vascular disease (PVD) can necessitate amputation. Osseointegration surgery is an emerging rehabilitation strategy for amputees. The investigators reported on the findings of six patients who had PVD requiring trans-tibial amputation (PVD-TTA) and either simultaneous or subsequent osseointegration (PVD-TTOI). A total of six patients (aged 36 to 84 years) with TTA and pre-existing PVD underwent osseointegration between 2014 and 2016 and were followed up for 3 to 5 years. Pre- and post-operative clinical and functional outcomes (pain, prosthesis wear time, mobility, walking ability, and quality of life [QOL]) and adverse events (AEs, including infection, fracture, implant failure, revision surgery, additional amputation, and death) were prospectively recorded. All patients' mobility improved following osseointegration; three patients initially required the use of a wheelchair, precluding baseline walking tests; the other three were classified as K level 1 or 2, with a mean baseline Timed Up and Go (TUG) test of 14.0 ± 2.2 seconds and a 6-Minute Walk Test (6MWT) of 262 ± 75 meters. At the time of the latest follow-up, all patients were K level 2 or 3, with a mean TUG of 12.7 ± 7.2 seconds and a 6MWT of 353 ± 148 meters; four patients wore their prosthesis for 16 hours or more daily. Three patients experienced superficial soft-tissue infections, while one other patient had recurrent infections 2.8 years after osseointegration, requiring debridement and trans-femoral amputation; this patient died two days following surgery from myocardial infarction (MI) caused by coronary atherosclerosis. The authors concluded that all six patients who underwent PVD-TTOI in this case series survived through two years. Patients who initially used a wheelchair achieved and maintained independent, unaided ambulation until PVD-related impairments in the contralateral leg occurred in one patient. Patients previously using a traditional socket prosthesis reported improvements in mobility and QOL. One patient's death underscored the importance of careful patient selection. However, marked improvement in the other five patients suggested cautious optimism that PVD-TTA is not an absolute contraindication for osseointegration; conscientious further investigation appears appropriate. Level of Evidence = IV.

The authors noted that the main drawback of the trial was the small cohort size, consisting of only 6 patients. Additionally, there were multiple differences among the patients: 3 were long-term amputees, while the other 3 had primary amputations with simultaneous osseointegration. There was also variation in specific dysvascular etiologies, age, co-morbidities, and potentially other relevant factors, such as employment and depression status, which were not evaluated.

Akhtar et al. (2022) stated that management of total knee replacement (TKR) infection may sometimes necessitate knee fusion (KF) or transfemoral amputation (TFA), both of which are associated with low mobility and quality of life (QOL). Transcutaneous osseointegration for amputees (TOFA) offers superior mobility and QOL compared to traditional socket prostheses but has not been studied in patients with a history of infected TKR. The investigators tested the hypothesis that patients who have undergone TFA or KF following infected TKR achieve better mobility and QOL after TF osseointegration. They conducted a retrospective evaluation of a prospectively maintained registry, identifying 10 patients with prior infected TKR. Mobility assessments (daily prosthesis wear time, K-level, TUG, 6MWT) and QOL surveys (Questionnaire for Persons with a Transfemoral Amputation Global, Mobility, and Problem scores) were compared pre-operatively and after at least 2 years. Significant improvements were observed in daily wear hours, K-level, 6MWT, and Questionnaire for Persons with a Transfemoral Amputation Global and Problem scores (p < 0.05). Within one year, 4 patients (40%) required additional surgeries. After several years, 7 patients (70%) had at least one additional surgery, and 5 (50%) had multiple surgeries, averaging 1 debridement and 1.3 soft-tissue refashionings per patient; one patient died of newly diagnosed cancer one year after transcutaneous osseointegration. The authors concluded that TF osseointegration provided significantly better mobility and QOL compared to KF or TFA with traditional socket prostheses following infected TKR. They also noted that improvements in technique to prevent subsequent surgeries may enhance the overall experience.

The authors acknowledged that the main drawback of this study was the small cohort of 10 subjects. There was considerable heterogeneity in demographic characteristics and prior surgical history among the patients: some had KF, while others had TFA, for varying durations before TOFA. The merits of the study included a minimum 2-year follow-up for all subjects (except the deceased patient) and attention to mobility and QOL data metrics. Several potential sources of bias were identified. TOFA remains relatively obscure and financially expensive, limiting patient awareness and access. Additionally, highly functional and satisfied patients with KF or TFA may not seek TOFA, potentially biasing the selection in this study. No patients were lost to follow-up, which limited reporting bias. The team’s high-volume TOFA experience may also bias the reproducibility of the results.

Mohamed et al. (2022) stated that septic loosening and stem breakage due to metal fatigue are rare but well-known causes of orthopedic implant failure. This issue may also affect the components of the osseointegrated implant system for individuals with transfemoral (TF) amputation who subsequently undergo revision. Identifying risk factors is crucial to minimize the frequency of revision surgery following implant breakage. In a retrospective comparative study, these investigators aimed to determine: (i) the proportion of patients who received an osseointegrated implant following TF amputation and underwent revision surgery, and the causes of those revisions; and (ii) the factors associated with revision surgery when stratified by the location of mechanical failure and (septic) loosening (intra-medullary stem versus dual cone adapter). Between May 2009 and July 2015, the researchers treated 72 patients with an osseointegrated implant. Inclusion criteria required a minimum follow-up of 5 years and a standard press-fit cobalt-chromium-molybdenum (CoCrMb) TF osseointegrated implant. Based on these criteria, 83% (60 of 72) of patients were eligible; a further 3% (2 of 60) were excluded due to lack of informed consent (n = 1) and loss to follow-up (n = 1). Ultimately, 81% (58 of 72) of patients were included for analysis. The authors compared patient characteristics (gender, age, and body mass index [BMI]), implant details (diameter of the intra-medullary stem, length of the dual cone, and implant survival time), and event characteristics (infectious complications and distal bone resorption). Data were retrieved from electronic patient files and the authors’ cloud-based database, analyzed by individuals not involved in patient care. Failures were categorized as: (i) mechanical failures, defined as breakage of the intra-medullary stem or dual-cone adapter, or (ii) (septic) loosening of the osseointegrated implant. A total of 34% (20 of 58) of patients underwent revision surgery. In 12% (7 of 58) of patients, the reason for revision was due to intra-medullary stem failures (6 breakages, 1 septic loosening), and in 22% (13 of 58) of patients, it was due to dual-cone adapter failure (10 weak-point breakages and 4 distal taper breakages; 1 patient broke both the weak-point and the dual-cone adapter). Smaller median stem diameter (failure: 15 mm [inter-quartile range (IQR) 1.3], non-failure: 17 mm; IQR 2.0, difference of medians 2 mm; p < 0.01) and a higher median number of infectious events (failure: 6; IQR 11, non-failure: 1; IQR 3.0, difference of medians -5; p < 0.01) were associated with revision intra-medullary stem surgery. No risk factors could be identified for broken dual-cone adapters. The authors concluded that possible risk factors for system failure of this osseointegration implant included small stem diameter and a high number of infectious events. They did not find factors associated with dual-cone adapter weak-point failure and distal taper failure, likely due to the small sample size. When treating a person with a lower-limb amputation using a CoCrMb osseointegrated implant, the researchers recommended avoiding a small stem diameter. They stated that further investigation with longer follow-up is needed to study the success of revised patients. Level of Evidence = III.

Black et al. (2022) noted that patients with transfemoral (TF) and transtibial (TT) amputations generally rely on socket-suspended (SS) prostheses for ambulation. The use of these aids can be complicated by poor fit, leading to tissue damage, pain at the socket-limb interface, and an inability to ambulate. Osseointegrated implants (OIs) directly anchor a prosthesis to the patient's residual limb, eliminating these issues. However, they require customized components and additional surgeries. In a retrospective chart review, these researchers conducted the first cost-benefit analysis of OI prostheses compared to SS prostheses for lower limb amputees in the U.S. This study included all patients who received unilateral lower limb OI prostheses at the authors’ institution. Costs were calculated using a bottom-up approach with Current Procedural Terminology (CPT) codes; utilities and SS prosthesis costs were derived from previous studies. A Monte Carlo model was used to project costs and lifetime quality-adjusted life years (QALY) for OI and SS prostheses, and the incremental cost-effectiveness ratio (ICER) of OI compared to SS prostheses was determined. A total of 25 patients (12 female) were included in the study, with a mean follow-up of 17 months post-implantation. The average cost of OI surgery was $54,463; 20% of patients required pre-implantation soft tissue revision surgery ($49,191). Complication rates per year and average costs were as follows: soft tissue infection (29%, $435), bone/implant infection (11%, $11,721), neuroma development (14%, $14,659), and mechanical failure (17%, $46,513); the ICER was $44,660. A cost-effectiveness acceptability curve demonstrated that OI was favored over SS in 78% of cases at a willingness-to-pay of $100,000 per QALY. In a one-way sensitivity analysis, the ICER was most sensitive to the mechanical failure rate, mechanical failure cost, and prior SS prosthesis costs. The authors concluded that the model showed that OI prostheses provided a higher QOL at affordable costs compared to poorly tolerated SS prostheses in patients with lower limb amputations in the U.S. The cost-effectiveness was largely determined by the patient's previous SS prosthesis costs and was limited by the frequency and costs of OI mechanical failure. The researchers stated that more research is needed to understand the long-term benefits and risks of OI prostheses.

In a retrospective study, Orgel et al. (2022) examined differences in functional outcomes and satisfaction between patients treated with transcutaneous osseointegrated prosthetic systems (TOPS) and those using socket prostheses after TF amputation. This analysis included patients from a single center and was conducted between February 2017 and December 2018. A total of 139 patients with prostheses were included and divided into two comparable groups (socket and TOPS group). Incomplete data sets were excluded, resulting in 36 subjects for the socket group and 33 for the TOPS group. Functional outcomes and satisfaction were evaluated using Patient Reported Outcome Measures (PROMs), including the Questionnaire for Persons with a Transfemoral Amputation (Q-TFA), EQ-5D-5L, Satisfaction with Prosthesis Questionnaire (SAT-PRO), Prosthesis Mobility Questionnaire (PMQ 2.0), and Functional Independence Measure (FIM). Significant results favoring TOPS patients were identified for the EQ-5D 5L (p = 0.004), Q-TFA (p = 0.000), SAT-PRO (p = 0.000), and PMQ 2.0 (p = 0.000). No statistical significance was found for FIM (p = 0.318). The authors concluded that in this study, TF amputees treated with TOPS showed significantly higher scores for mobility and satisfaction, indicating the high potential of TOPS in the prosthetic treatment of patients with TF amputation regarding their functional abilities in daily life.

The analysis had several drawbacks. The researchers noted that the high percentage of excluded data due to incomplete information should be critically considered. Many patients often did not complete the entire questionnaires, as some subjects only visited the outpatient clinic once. They returned the incomplete questionnaire, so the missing information only became apparent during the anonymous retrospective analysis, and the investigators could not complete the data. Additionally, this was a retrospective study with a small sample size, although it was relatively large compared to the current literature on this topic. Furthermore, the inconsistency of descriptive data concerning the socio-cultural sector should also be highlighted. This inconsistency could be explained by the fact that these were discrete and personal topics on which not every subject wanted to provide information. A further limitation of the study was the study design itself; it is well known that prospective study designs offer much more value, but this dataset was created retrospectively.

Potter et al. (2025) stated that individuals who have undergone TF amputation often have difficulty donning and using a conventional socket prosthesis. Osseointegrated prostheses may alleviate certain issues, potentially resulting in better outcomes; however, few prospective studies have examined these outcomes or quantified the purported benefits. The researchers aimed to address the following questions: First, did PROMs improve between baseline and 2-year follow-up among those who underwent osseointegration surgery after TF amputation? Second, what was the frequency and severity of early complications related to the osseointegration procedures? Third, what was the minimum clinically important difference (MCID) in a global PROM in this patient population? In a prospective observational study conducted between October 2017 and October 2023, the investigators enrolled 41 subjects to undergo TF osseointegration surgery using the Osseointegrated Prostheses for the Rehabilitation of Amputees implant system for patients who had trouble using traditional socket-based prostheses. Of those, 5% (2 of 41) did not undergo surgery, 2% (1 of 41) were lost to follow-up, and 2% (1 of 41) died before the final 2-year follow-up, resulting in 90% (37 of 41) available for analysis. Subjects completed the validated Q-TFA and the Patient-Reported Outcomes Measurement Information System (PROMIS) questionnaire before surgery and at 3, 6, 12, and 24 months following the two-stage procedure. A total of 37 subjects (3 women and 34 men; mean ± SD age of 38 ± 10 years) reached the 24-month follow-up visit, and 4 subjects withdrew from the trial. The researchers tabulated the frequency and types of surgical complications experienced by patients and calculated the anchor-based MCID for the Q-TFA global score (0 to 100 maximum). The Q-TFA's global score was generated based on answers to three questions: "How would you summarize your level of function with your current prosthesis?", "How would you summarize the problems you experience with your current prosthesis?", and "How would you summarize your overall situation as an amputee?" Using the sum of the numerical scores for the three questions, the investigators found the difference between the baseline and the final follow-up for the subjects. They then took the first quartile of the difference to represent the median change in the lower 25% of the data and used this value as the MCID. Scores in the study group improved in nearly all domains of the Q-TFA and PROMIS, including those related to prosthetic use, prosthetic mobility, and physical function (all p < 0.05). Participants developed superficial infections in 29% (15 of 51) of implanted limbs, all of which were treated successfully with antibiotics alone; 7 patients developed deep infections, only 1 of which involved the bone and implant. The anchor-based MCID in the Q-TFA global score was calculated as 17 out of 100 for this study population. The authors concluded that functional patient-reported outcomes improved in multiple domains among this cohort who underwent osseointegration surgery after TF amputation, revealing the promise of this technology for patients with unsatisfactory function using conventional socket-based prostheses. Infections and other complications were lower than in previous trials of osseointegration after limb loss. The researchers stated that the novel MCID reported could be employed to examine whether patients have clinically important improvements in future osseointegration surgery studies comparing results between different implants, surgical techniques, and patient populations. Level of Evidence = II.

Forsberg et al. (2025) noted that patients who have undergone trans-humeral (TH) amputation often have difficulty wearing conventional socket-based prostheses, resulting in frequent dissatisfaction and abandonment of the prosthesis. Osseointegration surgery may alleviate or mitigate many of these issues by providing a firm, reliable attachment between the humerus and the prosthesis, potentially leading to better functionality and QOL; however, it is unclear whether the risks inherent to transdermal bone-anchored implants would outweigh the potential functional benefits. The investigators addressed the following two questions: First, were there improvements in patient-reported outcome measures (PROMs) at 2 years among patients with TH amputations undergoing osseointegration compared to pre-surgical function? Second, what was the frequency and severity of complications related to the osseointegration procedures? In a prospective observational study conducted between October 2016 and April 2021, the researchers recruited 12 active duty service members, retirees, and healthcare beneficiaries to undergo TH osseointegration surgery using the OPRA implant system. The primary indication was difficulty wearing a traditional socket-based prosthesis after extended efforts to do so, with a residual humerus of 10 cm or greater. Exclusion criteria included a residual humerus of less than 10 cm, BMI greater than 35 kg/m², severe peripheral vascular disease including diabetes, use of immune-suppressant medications, pregnancy, and inability to sign their own consent. A total of 24 patients were screened, and 12 met the inclusion criteria. All 12 subjects (all men with a mean ± SD age of 38 ± 12 years) completed the minimum follow-up time of 2 years for this analysis. The majority of patients' mechanisms of injury were blast-related (10 of 12), followed by motor vehicle collision (2 of 12). All 12 subjects in this prospective FDA early feasibility study underwent both Stage 1 (fixture implantation into the humerus) and Stage 2 (muscle and skin fashioning) surgery, and none were lost to follow-up at a minimum of 2 years after April 2021. Subjects completed the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire, the Defense and Veterans Pain Rating Scale (DVPRS), and items from three domains of the PROMIS before surgery and at 3, 6, 12, and 24 months after the second stage of the procedure. They also reported their prosthetic use time in hours per day and days per week. The researchers recorded the frequency of complications related to the procedure, including soft tissue, mechanical, and infectious complications. Subjects showed improvements in mean ± SD DASH scores between baseline (36 ± 23) and a minimum of 2-year follow-up (19 ± 13) (mean difference [MD] of 17; 95% confidence interval [CI]: 1 to 33; p = 0.04), and they increased their days per week of prosthetic use time between baseline (4 ± 3) and the 2-year follow-up (7 ± 1) (MD of 3; 95% CI: 1 to 5; p = 0.02). The investigators found no difference in the physical function score (p = 0.47), pain interference score (p = 0.46), pain behavior score (p = 0.16), the DVPRS (p = 0.58), or prosthetic use time in hours per day (p = 0.09). They observed no superficial soft tissue infections; however, they noted 2 soft tissue complications, 2 mechanical complications, and 1 skin penetration aperture complication consisting of marginal necrosis that healed uneventfully. No patients who developed these complications returned to the operating room. The authors concluded that this FDA early feasibility study showed improvements in patients' DASH scores and prosthetic use, suggesting that TH osseointegration using the OPRA implant system is a promising approach for patients who have lost a limb. Complications were relatively minor and treatable, and no infections were observed, which was consistent with previous evidence indicating that infections may be considerably less frequent for those living with TH amputation than for those who have undergone osseointegration for lower extremity amputations. Thus, the technique appeared promising in this patient population, with the caveat that this was a preliminary study in a very small selected patient population. Moreover, the researchers stated that these findings could be used to justify the use of the OPRA implant system in appropriate patients living with TH amputations, aid in informing future clinical trial design, and support a Pre-market Approval (PMA) application with the FDA. Level of Evidence = II.

Clinical Evaluation of Fall Risk in Older Adults Who Use Lower-Limb Prostheses

Finco et al. (2023) stated that no reviews or evidence-based clinical protocols exist to examine fall risk in older adults who use lower-limb prostheses, despite falls being prevalent and costly in this population. In a scoping review, these investigators examined assessments, defined as clinical outcome measures and gait parameters, associated with fall risk in this population to determine if a systematic review is needed and help inform an evidence-based clinical protocol. Google Scholar, PubMed, and Scopus were searched on April 19, 2022 to include peer-reviewed original research. Included studies reported relationships between falls and clinical outcome measures or gait parameters in older adults who use TT or TF prostheses. Clinical outcome measures included self-reported questionnaires and functional mobility tests. Gait parameters included spatiotemporal, kinematic, and kinetic data during walking and stair negotiation. A total of 19 studies were included. Clinical outcome measure scores, gait parameter data, and cut-off scores by fall status (non-fallers, single fallers, recurrent fallers) were summarized. A total of 6 studies determined clinical outcome measures that had statistically significant associations with falls, and 2 studies determined gait parameters that had statistically significant associations with falls. The authors concluded that the majority of studies found that no clinical outcome measure or gait parameter alone was effective in identifying fall risks in this population. These investigators stated that future research should examine a combination of assessments and collect prospective fall data to move towards establishing an evidence-based protocol to examine fall risk in older adults using lower-limb prostheses.

Adjustable Click Prosthesis (RevoFit)

The adjustable click prosthesis is a self-adjustable prosthetic socket that features a click reel consisting of an adjustable dial, strong lightweight laces, and lace guides. The dial incorporates a gearing mechanism that advances the lace and moveable portions. Turning the click reel engages the lacing system, allowing for adjustments in predetermined areas of the socket tailored to each individual’s needs. This design is intended to provide control over compression and expansion to manage fluctuations in residual limb volume and facilitate ease of donning and doffing.

Dillingham et al. (2019) stated that there is a need for an adjustable socket to accommodate changes in residual limb volume and shape. Additionally, global limb loss rates are rising, creating a significant unmet need for affordable and accessible prosthetic systems. In a prospective, 2-week, single-group, pre-post intervention study, these researchers examined the use of an immediate fit modular prosthetic system (iFIT Prosthetics, LLC). Subjects were at least 6 months post-amputation and walking with a conventional prosthesis, and they were free of skin wounds, other neurological disorders, and severe pain conditions. Participants were fitted with an immediate fit prosthesis and instructed to wear it for a 2-week evaluation period, following a progressive wearing schedule. Outcome measurements were completed at the 2-week follow-up, focusing on self-reported satisfaction, gait biomechanics, and intra-socket peak pressures. A total of 26 subjects were enrolled, with 22 completing the study. The average age was 50 years (SD ± 10.2), with 4 women; 16 were dysvascular, and 10 had traumatic etiologies. Significant differences (p = 0.03) in self-reported satisfaction favored the iFIT device (29.33, SD ± 4.51) compared to the conventional device (25.52, SD ± 6.8). No falls or limb ischemia were reported. Gait biomechanics showed no differences across temporal characteristics, but intra-socket peak pressures were significantly lower for the iFIT prostheses overall (p = 0.0014), at the anterior tibia (p = 0.0002), and the lateral side of the residual limb (p = 0.013). The authors concluded that the iFIT TT prosthetic system appeared safe in this short-term, single-group, pre-post study, providing preliminary evidence to support its feasibility. It compared favorably to participants' conventional prostheses across all outcome measures. With its cost, adjustability, and accessibility advantages, this device may prove useful for individuals with TT amputations. They also stated that a larger multi-center study is needed to confirm these findings. Level of Evidence = III.

Devin et al. (2023) noted that fluctuations in residual limb volume during daily activities are common among lower-limb amputees. This can result in frequent changes to fit, which cannot be accommodated by commonly used prosthetic sockets. The real-time effects of these minor socket fit changes on interface biomechanics have not been extensively studied. Amputees often use different layers of socks to accommodate volume fluctuations, enabling adjustments to socket fit. The researchers altered socket fit levels by adding or removing sock layers for a TT amputee who typically donned 2 sock layers, simulating looser and tighter socket fits. Interface pressure and shear sensors were placed at known prominent load-bearing sites of the TT residuum/socket interface, such as the patellar tendon (PT), popliteal fossa (PF), and anterior-distal (AD) end, to measure real-time biomechanical interactions during standing and level walking. Although socket fit level was only slightly modified, changes in interface pressure and shear across anatomical sites were observed. A tighter fit corresponded to notable pressure reduction at the AD during early stance and pressure increase at the PT during terminal stance due to the residuum being pushed up. Shear-to-pressure ratios were used to evaluate comfort, while pressure and shear-time integrals were used to examine tissue health. The authors observed more notable changes at tissue sites (e.g., AD and PF) and concluded that a combined evaluation of pressure and shear, including shear-to-pressure ratios and time integrals, may provide insight for residuum care.

The authors acknowledged that this study was limited to one TT subject as a control to test different socket fits via changes in sock layers. They suggested that future work should expand to include different amputees to gain a broader population assessment. While this study simulated changes in fit, it did not evaluate the effectiveness of altering the number of socks on residual limb volume fluctuations. Nevertheless, the results corroborated the complex interface biomechanics that can be affected by minor socket fit changes.

Baldock et al. (2023) stated that the prosthetic socket is a key component influencing prosthesis satisfaction, with poorly fitting sockets linked to prosthesis abandonment and reduced community participation. The investigators reviewed adjustable socket designs, which have the potential to improve prosthetic fit and comfort by accommodating residual limb volume fluctuations and alleviating undue socket pressure. They conducted systematic literature and patent searches across multiple databases to identify studies and patents discussing adjustable prosthetic sockets. A total of 50 studies and 63 patents were identified for inclusion, representing 35 different designs used in literature and 16 commercially available products. Adjustable sockets are becoming more prevalent, with 73% of publications (literature, patents, and news) occurring within the last decade. Two key design characteristics were identified: the principle of adjustability (inflatable bladders, moveable panels, circumferential adjustment, variable length) and surface form (conformable, rigid multi-degrees of freedom [DOF], and rigid single DOF). Inflatable bladders contributed to 40% of literature-used designs, with only one identified commercially available design (n = 16) using this approach. In contrast, circumferential adjustment designs covered 75% of identified industry designs compared to only 36% of literature devices. Clinical studies were generally small in size, and only 17.6% examined commercially available sockets. The authors concluded that there are clear differences in design focus between industry and researchers, with the justification for design choice and range of adjustment often being unclear. While comfort is frequently reported as improved with adjustable sockets, the rationale behind this was not often discussed, and small study sizes reduced the viability of outcomes. They noted that many adjustable sockets lack appropriate safety features to limit over- or under-tightening, which may present a risk of tissue damage or inadequate coupling, affecting function and satisfaction. Additionally, the relationship between design and comfort or function was rarely examined, representing a significant gap in the literature. The review highlighted the need for improved collaboration between academia and industry, as a strong disconnect was observed between commercial devices and published research studies.

The researchers stated that future investigations should focus on improving the exchange of knowledge between researchers and industry, noting that 11 of the 16 commercial designs identified (68.75%) were not supported by published clinical studies. Using scientific methods to analyze these designs would be beneficial for understanding the effectiveness of each design group and identifying which patient sub-groups could benefit most from each design, potentially leading to improved commercial designs and more relevant clinical studies. Furthermore, across all studies, there was little to no investigation or discussion regarding what quantifies a well-fitting prosthetic socket, an area of research that is currently lacking and needs to be understood to inform future socket design. To achieve this, it is suggested that future investigations examine the relationship between socket design, mechanical coupling, comfort, and residual limb tissue health. Lastly, adjustable sockets could be effectively employed to analyze this due to their ability to alter their coupling with the residual limb with relative ease and repeatability.

Sure Stance Knee

The Sure Stance Knee is a non-microprocessor-controlled, 4-bar pneumatic swing-phase control knee equipped with a mechanical stance-phase control lock. The weight-activated stance feature engages up to 35 degrees of knee flexion, significantly reducing the likelihood of falls and injuries during common stumbles or missteps. In contrast, a standard 4-bar pneumatic knee does not provide stability beyond a few degrees of flexion. If a patient bears weight on a basic 4-bar pneumatic knee during flexion (for example, if they stub their toe), the knee may buckle, leading to a fall. Such knee buckling is a common cause of injury among individuals with transfemoral (TF) amputations.

Ontario Health’s technology assessment on “Stance-control knee-ankle-foot orthoses for people with knee instability” (2021) noted that knee instability can arise from various causes, including neuromuscular diseases, central nervous system (CNS) conditions, and trauma. For individuals with knee instability, knee orthotic devices are prescribed to assist with standing, walking, and performing tasks. The researchers conducted a health technology assessment of stance-control knee-ankle-foot orthoses (SCKAFOs) for people with knee instability, evaluating the safety, effectiveness, and budget impact of publicly funding SCKAFOs, as well as patient preferences and values. They performed a systematic literature search of the clinical evidence and examined the risk of bias in each included study using the Risk of Bias in Non-randomized Studies (RoBANS) tool, along with assessing the quality of the body of evidence according to the GRADE Working Group criteria. Additionally, they conducted a systematic economic literature search and analyzed the budget impact of publicly funding SCKAFOs for individuals with knee instability in Ontario. They did not perform a primary economic evaluation due to limited comparative clinical evidence to inform an economic model. The reference case budget impact analysis was conducted from the perspective of the Ontario Ministry of Health, comparing the total costs of a basic mechanical SCKAFO and locked knee-ankle-foot orthosis (LKAFO) for individuals with knee instability. The authors also performed scenario analyses varying parameters such as the price of all classes of SCKAFO (mechanical, electronic, and micro-processor) and the uptake of SCKAFOs. To contextualize the potential value of SCKAFOs, they spoke with individuals experiencing knee instability. The clinical evidence review included four studies, and the researchers were uncertain if SCKAFOs improved walking ability, energy consumption, or activities of daily living (ADL) compared to LKAFOs (GRADE: Very low). The economic evidence review identified one cost-analysis suggesting that the costs of orthotic devices like LKAFOs and SCKAFOs are highly variable based on material costs, professional time, and customization required for individual patients. The budget impact of publicly funding mechanical SCKAFOs in Ontario over the next five years (at a full device cost of $10,784) ranged from an additional $0.50 million in year 1 (at a 30% uptake rate in the target population of 429 eligible people) to $0.83 million in year 5 (at a 50% uptake rate), totaling $3.34 million over five years. The greatest increase in budget impact in the scenario analysis came from the micro-processor SCKAFO device, which had an additional cost of $10.07 million in year 1, increasing to $16.78 million in year 5. When the cost of a mechanical SCKAFO device was reduced to $7,384, the five-year budget impact decreased to $0.89 million (compared to $3.34 million in the reference case). Individuals with knee instability reported a preference for a device that would provide a more typical gait; however, starting with this type of device would be easier than switching from an existing LKAFO. The authors concluded that they were uncertain if SCKAFOs improved walking ability, energy consumption, or ADL (GRADE: Very low) compared to LKAFOs.

Liang et al. (2022) stated that prosthetic knees are advanced medical devices designed to simulate normal biological knee function for individuals with TF amputation. A wide variety of complex mechanical mechanisms and components have been employed; however, their relevance to the walking biomechanics of users is often unclear in the design process. The researchers aimed to bridge this knowledge gap by providing a review of prosthetic knees from a biomechanical perspective, including stance stability, early-stance flexion, and swing resistance, which directly relate mechanical mechanisms to perceived walking performance, such as fall avoidance, shock absorption, and gait symmetry. The prescription criteria and selection of prosthetic knees depend on the interaction between the user and the prosthesis, which includes five functional levels from K0 to K4. Misunderstood functions and improper adjustments of knee prostheses may lead to reduced stability, restricted stance flexion, and unnatural gait for users. This review identified current commercial and recently studied prosthetic knees to provide a new paradigm for prosthetic knee analysis and facilitate the standardization and optimization of prosthetic knee design. This may also enable the design of functional mechanisms and components tailored to regain lost functions for specific individuals, thus providing individualized product design. The Sure Stance Knee is a type of passive prosthetic knee based on walking functions. The DAW Sure-Stance Knee consists of a 4-bar linkage and a frictional weight-activated brake mechanism, where the posterior upper pivot shafts act as the brake drum surrounded by a brake clamp. Brake action can also be achieved in polycentric knees via hyperextension-controlled units, such as in the Blatchford KX06 knee. With the aid of a swing and stance (SNS) cylinder, the knee can flex only with hyper-extension torque at pre-swing. The centrode can thus be optimized in the zone of voluntary control, helping individuals with amputation achieve higher activity levels. The Sure Stance Knee’s Stumble Control feature locks flexion under load from 0 to 35 degrees, while extension remains unlocked, allowing the user to smoothly regain balance.

Raijmakers et al. (2024) noted that SCKAFOs ensure knee stability by locking during stance while allowing knee flexion during swing. Differences in the function of knee joints and building principles between devices may affect their effectiveness. In a prospective, uncontrolled intervention study, these investigators examined the preliminary effectiveness of a NEURO TRONIC on safety outcomes, net energy cost (EC), and user experiences in individuals already using an E-MAG Active SCKAFO. A total of 10 subjects with flaccid lower extremity muscle weakness, including the quadriceps, due to neuromuscular disorders and already using an E-MAG Active SCKAFO were provided with a newly fabricated NEURO TRONIC SCKAFO. Outcomes included knee joint locking failures and unlocking failures (ULFs) (i.e., the percentage of steps the knee joint failed to lock/unlock) when walking under challenging conditions on an instrumented treadmill while wearing a safety harness; net EC (J/kg per meter) assessed with a 6-Minute Walk Test (6MWT) at a comfortable speed; 3D gait kinematics and kinetics; and patient-reported outcomes. No differences between devices were found for knee joint locking failures (both devices 0%) and ULFs (9.9% for the NEURO TRONIC versus 13.9% for the E-MAG Active SCKAFO). The mean (standard deviation [SD]) net EC with the NEURO TRONIC SCKAFO was 8.2% (from 3.68 [0.81] to 3.38 [0.75] J/kg per meter, p = 0.123) lower, although not significantly, compared to the E-MAG Active SCKAFO. Significant improvements with the NEURO TRONIC SCKAFO were found for ankle power (p = 0.003), perceived walking effort (p = 0.014), and reported falls (p = 0.034). The authors concluded that both the NEURO TRONIC SCKAFO and the E-MAG Active SCKAFO were safe in terms of knee joint locking, while ULFs were frequent with both devices. The net EC with the NEURO TRONIC SCKAFO decreased, although not significantly, by 8.2%, likely due to insufficient power. Perceived walking effort favored the NEURO TRONIC SCKAFO. Moreover, the researchers stated that larger, randomized controlled trials (RCTs) are needed to compare differences in effectiveness between devices.

The authors acknowledged several drawbacks in this study. First, the trial had a small sample size (n = 10), which affected statistical power and made it difficult to draw firm conclusions about the investigated devices. Studies on SCKAFOs would benefit from larger sample sizes when comparing KAFO properties, such as joints, materials, and building principles. This would allow for a better understanding of the impact of these individual aspects on functioning with the SCKAFO. Given the elaborate nature of KAFO research, this would require costly, large, multi-center studies. Second, the inclusion of satisfied E-MAG Active SCKAFO users could have resulted in selection bias, as less satisfied users might have experienced a more positive effect on outcomes when provided with a NEURO TRONIC SCKAFO. Third, the SCKAFOs used in this trial were expensive devices in terms of materials and fabrication costs, which may limit their applicability in certain regions worldwide.

Powered Ankle

In recent years, numerous prosthetic ankle-foot devices have been developed to meet the demands of sloped walking for individuals with lower-limb amputation. The goal of a study by Koehler-McNicholas et al. (2017) was to compare the performance of a passive hydraulic ankle-foot prosthesis to two related non-hydraulic ankles, focusing on their ability to minimize the socket reaction moments of individuals with transtibial amputation during various sloped walking tasks. After a two-week accommodation period, kinematic data were collected from seven subjects with transtibial amputation walking on an instrumented treadmill set at different slopes. The investigators reported that, overall, the study did not find significant differences in the torque at the distal end of the prosthetic socket between the hydraulic ankle-foot prosthesis and other related designs (rigid ankle, multiaxial ankle) during the single-support phase of walking. Additionally, socket comfort and perceived exertion were not significantly different among the ankle-foot prostheses tested. The investigators concluded that these results indicate a need for further research to determine whether more advanced designs (e.g., those with microprocessor control of hydraulic features or powered ankle-foot designs) can provide more biomimetic function for prosthesis users.

Kaluf et al. (2021) examined the benefits of hydraulic- and microprocessor-controlled prosthetic ankles for patients classified as limited community ambulators. They evaluated four different treatment configurations using a randomized crossover study design: the participant's current flexible keel (FK) prosthetic foot, an energy-storage-and-return foot (ESAR), a hydraulic ankle (HA), and a microprocessor ankle (MPA). After a two-week accommodation period, both patient-reported and performance-based outcome measures were recorded for each ankle-foot system. A StepWatch activity monitor and two-dimensional video motion analysis were also utilized to evaluate each system. Only one participant meeting the inclusion criteria was recruited. The patient-reported mobility and socket fit scores were highest with the HA system. When assessed on slopes and stairs, the MPA demonstrated advantages in hill ascent and stair descent. Considering walking speed and perceived exertion together, the HA system allowed for a similar walking speed but with lower exertion compared to fixed-ankle systems. The patient-reported outcomes related to low back pain and balance confidence did not yield useful data for interpretation. Two-dimensional video motion analysis indicated that both the HA and MPA contributed to improved ankle and knee postures when ascending and descending slopes. The step activity data showed the greatest activity levels with the HA. The investigators noted that the results from the outcome measures indicated varying levels of benefit across all four treatment configurations. Both the HA and MPA received favorable scores in various performance-based outcome measures, but the HA scored most favorably in the majority of patient-reported outcome measures. The investigators concluded that the results demonstrate varying benefits of microprocessor- and hydraulic-controlled prosthetic components over fixed-ankle ESAR and FK feet, based on both performance-based and patient-reported outcome measures. They emphasized the need for further studies to fully evaluate these benefits in larger sample sizes.

NEURO HiSWING R+

The NEURO HiSWING R+ is a microprocessor‑controlled, multifunction ankle joint that is used as an addition to a lower extremity orthosis for individuals with neurological or neuromuscular impairments (CMS, 2026). It is exempt from FDA premarket notification requirements and is designed to actively control plantarflexion and dorsiflexion during gait through sensor‑driven, real‑time adjustments. The system uses an integrated microprocessor, sensors, hydraulic components, and a built‑in power source to detect walking conditions and adapt ankle alignment and resistance on slopes, stairs, and level surfaces, thereby improving stability, symmetry, and safety during ambulation. The device offers multiple operating modes that allow independent adjustment for incline and decline walking, stair ascent and descent, and plantarflexion for sitting, helping to maintain appropriate joint alignment and reduce excessive forces on the knee. There is a lack of peer‑reviewed, device‑specific clinical literature cfor the NEURO HiSWING R+.

The Walkasins Lower Limb Sensory Prosthesis

The Walkasins lower limb sensory prosthesis is a wearable device that is intended to improve balance and reduce fall risk in patients with foot peripheral neuropathy (PN). This device uses a receptor sole to sense contact between the patient’s foot and the ground, and is connected to a monitor worn around the ankle that transmits those signals to the patient’s lower leg.

Koehler-McNicholas et al. (2019) stated that PN may cause loss of sensory information from plantar cutaneous mechanoreceptors that is important for balance control and falls management. In a randomized-controlled, cross-over study, these investigators examined short-term effects of using Walkasins ((RxFunction Inc., Eden Prairie, MN), an external lower-limb sensory neuro-prosthesis, on clinical outcomes of balance and gait in persons who reported PN and balance problems. The device replaced lost plantar sensation with tactile balance information that modulates cutaneous mechanoreceptors above the ankle where sensation is intact. A total of 31 male community-dwelling veterans, 56 to 84 years of age with insensate feet and balance problems participated in this study. Initial Functional Gait Assessment (FGA), gait speed, and 4-Stage Balance Test outcomes were assessed. After initial assessment, participants were randomly assigned to either wearing Walkasins turned ON, or OFF, and outcomes were re-assessed following a set of standardized balance exercises. Following a 1-hour rest and wash-out period, treatments were crossed-over between groups and a 3rd outcomes assessment was carried out. Before cross-over, 10 of 15 subjects in the ON-then-OFF group improved their FGA score by at least 4 points, the Minimal Clinically Important Difference (MCID), compared to 5 of 16 in the OFF-then-ON group. After cross-over, 7 of 16 subjects in the OFF-then-ON group improved by at least 4 points versus 2 of 15 in the ON-then-OFF group. ON treatment was associated with FGA improvement of 4.4 ± 3.7 points versus 1.5 ± 1.2 for the OFF treatment (p < 0.01). Overall, FGA scores changed from 15.2 ± 4.8 at initial assessment to 21.1 ± 5.2 after final assessment (p < 0.001). At the end of the 2 treatment sessions, 16 of the 31 individuals had improved their FGA score beyond 23, indicating normal fall-risk status. Moreover, these researchers stated that further investigations should examine the long-term benefits of the device to reduce fall risk and actual falls in patients with PN and balance problems.

The authors stated that while the findings of this study were promising, there were some drawbacks. First, neither the subjects nor the physical therapist evaluating the outcomes were blinded to whether the device was ON or OFF. Blinding subjects in this type of study would have been difficult since subjects were included only if they were able to feel stimulation from the device. In addition, when the device was turned ON, motor vibrations were audible. Thus, without more sophisticated methods to block the sound of the device, participants would know if the device was turned ON or OFF during the different assessments. These investigators believed concerns regarding effects of learning and/or fatigue due to multiple assessments in the study design were addressed via the minimization randomization process followed by a cross-over of treatments and by providing subjects a 60-min break before assessment #3 was carried out. Additionally, participants were provided rest as needed throughout the test session. Furthermore, involving completely blinded physical therapists was unfortunately beyond the scope of this trial. Instead, these researchers decided to use 1 experienced physical therapist to perform all assessments of clinical outcomes; thus, avoiding inter-rater variability. Second, a full neurological examination to diagnose PN was not carried out, and was beyond the scope of this trial. Instead, these investigators relied on a combination of medical records and monofilament screening, which is commonly used clinically. Third, all subjects in this trial were men. This was not surprising since the veteran population is predominantly male, especially in the older veteran population where PN is most common. Although PN overall is prevalent in both men and women and is likely to cause similar problems with balance, interpretation of results from this trial should be limited to the elderly male population. These researchers stated that future studies should target a demographically diverse and representative patient population and address long-term effects of using a neuro-prosthesis to improve gait and balance function as well as QOL in individuals with PN who have balance problems.

Oddsson et al. (2020) noted that PN is associated with gait, balance problems and high fall risk. The walk2Wellness Trial examined the effects of long-term, home-based daily use of a wearable sensory prosthesis on gait function, balance, QOL and fall rates in PN patients. The device (Walkasins) partially substitutes lost nerve function related to plantar sensation providing directional tactile cues reflecting plantar pressure measurements during standing and walking. These researchers tested the null hypothesis that the FGA score would remain unchanged after 10 weeks of use Participants had PN with lost plantar sensation, gait and balance problems, an FGA score of less than 23 (high fall risk), and ability to sense tactile stimuli above the ankle. Clinical outcomes included FGA, gait speed, Timed Up and Go (TUG) and 4-Stage Balance Test. Patient-reported outcomes included Activities-Specific Balance Confidence (ABC) scale, Vestibular Disorders Activities of Daily Living (VADL) score, Patient-Reported Outcomes Measurement Information System (PROMIS) participation and satisfaction scores, pain rating, and falls. Evaluations were carried out at baseline and after 2, 6, and 10 weeks. Participants were not made aware of changes in outcomes. No additional balance interventions were allowed. A total of 45 participants of 52 enrolled across 4 sites completed in-clinic assessments. FGA scores improved from 15.0 to 19.1 (p < 0.0001), normal and fast gait speed from 0.86 m/s to 0.95 m/s (p < 0.0001) and 1.24 m/s to 1.33 m/s (p = 0.002), respectively, and TUG from 13.8 s to 12.5 s (p = 0.012); however, 4-Stage Balance Test did not improve. Several PROs were normal at baseline and remained largely unchanged. Interestingly, subjects with baseline ABC scores lower than 67% (high fall risk cut-off) increased their ABC scores (49.9% to 59.3%, p = 0.01), whereas subjects with ABC scores above 67% showed a decrease (76.6% to 71.8%, p = 0.019). Subjects who reported falls in the prior 6 months (n = 25) showed a decrease in the number of fall-risk factors (5.1 to 4.3, p = 0.023) and a decrease in fall rate (13.8 to 7.4 falls/1,000 days, p = 0.014); and 4 pre-study non-fallers (n = 20) fell during the 10 weeks. The authors conclude that a wearable sensory prosthesis presented a new way to treat gait and balance problems and managed falls in high fall-risk patients with PN. Moreover, these researchers stated that longer term data are needed to further examine actual decreases in falls.

The authors stated that this study had several drawbacks. First, this trial was not blinded, lacked a control group and a placebo treatment. Unfortunately, it is not feasible to blind subjects from treatment in the current study since being able to feel the tactile stimuli from the device was an inclusion criterion. Using some form of random pattern stimuli as a sham may be possible, although it is not known if such stimuli may have an effect of their own and it would not aid in addressing the question whether using the device as currently designed, according to principles of sensorimotor control of balance and gait, has an effect on gait and balance function. Thus, the best placebo treatment would likely be wearing a device that is turned off. However, without using some form of deceit claiming the device is working although it cannot be felt, it would likely be difficult to recruit participants for such research and/or to ensure long-term compliance. Furthermore, incorporating a minimal stimulation amplitude as a sham, assuming it has no effect may be incorrect since studies implementing stochastic resonance using subsensory mechanical noise have shown improvement in balance. Additionally, using a randomized controlled, cross-over design, these investigators recently reported in-clinic improvements in clinical outcomes when the Walkasins device was worn and turned on as compared to turned off (Koehler-McNicholas et al., 2019). As a consequence, these researchers felt comfortable incorporating a single treatment arm design knowing the in-clinic effects. Furthermore, any placebo effects were likely decreased by not systematically informing subjects regarding any changes in outcomes and minimizing encouragement during interactions with subjects that could affect expectation and beliefs in the treatment, and prohibiting any additional balance training/therapy intervention during the 10 weeks of the trial. Second, if the effects in this study were placebo, the findings should align with research findings on the placebo arm of randomized, placebo-controlled trials (Wartolowska et al., 2016). A systematic review of temporal changes in the placebo arm across 47 surgical randomized control trials found that effects size of subjective outcomes was large (0.64), while effect size of objective clinical outcomes was small (0.11) (Wartolowska et al., 2016). In addition, major differences in placebo-effect sizes have been reported with subject-reported self-perception effects being larger than observer-based ratings (Rief et al., 2009). On the contrary, effect sizes in the current study were large for the clinical outcomes and small for the self-reported outcomes, supporting the interpretation that effects were due to device use and not placebo. Further support of this view included relatively high subject compliance and reported device use and, a low subject drop-out rate of 13.5% as well as the sustained duration and continued gradual improvement in clinical outcomes throughout the 10-week period; however, conclusive causality could not be determined due to the limitations of the single-arm study design. Third, although subjects were instructed to use the device as much as possible throughout their regular daily activities, the range of reported device use was large. However, the intent was to not impose changes in activity levels, but rather just added the device to regular daily routines. Considering the large range of health issues in this cohort of patients, the variability in device use may simply reflect variability in common daily activity levels in this population of individuals. Subjects who were mostly inactive throughout the day, may have reported less device use. Enrollment of mostly male subjects was a weakness, which was partly due to nearly 50% of the subjects being veterans, who especially in this older generation were predominantly male.

Wrisley et al. (2021) stated that PN can result in either partial or complete loss of distal sensation resulting in an increased fall risk. Walkasins uses a shoe insert to detect the magnitude and direction of sway and sends signals to a leg unit that provides sensory balance cues. In a single-case report, these investigators described the long-term influence of the Walkasins lower limb sensory neuro-prosthesis on balance and gait for an individual with diabetic PN. Subject was an 51-year-old man with a 3-year history of PN and a 10-year history of type II diabetes mellitus (T2DM) who was fitted bilaterally with Walkasins and used them 8 to 10 hours/day for more than 2 years. Although, vibration and tactile sensation thresholds were severely impaired at his 1st metatarsophalangeal (MTP) joint and the lateral malleolus bilaterally, he could perceive tactile stimuli from the Walkasins above the ankles. Following Walkasins use, his ABC scores improved from 33% to 80%. His mean VADL scores decreased from 3.54 to 1. His FGA scores increased from 13/30 to 28/30 and his miniBESTest scores improved from 15/28 to 26/28. Gait speed increased from 0.23 to 1.5 m/s. The patient described a decrease in pain and cramping throughout his lower extremities and an increase in function. The authors concluded that gait and balance improved with the use of the Walkasins and participation in a wellness program. This improvement suggested that the use of sensory substitution devices, such as the Walkasins, may replace sensory deficits related to gait and balance dysfunction experienced by patients with PN. Moreover, these researchers stated that additional long-term clinical trials are needed to examine if this is true and generalizable to the population of people with PN; further investigations are also needed to determine the optimum residual sensory function needed to use the Walkasins and the need for gait and balance training simultaneously.

Oddsson et al. (2022) noted that they recently reported that individuals with impaired plantar sensation and high fall risk due to sensory PN improved gait and balance function following 10 weeks of use of Walkasins that provides directional specific mechanical tactile stimuli related to plantar pressure measurements during standing and walking. These investigators reported 26-week outcomes and compared pre- and in-study fall rates. They expected improvements in outcomes and reduced fall rates reported after 10 weeks of use to be sustained. Participants had clinically diagnosed PN with impaired plantar sensation, high fall risk (FGA score of less than 23) and ability to sense tactile stimuli above the ankle at the location of the device. Additional outcomes included 10 m gait speed, TUG, 4-Stage Balance Test, and self-reported outcomes, including Activities-Specific Balance Confidence scale and Vestibular Disorders Activities of Daily Living Scale. Participants tracked falls using a calendar. These researchers assessed falls and self-reported outcomes from 44 individuals after 26 weeks of device use; 30 of them conducted in-person testing of clinical outcomes. Overall, improvements in clinical outcomes seen at 10 weeks of use remained sustained at 26 weeks with statistically significant increases compared to baseline seen in FGA scores (from 15.0 to 19.2), self-selected gait speed (from 0.89 to 0.97 m/s), and 4-Stage Balance Test (from 25.6 to 28.4 s), indicating a decrease in fall risk. Non-significant improvements were observed in TUG and fast gait speed. Overall, 39 falls were reported; 31 of them did not require medical treatment and 4 caused severe injury. Participants who reported falls over 6 months before the study had a 43% decrease in fall rate during the study as compared to self-report 6-month pre-study (11.8 versus 6.7 falls/1,000 patient days, respectively, p < 0.004), similar to the 46% decrease reported after 10 weeks of use. The authors concluded that a wearable sensory prosthesis could improve outcomes of gait and balance function and substantially reduced incidence of falls during long-term use. The sustained long-term benefits in clinical outcomes reported here lessened the likelihood that improvements were placebo effects.

The authors stated that this study had several drawbacks. First, It was an unblinded, single-arm trial. The decision to carry out a single-arm trial was based on several factors, including previous results from an in-clinic randomized-controlled, cross-over study showing improved FGA scores when using the device turned ON compared to OFF (Koehler-McNicholas et al., 2019). Second, data from the 1st-in-human, long-term use study showed remarkable improvements in clinical outcomes in a patient with PN using the device for 1 year following over 5 months of balance physical therapy with limited improvement (Wrisley et al., 2021). This individual continued to use the device daily, now for more than 4 years. Third, blinding participants in a study using this kind of intervention is challenging and may not really be viable unless some form of deception is used since a requirement to use the device is perceiving the tactile stimuli. Consequently, the most feasible placebo treatment for a control group would likely be wearing a device that is non-functional.

Hsu et al. (2022) stated that foot sole somatosensory impairment associated with PN is common and a strong independent risk factor for gait disturbance and falls in the elderly. Walkasins has been reported to improve gait and mobility in individuals with PN by providing afferent input related to foot sole pressure distributions via lower-leg mechanical tactile stimulation. Given that gait and mobility are regulated by sensorimotor and cognitive brain networks, it is possible that improvements in gait and mobility from wearing the Walkasins may be associated with elicited neuroplastic changes in the brain. In a pilot study, these researchers examined changes in brain network connectivity after 26 weeks of daily use of the prosthesis among individuals with PN and balance problems. In this exploratory study, assessments of participant characteristics, FGA, and resting-state functional magnetic resonance imaging (fMRI) were completed at study baseline and 26 weeks follow-up. These investigators found that among those who have completed the study (n = 8; mean age of 73.7 years), they observed a 5-point improvement in FGA performance as well as significant changes in network connectivity over the 26 weeks that were correlated with improved FGA performance. Specifically, greater improvement in FGA score over 26 weeks was associated with increased connectivity within the Default Mode Network (DMN; p < 0.01), the Somatosensory Network (SMN; p < 0.01), and the Fronto-parietal Network (FPN; p < 0.01). FGA improvement was also correlated with increased connectivity between the DMN and the FPN (p < 0.01), and decreased connectivity between the SMN and both the FPN (p < 0.01) and cerebellum (p < 0.01). The authors concluded that the findings of this exploratory, pilot study suggested that 26 weeks of daily use of the Walkasins device may provide beneficial neural modulatory changes in brain network connectivity via the sensory replacement stimulation that are relevant to gait improvements among older adults with PN.

The authors stated that this study had 2 main drawbacks. First, given the small sample size (n = 8) and the exploratory nature of this study, these findings and the discussed underlying functional connectivity patterns should be cautiously interpreted. Future studies with a larger sample size and clinically-matched control group are needed to confirm these preliminary findings. Increasing the overall sample size with the addition of a control group would also enable more comprehensive statistical analyses and a more exhaustive list of networks/regions of interest to better understand the neural mechanistic pathways underpinning the marked functional improvements after using Walkasins. A larger RCT would also allow long-term investigations of plausible prolonged neural and physical benefits of the Walkasins. Second, these investigators could not rule out potential confounding effects of neural degenerative pathologies or cognitive impairments.

Kahya et al. (2023) stated that mounting evidence suggested that wearable technologies using peripheral neuromodulation could provide novel ways of improving mobility and gait function in various patient populations including the elderly. In a narrative review, these investigators provided an overview of wearable technologies/devices to improve mobility and gait function via non-invasive peripheral neuromodulation in older adults over the age of 65 years and indicated the suggested mechanism of action behind these technologies. These investigators carried out searches for studies and conference abstracts written in English, using the following databases: Embase Classic+Embase from 1947 to July 15, 2021; Ovid Medline; Epub Ahead of Print, In-Process, In-Data-Review & Other Non-Indexed Citations, Daily and Versions from 1946 to July 15, 2021; PubMed; and Scopus. A total of 41 technologies met the inclusion/exclusion criteria. These researchers found that the primary implementation of the 41 technologies could be divided into 3 main categories: sensory substitution, sensory augmentation (open loop, closed loop), and motor stimulation. Using these technologies, various aspects of mobility were treated or addressed, including, gait function, fall risk, foot-drop, navigating environment, and postural control. Three devices: Suralis, the SurroGait Rx, and Walkasins address the loss of sensation in the leg or foot resulting from amputation or sensory neuropathy. The authors concluded that this narrative review summarized wearable technologies that are currently commercially available and in stages of research and development. Overall, available evidence suggested that wearable peripheral neuromodulation technologies could improve aspects of mobility for the elderly. Future research may examine and consider the physiological mechanisms behind these technologies to foster further product advancements and patient outcomes. Since most of the technologies reviewed are intended for training purposes or intermittent use, the need for technologies intended for daily, long-term use may point to areas for additional research or product development once initial functional gains are made. Furthermore, these investigators noted that terminology used within the reviewed studies, especially the definition of “neuromodulation” as it relates to the peripheral nervous system, varied across disciplines and technology focus. Literature consensus and consistent definitions, especially among the sub-categories of neuromodulation, are needed to advance research in peripheral neuromodulation. Lasty, with the advancements in and availability of new technologies, there may be further opportunities for wearable technologies to enhance or address other common mobility impairments not reported in this review, especially for those who cannot walk independently. These researchers stated that even though these technologies represent exciting advancements, it is important to acknowledge their limitations. The literature reports mixed results to demonstrate the long-term retention and carry-over effect after the use of these technologies. Furthermore, there is a lack of information regarding the optimal usage time to achieve the best outcomes to improve gait and mobility. In addition, the studies included in this review had limited sample sizes and heterogeneous populations; thus, it was challenging to generalize the application and benefits of these technologies for older adults over the age of 65. Many studies also combined the technology or device with exercise intervention or therapy with limited long-term follow-up, making it difficult to discern the actual contribution of the technology to participants’ improvements. Other limitations of current research in wearable technologies include the difficulty of blinding participants, the potential for a placebo effect, and publication bias toward positive results; however, determining the quality of evidence of the 41 technologies reviewed was outside the scope of this study. Finally, AEs with technologies are certainly possible and long-term effects of technologies may be unknown. Many technologies reviewed do not report adverse effects and are considered to be non-significant or low risk devices.

In summary, there is insufficient evidence to support the use of lower limb sensory prostheses (e.g., Walkasins). Further investigations, including those with comparative interventions and larger sample sizes, are needed to determine the safety and benefit of lower limb sensory prostheses.

Appendix

Clinical assessments of a member’s rehabilitation potential should be based on the following classification levels:

Table: Classification levels and Clinical assessments of a member's rehabilitation potential
Levels	Clinical Assessment of Member Rehabilitation Potential
Level 0	Does not have the ability or potential to ambulate or transfer safely with or without assistance and a prosthesis does not enhance their quality of life or mobility.
Level 1	Has the ability or potential to use a prosthesis for transfers or ambulation on level surfaces at fixed cadence. Typical of the limited and unlimited household ambulator.
Level 2	Has the ability or potential for ambulation with the ability to traverse low level environmental barriers such as curbs, stairs or uneven surfaces. Typical of the limited community ambulator.
Level 3	Has the ability or potential for ambulation with variable cadence. Typical of the community ambulator who has the ability to traverse most environmental barriers and may have vocational, therapeutic, or exercise activity that demands prosthetic utilization beyond simple locomotion.
Level 4	Has the ability or potential for prosthetic ambulation that exceeds basic ambulation skills, exhibiting high impact, stress, or energy levels. Typical of the prosthetic demands of the child, active adult, or athlete.

For medically necessary frequency of replacement of prosthetics, see Medi-Cal. Orthotics and prosthetics. Frequency limits on prosthetics. Ortho cd fre 2. Provider Manual. Sacramento, CA: California Department of Health Care Services; August 2010. Available at: Medi-Cal:Provider Manuals. Accessed August 15, 2012.

Note: Consistent with DME MAC policy, when an initial below knee prosthesis (L5500) or a preparatory below knee prosthesis (L5510-L5530, L5540) is provided, prosthetic substitutions and/or additions of procedures and components are considered medically necessary in accordance with the functional level assessment except for codes L5629, L5638, L5639, L5646, L5647, L5704, L5785, L5962, and L5980 which will be considered not medically necessary. K-3 and higher level components are considered not medically necessary with a preparatory prosthesis.

Addition to lower extremity, below knee, acrylic socket (L5629)
Addition to lower extremity, below knee, leather socket (L5638)
Addition to lower extremity, below knee, wood socket (L5639)
Addition to lower extremity, below knee, air-fluid, gel or equal, cushion socket (L5646)
Addition to lower extremity, below knee suction socket (L5647)
Custom shaped protective cover, below knee (L5704)
Addition, exoskeletal system, below knee, ultra-light material (titanium, carbon fiber or equal) (L5785)
Addition, endoskeletal system, below knee, flexible protective outer surface covering system (L5962)
All lower extremity prostheses, flex foot system (L5980)

Consistent with DME MAC policy, when a below knee preparatory prefabricated prosthesis (L5535) is provided, prosthetic substitutions and/or additions of procedures are considered medically necessary in accordance with the functional level assessment except for codes L5620, L5629, L5645, L5646, L5670, L5676, L5704, and L5962 which will be considered not medically necessary. K-3 and higher level components are considered not medically necessary with a preparatory prosthesis.

Addition to lower extremity, test socket, below knee (L5620)
Addition to lower extremity, below knee, acrylic socket (L5629)
Addition to lower extremity, below knee, flexible inner socket, external frame (L5645)
Addition to lower extremity, below knee, air, fluid, gel or equal, cushion socket (L5646)
Addition to lower extremity, below knee, molded supracondylar suspension ('PTS' or similar) (L5670)
Addition to lower extremity, below knee, knee joints, single axis, pair (L5676)
Custom shaped protective cover, below knee (L5704)
Addition, endoskeletal system, below knee, flexible protective outer surface covering system (L5962)

Consistent with DME MAC policy, when an above knee initial prosthesis (L5505) or an above knee preparatory (L5560-L5580, L5590-L5600) prosthesis is provided, prosthetic substitution and/or additions of procedures and components are considered medically necessary in accordance with the functional level assessment except for codes L5610, L5631, L5640, L5642, L5644, L5648, L5705, L5706, L5964, L5980, and L5710-L5780, L5790-L5795 which will be considered not medically necessary. K-3 and higher level components are considered not medically necessary with a preparatory prosthesis.

Addition to lower extremity, endoskeletal system, above knee, hydracadence system (L5610)
Addition to lower extremity, above knee or knee disarticulation, acrylic socket (L5631)
Addition to lower extremity, knee disarticulation, leather socket (L5640)
Addition to lower extremity, above knee, leather socket (L5642)
Addition to lower extremity, above knee, wood socket (L5644)
Addition to lower extremity, above knee, air, fluid, gel or equal, cushion socket (L5648)
Custom shaped protective cover, above knee (L5705)
Custom shaped protective cover, knee disarticulation (L5706)
Addition, endoskeletal system, above knee, flexible protective outer surface covering system (L5964)
All lower extremity prostheses, flex foot system (L5980)
Addition, exoskeletal knee-shin system, single axis, manual lock (L5710)
Additions, exoskeletal knee-shin system, single axis, manual lock, ultra-light material (L5711)
Addition, exosketal knee-shin system, single exis, friction swing and stance phase control (safety knee) (L5712)
Addition, exoskeletal knee-shin system, single axis, variable friction swing phase control (L5714)
Addition, exoskeletal knee-shin system, polycentric, mechanical stance phase lock (L5716)
Addition, exoskeletal knee-shin system, polycentric, friction swing and stance phase control (L5718)
Addition, exosketal knee-shin system, single axis, pneumatic swing, friction stance phase control (L5722)
Addition, exoskeletal knee-shin system, single axis, fluid swing phase control (L5724)
Addition, exoskeletal knee-shin system, single axis, external joints fluid swing phase control (L5726)
Addition, exoskeletal knee-shin system, single axis, fluid swing and stance phase control (L5728)
Addition, exoskeletal knee-shin system, single axis, pneumatic/hydra pneumatic swing phase control (L5780)
Addition, exoskeletal system, above knee, ultra-light material (titanium, carbon fiber or equal) (L5790)
Addition, exoskeletal system, hip disarticulation, ultra-light material (titanium, carbon fiber or equal) (L5795)

Consistent with DME MAC policy, when an above knee preparatory prefabricated prosthesis (L5585) is provided, prosthetic substitution and/or additions of procedures and components are considered medically necessary in accordance with the functional level assessment except for codes L5624, L5631, L5648, L5651, L5652, L5705, L5706, L5964, and L5966 which will be considered not medically necessary. K-3 and higher level components are considered not medically necessary with a preparatory prosthesis.

Addition to lower extremity, test socket, above knee (L5624)
Addition to lower extremity, above knee or knee disarticulation, acrylic socket (L5631)
Addition to lower extremity, above knee, air, fluid, gel or equal, cushion socket (L5648)
Addition to lower extremity, above knee, flexible inner socket, external frame (L5651)
Addition to lower extremity, suction suspension, above knee or knee disarticulation socket (L5652)
Custom shaped protective cover, above knee (L5705)
Custom shaped protective cover, knee disarticulation (L5706)
Addition, endoskeletal system, above knee, flexible protective outer surface covering system (L5964)
Addition, endosketal system, hip disarticulation, flexible protective outser surface covering system (L5966)

Codes for ultra-light materials may only be used when materials such as carbon fiber, fiberglass, Kevlar, or other advanced composite lamination materials are used in the fabrication of a socket for an endoskeletal prosthesis. They are not used for ultralight materials used in other components of a prosthesis – e.g., knee/shin system, pylon, ankle, foot, etc.

Consistent with CMS policy, the only products which may be billed using the following list of HCPCS codes are those for which a written coding verification review (CVR) has been made by the Pricing, Data Analysis, and Coding (PDAC) contractor and subsequently published on the appropriate Product Classification List: L5856, L5857, L5858, L5969, L5973, L5980, and L5987 (microprocessor-controled lower limbs).

Information concerning the documentation that must be submitted to the PDAC for a CVR can be found on the PDAC website or by contacting the PDAC. A Product Classification List with products which have received a coding verification can be found on the PDAC website. The effective date of the CVR is included for each code.

Product information such as manufacturer make and model, part number and manufacturer part name must be recorded by the prosthetist in the medical records for major components such as protective covers, knees, feet, ankles, rotation devices, adaptors and shock absorbers.

Note: Procedure code L7700 is not intended for use with mechanical socket suspensions such as a pin-lock system. It may be made of any suitable material. L7700 may be used with upper or lower extremity sockets. Unit of service (UOS) is 1 (one) item per prosthesis. This code is not to be used to bill for gaskets, seals, or other sealing materials that are included as part of an insert. Integrated seals are included in the code for the insert. Separate billing of integrated gaskets or seals as l7700 is considered unbundling.

Note: Air, fluid, gel or equal, cushion sockets are included in the socket insert and not separately payable. There must be documentation that additional fluid, air cushioning, or gel cushioning is provided in the fabrication of socket.

Passive hydraulic ankles (non-microprocessor) may be helpful for reducing the pressures that may occur in the socket, reducing the associated discomfort, increasing stability, and allowing for better adaptation across a broader range of surfaces and elevations. Hydraulically-regulated movement of a mechanical ankle allows for a more natural “rocking” motion of the ankle and foot during walking. Passive hydraulic ankles (non-microprocessor) (L5968) are considered medically necessary in K2 and above prosthesis.

References

The above policy is based on the following references:

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Last Review 09/10/2026

Effective: 11/13/2001

Next Review: 06/24/2027
Review History
Definitions

Lower Limb Prostheses

Table Of Contents

Policy

Scope of Policy

Medical Necessity

Criteria for Lower Limb Prostheses

Medically Necessary Prostheses and Accessories

Foot Prosthesis

Knee Prosthesis

Ankle Prosthesis

Hip Prosthesis

Sockets

Accessories

Microprocessor-Controlled Lower Limb Prostheses

Microprocessor-Controlled Ankle

Protective Outer Surface Covering Systems

Non-Medically Necessary Prostheses

Experimental, Investigational, or Unproven

Cosmetic

Plan Limitations and Exclusions

Consistent with DME MAC policy:

Consistent with DME MAC policy:

Consistent with DME MAC policy:

Correct Coding of Endoskeletal Prosthetic Knee-Shin Systems

Related Policies

CPT Codes / HCPCS Codes / ICD-10 Codes

Other CPT codes related to the CPB:

HCPCS codes covered if selection criteria are met:

HCPCS codes not covered for indications listed in the CPB:

ICD-10 codes covered if selection criteria are met:

Protective outer covering systems:

HCPCS codes covered if selection criteria are met:

Microprocessor-controlled leg prostheses:

HCPCS codes covered if selection criteria are met:

HCPCS codes not covered for indications listed in the CPB:

ICD-10 codes covered if selection criteria are met:

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

Adjustable click systems (e.g., Revo and Boa click systems):

HCPCS codes not covered for indications listed in the CPB:

Adjustable click systems (e.g., Revo and Boa click systems) - no specific code:

Background

Powered Lower Limb Prosthesis

Proprio Foot

Pro-Flex Foot

Osseointegrated Lower Limb Prosthetic Devices

Clinical Evaluation of Fall Risk in Older Adults Who Use Lower-Limb Prostheses

Adjustable Click Prosthesis (RevoFit)

Sure Stance Knee

Powered Ankle

NEURO HiSWING R+

The Walkasins Lower Limb Sensory Prosthesis

Appendix

References

Policy History

Additional Information