Coverage Policy Manual
Policy #: 2006011
Category: DME
Initiated: April 2006
Last Review: June 2018
  Microprocessor-Controlled Prostheses for the Lower Limb

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 have the capability to maneuver on uneven terrain and with variable gait.
 
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 be quite different than a younger, active person. In general, key elements of a prosthetic knee design involve providing stability during both the stance and swing phase of the gait. Prosthetic knees also 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 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 that is 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 generally 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.
 
Microprocessor-Controlled Prosthetic Knees
Microprocessor-controlled prosthetic knees have been developed, including the Intelligent Prosthesis (Blatchford, U.K.), the Adaptive (Endolite, England), the Rheo (Ossur, Iceland), the C-Leg and Genium Bionic Prosthetic System (Otto Bock Orthopedic Industry, Minneapolis, MN), 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. For example, the prosthetist can specify several different optimal adjustments that the computer later selects and applies according to the pace of ambulation. In addition, these devices (with the exception of 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, they 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. The C-Leg was cleared for marketing in 1999 through the 510(k) process of the U.S. Food and Drug Administration (FDA, K991590). Next generation devices such as the Genium Bionic Prosthetic system utilize additional environmental input (e.g., gyroscope and accelerometer) and more sophisticated processing that is intended to create more natural movement. One proposed improvement in function is step-over-step stair ascent.
 
Microprocessor-Controlled Ankle-foot Prostheses
Microprocessor-controlled ankle-foot prostheses are being developed for transtibial amputees. These include the Proprio Foot® (Ossur) and the iPED (developed by Martin Bionics LLC 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. The intent of the technology is 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 prosthesis that is commercially available at this time and is a class-I device that is exempt from 510(k) marketing clearance. The manufacturer must register the prosthesis with the restorative devices branch of the FDA and keep a record of any complaints but does not have to undergo a full review. Information on the Ossur website indicates 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).
 
Powered Prostheses
In development are lower-limb prostheses that also replace muscle activity in order 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. 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. The Power Knee (Ossur), which is designed to replace muscle activity of the quadriceps, uses artificial proprioception with sensors similar to the Proprio Foot in order to anticipate and respond with the appropriate movement required for the next step. The Power Knee is currently in the initial launch phase in the United States.
 
Regulatory Status
Manufacturers must register prostheses with the restorative devices branch of the U.S. Food and Drug Administration (FDA) and keep a record of any complaints but do not have to undergo a full FDA review.
 
 

Policy/
Coverage:
Effective, February 2010
A microprocessor-controlled knee meets member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes in amputees who meet the following requirements:
    • demonstrated need for long distance ambulation at variable rates (use of the limb in the home or for basic community ambulation is not sufficient to justify provision of 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 does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes in individuals who do not meet these criteria.
 
For contracts without primary coverage criteria, a microprocessor-controlled knee in individuals who do not meet these criteria is considered investigational.  Investigational services are exclusions in most member benefit certificate of coverage.
 
A powered knee, microprocessor-controlled foot or powered foot does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For contracts without primary coverage criteria, a powered knee, microprocessor-controlled foot or powered foot in individuals who do not meet these criteria is considered investigational.  Investigational services are exclusions in most member benefit certificate of coverage.
 
 
Effective,  April 2006 - January 2010
A microprocessor-controlled prosthetic knee meets primary coverage criteria for effectiveness and is covered for members who are:
Amputees with mobility level “able to walk outdoors without limitations” or “able to walk outdoors without limitations plus engage in high performance activities” with at least one of the following findings:
    • Diseases and/or complications due to an injury that increase the disability caused by the amputation
    • Neuromuscular deficiencies of the extremities including deficiencies of the residual limb motor system
    • Employees with professional activities requiring a high level of safety or long walking and standing
    • People having parental authority for children up to an age of 6 years
    • People with unilateral hip disarticulation amputation, and patients with hemipelvectomy amputation with good walking ability
    • People climbing stairs often (>100 per day), walking on slopes or uneven ground
    • Active amputee able to walk fast (>5 kmph or 3 mph) and/or walking long distances (.5 km or 3 miles per day)
Any other use of a microprocessor-controlled prosthetic knee is not covered based on benefit certificate primary coverage criteria that there be scientific evidence of effectiveness.
 
For contracts without primary coverage criteria, the use of  microprocessor-controlled prosthetic knee in any circumstance not specifically stated as covered is considered investigational and is not covered.  Investigational services are an exclusion in the member benefit contract.  
 
Allowances for the microprocessor-controlled prosthetic knee, or its components, are subject to any contract limitations for DME services.

Rationale:
Relevant outcomes for microprocessor-controlled knee prostheses may include the patient’s perceptions of subjective improvement attributable to the prosthesis and level of activity/function. In addition, the energy costs of walking or gait analysis may be a more objective measure of the clinical benefit of the microprocessor-controlled prosthesis.
 
Published data on the microprocessor-controlled knee prostheses are minimal; the bulk of the literature focuses on the Intelligent Prosthesis, which while similar to the C-LEG is not distributed in this country. Kirker and colleagues reported on the gait symmetry, energy expenditure, and subjective impression of the Intelligent Prosthesis in 16 patients with an above knee amputation related to trauma or congenital anomaly.  The patients had previously functioned adequately with a pneumatic swing phase control unit and were offered a trial of an Intelligent Prosthesis (IP). At the beginning of the study the patients had been using the IP for between 1 and 9 months. The patients responded to a questionnaire using a visual analog scale regarding how much effort was needed to walk at their normal, faster, and slower speeds on smooth level surfaces, outdoors or at work, up and down a slope, and up and down steps. The patients also indicated their overall preference for one or the other. Subjects reported that significantly less effort was required when using the IP prosthesis to walk at normal or high speeds, but there was no difference for a slow gait. Effort was reduced walking outdoors or at work. Subjects reported a strong preference for the IP versus the standard pneumatic leg.
 
Datta and Howitt reported on the results of a questionnaire survey of 22 amputees who were switched from pneumatic swing phase control prostheses to an IP device.  All patients were otherwise fit and fairly active. The questionnaire focused on functional attributes of the 2 prostheses, such as speed of walking, and walking up and down stairs, energy levels, and naturalness of the gait. All subjects reported that the IP was an improvement over the conventional prosthesis. The main benefits suggested by this subjective study were the ability to walk at various speeds, reduction of effort of walking, and patients' perception of improvement of walking pattern.
 
Buckley and colleagues focused on a comparison of the energy cost of an IP with a pneumatic swing phase control unit in 3 patients.  Two subjects showed a decrease in energy consumption, while a third showed no change. Another study of 1 patient also reported lower oxygen consumption with an IP prosthesis.  Obviously, few conclusions can be drawn from these small trials.  In summary, there are minimal published data on microprocessor-controlled knee prostheses in the English literature.
 
In 2000, the Veteran’s Administration Technology Assessment Program issued a “short report” on computerized lower limb prostheses.   This report, which considered the same data as that referenced here, offered the following observations and conclusions:
    1. Energy requirements of ambulation (compared to requirements with conventional prostheses) are decreased at walking speeds slower or faster than the amputee’s customary speed, but are not significantly different at customary speeds.
    2. 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 deficit in the reintegration of amputees to normal living, particularly those related to decreased recreational opportunities.
    3. Users’ perceptions of the microprocessor-controlled prosthesis are favorable. Where such decisions are recorded or reported, the vast majority of study participants choose not to return to their conventional prosthesis or keep these only as back-up to acute problems with the computerized one.
    4. 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.
    5. Mechanical failure is recorded in some of the studies, but seems to be rare. The manufacturer indicates that some C-LEGs have been used for extended periods (up to 5 years) without mechanical or electrical problems.
 
The UK Medical Devices Agency has conducted an evaluation of the Endolite Intelligent Prosthesis, with generally favorable results. Recognizing constraints related to the substantial cost of the prosthesis, the UK National Health Service makes it available to a wide range of patients, and has arranged with the manufacturer for a program to lend critical components, should these components of the prosthesis require factory repair.
 
2007 Update
One industry-sponsored study assessed function, performance, and preference for the C-Leg in 21 unilateral transfemoral amputees using an A-B-A-B design (Hafner, 2007).  Subjects were fully accustomed to a mechanical knee system (various types) and were required to show proficiency in ambulating on level ground, inclines, stairs, and uneven terrain prior to enrollment. Of the 17 subjects (81%) who completed the study, patient satisfaction was significantly better with the microprocessor-controlled prosthesis as measured by the Prosthesis Evaluation Questionnaire (PEQ). Fourteen preferred the microprocessor-controlled prosthesis, 2 preferred the mechanical system, and one had no preference. Subjects reported fewer falls, lower frustration with falls, and an improvement in concentration. Objective measurements on the various terrains were less robust, showing improvements only for descent of stairs and hills. Average performance on stair descent improved from a step-to pattern with a rail to a step-over-step with a rail and assistive device. The C-Leg improved hill descent from requiring an assistive device to using a step-to pattern without an assistive device. Unaffected were stair ascent, step frequency, step length, and walking speed. The subjective improvement in concentration was reflected by a small (nonsignificant) increase in walking speed while performing a complex cognitive task (reversing a series of numbers provided by cell phone while walking on a city sidewalk).
 
All lower-limb amputees returning from Operation Iraqi Freedom and Operation Enduring Freedom currently receive a microprocessor-controlled prosthesis from the Department of Veterans Affairs (VA); 155 veterans were provided with a C-Leg in 2005.  A series of papers from the VA reports results from a within-subject comparison of the C-Leg to a hydraulic Mauch SNS knee (Orendurff, 2006) (Klute, 2006) (Williams, 2006).  Eight (44%) of the 18 functional level 2–3 subjects recruited completed the study; most withdrew due to the time commitment of the study or other medical conditions, 2 could not be adequately fit, and 1 could not acclimate to the C-Leg. Of the 8 remaining subjects, half showed a substantial decrease in oxygen cost when using the C-Leg, resulting in a marginal improvement in gait efficiency for the group (Orendurff, 2006).  The improvement in gait efficiency was hypothesized to result in greater ambulation, but a 7-day activity monitoring period in the home/community showed no difference in the number of steps taken per day or the duration of activity (Klute, 2006).  Cognitive performance, assessed by standardized neuropsychological tests while walking a wide hallway in 5 of the subjects, was not different for semantic or phonemic verbal fluency, and not significantly different for working memory when wearing the microprocessor-controlled prosthesis (Williams, 2006).  Although the study lacked sufficient power, results showed a 50% decrease in errors on the working memory task (1.63 vs. 0.88). Thus, the effect of this device on objective measures of cognitive performance cannot be determined from this study. Subjective assessment revealed a perceived reduction in attention to walking while performing the cognitive test (effect size of 0.79) and a reduction in cognitive burden with the microprocessor-controlled prosthesis (effect size of 0.90). Seven of the 8 subjects preferred to keep the microprocessor-controlled prosthesis at the end of the study (Klute, 2006).  The authors noted that without any prompting, all of the subjects had mentioned that stumble recovery was their favorite feature of the C-Leg.
 
Two small studies of high functioning amputees (functional level 3–4, n=8 and 10) compared performance with the subject’s own C-Leg to a mechanical model (Johansson, 2005) (Seymour, 2007).  With little or no acclimation time for the mechanical knee, the studies found that use of the C-Leg resulted in faster time on an obstacle course, a smoother gait, and improved efficiency of hip work. A survey of 8 amputees who had previously switched to a C-Leg found that this group of patients felt less fatigued, safer due to a reduced incidence from falls, and more motivated and self-confident when using the C-Leg in comparison with their previous mechanical model (Swanson, 2005).  Given the highly selected patient populations and bias in experimental design, the only information provided by these studies is that some current users are satisfied with the microprocessor-controlled knees and that they perform adequately for some people.
 
Although the literature indicates that microprocessor-controlled knees may perform at least as well as mechanical prostheses, objective evidence of incremental improvement in activities of daily living (e.g., falls and activity levels) is lacking. This may be due, in part, to the individualized prescription of prosthetic components and the difficulty of designing and collecting objective measures of recovery or rehabilitation. The literature does indicate a strong preference for prosthetic knees that controls both stance and swing in selected patients. The perceived benefits include an increase in stability, a decrease in falls, and a decrease in the cognitive burden associated with monitoring the prosthesis. As described in the VA short report, “users’ perceptions may be particularly important for evaluating a lower limb prosthesis, given the magnitude of the loss involved…. 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.”
 
It was concluded that a microprocessor-controlled knee may provide incremental benefit for some individuals. Those considered most likely to benefit from these prostheses have both the potential and need for frequent ambulation at variable cadence, on uneven terrain, or on stairs. The potential to achieve a high functional level with a microprocessor-controlled knee includes having the appropriate physical and cognitive ability to be able to use the advanced technology.
 
2009 Update
Two reports were published describing a within subject objective comparison of mechanical and microprocessor controlled knees in 15 transfemoral amputees (Kaufman, 2007) (Kaufman, 2008). Following testing with the subject’s usual mechanical prosthesis, the amputees were given an acclimation period of 10 to 39 weeks (average of 18 weeks) with a microprocessor knee before repeat testing. The 2007 report described results from objective balance and gait measurements; measures of energy efficiency and expenditure were reported in 2008. Patients rated the microprocessor knee as better than the mechanical prosthesis in 8 of 9 categories of the prosthesis evaluation questionnaire. Objective gait measurement included knee flexion and the peak extensor moment during stance measured by a computerized video motion analysis system. Both the extensor moment and knee flexion were significantly different for the 2 prostheses, indicating a reduction in active contraction of the hip extensors to “pull back” and force the prosthetic knee into extension and resulting in a more natural gait with the microprocessor knee. Balance was improved by about 10%, as objectively determined with a computerized dynamic posturography platform. Total daily energy expenditure was assessed over 10 days in free-living conditions. Both daily energy expenditure and the proportion of energy expenditure attributed to physical activity increased. Although the subjects perceived that it was easier to walk with the microprocessor-controlled knee than the mechanical prosthesis, energy efficiency while walking on a treadmill was not significantly different (2.3% change). Taken together, the results indicated that amputees spontaneously increased their daily physical activity outside of the laboratory setting when using a microprocessor knee. These objective assessments support the previously described findings of improved subjective experience with the microprocessor knee.
 
Additional Information
Otto Bock, the manufacturer of the C-Leg has provided the following potential patient selection criteria:
Amputees with mobility level “able to walk outdoors without limitations” and “able to walk outdoors without limitations plus engage in high performance activities” with at least one of the following findings:
    • Diseases and/or complications due to an injury that increase the disability caused by the amputation
    • Neuromuscular deficiencies of the extremities including deficiencies of the residual limb motor system
    • Employees with professional activities requiring a high level of safety or long walking and standing
    • People having parental authority for children up to an age of 6 years
    • People with unilateral hip disarticulation amputation, and patients with hemipelvectomy amputation with good walking ability.
    • People climbing stairs often (>100 per day), walking on slopes or uneven ground
    • Active amputee able to walk fast (>5 kph or 3 mph) and/or walking long distances (5 km or 3 miles per day)
 
2010 Update
An updated literature search of the MEDLINE database was performed in January 2010. Hafner and Smith evaluated the impact of the microprocessor-controlled prosthesis on function and safety in level K2 and K3 amputees (Hafner, 2009). The K2 ambulators tended to be older (57 vs. 42 years), but this did not achieve statistical significance in this sample (p = 0.05). In this per-protocol analysis, 8 level K2 and 9 level K3 amputees completed testing with their usual mechanical prosthesis, then with the microprocessor-controlled prosthesis, a second time with their passive prosthesis, and then at 4, 8, and 12 months with the prosthesis that they preferred/used most often. Only subjects who completed testing at least twice with each prosthesis were included in the analysis (4 additional subjects did not complete the study due to technical, medical, or personal reasons). Similar to the group’s 2007 report, performance was assessed by questionnaires and functional tasks including hill and stair descent, an attentional demand task, and an obstacle course (Hafner, 2007).  Self-reported measures included concentration, multitasking ability, and numbers of stumbles and falls in the previous 4 weeks. Both K2 and K3 level amputees showed significant improvements in mobility and speed (ranging from 7% to 40%), but little difference in attention with the functional assessments. The self-reported numbers of stumbles and falls in the prior 4 weeks was found to be lower with the microprocessor-controlled prosthesis. For example, in the K2 level amputees, stumbles decreased from an average of 4.0 to 2.7 per month, semi-controlled falls from 1.6 to 0.6, and uncontrolled (i.e., complete) falls from 0.5 to 0.0 when using the microprocessor-controlled knee. Re-evaluation of each participant’s classification level at the conclusion of the study showed that 50% of the participants originally considered to be K2 ambulators were now functioning at level K3 (about as many K3 ambulators increased as decreased functional level). These results are consistent with the Veteran’s Health Administration Prosthetic Clinical Management Program clinical practice recommendations for microprocessor knees, which state that use of microprocessor knees may be indicated for Medicare Level K2, 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 if the patient has cardiovascular reserve, strength, and balance to utilize the prosthesis.
 
Microprocessor-Controlled Ankle-Feet Prostheses
A 2008 Cochrane review of ankle-foot prostheses concluded that there was insufficient evidence from high quality comparative studies for the overall superiority of any individual type of prosthetic ankle-foot mechanism (Hofstad, 2004). In addition, the authors noted that the vast majority of 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 should 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.
 
In 2009, Alimasuj et al. reported gait analysis with the Proprio Foot in 16 transtibial K3-K4 amputees during stair ascent and stair descent (Alimusaj, 2009). Results with the adaptive ankle (allowing 4 degrees 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 be increased in 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 degrees in the stair mode is small compared to physiologic ankle angles, and the lack of power generation with this quasi-passive design may also limit its clinical benefit.
 
Au and colleagues have reported the design and development of the powered ankle-foot prosthesis; however, clinical evaluation of the prototype was performed in a single patient (Au, 2008).
 
Technology Assessments, Guidelines and Position Statements
The VA’s Prosthetic and Sensory Aids Strategic Healthcare Group was directed by the Under Secretary for Health to establish a Prosthetic Clinical Management Program to coordinate the development of clinical practice recommendations for prosthetic prescriptive practices. The New Technology Subgroup of the Pre-Post National Amputation Workgroup met in April 2004 to develop a proposal to define patient selection and identification criteria for microprocessor-prosthetic knees. Their proposal was based on recommendations arising from the May 2003 Microprocessor Prosthetic Knee Forum, hosted at Walter Reed Army Medical Center and sponsored and funded by the American Academy of Orthotists and Prosthetists.
 
2012 Update
A review of the literature through March 2012 did not reveal any new information that would prompt a change in the coverage statement. The following is a summary of the relevant studies that were identified.
 
Microprocessor-Controlled Knee
A 2010 systematic review evaluated safety and energy efficiency of the C-leg microprocessor-controlled prosthetic knee in transfemoral amputees (Highsmith, 2010). Eighteen comparative studies were included that used objective/quantifiable outcome measures with the C-leg in one arm of the trial. Due to heterogeneity, meta-analyses were not performed. The 7 papers on safety had low methodologic quality and a moderate risk of bias, showing an improvement in some safety or surrogate safety measure. Effect sizes ranged from 0.2 (small) to 1.4 (large). Of the 8 papers identified on energy efficiency, 1 was considered to be of high methodologic quality, and 5 were considered to be of low quality. Two of the trials reported a statistical improvement in energy efficiency, and 4 reported some improvement in efficiency or speed that failed to reach statistical significance. There were no adverse events, safety concerns, or detriments to energy efficiency reported in association with use of the C-leg.
 
Theeven and colleagues assessed the effect of microprocessor-controlled prosthetic knee joints on functional performance in 28 Medicare Level K2 ambulators in 2011 (Theeven, 2011). Functional performance was assessed with participants performing 17 simulated activities of daily living, first using their own mechanically controlled knee and then with 2 types of microprocessor-controlled knee joints (C-Leg and C-Leg Compact) in a randomized order with 1 week of acclimation. Performance times were significantly improved for the subset of activities that required balance while standing but not for other activities. Stratifying participants into low, intermediate, and high functional mobility level showed that the 2 higher functioning subgroups performed significantly faster using microprocessor controlled knee joints.
 
Another study compared the C-Leg Compact (stance phase only) with the participant’s usual mechanical prosthetic knee joint on ramp and community walking in 10 Medicare functional level K2 ambulators (Burnfield, 2012) Seven of the 10 subjects used upper extremity assistive devices (e.g., a cane or walker) while ambulating. Gait analysis and functional assessments were conducted first with the participant’s mechanical knee and then, after training and a 3-month accommodation period, with the C-Leg Compact. Ramp ascent and descent were 28% and 36% faster, respectively, with the C-Leg Compact due to increases in stride length (17%) and cadence (16%). Participants also had significantly faster Timed Up and Go test (17.7 vs. 24.5 seconds) and higher functional questionnaire scores on the Prosthetic Evaluation Questionnaire (PEQ). At the end of the study, the participants chose which prosthesis to keep; all 9 who were offered the opportunity selected the C-Leg Compact.
 
Microprocessor-Controlled Ankle-Feet Prostheses
Au and colleagues have reported the design and development of the powered ankle-foot prosthesis (PowerFoot Biom); however, clinical evaluation of the prototype was performed in a single patient. (21) In a conference proceeding from 2011, Mancinelli et al. describe a comparison of a passive-elastic foot and the PowerFoot Biom in 5 transtibial amputees (Mancinelli, 2011). 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=0.06).
 
2013 Update
This policy is updated with a literature search through May 2013. There was no new information identified that would prompt a change in the coverage statement. The following is a summary of the key identified literature.
 
Microprocessor-Controlled Knee
 
C-Leg
A 2013 study by Highsmith et al. used a within-subjects pre- post- design, first evaluating outcomes with a nonmicroprocessor-controlled prosthesis followed by the same evaluation after receiving a microprocessor-controlled prosthesis. These researchers reported significantly improved descent times by 23% (6.0 vs. 7.7 seconds) and Hill Assessment Index scores (8.9 vs. 7.8) with a C-Leg compared to the subjects’ own non-microprocessor prosthetic knees (Highsmith, 2013).
 
C-Leg Compact
Perceived performance was improved with the C-Leg for some subscales of the Prosthesis Evaluation Questionnaire (PEQ), but this did not translate to an increase in activity level (Theeven, 2012). With the C-Leg Compact, 2 of 8 subscales on the PEQ were improved, and only in the subgroup with high functional mobility. There was no change in activity level with the C-Leg or C-Leg Compact when compared to the mechanically controlled knee.
 
Genium
The Genium prosthesis was compared to the subject’s own C-Leg in a cross-over study with 11 transfemoral amputees (Bellmann, 2012). This was a manufacturer-sponsored biomechanical study (e.g., comparison of ground reaction forces, flexion angles, load distribution) that did not evaluate clinical outcomes.
 
Microprocessor-Controlled Ankle-Feet Prostheses
 
Proprio Foot
A 2012 randomized within-subject crossover study compared self-reported and objective performance outcomes for 4 types of prosthetic feet, including the Proprio Foot (Gailey, 2012). Ten patients with transtibial amputation were tested with their own prosthesis and then after 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 PEQ 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 between the types of prostheses.
 
PowerFoot Biom
In 2012, Ferris et al. reported a pre-post comparison of the PowerFoot Biom with the patient’s own energy-storing and -returning foot (ESR) in 11 patients with transtibial amputation. Results for both prostheses were also compared with 11 matched controls who had intact limbs (Ferris, 2012). In addition to altering biomechanical measures, the powered ankle-foot increased walking velocity compared to the ESR prosthesis and increased step length compared to 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 may not be possible with a uniarticular device. Physical performance measures were not significantly different between the 2 prostheses, and there were no significant differences between conditions on the PEQ. Seven patients preferred the PowerFoot and 4 preferred the ESR. Compared to controls with intact limbs, the PowerFoot had reduced range of motion, but greater ankle peak power.
 
Another similar, small pre- post- study from 2012 (7 amputees and 7 controls) found gross metabolic cost and preferred walking speed to be more similar to non-amputee controls with the PowerFoot Biom than with the patient’s own ESR (Herr, 2012).
  
 
2014 Update
A literature search conducted through May 2014 did not reveal any new information that would prompt a change in the coverage statement. The key identified literature is summarized below.
 
C-Leg Compact
Level walking and ramp walking were assessed in 10 level K2 ambulators with the C-Leg Compact and with the participant’s usual mechanical prosthetic knee joint (Burnfield, 2012; Eberly, 2013). Seven of the 10 subjects used upper extremity assistive devices (eg, a cane or walker) while ambulating. Participants were tested first with their own prosthesis, and then with the C-Leg Compact after a 3-month acclimation period. Use of the C-Leg Compact led to a significant increase in velocity (20%), cadence (9%-10%), stride length (12%-14%), single-limb support (1%), and heel-rise timing (18%) with level walking. Ramp ascent and descent were 28% and 36% faster, respectively, with the C-Leg Compact due to increases in stride length (17%) and cadence (16%) on the ramp. Participants also had significantly faster Timed Up and Go test (17.7 vs 24.5 seconds) and higher functional scores on the PEQ. At the end of the study, the participants chose which prosthesis to keep; all 9 who were offered the opportunity selected the C-Leg Compact.
 
Proprio Foot
Gait analysis with the Proprio Foot was evaluated in 16 transtibial K3-K4 amputees during stair and ramp ascent and descent. Results with the adaptive ankle (allowing 4 degrees 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 be increased in 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 degrees 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 plantar flexed ankle (adaptive mode) during ramp descent. Another small within-subject study (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 (Darter, 2014).
 
Another study found a lower energy cost of floor walking with the Proprio Foot compared with a dynamic carbon fiber foot in 10 transtibial amputees (Delussu, 2013). 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.
 
2015 Update
A literature search conducted through May 2015 did not reveal any new information that would prompt a change in the coverage statement. The key identified literature is summarized below.
 
Rheo Knee
A small industry-sponsored study compared the Rheo Knee II with the subject’s own non-microprocessor controlled knee in 10 patients with a functional level of K2 (n=2), K3 (n=5) or K4 (n=3) (Prinsen, 2014). There was little difference in performance between the two prostheses as assessed with the PEQ, Activities-specific Balance Confidence scale, TUG, Timed up and down stairs, Hill Assessment Index, Stairs Assessment Index, Standardized Walking Obstacle Course, and One Leg Balance Test. One limitation of this study is that although participants had an 8-week acclimation period, they did not receive step-over-step training on stairs and ramps before being tested with the microprocessor knee.
 
Ongoing and Unpublished Clinical Trials
(NCT02382991) industry sponsored or cosponsored trial; Randomized, Cross-over Study Comparing the Efficacy of the 3C60 Knee Against Non-microprocessor Controlled Knees on the Risk of Falling and Locomotor Skills of Moderately Active Persons With Leg Amputation Above Knee or Knee Disarticulation; planned enrollment 40; projected completion date Sep 2015.
 
(NCT02240186) Comparative Effectiveness Between Microprocessor Knees and Non-Microprocessor Knees; planned enrollment 50; projected completion date Jun 2016
 
2018 Update
A literature search conducted using the MEDLINE database did not reveal any new information that would prompt a change in the coverage statement.
 

CPT/HCPCS:
L5856Addition to lower extremity prosthesis, endoskeletal knee-shin system, microprocessor control feature, swing and stance phase, includes electronic sensor(s), any type
L5857Addition to lower extremity prosthesis, endoskeletal knee-shin system, microprocessor control feature, swing phase only, includes electronic sensor(s), any type
L5858Addition to lower extremity prosthesis, endoskeletal knee shin system, microprocessor control feature, stance phase only, includes electronic sensor(s), any type
L5973Endoskeletal ankle foot system, microprocessor controlled feature, dorsiflexion and/or plantar flexion control, includes power source

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