Description:
Microprocessor-controlled prostheses use feedback from sensors to adjust joint movement on a real-time as-needed basis. Active joint control is intended to improve safety and function, particularly for patients who can maneuver on uneven terrain and with variable gait.

For individuals who have a transfemoral amputation who receive a prosthesis with a microprocessor-controlled knee, the evidence includes a number of within-subject comparisons of microprocessor-controlled knees vs non-microprocessor-controlled knee joints. Relevant outcomes are functional outcomes, health status measures, and quality of life. For K3- and K4-level amputees, studies have shown an objective improvement in function on some outcome measures, particularly for hill and ramp descent, and strong patient preference for microprocessor-controlled prosthetic knees. Benefits include a more normal gait, an increase in stability, and a decrease in falls. The evidence in Medicare level K2 ambulators suggests that a prosthesis with stance control only can improve activities that require balance and improve walking in this population. For these reasons, a microprocessor-controlled knee may provide incremental benefit for these individuals. The potential to achieve a higher functional level with a microprocessor-controlled knee includes having the appropriate physical and cognitive ability to use the advanced technology. The evidence is sufficient to determine that the technology results in a meaningful improvement in the net health outcome.

For individuals who have a transfemoral amputation who receive a prosthesis with a powered knee, the evidence includes limited data. Relevant outcomes are functional outcomes, health status measures, and quality of life. The limited evidence available to date does not support an improvement in functional outcomes using a powered knee prostheses with standard prostheses. The evidence is insufficient to determine the effects of the technology on health outcomes.

For individuals who have a tibial amputation who receive a prosthesis with a microprocessor-controlled ankle-foot, the evidence includes limited data. Relevant outcomes are functional outcomes, health status measures, and quality of life. The limited evidence available to date does not support an improvement in functional outcomes using microprocessor-controlled ankle-foot prostheses compared with standard prostheses. The evidence is insufficient to determine the effects of the technology on health outcomes.

For individuals who have a tibial amputation who receive a prosthesis with a powered ankle-foot, the evidence includes no data. Relevant outcomes are functional outcomes, health status measures, and quality of life. The evidence is insufficient to determine the effects of the technology on health outcomes.

Background 
LOWER-EXTREMITY PROSTHETICS
More than 100 different prosthetic ankle-foot and knee designs are currently available. The choice of the most appropriate design may depend on the patient’s underlying activity level. For example, the requirements of a prosthetic knee in an elderly, largely homebound individual will differ from those of a younger, active person. Key elements of a prosthetic knee design involve providing stability during both the stance and swing phase of the gait. Prosthetic knees vary in their ability to alter the cadence of the gait, or the ability to walk on rough or uneven surfaces. In contrast to more simple prostheses, which are designed to function optimally at one walking cadence, fluid and hydraulic-controlled devices are designed to allow amputees to vary their walking speed by matching the movement of the shin portion of the prosthesis to the movement of the upper leg. For example, the rate at which the knee flexes after “toe-off” and then extends before heel strike depends in part on the mechanical characteristics of the prosthetic knee joint. If the resistance to flexion and extension of the joint does not vary with gait speed, the prosthetic knee extends too quickly or too slowly relative to the heel strike if the cadence is altered. When properly controlled, hydraulic or pneumatic swing-phase controls allow the prosthetist to set a pace adjusted to the individual amputee, from very slow to a race-walking pace. Hydraulic prostheses are heavier than other options and require gait training; for these reasons, these prostheses are prescribed for athletic or fit individuals. Other design features include multiple centers of rotation, referred to as “polycentric knees.” The mechanical complexity of these devices allows engineers to optimize selected stance and swing-phase features. 

Regulatory Status
According to the manufacturers, microprocessor-controlled prostheses are considered a class I device by the FDA and are exempt from 510(k) requirements. This classification does not require submission of clinical data regarding efficacy but only notification of FDA prior to marketing. FDA product codes: ISW, KFX.

Related Policies
10404 Myoelectric Prosthetic Components for the Upper Limb
80301 Functional Neuromuscular Electrical Stimulation

Policy:
A microprocessor-controlled knee may be considered MEDICALLY NECESSARY in amputees who meet the following requirements:

• Demonstrated need for long distance ambulation at variable rates (use of the limb in the home or basic community ambulation is not sufficient to justify provision of the the computerized limb over standard limb applications)
  OR demonstrated patient need for regular ambulation on uneven terrain or for regular use on stairs (use of the limb for limited stair climbing in the home or employment environment is not sufficient evidence for prescription of this device over standard prosthetic application), AND
• physical ability, including adequate cardiovascular and pulmonary reserve, for ambulation at faster than normal walking speed, AND
• adequate cognitive ability to master use and care requirements for the technology.

A microprocessor-controlled knee is considered NOT MEDICALLY NECESSARY for those who do not meet the above criteria.

A powered knee is considered INVESTIGATIONAL.

A microprocessor-controlled or powered ankle-foot is considered INVESTIGATIONAL.

The vacuum-assisted socket system (VASS^TM) is considered INVESTIGATIONAL and, therefore, not a covered benefit.

Policy Guidelines
Amputees should be evaluated by an independent qualified professional to determine the most appropriate prosthetic components and control mechanism. A trial period may be indicated to evaluate the tolerability and efficacy of the prosthesis in a real-life setting. Decisions about the potential benefits of microprocessor-knees involve multiple factors including activity levels, as well as the patient's physical and cognitive ability. A patient's need for daily ambulation of at least 400 continuous yards, daily and frequent ambulation at variable cadence or on uneven terrain (e.g., gravel, grass, curbs), and daily and frequent use of ramps and/or stairs (especially stair descent) should be considered as part of the decision. Typically, daily and frequent need of two or more of these activities would be needed to show benefit.

For patients in whom the potential benefits of the microprocessor knees are uncertain, patients may first be fitted with a standard prosthesis to determine their level of function with the standard device.

The following are guidelines from the Veterans Health Administration Prosthetic Clinical Management Program Clinical Practice Recommendations for Microprocessor Knees. (1)

PATIENT SELECTION AND IDENTIFICATION

1. Contraindications for use of the microprocessor knee should include
   • Any condition that prevents socket fitting, such as a complicated wound or intractable pain that precludes socket wear.
   • Inability to tolerate the weight of the prosthesis.
   • Medicare Level K 0 — no ability or potential to ambulate or transfer.
   • Medicare Level K 1 — limited ability to transfer or ambulate on level ground at fixed cadence.
   • Medicare Level K 2 — limited community ambulator that does not have the cardiovascular reserve, strength and balance to improve stability in stance to permit increased independence, less risk of falls and potential to advance to a less-restrictive walking device.
   • Inability to use swing and stance features of the knee unit.
   • Poor balance or ataxia that limits ambulation.
   • Significant hip flexion contracture (over 20 degrees).
   • Significant deformity of remaining limb that would impair ability to stride
   • Limited cardiovascular and/or pulmonary reserve or profound weakness.
   • Limited cognitive ability to understand gait sequencing or care requirements.
   • Long distance or competitive running.
   • Falls outside of recommended weight or height guidelines of manufacturer.
   • Specific environmental factors, such as excessive moisture or dust, or inability to charge the prosthesis.
   • Extremely rural conditions where maintenance ability is limited.
2. Indications for use of the microprocessor knee should include:
   • Adequate cardiovascular and pulmonary reserve to ambulate at variable cadence.
   • Adequate strength and balance in stride to activate the knee unit.
   • Should not exceed the weight or height restrictions of the device.
   • Adequate cognitive ability to master technology and gait requirements of device.
   • Hemi-pelvectomy through knee-disarticulation level of amputation, including bilateral; lower extremity amputees are candidates if they meet functional criteria as listed.
   • Patient is an active walker and requires a device that reduces energy consumption to permit longer distances with less fatigue.
   • Daily activities or job tasks that do not permit full focus of concentration on knee control and stability, such as uneven terrain, ramps, curbs, stairs, repetitive lifting and/or carrying.
   • Medicare Level K 2 — limited community ambulator, but only if improved stability in stance permits increased independence, less risk of falls and potential to advance to a less restrictive walking device, and patient has cardiovascular reserve, strength and balance to use the prosthesis. The microprocessor enables fine-tuning and adjustment of the hydraulic mechanism to accommodate the unique motor skills and demands of the functional level K2 ambulator.
   • Medicare Level K 3 — unlimited community ambulator.
   • Medicare Level K 4 — active adult, athlete who has the need to function as a K 3 level in daily activities.
   • Potential to lessen back pain by providing more secure stance control, using less muscle control to keep knee stable.
   • Potential to unload and decrease stress on remaining limb.
   • Potential to return to an active lifestyle.
3. Physical and Functional Fitting Criteria for New Amputees:
   • New amputees may be considered if they meet certain criteria as outlined above.
   • Premorbid and current functional assessment important determinant.
   • Requires stable wound and ability to fit socket.
   • Immediate postoperative fit is possible.
   • Must have potential to return to active lifestyle.

There are specific HCPCS codes that describe the microprocessor-controlled knee prosthesis:

L5856: Addition to lower extremity prosthesis, endoskeletal knee-shin system, microprocessor control feature, swing and stance phase, includes electronic sensor(s), any type
L5857: Addition to lower extremity prosthesis, endoskeletal knee-shin system, microprocessor control feature, swing phase only, includes electronic sensor(s), any type
L5858: Addition to lower extremity prosthesis, endoskeletal knee skin system, microprocessor control feature, stance phase only, includes electronic sensor(s), any type

There is a specific HCPCS code for ankle-foot system with a microprocessor-control feature:

L5973: Endoskeletal ankle foot system, microprocessor controlled feature, dorsiflexion and/or plantar flexion control, includes power source

Benefit Application
BlueCard/National Account Issues
Contractual or benefit limitations on durable medical equipment or prostheses upgrades may be applicable.

New technologies that utilize microprocessor control are being developed. Based on currently available evidence, no microprocessor-controlled device has been shown to have better outcomes than other (e.g., earlier) models. If more costly, the prosthesis would be considered not medically necessary using the Medical Policy Reference Manual definition of medical necessity. Benefit or contract language describing the "least costly alternative" may also be applicable to prostheses.

Rationale 
This evidence review was created in October 2003 and has been updated regularly with searches of the PubMed database. The most recent literature update was performed through Jan. 24, 2022.

Evidence reviews assess the clinical evidence to determine whether the use of a technology improves the net health outcome. Broadly defined, health outcomes are length of life, quality of life, and ability to function, including benefits and harms. Every clinical condition has specific outcomes that are important to patients and to managing the course of that condition. Validated outcome measures are necessary to ascertain whether a condition improves or worsens; and whether the magnitude of that change is clinically significant. The net health outcome is a balance of benefits and harms.

To assess whether the evidence is sufficient to draw conclusions about the net health outcome of a technology, 2 domains are examined: the relevance and the quality and credibility. To be relevant, studies must represent 1 or more intended clinical use of the technology in the intended population and compare an effective and appropriate alternative at a comparable intensity. For some conditions, the alternative will be supportive care or surveillance. The quality and credibility of the evidence depend on study design and conduct, minimizing bias and confounding that can generate incorrect findings. The randomized controlled trial (RCT) is preferred to assess efficacy; however, in some circumstances, nonrandomized studies may be adequate. RCTs are rarely large enough or long enough to capture less common adverse events and long-term effects. Other types of studies can be used for these purposes and to assess generalizability to broader clinical populations and settings of clinical practice.

Microprocessor-Controlled Prosthetic Knees for Individuals With Transfemoral Amputation
Clinical Context and Therapy Purpose
The purpose of microprocessor-controlled prosthetic knees in patients who have transfemoral amputation is to improve activity and function.

The question addressed in this evidence review is: Does microprocessor-controlled prosthetic knees improve the net health outcome in individuals with transfemoral amputations?

The following PICO was used to select literature to inform this review.

Populations
The relevant population of interest is people with transfemoral amputation.

Interventions
The therapies being considered are prostheses with a microprocessor-controlled knee.

Microprocessor-controlled prosthetic knees have been developed, including the Intelligent Prosthesis (Blatchford); the Adaptive (Endolite); the Rheo Knee^® (Össur); the C-Leg^®, Genium™ Bionic Prosthetic System, and the X2 and X3 prostheses (Otto Bock Orthopedic Industry); and Seattle Power Knees (3 models include Single Axis, 4-bar, and Fusion, from Seattle Systems). These devices are equipped with a sensor that detects when the knee is in full extension and adjusts the swing phase automatically, permitting a more natural walking pattern of varying speeds. The prosthetist can specify several different optimal adjustments that the computer later selects and applies according to the pace of ambulation. Also, these devices (except the Intelligent Prosthesis) use microprocessor control in both the swing and stance phases of gait. (The C-Leg Compact provides only stance control.) By improving stance control, such devices may provide increased safety, stability, and function. For example, the sensors are designed to recognize a stumble and stiffen the knee, thus avoiding a fall. Other potential benefits of microprocessor-controlled knee prostheses are improved ability to navigate stairs, slopes, and uneven terrain and reduction in energy expenditure and concentration required for ambulation. In 1999, the C-Leg was cleared for marketing by the U.S. Food and Drug Administration (FDA) through the 510(k) process (K991590). Next-generation devices such as the Genium Bionic Prosthetic system and the X2 and X3 prostheses use additional environmental input (e.g., gyroscope and accelerometer) and more sophisticated processing that is intended to create more natural movement. One improvement in function is step-over-step stair and ramp ascent. They also allow the user to walk and run forward and backward. The X3 is a more rugged version of the X2 that can be used in water, sand, and mud. The X2 and X3 were developed by Otto Bock as part of the Military Amputee Research Program.

Comparators
The relevant comparator is a prosthesis with a conventional knee.

Outcomes
Relevant outcomes are functional outcomes, health status measures, and quality of life. Relevant outcomes for microprocessor-controlled lower-limb prostheses may include the patient’s perceptions of subjective improvement attributable to the prosthesis and level of activity or function. Also, the energy costs of walking or gait efficiency may be a more objective measure of the clinical benefit of the microprocessor-controlled prosthesis.

Study Selection Criteria
Methodologically credible studies were selected using the following principles:

• To assess efficacy outcomes, comparative controlled prospective trials were sought, with a preference for RCTs.
• In the absence of such trials, comparative observational studies were sought, with a preference for prospective studies.
• To assess long-term outcomes and adverse events, single-arm studies that capture longer periods of follow-up and/or larger populations were sought.
• Studies with duplicative or overlapping populations were excluded.

Review of Evidence
In 2000, the Veterans Administration Technology Assessment Program issued a report on computerized lower-limb prostheses¹ This report offered the following observations and conclusions:

• Energy requirements of ambulation (vs requirements with conventional prostheses) are decreased at walking speeds slower or faster than the amputee’s customary speed but do not differ significantly at customary speeds.
• Results on the potentially improved ability to negotiate uneven terrain, stairs, or inclines are mixed. Such benefits, however, could be particularly important to meeting existing deficits in the reintegration of amputees to normal living, particularly those related to decreased recreational opportunities.
• Users’ perceptions of the microprocessor-controlled prosthesis are favorable. Where such decisions are recorded or reported, most study participants choose not to return to their conventional prosthesis or to keep these only as a backup to acute problems with the computerized one.
• Users’ perceptions may be particularly important for evaluating a lower-limb prosthesis, given the magnitude of the loss involved, along with the associated difficulty of designing and collecting objective measures of recovery or rehabilitation. However resilient the human organism or psyche, loss of a limb is unlikely to be fully compensated. A difference between prostheses sufficient to be perceived as distinctly positive to the amputee may represent the difference between coping and a level of function recognizably closer to the preamputation level.

The primary literature consists of small (sample range, 7 to 50 patients) within-subject comparisons of microprocessor-controlled with non-microprocessor-controlled prostheses in transfemoral amputees. These studies are described in Tables 1 and 2, divided by the Medicare Functional Level. Medicare Functional Level K2 describes a limited community ambulator who is able to traverse low barriers, such as curbs, and walk with a fixed cadence. Medicare Functional Level K3 describes a community ambulator who is able to traverse most barriers at variable cadence and may have activities beyond basic locomotion. Medicare Functional Level K4 exceeds basic ambulation skills and includes activities with high impact or stress that would be performed by a child, athlete, or active adult. The C-Leg compact provides stance control only and has been tested primarily in the more limited Medicare Functional Level K2 amputees. The C-Leg, which provides both stance and swing control, has been tested in Medicare Functional Level K3 and K4 amputees, in addition to Medicare Functional Level K2 amputees.

About half of the studies first tested participants with their own non-microprocessor prosthesis followed by an acclimation period and testing with the microprocessor-controlled knee (Table 1). The other studies used an alternating or randomized order, with more than 1 test session for each type of prosthesis. Most studies compared performance in laboratory activities and about half also included a period of home use.

Table 1. Within-Subject Study Characteristics of the Microprocessor Knee

Study	Study Location	Country	N	Participants	MPK	NMPK	Home Monitoring
K2 ambulators
Theeven et al. (2011, 2012)2,3	Activity at home and lab-simulated ADLs	Netherlands	28	Functional level K2	C-Leg and C-Leg compact 1-wk acclimation	Own NMPK	1 wk for each prosthesis
Burnfield et al. (2012)4	Level and ramp walking	U.S.	10	Functional level K2	C-Leg compact 3-mo acclimation	Own NMPK
K2 to K3 ambulators
VA (2006)5,6,7	Lab and home	U.S.	8	Functional level K2 to K3	C-Leg	Hydraulic	1 wk
Hafner and Smith (2009)8	A-B-A-(A or B) design in lab and city sidewalk	U.S.	8 K2 9 K3	Functional level K2 to K3	Retest in lab with preferred prosthesis	Retest in lab with preferred prosthesis	Prior 4 wk from 4-, 8-, and 12-mo tests
Highsmith et al. (2013)9	Ramp		21	Independent community ambulator	C-leg with 3-mo acclimation	Own NMPK
Howard et al. (2018)10	4-wk laboratory sessions for each phase (A-B-A or B-A-B)	U.S.	1 K2 6 K3	Functional level K2 or K3	Rheo Knee	Own NMPK	PROs for 3 wk prior to use
Hafner et al. (2007)11	A-B-A-B design in lab and city sidewalk	U.S.	17	Proficient community ambulator		Own mechanical
Kaufman et al. (2018)12	Free living environment	U.S.	50 K2	Functional level K2 or K3	One of 4 MPK devices	Own NMPK	Functional measures and PROs 10 wks
K3 to K4 ambulators
Kaufman et al. (2007, 2008)13,14	Lab and home	U.S.	15	Functional level K3 or K4	MPK acclimation of 10 – 39 wk	Own NMPK	10 d
Johansson et al. (2005)15	Laboratory and 0.25-mile indoor track	U.S.	8	Functional level K3 or K4	10-h acclimation if not owned	10-h acclimation if not owned
K2 to K4 ambulators
Carse et al. (2021)16	Laboratory and 12m indoor walkway	Scotland	5 K2 17 K3 10 K4	Functional level K2, K3 or K4		Own NMPK

ADLs: activities of daily living; MPK: microprocessor knee; NMPK: non-microprocessor knee; PROs: patient-reported outcomes; VA: Veterans Administration.

Results of these studies are described in Table 2 and summarized below:

• In K2 ambulators, the C-Leg and C-Leg compact improved performance on simulated activities of daily living that required balance, for walking on level ground and ramps, and led to a faster time to stand up from a seated position and move forward (Timed Up and Go test). In the single study that measured activity levels at home, use of a microprocessor-controlled knee did not increase objectively measured activity.
• In studies that included K2 to K3 ambulators, use of a microprocessor-controlled knee increased balance, mobility, speed, and distance compared with performance using the participant’s prosthesis. In studies that included independent or proficient community ambulators, the greatest benefit was for the descent of stairs and hills. Normal walking speed was not increased. In a study that primarily included K2 ambulatory, there was a reduction in falls demonstrated by the change from baseline while using a microprocessor knee and an increase in falls with reversion to a non-microprocessor knee.
• In studies that included K3 to K4 ambulators, use of a prosthesis with a microprocessor-controlled knee resulted in a more natural gait, and an increase in activity at home. Participants voiced a strong preference for the microprocessor knee.
• Irrespective of the Medicare Functional Level from K2 to K4, all studies reported that participants preferred the C-Leg or C-Leg compact over their non-microprocessor prosthesis.

Table 2. Outcomes With Microprocessor Knee Prosthesis Versus a Non-Microprocessor Knee

Study	Performance	Gait Efficiency	Preference (Self-Report or PEQ)	Activity at Home
K2 ambulators
Theeven et al. (2011, 2012)2,3	Improved simulated ADLs for activities requiring balance		Subjective benefit on PEQ No preference for C-Leg over C-Leg compact	No difference in objectively measured activity level
Burnfield et al. (2012)4	Improved walking on level ground, ramps, and faster TUG (17.7 s vs. 24.5 s)		PEQ All wanted to keep the C-Leg compact
K2 to K3 ambulators
VA (2006)5,6,7		Marginally improved	7 of 8 participants preferred the MPK	No difference
Hafner and Smith (2009)8	Improved mobility and speed			Decrease in self-reported stumbles and falls
Highsmith et al. (2013)9	Improved hill descent time (6.0 s vs. 7.7 s) and HAI
Howard et al. (2018)10	Improved 6MWT, BBS, and AMP, but inconsistent for normal walking speed and L test	Improved Physiological Cost Index	Preference for MPK in 6 of 7 participants PEQ superior in 5 of 7
Hafner et al. (2007)11	Improved for descent of stairs and hills only		Subjective improvement with MPK
Kaufman et al. (2018)12	Reduction in falls			Subjective improvement in PEQ satisfaction with MPK
K3 to K4 ambulators
Kaufman et al. (2007, 2008)13,14	More natural gait	No significant difference	Preferred MPK	Increased
Johansson et al. (2005)15	More natural gait and decrease in hip work	Oxygen consumption reduced for Rheo but not C-Leg	Preferred MPK
K2 to K4 ambulators
Carse et al. (2021)16		Improved GPS and walking velocity, step length, vertical ground reaction force symmetry index, and center of mass deviation

       
ADL: activity of daily living; AMP: amputee mobility predictor; BBS: Berg Balance Scale; GPS, gait profile score; HAI: Hill Assessment Index; MPK: microprocessor knee; NMPK: non-microprocessor knee; PEQ: Prosthesis Evaluation Questionnaire; 6MWT: 6-minute walk test; TUG: Timed Up & Go; VA: Veterans Administration.

Section Summary: Microprocessor-Controlled Knee
The literature consists of a number of small within-subject comparisons of microprocessor-controlled knees with non-microprocessor-controlled knee joints. Studies of prostheses with microprocessor knees in Medicare Functional Level K3 and K4 amputees have shown objective improvements in function on some outcome measures and strong patient preference for the microprocessor-controlled prosthetic knees. The evidence in Medicare Functional Level K2 ambulators suggests that a prosthesis with stance control only can improve activities that require balance and improve walking in this population. Only 1 biomechanical study of the next-generation Genium prosthesis was identified. One small study found little difference in performance between the Rheo Knee II and the user’s own non-microprocessor-controlled knee.

Powered-Knee Prostheses for Individuals with Transfemoral Amputation
Clinical Context and Therapy Purpose
The purpose of powered-knee prostheses in patients who have transfemoral amputation is to improve activity and function.

The question addressed in this evidence review is: Does powered-knee prostheses improve the net health outcome in individuals with transfemoral amputation?

The following PICO was used to select literature to inform this review.

Populations
The relevant population of interest is people with transfemoral amputation.

Interventions
The therapies being considered are powered-knee prostheses.

The Power Knee™ (Össur), which is designed to replace muscle activity of the quadriceps, uses artificial proprioception with sensors similar to the Proprio Foot to anticipate and respond with the appropriate movement required for the next step.

Comparators
The relevant comparator is a prosthesis with a conventional knee.

Outcomes
Relevant outcomes are functional outcomes, health status measures, and quality of life. Relevant outcomes may include the patient’s perceptions of subjective improvement attributable to the prosthesis and level of activity or function. Also, the energy costs of walking or gait efficiency may be a more objective measure of the clinical benefit of the microprocessor-controlled prosthesis.

Study Selection Criteria
Methodologically credible studies were selected using the following principles:

• To assess efficacy outcomes, comparative controlled prospective trials were sought, with a preference for RCTs.
• In the absence of such trials, comparative observational studies were sought, with a preference for prospective studies.
• To assess long-term outcomes and adverse events, single-arm studies that capture longer periods of follow-up and/or larger populations were sought.
• Studies with duplicative or overlapping populations were excluded.

Review of Evidence
We did not identify any literature on powered knee prostheses.

Microprocessor-Controlled Prosthetic Ankle-Foot for Individuals With Tibial Amputation
Clinical Context and Therapy Purpose
The purpose of microprocessor-controlled prosthetic ankle-foot in patients who have tibial amputation is to improve activity and function.

The question addressed in this evidence review is: Does microprocessor-controlled prosthetic ankle-foot improve the net health outcome in individuals with tibial amputation?

The following PICO was used to select literature to inform this review.

Populations
The relevant population of interest is people with tibial amputation.

Interventions
The therapies being considered are microprocessor-controlled ankle-foot prostheses.

Microprocessor-controlled ankle-foot prostheses have been developed for transtibial amputees. These include the Proprio Foot^® (Össur), the iPED (developed by Martin Bionics and licensed to College Park Industries), and the Elan Foot (Endolite). With sensors in the feet that determine the direction and speed of the foot’s movement, a microprocessor controls the flexion angle of the ankle, allowing the foot to lift during the swing phase and potentially adjust to changes in force, speed, and terrain during the step phase. This technology is designed to make ambulation more efficient and prevent falls in patients ranging from the young, active amputee to the elderly, diabetic patient. The Proprio Foot^® and Elan Foot are microprocessor-controlled foot prostheses that are commercially available at this time and are considered class I devices that are exempt from 510(k) marketing clearance. Information on the Össur website indicates the use of the Proprio Foot^® for low- to moderate-impact for transtibial amputees who are classified as level K3 (i.e., community ambulatory, with the ability or potential for ambulation with variable cadence).

Comparators
The relevant comparator is a prosthesis with a conventional ankle/foot.

Outcomes
Relevant outcomes are functional outcomes, health status measures, and quality of life. Relevant outcomes may include the patient’s perceptions of subjective improvement attributable to the prosthesis and level of activity or function. Also, the energy costs of walking or gait efficiency may be a more objective measure of the clinical benefit of the microprocessor-controlled prosthesis.

Study Selection Criteria
Methodologically credible studies were selected using the following principles:

• To assess efficacy outcomes, comparative controlled prospective trials were sought, with a preference for RCTs.
• In the absence of such trials, comparative observational studies were sought, with a preference for prospective studies.
• To assess long-term outcomes and adverse events, single-arm studies that capture longer periods of follow-up and/or larger populations were sought.
• Studies with duplicative or overlapping populations were excluded.

Review of Evidence
A Cochrane review by Hofstad et al. (2004), which evaluated ankle-foot prostheses, concluded that there was insufficient evidence from high-quality comparative studies for an overall superiority of any individual type of prosthetic ankle-foot mechanism.¹⁷ Also, reviewers noted that most clinical studies on human walking have used standardized gait assessment protocols (e.g., treadmills) with limited “ecological validity,” and recommended that for future research, functional outcomes be assessed for various aspects of mobility such as making transfers, maintaining balance, level walking, stair climbing, negotiating ramps and obstacles, and changes in walking speed.

Proprio Foot
Gait analysis with the Proprio Foot was evaluated in 16 transtibial K3 – K4 amputees during stair and ramp ascent and descent.^18,19 Results with the adaptive ankle (allowing 4° of dorsiflexion) were compared with tests conducted with the same prosthesis but at a fixed neutral angle (similar to other prostheses) and with results from 16 healthy controls. Adaptive dorsiflexion was found to increase during the gait analysis; however, this had a modest impact on other measures of gait for either the involved or uninvolved limb, with only a “tendency” to be closer to the controls, and the patient’s speed was not improved by the adapted ankle. The authors noted that an adaptation angle of 4° in the stair mode is small compared with physiologic ankle angles, and the lack of power generation with this quasi-passive design may also limit its clinical benefit. For walking up and down a ramp, the adapted mode resulted in a more normal gait during ramp ascent, but not during ramp descent. Some patients reported feeling safer with the plantarflexed ankle (adaptive mode) during ramp descent. Another small within-subject study (2014; N = 6) found no benefit of an active Proprio Foot compared with the same prosthesis turned off with level walking or with slope ascent or descent.²⁰

Self-reported and objective performance outcomes for 4 types of prosthetic feet, including the Proprio Foot, were evaluated in a randomized within-subject crossover study reported by Gailey et al (2012).²¹ Ten patients with transtibial amputation were initially tested with their prosthesis and tested again following training and a 2-week acclimation period with the SACH (solid ankle cushion heel), SAFE (stationary attachment flexible endoskeletal), Talux, and Proprio Foot in a randomized order. No differences between prostheses were detected by the self-reported Prosthesis Evaluation Questionnaire and Locomotor Capabilities Index, or for the objective 6-minute walk test. Steps per day and hours of daily activity between testing sessions did not differ by type of prosthesis.

Another study by Delussu et al. (2013) found a lower energy cost of floor walking with the Proprio Foot compared with a dynamic carbon fiber foot in 10 transtibial amputees.²² However, the study found no significant benefit for walking stairs or ramps, for the Timed Up and Go test, or for perceived mobility or walking ability.

Thomas-Pohl et al. (2021) compared 3 different types of ankle-foot prostheses, including the Proprio Foot, in a within-subject crossover study.²³ The primary outcome was to evaluate the ability of these prostheses to adapt to ground inclination. Six patients tested each of the 3 devices; each data acquisition was preceded with a 2-week acclimation period and was followed by a 3-week wash-out period with the patient's energy storing and returning foot. Overall the study found that microprocessor prostheses allowed for better posture and a reduction of residual knee moment on positive and/or negative slope when compared to the patients' energy storing and returning feet. Patients exhibited the most symmetric balance when they wore the Proprio Foot compared to the other microprocessor feet, but clinical functional tests between microprocessor prostheses and other feet did not differ greatly.

Section Summary: Microprocessor-Controlled Ankle-Foot Prostheses
Several small studies have been reported with microprocessor-controlled prostheses for transtibial amputees. The evidence to date is insufficient to support an improvement in functional outcomes compared with the same device in the off-mode or compared with energy-storing and energy-returning prostheses. Larger, higher-quality studies are needed to determine the impact of these devices on health outcomes with greater certainty.

Powered Ankle-Foot Prostheses for Individuals With Tibial Amputation
Clinical Context and Therapy Purpose
The purpose of powered ankle-foot prostheses in patients who have tibial amputation is to improve activity and function.

The question addressed in this evidence review is: Does powered ankle-foot prostheses improve the net health outcome in individuals with tibial amputations?

The following PICO was used to select literature to inform this review.

Populations
The relevant population of interest is people with tibial amputation.

Interventions
The therapies being considered are powered ankle-foot prostheses.

In development are lower-limb prostheses that also replace muscle activity to bend and straighten the prosthetic joint. For example, the PowerFoot BiOM^® (developed at the Massachusetts Institute of Technology and licensed to iWalk) is a myoelectric prosthesis for transtibial amputees that uses muscle activity from the remaining limb for the control of ankle movement (see evidence review 1.04.04 for a description of myoelectric technology). This prosthesis is designed to propel the foot forward as it pushes off the ground during the gait cycle, which in addition to improving efficiency, has the potential to reduce hip and back problems arising from an unnatural gait with use of a passive prosthesis. This technology is limited by the size and the weight required for a motor and batteries in the prosthesis.

Comparators
The relevant comparator is a prosthesis with a conventional ankle/foot.

Outcomes
Relevant outcomes are functional outcomes, health status measures, and quality of life. Relevant outcomes may include the patient’s perceptions of subjective improvement attributable to the prosthesis and level of activity or function. Also, the energy costs of walking or gait efficiency may be a more objective measure of the clinical benefit of the microprocessor-controlled prosthesis.

Study Selection Criteria
Methodologically credible studies were selected using the following principles:

• To assess efficacy outcomes, comparative controlled prospective trials were sought, with a preference for RCTs.
• In the absence of such trials, comparative observational studies were sought, with a preference for prospective studies.
• To assess long-term outcomes and adverse events, single-arm studies that capture longer periods of follow-up and/or larger populations were sought.
• Studies with duplicative or overlapping populations were excluded.

Review of Evidence
PowerFoot BiOM
Au et al. (2008) reported on the design and development of the powered ankle-foot prosthesis (PowerFoot BiOM); however, clinical evaluation of the prototype was performed in a single patient.²⁴

Ferris et al. (2012) reported on a pre-post comparison of the PowerFoot BiOM with the patient’s own energy-storing and energy-returning foot in 11 patients with transtibial amputation. Results for both prostheses were also compared with 11 matched controls who had intact limbs.²⁵ In addition to altering biomechanical measures, the powered ankle-foot increased walking velocity compared with the energy-storing and energy-returning prosthesis and increased step length compared with the intact limb. There appeared to be an increase in compensatory strategies at proximal joints with the PowerFoot; the authors noted that normalization of gait kinematics and kinetics might not be possible with a uniarticular device. Physical performance measures did not differ significantly between the prostheses, and there were no significant differences between conditions on the Prosthesis Evaluation Questionnaire. Seven patients preferred the PowerFoot and 4 preferred the energy-storing and energy-returning prostheses. Compared with controls with intact limbs, the PowerFoot had a reduced range of motion but provided greater ankle peak power.

In another similar, small pre-post study (7 amputees, 7 controls), Herr and Grabowski (2012) found gross metabolic cost and preferred walking speed to be more similar to nonamputee controls with the PowerFoot BiOM than with the patient’s own energy-storing and energy-returning prostheses.²⁶

In a conference proceeding, Mancinelli et al. (2011) described a comparison of a passive-elastic foot and the PowerFoot BiOM in 5 transtibial amputees.²⁷ The study was supported by the U.S. Department of Defense, and, at the time of testing, the powered prosthesis was a prototype, and subjects’ exposure to the prosthesis was limited to the laboratory. Laboratory assessment of gait biomechanics showed an average increase of 54% in the peak ankle power generation during late stance. Metabolic cost, measured by oxygen consumption while walking on an indoor track, was reduced by an average of 8.4% (p = .06).

Section Summary: Powered Ankle-Foot Prostheses
Several small studies have been reported with powered ankle-foot prostheses for transtibial amputees. The evidence to date is insufficient to support an improvement in functional outcomes.

Summary of Evidence
For individuals who have a transfemoral amputation who receive a prosthesis with a microprocessor-controlled knee, the evidence includes a number of within-subject comparisons of microprocessor-controlled knees versus non-microprocessor-controlled knee joints. Relevant outcomes are functional outcomes, health status measures, and quality of life. For K3- and K4-level amputees, studies have shown an objective improvement in function on some outcome measures, particularly for hill and ramp descent, and strong patient preference for microprocessor-controlled prosthetic knees. Benefits include a more normal gait, increased stability, and a decrease in falls. The evidence in Medicare level K2 ambulators suggests that a prosthesis with stance control only can improve activities that require balance and improve walking in this population. For these reasons, a microprocessor-controlled knee may provide incremental benefit for these individuals. The potential to achieve a higher functional level with a microprocessor-controlled knee includes having the appropriate physical and cognitive ability to use the advanced technology. The evidence is sufficient to determine that the technology results in an improvement in the net health outcome.

For individuals who have a transfemoral amputation who receive a prosthesis with a powered knee, the evidence includes no data. Relevant outcomes are functional outcomes, health status measures, and quality of life. The evidence is insufficient to determine that the technology results in an improvement in the net health outcome.

For individuals who have a tibial amputation who receive a prosthesis with a microprocessor-controlled ankle-foot, the evidence includes limited data. Relevant outcomes are functional outcomes, health status measures, and quality of life. The limited evidence available to date does not support an improvement in functional outcomes using microprocessor-controlled ankle-foot prostheses compared with standard prostheses. The evidence is insufficient to determine that the technology results in an improvement in the net health outcome.

For individuals who have a tibial amputation who receive a prosthesis with a powered ankle-foot, the evidence includes limited data. Relevant outcomes are functional outcomes, health status measures, and quality of life. The limited evidence available to date does not support an improvement in functional outcomes using powered ankle-foot prostheses compared with standard prostheses. The evidence is insufficient to determine that the technology results in an improvement in the net health outcome.

The purpose of the following information is to provide reference material. Inclusion does not imply endorsement or alignment with the evidence review conclusions.

Practice Guidelines and Position Statements
Guidelines or position statements will be considered for inclusion in Supplemental Information if they were issued by, or jointly by, a U.S. professional society, an international society with U.S. representation, or National Institute for Health and Care Excellence (NICE). Priority will be given to guidelines that are informed by a systematic review, include strength of evidence ratings, and include a description of management of conflict of interest.

U.S Department of Veterans Affairs/Department of Defense
In 2019, the Veterans Affairs/Department of Defense Clinical Practice Guideline for Rehabilitation of Individuals with Lower Limb Amputation made the following recommendations:²⁸

"We suggest offering microprocessor knee units over non-microprocessor knee units for ambulation to reduce risk of falls and maximize patient satisfaction. There is insufficient evidence to recommend for or against any particular socket design, prosthetic foot categories, and suspensions and interfaces. (From Table 3. Clinical practice guideline evidence-based recommendations and evidence strength)."

U.S. Preventive Services Task Force Recommendations
Not applicable

Ongoing and Unpublished Clinical Trials
Some currently unpublished trials that might influence this review are listed in Table 3.

Table 3. Summary of Key Trials

NCT No.	Trial Name	Planned Enrollment	Completion Date
Ongoing
NCT03204513	Impact of Powered Knee-Ankle Prosthesis Leg on Everyday Community Mobility and Social Interaction	15	Dec 2021
NCT04630457	Safety and Effectiveness of Electronically Controlled Prosthetic Ankle in Patients With Transtibial Amputation	42	Dec 2024
NCT04784429	Assessing Outcomes With Microprocessor Knee Utilization in a K2 Population (ASCENT K2)	100	Dec 2026
Unpublished
NCT02864693	Comparative Effectiveness of Microprocessor Controlled and Carbon Fiber Energy Storing and Returning Prosthetic Feet in Persons With Unilateral Transtibial Amputation	30	Apr 2018 (Results submitted, pending quality control review)
NCT04112901	Activity, Mobility, Social Functioning, Mental Health and Quality of Life Outcomes in Limited Mobility Transfemoral and Knee Disarticulation Amputees Using Microprocessor-Controlled Knees or Non-Microprocessor Controlled Knees in the United Kingdom: A Cohort Study	330	May 2020

NCT: national clinical trial.

References: 

1. Flynn K. Short Report: Computerized lower limb prosthesis (VA Technology Assessment Program). No. 2. Boston, MA: Veterans Health Administration; 2000.
2. Theeven P, Hemmen B, Rings F, et al. Functional added value of microprocessor-controlled knee joints in daily life performance of Medicare Functional Classification Level-2 amputees. J Rehabil Med. Oct 2011; 43(10): 906-15. PMID 21947182
3. Theeven PJ, Hemmen B, Geers RP, et al. Influence of advanced prosthetic knee joints on perceived performance and everyday life activity level of low-functional persons with a transfemoral amputation or knee disarticulation. J Rehabil Med. May 2012; 44(5): 454-61. PMID 22549656
4. Burnfield JM, Eberly VJ, Gronely JK, et al. Impact of stance phase microprocessor-controlled knee prosthesis on ramp negotiation and community walking function in K2 level transfemoral amputees. Prosthet Orthot Int. Mar 2012; 36(1): 95-104. PMID 22223685
5. Orendurff MS, Segal AD, Klute GK, et al. Gait efficiency using the C-Leg. J Rehabil Res Dev. Mar-Apr 2006; 43(2): 239-46. PMID 16847790
6. Klute GK, Berge JS, Orendurff MS, et al. Prosthetic intervention effects on activity of lower-extremity amputees. Arch Phys Med Rehabil. May 2006; 87(5): 717-22. PMID 16635636
7. Williams RM, Turner AP, Orendurff M, et al. Does having a computerized prosthetic knee influence cognitive performance during amputee walking?. Arch Phys Med Rehabil. Jul 2006; 87(7): 989-94. PMID 16813788
8. Hafner BJ, Smith DG. Differences in function and safety between Medicare Functional Classification Level-2 and -3 transfemoral amputees and influence of prosthetic knee joint control. J Rehabil Res Dev. 2009; 46(3): 417-33. PMID 19675993
9. Highsmith MJ, Kahle JT, Miro RM, et al. Ramp descent performance with the C-Leg and interrater reliability of the Hill Assessment Index. Prosthet Orthot Int. Oct 2013; 37(5): 362-8. PMID 23327837
10. Howard CL, Wallace C, Perry B, et al. Comparison of mobility and user satisfaction between a microprocessor knee and a standard prosthetic knee: a summary of seven single-subject trials. Int J Rehabil Res. Mar 2018; 41(1): 63-73. PMID 29293160
11. Hafner BJ, Willingham LL, Buell NC, et al. Evaluation of function, performance, and preference as transfemoral amputees transition from mechanical to microprocessor control of the prosthetic knee. Arch Phys Med Rehabil. Feb 2007; 88(2): 207-17. PMID 17270519
12. Kaufman KR, Bernhardt KA, Symms K. Functional assessment and satisfaction of transfemoral amputees with low mobility (FASTK2): A clinical trial of microprocessor-controlled vs. non-microprocessor-controlled knees. Clin Biomech (Bristol, Avon). Oct 2018; 58: 116-122. PMID 30077128
13. Kaufman KR, Levine JA, Brey RH, et al. Gait and balance of transfemoral amputees using passive mechanical and microprocessor-controlled prosthetic knees. Gait Posture. Oct 2007; 26(4): 489-93. PMID 17869114
14. Kaufman KR, Levine JA, Brey RH, et al. Energy expenditure and activity of transfemoral amputees using mechanical and microprocessor-controlled prosthetic knees. Arch Phys Med Rehabil. Jul 2008; 89(7): 1380-5. PMID 18586142
15. Johansson JL, Sherrill DM, Riley PO, et al. A clinical comparison of variable-damping and mechanically passive prosthetic knee devices. Am J Phys Med Rehabil. Aug 2005; 84(8): 563-75. PMID 16034225
16. Carse B, Scott H, Brady L, et al. Evaluation of gait outcomes for individuals with established unilateral transfemoral amputation following the provision of microprocessor controlled knees in the context of a clinical service. Prosthet Orthot Int. Jun 01 2021; 45(3): 254-261. PMID 34016870
17. Hofstad C, Linde H, Limbeek J, et al. Prescription of prosthetic ankle-foot mechanisms after lower limb amputation. Cochrane Database Syst Rev. 2004; (1): CD003978. PMID 14974050
18. Alimusaj M, Fradet L, Braatz F, et al. Kinematics and kinetics with an adaptive ankle foot system during stair ambulation of transtibial amputees. Gait Posture. Oct 2009; 30(3): 356-63. PMID 19616436
19. Fradet L, Alimusaj M, Braatz F, et al. Biomechanical analysis of ramp ambulation of transtibial amputees with an adaptive ankle foot system. Gait Posture. Jun 2010; 32(2): 191-8. PMID 20457526
20. Darter BJ, Wilken JM. Energetic consequences of using a prosthesis with adaptive ankle motion during slope walking in persons with a transtibial amputation. Prosthet Orthot Int. Feb 2014; 38(1): 5-11. PMID 23525888
21. Gailey RS, Gaunaurd I, Agrawal V, et al. Application of self-report and performance-based outcome measures to determine functional differences between four categories of prosthetic feet. J Rehabil Res Dev. 2012; 49(4): 597-612. PMID 22773262
22. Delussu AS, Brunelli S, Paradisi F, et al. Assessment of the effects of carbon fiber and bionic foot during overground and treadmill walking in transtibial amputees. Gait Posture. Sep 2013; 38(4): 876-82. PMID 23702342
23. Thomas-Pohl M, Villa C, Davot J, et al. Microprocessor prosthetic ankles: comparative biomechanical evaluation of people with transtibial traumatic amputation during standing on level ground and slope. Disabil Rehabil Assist Technol. Jan 2021; 16(1): 17-26. PMID 31535903
24. Au S, Berniker M, Herr H. Powered ankle-foot prosthesis to assist level-ground and stair-descent gaits. Neural Netw. May 2008; 21(4): 654-66. PMID 18499394
25. Ferris AE, Aldridge JM, Rabago CA, et al. Evaluation of a powered ankle-foot prosthetic system during walking. Arch Phys Med Rehabil. Nov 2012; 93(11): 1911-8. PMID 22732369
26. Herr HM, Grabowski AM. Bionic ankle-foot prosthesis normalizes walking gait for persons with leg amputation. Proc Biol Sci. Feb 07 2012; 279(1728): 457-64. PMID 21752817
27. Mancinelli C, Patritti BL, Tropea P, et al. Comparing a passive-elastic and a powered prosthesis in transtibial amputees. Annu Int Conf IEEE Eng Med Biol Soc. 2011; 2011: 8255-8. PMID 22256259
28. Webster JB, Crunkhorn A, Sall J, et al. Clinical Practice Guidelines for the Rehabilitation of Lower Limb Amputation: An Update from the Department of Veterans Affairs and Department of Defense. Am J Phys Med Rehabil. Sep 2019; 98(9): 820-829. PMID 31419214

Coding Section

Codes	Number	Description
ICD-9 Diagnosis	897.2-897.7	Traumatic amputation of leg; code range for above the knee amputation(s)
	V43.65	Organ or tissue replaced by other means; knee
HCPCS		See Policy Guidelines
	K1014 (effective 04/01/2021)	Addition, endoskeletal knee-shin system, 4 bar linkage or multiaxial, fluid swing and stance phase control (ALLUX MPK knee by Proteor)
ICD-10-CM (effective 10/01/15)	S78.011-S78.929	Traumatic amputation of hip and thigh; code range
	Z96.651-Z96.659	Presence of artificial knee joint; code range
ICD-10-PCS (effective 10/01/15)		Not applicable. ICD-10-PCS codes are only used for inpatient services. There are no ICD procedure codes for devices.
Type of Service
Place of Service

Procedure and diagnosis codes on Medical Policy documents are included only as a general reference tool for each policy. They may not be all-inclusive.

This medical policy was developed through consideration of peer-reviewed medical literature generally recognized by the relevant medical community, U.S. FDA approval status, nationally accepted standards of medical practice and accepted standards of medical practice in this community, Blue Cross Blue Shield Association technology assessment program (TEC) and other nonaffiliated technology evaluation centers, reference to federal regulations, other plan medical policies, and accredited national guidelines.

"Current Procedural Terminology © American Medical Association. All Rights Reserved" 

History From 2014 Forward     

08/24/2022	Annual review, no change to policy intent. Updating rationale and references.
08/02/2021	Annual review, no change to policy intent. Updating coding, rationale and references.
04/12/2021	Adding code 'K1014' to Coding Section. No other changes made.
08/01/2020	Annual review, no change to policy intent. Updating rationale and references.
08/01/2019	Annual review, no change to policy intent. Updating description, background, rationale and references.
08/23/2018	Annual review, no change to policy intent. Updating background, regulatory status, rationale and references.
08/09/2017	Annual review, no change to policy intent.
08/03/2016	Annual review, no change to policy intent.
08/12/2015	Annual review, no change to policy intent. Updated background, description, guidelines, rationale, references and regulatory status. Added coding.
08/06/2014	Annual review. Added related policies. Updated background, description, rationale and references. No change to policy intent.