This document addresses the use of microprocessor controlled lower limb prostheses including, but not limited to, the Otto-Bock C-Leg device^®_, the Genium™ Bionic Prosthetic System, the Ossur RheoKnee^®_, the Proprio Foot^®_, the Endolite Intelligent Prosthesis^®_, and the PowerFoot BiOM.

Medically Necessary:

The use of a microprocessor controlled lower limb prosthesis (e.g., Otto-Bock C-Leg device^®_, Otto-Bock Genium™ Bionic Prosthetic System, the Ossur RheoKnee^® or the Endolite Intelligent Prosthesis^®), is considered medically necessary for transfemoral (above knee) and knee disarticulation amputees when all of the criteria set forth in (A) and (B) below have been met:

A) Selection criteria:

1. Individual has adequate cardiovascular reserve and cognitive learning ability to master the higher level technology and to allow for faster than normal walking speed; and
2. Individual has demonstrated the ability to ambulate faster than their baseline rate using a standard prosthetic application with a swing and stance control knee; and
3. Individual has a documented need for daily long distance ambulation (i.e., greater than 400 yards) at variable rates.  (In other words, use within the home or for basic community ambulation is not sufficient to justify the computerized limb over standard limb applications); and
4. Individual has a demonstrated need for regular ambulation on uneven terrain or regular use on stairs.  Use of limb for limited stair climbing in the home or place of employment is not sufficient to justify the computerized limb over standard limb applications.

B) Documentation and performance criteria:

1. Complete multidisciplinary assessment of individual including an evaluation by a trained prosthetic clinician.  The assessment must objectively document that all of the above selection criteria have been evaluated and met. 

Not Medically Necessary: 

The use of a microprocessor controlled leg prosthesis is considered not medically necessary in all other cases, including when the criteria above have not been met.

Investigational and Not Medically Necessary: 

The use of a microprocessor controlled foot-ankle prosthesis (e.g., Proprio Foot^®_, PowerFoot BiOM) is considered investigational and not medically necessary for all indications.

At this time, the available peer-reviewed published literature addressing the clinical benefit of microprocessor controlled lower limb prostheses is limited to non-randomized controlled clinical trials, and case series of limited size.  Additionally, the majority of these studies have involved highly selected subjects who were otherwise in good health.  

One publication by Hafner and others (2007) reports the findings of a small, non-randomized, cross-over controlled design study in which each subject was exposed to two different prosthetic limb conditions (mechanical and microprocessor controlled C-Leg) twice during the trial.  This study included 21 subjects, each of whom used both a standard mechanical knee and lower limb prosthesis and the C-Leg microprocessor controlled prosthesis.  Subjects were recruited for participation from a local amputee population.  Seventeen subjects completed the study.  Subjects were told at the time of enrollment that they would be allowed to keep the test prosthesis whether or not they completed the trial.  The subjects began the trial with a two-month period using their standard prosthesis followed by an activity assessment and functional, performance and subjective perception evaluation.  Next, all subjects used the microprocessor controlled prosthesis until acclimation was demonstrated.  This was then followed by a two-month acclimation period with the microprocessor controlled prosthesis, ending with an activity assessment and functional, performance and subjective perception evaluation.  Subjects were then reverted back to the standard prosthesis for two weeks and again an activity assessment and functional, performance and subjective perception evaluation was done.  In the final stage of the trial, participants were allowed to use either one or both prosthetic devices over a four month period.  Daily use and activity levels were measured for each device.  The study concluded with a final activity assessment and functional performance and subjective perception evaluation with the microprocessor controlled device.  A variety of objective and subjective outcome measures were reported.  The authors reported no significant differences between the two prosthetic devices in terms of daily activity as measured by mean daily step frequency and mean estimated step distance, in performance on level or varied surfaces, or in cognitive demand during use of the devices.  They did note a significant improvement with the C-Leg prosthesis in subjects' Stair Assessment Index (SAI) scores, time to descend scores, and a surveyed preference for the microprocessor controlled C-Leg as compared with a mechanical prosthetic knee.  There was no difference noted in ascending stairs, but self reported frequency of stumbles and falls was lower for the C-Leg prosthesis.  Limitations of this study include its small size, lack of outcome comparisons to a group randomized to continued use of a standard prosthesis, and lack of control of the type of mechanical prosthesis used.  In addition, the period of time allowed for the subject to revert back to a standard prosthesis (two weeks) for a functional assessment prior to the 4-month combined use measures was quite limited.

An article by Williams and colleagues (2006) describes a randomized two-group crossover design study of C-Leg versus a standard hydraulic knee prosthesis (Mauch SNS^® knee).  Subjects were given a 3 month acclimation period for each device prior to testing.  This study was not blinded and was hampered by a significant drop-out rate (56%) that left only 8 participants in the evaluable study population.  The findings concluded that in non-demanding walking conditions with experienced amputees, participants reported the C-Leg® required less cognitive attention than the non-computerized knee.  However, this subjective experience did not translate into improved performance on neuropsychologic screening instruments or walking speed.

In another report of the same trial (Orendurf, 2006) the authors report that they found no significant difference between the groups in either oxygen efficiency or gait efficiency.  It is noted in the discussion section of this article that the programming of each C-Leg requires a high degree of tailoring to meet the needs of the user.  The authors comment that the parameters that were used by each of the study participants varied widely, with some preferring their C-Leg to operate in a manner not too dissimilar to that of a standard non-computerized limb, and others preferring significantly different functional parameters.  With this degree of variation, even within such a small study population, it would indicate that a much larger study population should be used in further studies of the C-Leg in order to control for this potential source of bias.

A non-randomized cross over study conducted by Kaufman and colleagues (2007) compared the computerized prosthetic knee to the standard hydraulic prosthesis in gait and balance parameters.  The study included 15 participants, who were allowed an average of 4.5 months of acclimation time with each device.  The authors indicate that there was a significant (p< 0.01) improvement in objective, standardized measures of both gait (knee flexor movement) and balance (Sensory Organization test) with the computerized prosthesis.  The investigators point out that the study included a select group of healthy, highly effective ambulators with no additional musculoskeletal conditions.  It is unclear what impact the use of computerized prosthetic knee devices may have on individuals with lower functional classifications.

Seymour and colleagues published a study comparing energy expenditure, obstacle course negotiation and quality of life (QOL) measures in 10 highly effective healthy ambulators who use both a C-Leg and a non-computerized prosthesis (2007).  This study had a 23% drop out rate.  A subset of participants (10 of 13) in this study underwent an eight minute energy consumption test on a treadmill using one of their prostheses, and then again using the other device after a 10 minute rest.  They were then asked to undergo a walking obstacle course eight times, four holding a laundry basket containing a 10 lb weight, and four times unencumbered.  Finally, they were asked to complete a standardized quality of life questionnaire (SF-36v2).  The authors report a statistically significant lower energy consumption rate for participants when wearing their C-Leg devices at both typical and fast paces.  On the obstacle course, statistical differences were noted in the number of steps taken, elapsed time, and the number of times participants stepped out of bounds during the unencumbered portion of the trial.  During the encumbered trial, the elapsed time (11.5 sec vs. 15.5 sec) was shorter for the C-Leg prosthesis group (p=0.007).  No stumbles or falls were reported in either group.  The results of the QOL questionnaire associated with wearing the C-Leg indicated that the participants were at or above the normative data available for the general population. 

A study by Kahle and colleagues (2008) investigated the impact of the C-Leg on several functional parameters, including stumbles, falls, performance in walking and stair descent and QOL.  The study involved 21 subjects, with 19 completing the study, and utilized a simple pre-test post-test design.  Participants in the study had a wide variation in physical status and health, but were all community ambulators.  Some participants utilized assistive devices for ambulation.  This is the first published study to include a mixed population.  The authors report significant improvement in the number of stumbles (p=0.006), but no significant improvement in the number of falls.  No statistical analysis was provided for either walking or stair descent performance.  Finally, there was a significant improvement (20%, p=0.007) in QOL scores with the C-Leg prosthesis.

The U.S. Department of Veterans Affairs Technology Assessment Program (VATAP, 2000) completed a systematic review of computerized lower limb prostheses in March 2000 and concluded that the:

• Energy requirements of ambulation (compared to requirements when using conventional prostheses) are decreased at walking speeds slower or faster than the amputee's customary speed, but are not significantly different at customary speeds.
• Results on the potential to improve ambulation on uneven terrain, stairs, or inclines were mixed; a study of 22 subjects by Datta and Howitt found that 77% found no difference in ascending or descending stairs but 59% found it easier to walk on slopes.
• Subjects did have a favorable perception of computerized prostheses and the vast majority of study participants chose not to return to their conventional prostheses.

Although the evidence continues to evolve, it is reasonable to consider microprocessor controlled lower limb prostheses appropriate for a select group of individuals meeting strict criteria for fitness, health, and daily utilization expectations.  However, these devices may not be appropriate for all potential users.  Since the device produces definite but marginal improvements in functional capacity by reducing oxygen consumption and improving walking speed and safety when ambulating in more challenging environments (e.g., long distances, uneven terrain, regular use of stairs) the device is appropriate for users who face those challenges regularly.  In addition, the device requires substantial training to allow for faster than normal walking speed and a user should have adequate cognitive learning ability to master the higher level technology.  The criteria set forth above identify the potential users for whom the device may represent an improvement in functional capacity.

Published peer-reviewed evidence addressing the use of  microprocessor controlled foot-ankle prosthesis is limited.  One small study involved 12 subjects and measured socket pressures in individuals undergoing gait analysis during various locomotion tasks using the Proprio Foot (Ossur) for five walking conditions with and without the device's ankle adaptation mode (Wolf, 2009).  The study concluded that the adaptive ankle-foot prostheses favorably altered joint kinetics and stump pressures on stairs and ramps.  A second study involved 32 subjects, 16 healthy controls and 16 transtibial amputees (Alimusaj, 2009).  The subjects underwent 3-dimensional gait analysis on stairs.  Kinematics and kinetics of the lower limbs were compared during stair ascent and descent with the prosthetic foot set to a neutral ankle angle and then with an adapted dorsi-flexion ankle angle of 4 degrees.  Comparisons were also made between experimental group subjects and control subjects.  The study concluded that for both stair ascent and descent, the prosthesis resulted in an improvement in kinematic and kinetic measures of the knee with an increase of knee flexion and increase of the knee stability during stance.   Fradet and colleagues describe a nonrandomized controlled study involving 16 transtibial amputee subjects and 16 healthy controls (Fradet, 2010).  All participants underwent conventional 3D gait analysis while walking up and down a ramp. The authors reported that subjects, when using the foot ankle prosthesis in adaptive mode, exhibited more physiologic kinematics and kinetics of the lower limbs during ramp ascent but not during ramp descent. Additionally, subjects using the prosthesis in adaptive mode reported subjective feelings of being safer during ramp descent.  At this time, further study is needed to establish a meaningful clinical outcome benefit of the Proprio Foot over the conventional ankle-foot prosthesis.

Currently there is no peer-reviewed published evidence addressing the clinical efficacy of the PowerFoot BiOM microprocessor controlled foot-ankle prosthesis.  Such information is necessary to properly evaluate the impact of this device.

Prostheses are devices that are used to replace or compensate for the absence of a body part.  Such absence may be present at birth or due to amputation as the result of illness or trauma.  Prosthetic devices have been used to replace body parts from individual fingers to entire limbs.  Additionally, prostheses may include replacements for other body parts including breasts, eyes, and teeth.  There are a wide variety of prostheses for the replacement of limbs made from various materials using a wide range of technologies.

For prostheses used to replace lower limbs where the leg is missing from the knee or above, there is a need for a device to replace the normal function of the knee.  In people with intact legs, the knee naturally and automatically adjusts its action to the speed and stride of the person.  Conventional prosthetic legs use a pneumatic or hydraulic return mechanism to mimic the natural pendulum action of the knee.  This mechanism is usually set by a prosthetist to work at the individual's normal walking speed and does not allow any room for variation in speed.  Changes in an individual's walking speed require the individual to compensate for any delay in knee action through a variety of means including altering stride length and body position, among others.  Such maneuvers lead to an abnormal gait and require extra effort and concentration for what is normally an unconscious act.

Microprocessor controlled lower limb prostheses for the transfemoral amputee use computer-controlled mechanisms to detect step time and alter prosthetic function such as knee extension level to suit walking speed or angle of the terrain.  More advanced models, such as the Otto-Bock C-Leg^®_, have multiple sensors that gather and calculate data on various parameters such as the amount of vertical load, ankle movement, and knee joint movement in an attempt to mimic more natural leg function to provide stability and gait fluidity as needed on uneven terrains and/or during sports activities.  The claimed advantages of computerized leg prosthesis include a decreased level of effort in walking, improved symmetry of movement between legs leading to more natural movement, and the avoidance of falls.

For individuals who have lost a limb below the knee, there is a need for a device to replace the function of the ankle and foot.  Stair ambulation is limited in the transtibial amputee due to the neutral and fixed ankle position which exists in traditional prosthetic ankles.  Under study are newer prosthetic ankles which adjust the foot-ankle angle during the swing phase using sensor and microprocessor technologies to identify sloping gradients and the ascent or descent of stairs after the first step.  Users can place the foot fully on a step when climbing or descending stairs and it will automatically adapt the ankle position to enable the next step.  On ramp ascent and descent, adaptation begins on the second step and the device makes small adjustments until it reaches the degree of slope of the ramp.  The Proprio Foot^® is one such "quasi-passive" device.  The device is passive since no power is generated through the ankle in stance.  The device is also said to be designed to dorsiflex, or bring the toes closer to the shin, during the swing phase to improve ground clearance, improve gait symmetry and reduce the likelihood of falls.  Other claims include the device's ability to assist in standing from a seated position and plantar (bottom of the foot) flexion when kneeling, sitting and lying down.  Early pilot studies suggest that both during stair ascent and descent, the Proprio Foot improves knee flexion kinematics.  The weight of the Proprio Foot device is more than twice the weight of a conventional ankle-foot prosthetic such as the LP Vari-Flex (995g versus 405g).  Concern has been raised that because of its weight, the Proprio Foot might not benefit amputees with limited endurance and knee musculature.

Also, under study are active prosthetic ankle prostheses which do generate power during the ankle stance.  Early results are said to be promising, but these devices are bulky and of considerable weight due to the motor and batteries needed to generate power. 

Another type of microprocessor-controlled foot-ankle prosthetic device, the PowerFoot BiOM, is proposed to simulate the natural function of the foot by simulating the action of the ankle, Achilles tendon and calf muscles to move the individual forward when they step.  These devices utilize various sensors in the ankle and foot to detect foot position, direction, and force of movement.  This data is analyzed by several microcomputers that translate it into instructions for a motor-activated spring device in the sole of the prosthesis. The loaded spring device is released as the sensor detects that the user is taking a step forward, forcing the ball of the foot downwards and propelling the foot forward. The spring mechanism reloads itself in-between steps. This device uses batteries to operate this system and requires daily recharging.

The FDA classified the Proprio Foot as a Class I device and the PowerFoot as a class II device, both exempt from requirements for pre-market notification by submission and FDA review of a 510(k) clearance.  This is based on the level of active assistance provided and the perceived risk associated with these devices.

Computerized leg prosthesis: A prosthetic device for individuals with some degree of leg amputation which uses a computer microprocessor to adapt prosthetic function to environmental conditions that impact locomotion.

Kinematics: A study of motion without regard to the forces present; mathematical methods to describe motion.

Prosthesis: For the purposes of this document, a device used to replace or compensate for the absence of a limb.   Prostheses may be artificial replacements for a wide variety of body parts.

The following codes for treatments and procedures applicable to this document are included below for informational purposes.  Inclusion or exclusion of a procedure, diagnosis or device code(s) does not constitute or imply member coverage or provider reimbursement policy.  Please refer to the member's contract benefits in effect at the time of service to determine coverage or non-coverage of these services as it applies to an individual member.

When services may be Medically Necessary when criteria are met:

When services are Not Medically Necessary:
For the procedure codes listed above when criteria are not met, or when the code(s) describes a procedure indicated in the Position Statement section as not medically necessary.

When services are Investigational and Not Medically Necessary:

Future ICD-10 coding (effective 10/01/2013)
A draft of ICD-10 Coding related to this document, as it might look today, is available for reference and comments at: Appendix 1: Future ICD-10 coding

Peer Reviewed Publications:

1. 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. 2009; 30(3):356-363.
2. Chin T, Machida K, Sawamura S, et al.  Comparison of different microprocessor controlled knee joints on the energy consumption during walking in trans-femoral amputees: intelligent knee prosthesis (IP) versus C-leg.  Prosthet Orthot Int. 2006; 30(1):73-80.
3. Chin T, Sawamura S, Shiba R, et al. Effect of an Intelligent Prosthesis (IP) on the walking ability of young transfemoral amputees: comparison of IP users with able-bodied people. Am J Phys Med Rehabil. 2003; 82(6):447-451.
4. Datta D, Heller B, Howitt J. A comparative evaluation of oxygen consumption and gait pattern in amputees using Intelligent Prostheses and conventionally damped knee swing-phase control. Clin Rehabil. 2005; 19(4):398-403.
5. Fradet L, Alimusaj M, Braatz F, Wolf SI. Biomechanical analysis of ramp ambulation of transtibial amputees with an adaptive ankle foot system. Gait Posture. 2010; 32(2):191-198.
6. 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. 2007; 88(2):207-217.
7. 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. 2005; 84(8):563-575.
8. Kahle JT, Highsmith MJ, Hubbard SL. Comparison of nonmicroprocessor knee mechanism versus C-Leg on Prosthesis Evaluation Questionnaire, stumbles, falls, walking tests, stair descent, and knee preference. J Rehabil Res Dev. 2008; 45(1):1–14.
9. 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. 2008; 89(7):1380-1385.
10. Kaufman KR, Levine JA, Brey RH, et al. Gait and balance of transfemoral amputees using passive mechanical and microprocessor-controlled prosthetic knees. Gait Posture. 2007; 26(4):489-493.
11. Klute GK, Berge JS, Orendurff MS, et al.  Prosthetic intervention effects on activity of lower-extremity amputees. Arch Phys Med Rehabil. 2006; 87(5):717-722.
12. Orendurff MS, Segal AD, Klute GK, et al. Gait efficiency using the C-leg. J Rehabil Res Dev. 2006; 43(2):239-246.
13. Schmalz T, Blumentritt S, Jarasch R. Energy expenditure and biomechanical characteristics of lower limb amputee gait: the influence of prosthetic alignment and different prosthetic components. Gait Posture. 2002; 16(3):255-263.
14. Segal AD, Orendurff MS, Klute GK, et al. Kinematic and kinetic comparisons of transfemoral amputee gait using C-Leg and Mauch SNS prosthetic knees. J Rehabil Res Dev. 2006; 43(7):857-870.
15. Seymour R, Engbretson B, Kott K, et al. Comparison between the C-leg microprocessor-controlled prosthetic knee and non-microprocessor control prosthetic knees: a preliminary study of energy expenditure, obstacle course performance, and quality of life survey. Prosthet Orthot Int. 2007; 31(1):51-61.
16. Taylor MB, Clark E, Offord EA, Baxter C. A comparison of energy expenditure by a high level trans-femoral amputee using the Intelligent Prosthesis and conventionally damped prosthetic limbs. Prosthet Orthot Int. 1996; 20(2):116-121.
17. Williams RM, Turner AP, Orendurff M, et al.  Does having a computerized prosthetic knee influence cognitive performance during amputee walking? Arch Phys Med Rehabil. 2006; 87(7):989-994.
18. Wolf SI, Alimusaj M, Fradet L, et al. Pressure characteristics at the stump/socket interface in transtibial amputees using an adaptive prosthetic foot. Clin Biomech (Bristol, Avon). 2009; 24(10):860-865.   

Government Agency, Medical Society, and Other Authoritative Publications:

1. U.S. Department of Veteran's Affairs Technology Assessment Program. Short Report – Computerized lower limb prostheses.  March 2000. Available at: http://www4.va.gov/VATAP/Publications.asp.  Accessed September 2, 2011.
2. Washington State Department of Labor and Industries, Office of the Medical Director. Microprocessor-controlled prosthetic knees. Technology Assessment. 2002.
3. Workers' Compensation Board of British Columbia, Evidence Based Practice Group. A Review of Microprocessor-Controlled Knee Prostheses. 2003.

Above Knee Prosthetics
Adaptive Prosthesis
C-Leg^® Microprocessor Controlled Knee Prosthesis
Endolite^® Intelligent Prosthesis
Endolite^® Smart Adaptive knee
Genium™ Bionic Prosthetic System
iWalk PowerFoot BiOM
Lower Limb Prostheses, Microprocessor-Controlled
Microprocessor Controlled Foot-Knee Prosthesis
Microprocessor Controlled Lower Limb Prostheses
PowerFoot BiOM
Prostheses, Microprocessor-Controlled Lower Limb
Ossur Proprio Foot^®
Ossur RheoKnee^®
Seattle Limb Systems Power Knee^®
Trulife Power Knee^®

The use of specific product names is illustrative only.  It is not intended to be a recommendation of one product over another, and is not intended to represent a complete listing of all products available.