Medical Policies - DME

Lower Limb Prosthetics, Including Microprocessor Prosthetics


Effective Date:10-15-2017



ALERT: Health Care Services Corporation (HCSC) no longer maintains a Hanger Inc. Prosthetics & Orthotics Patient Assessment Validation Evaluation Tool (PAVET™) Evaluation for Microprocessor Knee (K-PAVET™) form on any of our web sites. To utilize the K-PAVET™ form for Microprocessor and Powered Knees, refer to the Hanger Inc., web site at “”.

General Criteria for Lower Limb Prostheses

Preparatory (also called initial or temporary) and permanent (also called definitive or non-temporary) lower limb prostheses may be considered medically necessary when the patient:

Is at functional level 1-4 (defined in Description section) or can be expected to reach functional level 1-4 within a reasonable period of time; and

Meets functional level criteria for prosthetic components (additions, substitutions, and/or replacements) as defined below in Tables I, II, and/or III; and

Is motivated to ambulate; and

Has received a physician prescription for the prosthesis as a result of a recent physician evaluation.

NOTE 1: Medical records should document the patient’s current functional capabilities and expected functional potential, including an explanation for any difference.

If the patient has functional level 0 (defined in Description section), lower limb prostheses are considered not medically necessary.

Microprocessor and Powered Knees

Microprocessor knees that have stance-phase or swing-and-stance phase microprocessors may be considered medically necessary for only those patients who meet ALL of the following criteria:

Patient is an appropriately active community ambulator, and

Patient has undergone extensive evaluation using the Hanger Inc. Prosthetics & Orthotics Patient Assessment Validation Evaluation Tool Evaluation for Microprocessor Knee (K-PAVET™) form (RAC form or Recovery Audit Contractor – Automated or Complex Review form) available on the Hanger Inc. web site (see ALERT above), and

Patient’s K-PAVET™ scores are between 40-72, as detailed in Table I:

Table I

K-PAVET™ Evaluation Criteria for Microprocessor Knee

If the K-PAVET™ Overall Score is:

Then the Microprocessor Knee is allowed for:


Stance phase only and may be considered medically necessary (e.g., OttoBock Compact™).

50-59 AND cadence score is (see NOTE 2) 14 and below,

Stance phase only and may be considered medically necessary (e.g., OttoBock Compact™).

50-59 AND cadence score is (see NOTE 2) 15 and above,

Swing-and-stance phase and may be considered medically necessary (e.g., OttoBock C-Leg™, Ossur Rheo™).


Swing-and-stance phase and may be considered medically necessary (e.g., OttoBock C-Leg®, Ossur Rheo™, Endolite Adaptive™).

NOTE 2: Cadence score is determined by the total of K-PAVET™ questions #1, #2, #7, #14, and #15.

Microprocessor knee is considered not medically necessary for the following patients:

Those who have a K-PAVET™ score less than 40, OR

Those who have a K-PAVET™ score 73 or greater as this high is unrealistic and indicates possible scoring discrepancy. (These patients should be re-evaluated.), OR

Those who do not meet ALL of the above criteria.

Microprocessor knees that have only swing-phase microprocessors are considered not medically necessary including, but not limited to, Endolite IP+™, Endolite Smart IP™, Intelligent Knee™, Seattle Power Knee™, and DAW®.

The Genium™ Bionic Prosthetic System microprocessor knee is considered experimental, investigational and/or unproven.

A powered knee is considered experimental, investigational and/or unproven, including but not limited to the Power Knee® (Ossur).

The lithium ion battery for the microprocessor knee is included with the knee, and is repaired or replaced by the manufacturer when needed. Repair or replacement of the battery is covered under the manufacturer’s warranty. When the manufacturer’s warranty has expired, necessary repair or replacement of the lithium ion battery is considered medically necessary.

Spare or extra batteries are considered not medically necessary, as they are convenience items.

One (1) lithium ion battery charger is considered medically necessary for each microprocessor knee.

More than one (1) battery charger for each knee is considered not medically necessary.

Microprocessor and Powered Foot/Ankle

Microprocessor-controlled or powered ankle/foot is considered experimental, investigational, and/or unproven including, but not limited to, ProPrio Foot® (Ossur), iPED® (Martin Bionics), PowerFoot BiOM® (iWalk), and Êlan® (Endolite).

Hydraulic Hip Prosthetic

A four-axis, hydraulic or pneumatic hip joint (e.g., Helix3DHip® [OttoBock]) may be considered medically necessary when the patient has an overall score of 50 or higher, AND cadence score (see NOTE 2) 15 or higher on the K-PAVET™ Evaluation, and the Helix3DHip will be used in conjunction with the OttoBock C-Leg®.

Prosthetic Components (i.e., additions, substitutions, replacements, and/or modifications)

Additions, substitutions, replacements, and/or modifications to lower limb prostheses (except microprocessor-controlled prosthetic knees) may be considered medically necessary based on the patient’s potential functional abilities (see Table II below).

EXCEPTION: Certain additions and substitutions to initial or preparatory prostheses are considered not medically necessary as detailed in Table III below, because initial/preparatory prostheses are temporary and include the necessary elements.

NOTE 3: Functional levels are defined in Description Section below.

Table II

Additions, Substitutions, Replacements for Permanent (Definitive, Non-Temporary) Prosthesis

Additions, substitutions and/or replacements that may be considered medically necessary for permanent/definitive/non-temporary prosthesis, based on functional level:


Level 1 or Greater

Level 2 or Greater

Level 3-4 or Greater

Knees (except microprocessor knees)

4-Bar knee, friction control

Universal multiplex, friction control

4-Bar knee, friction control

Universal multiplex, friction control

Pneumatic and hydraulic knees

4-Bar knee, friction control

Universal multiplex, friction control

Knee-Shin Systems

Exoskeletal knee-shin systems

Endoskeletal knee-shin systems

Exoskeletal knee-shin systems

Endoskeletal knee-shin systems

Exoskeletal knee-shin systems

Endoskeletal knee-shin systems


Axial rotation unit

Axial rotation unit

Axial rotation unit

Foot, Ankle/Foot

External keel SACH (solid ankle-cushion heel) foot

Single-axis ankle/foot

Flexible-keel foot

Multi-axial ankle/foot

External keel SACH foot

Single-axis ankle/foot

Flex foot system

Energy-storing foot

Multiaxial ankle/foot, dynamic response

Flex walk system or equal

Shank foot system with vertical loading pylon

Flexible-keel foot

Multi-axial ankle/foot

External keel SACH foot

Single-axis ankle/foot


All Levels:

1. Two test (diagnostic) sockets may be considered medically necessary for an individual prosthesis. More than 2 require documentation of medical necessity.

2. Socket replacements may be considered medically necessary with documentation of functional and/or physiological need. Examples include, but are not limited to:

Changes in residual limb,

Functional need changes.

Table III

Additions, Substitutions, Replacements for Initial (Preparatory, Temporary) Prosthesis

When these Temporary (Initial/Preparatory or Prefabricated Preparatory) Prostheses are covered:

Then these additions, substitutions and/or replacements are not covered as they are considered not medically necessary:

Below Knee (Initial or Preparatory),

Acrylic socket; leather socket; wood socket; air, fluid, or gel cushion socket; suction socket;

Protective covering;

Ultra-lightweight exoskeletal system;

Flex foot system.

Below Knee (Prefabricated Preparatory),

Test socket; acrylic socket; flexible inner socket; air, fluid, or gel cushion socket;

Protective outer covering;

Molded supracondylar suspension (PTS [patellar-tendon-supracondylar] or similar);

Single-axis knee joints.

Above Knee (Initial or Preparatory),

Acrylic socket; leather socket; wood socket; air, fluid, or gel cushion socket;

Protective outer covering;

Exoskeletal knee-shin system;

Endoskeletal hydra-cadence system;

Ultra-lightweight exoskeletal system;

Flex foot system.

Above Knee (Prefabricated Preparatory),

Test socket; acrylic socket; air, fluid, or gel cushion socket; flexible inner socket; suction suspension, socket;

Protective outer covering.

NOTE 4: Determination of coverage for selected prostheses and components with respect to potential functional levels represents the usual case. Exceptions will be considered on an individual case basis if additional documentation is provided that justifies the medical necessity.

Miscellaneous Additional Components

Prosthetic socks and harnesses may be considered medically necessary when essential to the use of the prosthesis.

More than 2 of the same socket inserts per individual prosthesis at the same time are considered not medically necessary.

When immediate postsurgical or early fitting procedures are provided, test (diagnostic) sockets are considered not medically necessary as test sockets cannot be used with these procedures.


Amputated and/or missing limbs result from accidents, disease, and congenital disorders. A lower limb prosthetic is a device or artificial substitute designed to replace the function and/or appearance of the absent limb.


More than 100 different prosthetic knee and ankle-foot 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, the 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.

The patient’s condition is an important factor to consider in choosing a prosthesis. To be functionally successful with a prosthesis, the patient must demonstrate sufficient trunk control, good upper body strength, static and dynamic balance, and adequate posture. The basic goals with prosthetic use are stability, ease of movement, energy efficiency, and appearance of a natural gait. The prescription for a prosthesis depends on the activity level and specific needs of each individual patient.

Clinical assessment of the patient’s rehabilitation potential should be based on the following functional levels (also defined by Centers for Medicare and Medicaid Services [CMS]) as shown in Table 1 below. Potential functional ability is based on the reasonable expectations of the prosthetist and treating physician, considering factors including, but not limited to: (1, 2)

a. The patient’s past history; and

b. The patient’s current condition including the status of the residual limb and the nature of other medical problems; and

c. The patient’s desire to ambulate.

Table 1: Functional Levels and Definition: (1, 2)


Definition of Function


Does not have the ability or potential to ambulate or transfer safely with or without assistance and a prosthesis does not enhance his/her quality of life or mobility.


Has the ability or potential to use a prosthesis for transfers or ambulating on level surfaces at fixed cadence; typical of the limited and unlimited household ambulator.


Has the ability or potential for ambulating with the ability to traverse environmental barriers such as curbs, stairs, or uneven surfaces; typical of the limited community ambulator.


Has the ability or potential for ambulating with variable cadence; typical of the community ambulator who has the ability to traverse most environmental barriers and may have vocational, therapeutic, or exercise activity that demands prosthetic utilization beyond simple locomotion.


Has the ability or potential for prosthetic ambulating that exceeds basic ambulating skills, exhibiting high impact, stress, or energy levels; typical of the prosthetic demands of the child, active adult, or athlete.

Generally, the earlier a prosthesis is fitted, the better it is for the amputee. Early ambulation helps keep the patient active, accelerates stump shrinkage, helps prevent flexion contractures, and can reduce phantom limb pain. Immediate postsurgical or early fitting procedures are typically performed in the hospital setting immediately after surgery. These procedures include specific dressings and fittings that are intended to prepare the residual limb for a prosthesis. An initial (preparatory) prosthesis and/or immediate postoperative prosthesis (IPOP) may be used to accelerate the rehabilitation process. It is intended to be temporary for several weeks or months until the stump stabilizes and a permanent (definitive) prosthesis is fitted. The base initial and preparatory prostheses include the necessary elements, and usually additions and/or substitutions are not required. However, many physicians prefer to postpone prosthetic intervention until the wound is healed. If necessary, a patient can be fitted for a definitive prosthesis without ever having a preparatory prosthesis. In this case, the socket fitting should be delayed until the residual limb is fully mature (usually 3-4 months) or until the patient’s weight and stump circumference have stabilized.

There is no precise prescription for lower limb prostheses as fitting a prosthesis is very individualized to each patient. A poorly designed or badly fitted prosthesis can be as disabling as the actual amputation. A prosthesis with components that are appropriate for functional level and physical condition helps the patient avoid future medical problems and injury to the residual limb.

Amputation level is a factor to consider in choosing a prosthesis. The following list identifies the base prosthesis for different levels of amputation:

Partial foot prosthesis (PFP): For absence of the foot and/or toes below the ankle.

Ankle (Syme's) prosthesis (SP): For absence of the foot and ankle just above the ankle joint.

Below knee prosthesis (BKP): For absence of the foot and ankle below the knee joint.

Above knee prosthesis (AKP): For absence of the foot, ankle, shin and thigh above the knee joint.

Knee disarticulation prosthesis (KDP): For absence of the foot, ankle and shin at the knee joint level.

Hip disarticulation prosthesis (HDP): For absence of the complete leg including the foot, ankle, shin and thigh at the hip joint level.

Hemipelvectomy prosthesis (HP): For absence of the complete leg including the foot, ankle, shin, thigh, hip and pelvis.

A lower limb prosthesis is made up of a base prosthesis combined with the possible addition of any of the following components:


Prosthetic sock or liner;

Socket inserts;

Pylon, or knee-shin system;

Articulating joint;

Suspension system;

Protective outer covering;

Foot, ankle, or foot-ankle system.

Each additional or “add-on” component requires justification with regard to medical necessity related to activities of daily living (ADLs).

The socket is the basis for the connection between the patient and the prosthesis, and a good fit is extremely important to the success of the prosthesis. The most common socket for the BKP is a patellar-tendon-bearing (PTB) design. With an AKP, the transected femur can support very little weight at its end, so the socket is designed to shift the weight onto the side of the thigh and the pelvis. The quadrilateral socket has a contoured area called the ischial seat that supports the ischium (part of the hip bone). The ischial containment socket is made of more flexible materials, and encapsulates the ischium in a way that provides more stability and control. Sockets can be flexible, expandable, or rigid, and are made of a variety of materials including wood, leather, polyester, acrylic, carbon, plastic, or a combination of these. For example, a rigid carbon frame over a flexible inner socket offers strength and stability with flexibility and comfort.

Prosthetic socks provide comfort and ventilation, and help prevent skin abrasion. They should be changed and laundered daily to reduce skin irritation and dermatitis. Prosthetic liners and socket inserts are made of soft material or gel that is molded to the residual limb and acts as an interface between the hard weight-bearing socket and the skin. The suspension system attaches the prosthesis to the residual limb. This system can be a variety of belts, wedges, straps, suction, inserts, or some combination of these.

Knee-shin systems can be exoskeletal (crustacean) or endoskeletal. The exoskeletal knee-shin system is a one-piece design that entails wood or foam enclosed by a hard plastic finish, usually shaped like a leg, and without interchangeable parts. This type of knee-shin system is very durable and simple. Because it is sturdy and heavy duty, it may be preferred by people who will be in harsh environments, such as farmers or other outdoor workers. Endoskeletal knee-shin systems are more complex and have interchangeable parts under a soft outer cover. Endoskeletal systems are lightweight and have many different component options, such as different knee units that can be introduced as the patient’s functional needs change.

Microprocessor-Controlled Prosthetic Knees

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.

The knee joint has three functions: provide support during stance phase of ambulation, produce smooth control during swing phase, and maintain unrestricted motion for sitting and kneeling. Microprocessor-controlled prosthetic knees have been developed, including the Intelligent Knee™ Prosthesis (IP) (Blatchford, England), the Adaptive™ (Endolite, England), the Rheo Knee® (Össur, Iceland), the C-Leg® (OttoBock Orthopedic Industry, Minneapolis, Minnesota), Genium™ Bionic Prosthetic System, and the X2 and X3 prostheses (OttoBock 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 IP) 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). The C-Leg® is versatile, controls both stance and swing, performs better on stairs, and must be combined with one of five specific foot devices. Next-generation devices such as the Genium™ Bionic Prosthetic system and the X2 and X3 prostheses utilize 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, for example, in water, sand, and mud. The X2 and X3 were developed by OttoBock as part of the Military Amputee Research Program.

Additional prosthetic knee options include:

The Rheo Knee® is very comparable to the C-Leg®, and can be combined with any foot device.

The Adaptive™ Knee also has both swing and stance control, but because it is lightweight, durable, and has more emphasis on swing than stance, this knee is well-suited to patients who are very strong and active at a higher functional level.

OttoBock’s C-Leg® Compact is designed for stability in stance phase, and does not have swing microprocessors. This knee would be a good choice for an appropriately active patient with focus on stability, where gait speed is not as important an issue.

Knees with processors for swing-only have a lesser degree of stance control, and are considered a clinical option when the patient has a higher activity level combined with a very high residual limb control; examples include the DAW®, Intelligent ™Knee, IP+™, Smart IP™, and Seattle Power™ Knee.

Manual locking knee is a very stable knee that is locked during gait. The patient releases the lock mechanism manually to sit down. This knee may be used for patients who have very short residual limb and/or poor hip strength and are unable to control the knee.

Single-axis constant friction knee has a simple hinge and single pivot point. These knees are set to walk at one speed, and do not have stance control.

Weight-activated stance control knee is a single-axis constant friction knee with a braking mechanism. When the patient puts his weight on the knee during gait, a braking mechanism is applied and the knee won’t buckle.

Polycentric knees, also referred to as 4-bar knees, have multiple centers of rotation allowing for stability at all phases of gait. The 4-bar linkage allows the knee to collapse better during the swing phase and to bend easier for sitting. These can incorporate a hydraulic or pneumatic unit to permit variable walking speeds.

Pneumatic or hydraulic knees have pistons inside cylinders containing air (pneumatic) or fluid (hydraulic); these units adjust gradually to changes in gait speed, which allows walking at variable speeds and permits a somewhat more natural gait.

Microprocessor-Controlled Foot-Ankle Prostheses

The basic functions of the prosthetic foot are to provide a stable weight bearing and shock absorbing surface, to replace lost muscle function, and to replicate the anatomic joint. Microprocessor-controlled ankle-foot prostheses are being developed for trans-tibial amputees. These include the ProPrio® Foot (Össur, Iceland), the iPED® (developed by Martin Bionics, Oklahoma City, Oklahoma, and licensed to College Park Industries, Warren, Michigan), and the Elan® Foot (Endolite, Miamisburg, Ohio). 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 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 web site indicates use of the ProPrio® Foot for low- to moderate-impact for trans-tibial amputees who are classified as level K3 (i.e., community ambulatory, with the ability or potential for ambulation with variable cadence).

Conventional prosthetic feet can be basic (non-articulated, unmoving), articulated or dynamic-response (energy-storing). Articulated feet have one or more joints. The single-axis foot has one joint, and can be used to help keep the knee stable. The multi-axis foot has motion about all three axes of the ankle and is good for walking on uneven surfaces. The multi-axis and dynamic-response feet are energy-storing feet. An energy-storing foot is capable of absorbing energy in a flexible keel (horizontal device in the foot) during the roll-over part of the stance phase of gait. The keel then springs back to provide push-off assistance to get the toe off the ground to start the swing phase. The simplest type of non-articulated the SACH plus the sole is able to conform to irregular surfaces, which makes it easier to walk on uneven terrain. The SAFE foot is also called a “flexible keel foot”. The SACH and SAFE feet are non-energy-storing feet.

Combined Powered (Knee-Ankle-Foot) 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, Inc., Bedford, Massachusetts) is a myoelectric prosthesis for trans-tibial 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 (Össur, Iceland), 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 U.S.

Hydraulic Prosthetic Hip

Fitting and wearing hip disarticulation prostheses presents several challenges, including poor gait pattern, socket discomfort, instability, loss of mobility, prosthesis weight and energy expenditure. The Canadian hip disarticulation prosthesis was developed by McLaurin more than 50 years ago, and is the “standard” hip disarticulation prosthesis. These prostheses move in a single plane, and require locking of the knee and hip for walking and unlocking to sit down. A new prosthetic hip joint, the Helix3DHip® (OttoBock Orthopedic Industry, Minneapolis, Minnesota), consists of a four-axis mechanism with hydraulic stance and swing-through phase control, which is reported to have the advantages of greater support and stability, and 3D movement similar to the ball joint of the natural hip, and more controlled heel strike. OttoBock has produced other modular single axis hydraulic hips available for patient utilization, known within the 7E series, which are still available.

Regulatory Status

Manufacturers must register prostheses with the Restorative Devices Branch of the FDA and keep a record of any complaints but do not have to undergo a full FDA review. FDA product codes: ISW, KFX.

Microprocessor-controlled prostheses are categorized as class I, exempt from the premarket notification (510[k]) requirements devices by the FDA.


This policy was created in 2006 and since then updated periodically using the MedLine database and assessments/reviews from the U.S. Veterans Administration (VA). The most recent update was performed through August 22, 2017. The following are key summaries to date.

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/function. In addition, the energy costs of walking or gait efficiency may be a more objective measure of the clinical benefit of the microprocessor-controlled prosthesis.

Microprocessor-Controlled Knee

The literature primarily consists of small within-subject comparisons of microprocessor-controlled versus pneumatic prostheses, along with systematic reviews of these studies.

In 2000, the VA Technology Assessment Program issued a “short report” on computerized lower-limb prosthesis. (3) This report offered the following observations and conclusions:

Energy requirements of ambulation (compared with 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.

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.

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 to keep these only as back-up 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.


A 2010 systematic review evaluated safety and energy efficiency of the C-leg® microprocessor-controlled prosthetic knee in trans femoral amputees. (4) Eighteen comparative studies were included that used objective/quantifiable outcome measures with the C-leg® in 1 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 articles 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®.

A number of lower-limb amputees returning from Operation Iraqi Freedom and Operation Enduring Freedom have received a microprocessor-controlled prosthesis from the Department of Veterans Affairs (VA); e.g., in 2005, 155 veterans were provided with a C-Leg®. (5) A series of papers from the VA report results from a within-subject comparison of the C-Leg® to a hydraulic Mauch SNS knee. (6-8) Eight (44%) of the 18 functional level 2 to 3 subjects recruited completed the study; most withdrew due to the time commitment of the study or other medical conditions. 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. (6) 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. (7) Cognitive performance, assessed by standardized neuropsychologic 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. (8) Although the study lacked sufficient power, results showed a 50% decrease in errors on the working memory task (1.63 versus 0.88, respectively). Due to the lack of power, 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, 0.79) and a reduction in cognitive burden with the microprocessor-controlled prosthesis (effect size, 0.90). Seven of the 8 subjects preferred to keep the microprocessor-controlled prosthesis at the end of the study. (7) The authors noted that without any prompting, all the subjects had mentioned that stumble recovery was their favorite feature of the C-Leg®.

Kaufman et al. published 2 reports (2007, 2008) describing a within-subject objective comparison of mechanical- and microprocessor-controlled knees in 15 trans-femoral amputees (12 men, 3 women; mean age, 42 years) with a Medicare Classification Level 3 or 4. (9, 10) Following testing with the subject’s usual mechanical prosthesis, the amputees were given an acclimation period of 10 to 39 weeks (average, 18 weeks) with a microprocessor knee before repeat testing. 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 approximately 10%, as objectively determined with a computerized dynamic post urography 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 in this study spontaneously increased their daily physical activity outside of the laboratory setting when using a microprocessor knee.

Johansson et al. assessed energy efficiency in 8 amputees while using the C-Leg®, Össur Rheo™, and hydraulic Mauch SNS knee. (11) The participants could ambulate at least at a functional classification K3 level and had approximately 10 hours of acclimatization with each prosthesis that was not his or her usual prosthesis (4 C-Leg®, 1 Rheo®, 1 Endolite, 1 Teh Lin, 1 Mauch). The order in which the knee systems were evaluated was randomized. Oxygen uptake was measured on a quarter mile indoor track, and kinematic and kinetic data were collected in a motion analysis laboratory with subjects walking at self-selected speeds. Compared with the Mauch knee, oxygen consumption was significantly reduced for the Rheo® (-5% reduction), but not for the C-leg® (-2%). The Rheo® and C-Leg® were found to result in enhanced smoothness of gait, a decrease in hip work production, a lower peak hip flexion moment at terminal stance, and a reduction in peak hip power generation at toe-off.

In a manufacturer-sponsored study from 2007, Hafner et al. evaluated function, performance, and preference for the C-Leg® in 21 unilateral trans femoral amputees using an A-B-A-B design. (12) 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 before 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 1 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. 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). A 2013 study by Highsmith et al. used a within-subjects pre and post design, first evaluating outcomes with a non-microprocessor-controlled prosthesis followed by the same evaluation after receiving a microprocessor-controlled prosthesis. These researchers reported significantly improved descent times by 23% (6.0 versus 7.7 seconds) and Hill Assessment Index scores (8.9 versus 7.8) with a C-Leg® compared with the subjects’ own non microprocessor prosthetic knees. (13)

Hafner and Smith evaluated the impact of the microprocessor-controlled prosthesis on function and safety in level K2 and K3 amputees. (14) The K2 ambulators tended to be older (57 versus 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. (12) Self-reported measures included concentration, multitasking ability, and numbers of stumbles and falls in the previous 4 weeks. Both level K2 and K3 amputees showed significant improvements in mobility and speed (range, 7%-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 level K2 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 when using the microprocessor-controlled knee. Reevaluation 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 Veterans 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 use the prosthesis. (1)

C-Leg® Compact

Two crossover studies evaluated the effect of the C-Leg® Compact (stance phase only) on functional performance in Medicare functional level K2 ambulators.

Functional performance with 17 simulated activities of daily living was assessed with the C-Leg® Compact in 28 level K2 ambulators. (15) Participants first used their own mechanically controlled knee and then with 2 types of microprocessor-controlled knee joints (C-Leg®, 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. Perceived performance was improved with the C-Leg® for some subscales of the PEQ, but this did not translate to an increase in activity level. (16) 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 with the mechanically controlled knee.

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. (17, 18) Seven of the 10 subjects used upper-extremity assistive devices (e.g., 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 (TUG) test (17.7 versus 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.


The Genium prosthesis was compared with the subject’s own C-Leg® in a crossover study with 11 trans femoral amputees. (19) This was a manufacturer-sponsored biomechanical study (e.g., comparison of ground reaction forces, flexion angles, load distribution) that did not evaluate clinical outcomes.

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). (20) There was little difference in performance between the 2 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.

Intelligent Prosthesis (IP™)

Early literature focused on the IP™, which is similar to the C-Leg®, but is not distributed in the United States. Kirker et al. reported on the gait symmetry, energy expenditure, and subjective impression of the IP™ in 16 patients who had been using a pneumatic prosthesis and were offered a trial of an IP. (21) At the beginning of the study, the patients had been using the IP™ for between 1 and 9 months. Using a visual analog scale, subjects reported that significantly less effort was required when using the IP prosthesis walking outdoors or at work at normal or high speeds, but there was no difference for a slow gait. 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. (22) All patients, who were otherwise fit and fairly active, reported that the IP™ was an improvement over the conventional prosthesis. The main subjective benefits were the ability to walk at various speeds, reduction of effort of walking, and patients' perception of improvement of walking pattern. Datta et al. also reported oxygen consumption at different walking speeds in 10 patients using an IP™ and a pneumatic swing gait prosthesis. (23) The IP was associated with less oxygen consumption at lower walking speeds only.

Section Summary: Microprocessor-Controlled Knee

The literature consists of a number of small within-subject comparisons of microprocessor-controlled knees versus hydraulic knee joints. Studies on the C-Leg® in Medicare level K3 and K4 amputees show objective improvements in function on some outcome measures and a strong patient preference for microprocessor-controlled prosthetic knees. Evidence on the C-Leg® Compact in Medicare level K2 ambulators is more limited but suggests a possible benefit. 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.

Microprocessor-Controlled Foot-Ankle Prostheses

A 2004 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. (24) In addition, the authors 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 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.

ProPrio® Foot

Gait analysis with the ProPrio® Foot was evaluated in 16 trans-tibial K3-K4 amputees during stair and ramp ascent and descent. (25, 26) 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 4o 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. (27)

In 2009, Wolf et al. published a study of 12 unilateral trans-tibial amputees who were provided with the ProPrio® foot and underwent an instrumental 3D gait analysis in level, stair, and incline ambulation. (28) Socket pressure was analyzed. When ascending stairs, there was a strong correlation between maximum knee movement and socket pressure. The most significant pressure changes were discovered when patients were descent ramp walking, with increase pressure to the anterior of the stump end. This pressure reading was almost twice as high when compare to level walking. The study authors found that modifying the angle of the prostheses for stairs and ramps ambulation brought the pressure to the stump closer to level walking.

Self-reported and objective performance outcomes for 4 types of prosthetic feet, including the ProPrio® Foot, were evaluated in a 2012 randomized within-subject crossover study. (29) Ten patients with trans-tibial 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.

During 6 testing sessions, 4 devices were studied by Agrawal et al. and published in 2015. (30) Following prosthetic training between sessions 1 and 2, 10 K-level-2 and K-level-3 unilateral trans-tibial patients tried each of the 4 prosthetic feet devices that included sensors to read the ramp-walking (ascent and descent) ambulation, to determine differences of symmetry in external work. During sessions 3-6, each patient tested 4 feet: SACH, stationary attachment flexible endoskeleton, Talux® (categories K1, K2, and K3, J-shaped ankle), and ProPrio® foot. The authors reported, “During ramp descent, K-level-2 subjects demonstrated higher symmetry in external work values with Talux® and ProPrio® foot external work values with the Talux® foot than the solid ankle cushion heel foot. Ramp ascent symmetry in external work values were not significantly different between feet.” They concluded that the prosthetic foot category appears to influence symmetry in the external work ambulation during descent ambulation than in ascent ambulation.

A 2016 study reported by Struchkov et al. assessed gait biomechanics of 9 unilateral trans-tibial amputees by comparing a microprocessor foot-ankle to non-microprocessor systems. (31) The patients walked down a 5-degree ramp. The reported outcome was the residual knee flexion during early stance phase was reduced. According to the authors, there was a trend towards reduced negative mechanical work at the residual knee with no difference in residual knee moment impulse when using the microprocessor system versus mechanical feet. The reduction of undesired knee flexion at the heel strike suggests the use of the microprocessor foot reduces the biomechanical compensations that the amputee are forced to make when using a mechanical, fixed-ankle feet.

Eight patients acting as their own controls were studied by Rosenblatt et al. in 2014. (32) The study objective was to assess the minimum toe clearance (MTC) changes that may increase the incidence of trips and falls. The 8 patients with trans-tibial unilateral amputations walked on a treadmill with their current foot at 2 grades and 3 velocities. They then repeated this activity using the ProPrio® foot. Results showed the MTC were larger by approximately 70% with the ProPrio® foot and the likelihood of tripping was reduced. Study analysis regression revealed that MTC with the ProPrio® foot to all 3 angles, with sensitivity of hip and ankle being greater; thereby the PrioPrio® foot may increaser user safety to minimize trips and falls.

Another study found a lower energy cost of floor walking with the ProPrio® Foot compared with a dynamic carbon fiber foot in 10 trans-tibial amputees. (33) However, the study found no significant benefit for walking stairs or ramps, for the TUG test, or for perceived mobility or walking ability.

PowerFoot BiOM®

Au et al. reported the design and development of the powered ankle-foot prosthesis (PowerFoot BiOM®) in 2008; however, clinical evaluation of the prototype was performed in a single patient. (34)

In 2012, Ferris et al. reported a pre-post comparison of the PowerFoot BiOM® with the patient’s own energy-storing and -returning (ESR) foot in 11 patients with trans-tibial amputation. Results for both prostheses were also compared with 11 matched controls who had intact limbs. (35) In addition to altering biomechanical measures, the powered ankle-foot increased walking velocity compared with the ESR 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 BiOM®; 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 BiOM® and 4 preferred the ESR. Compared with controls with intact limbs, the PowerFoot BiOM® had reduced range of motion, but greater ankle peak power.

Another similar, small pre-post study from 2012 (7 amputees, 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. (36)

In a conference proceeding from 2011, Mancinelli et al. described a comparison of a passive-elastic foot and the PowerFoot BiOM® in 5 trans-tibial amputees. (2) The study was supported by the U.S. Department of Defense (DoD), 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).

Section Summary: Microprocessor-Controlled Foot-Ankle Prostheses

Several small studies have been reported with microprocessor-controlled and powered foot-ankle prostheses for trans-tibial amputees. Evidence to date remains insufficient to support an improvement in functional outcomes when compared with the same device in the off-mode or compared with ESR prostheses. Larger, higher quality studies are needed to determine the impact of these devices on health outcomes with greater certainty.

Hydraulic Prosthetic Hip

The literature primarily consists of a limited number of small within-subject reviews of post-hip disarticulation rehabilitation utilizing prosthetics for patients having had a congenital anomaly, trauma-related, cancer-related, and dysvascular amputations. (37) A retrospective review of 43 patients during a 10-year span found that 18 (43%) of the patients were candidates for a prosthetic fitting following hip disarticulation or hemipelvectomy. (38)

Of the 12 patients retrospectively studied by Ferrapie et al., those who did not die due to the disease causing the initial ambulation, inpatient rehabilitation began at 14 days following amputation surgery. (39) Prosthetic training started on day 13 of admission to the rehab facility. Of those who survived their disease (n=6) and were discharged to home, 2 were able to walk indoors without assistance at discharged. This was followed by 5 wearing their prosthesis all day, 2 participating in a sport, and 4 driving their vehicles. All patients who were active had gone back to work.

Low patient acceptance of a hip disarticulation style prosthetic along with poor gait pattern, socket discomfort, prosthetic weight, mobility loss, instability, and high-energy consumption are contributing factors to patient utilization. (40) A study in 2010 from Ludwig et al. compared 2 prosthetic hip joints, both from OttoBock HealthCare, Helix3DHip® and the 7E7 (Modular Hip Joint Free Mot. Titan). (40) Six amputees were analyzed using 6 charged coupled twice device cameras and 2 force plate sensor systems evaluating kinematics and kinetics. The Helix3D Hip® revealed reduction in pelvic tilt range and slowed stance when compared with the 7E7. However, the Helix3D reduced gait abnormalities. Without either device, the conclusion would be the lack of any ambulation ability by these 6 patients.

Section Summary: Hydraulic Prosthetic Hip

The few studies addressing post hip disarticulation reveal that without a hip prosthetic, patients would lack mobility outside of wheelchairs and crutches. For those active patients, return to improved functionality, such as ambulation, sports participation, or driving, is a critical step in rehabilitation and improve physical fitness. Evidence is sufficient to support an improvement in functional outcomes when patients can utilize a hip prosthesis that is well-fitted, properly trained, low weight and energy impact, and improved stability.

Ongoing and Unpublished Clinical Trials

Some ongoing trials that might influence this policy are listed in Table 2.

Table 2. Summary of Key Trials

NCT Number

Trial Name

Planned Enrollment

Completion Date



Comparative Effectiveness Between Microprocessor Knees and Non-Microprocessor Knees


Oct 2017

NCT02765035 a

C-Leg 3 and C-Leg 4 Study in Trans-femoral Amputees


Dec 2017


Comparative Effectiveness of Microprocessor Controlled and Carbon Fiber Prosthetic Feet in Trans-tibial Amputees


Sep 2017



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


Sep 2015 (completed)

Table Key:

NCT: National Clinical Trial;

a: Denotes industry-sponsored or cosponsored trial.

Practice Guidelines and Position Statements

Veteran’s Administration (VA)

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. (1) 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 (AAOP).

The resulting VA Clinical Practice Recommendations for microprocessor knees (1) are as follows:

Patient Selection and Identification:

1. Contraindications for use of the microprocessor knee should include:

a. Any condition that prevents socket fitting, such as a complicated wound or intractable pain which precludes socket wear;

b. Inability to tolerate the weight of the prosthesis;

c. Medicare Level K 0-no ability or potential to ambulate or transfer;

d. Medicare Level K 1-limited ability to transfer or ambulate on level ground at fixed cadence;

e. 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;

f. Inability to use swing and stance features of the knee unit;

g. Poor balance or ataxia that limits ambulation;

h. Significant hip flexion contracture (over 20 degrees);

i. Significant deformity of remaining limb that would impair ability to stride;

j. Limited cardiovascular and/or pulmonary reserve or profound weakness;

k. Limited cognitive ability to understand gait sequencing or care requirements;

l. Long distance or competitive running;

m. Falls outside of recommended weight or height guidelines of manufacturer;

n. Specific environmental factors-such as excessive moisture or dust, or inability to charge the prosthesis;

o. Extremely rural conditions where maintenance ability is limited.

2. Indications for use of the microprocessor knee should include:

a. Adequate cardiovascular and pulmonary reserve to ambulate at variable cadence;

b. Adequate strength and balance in stride to activate the knee unit;

c. Should not exceed the weight or height restrictions of the device;

d. Adequate cognitive ability to master technology and gait requirements of device;

e. Hemi-pelvectomy through knee-disarticulation level of amputation, including bilateral; lower extremity amputees are candidates if they meet functional criteria as listed;

f. Patient is an active walker and requires a device that reduces energy consumption to permit longer distances with less fatigue;

g. 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;

h. 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;

i. Medicare Level K 3-unlimited community ambulator;

j. Medicare Level K 4-active adult, athlete who has the need to function as a K 3 level in daily activities;

k. Potential to lessen back pain by providing more secure stance control, using less muscle control to keep knee stable;

l. Potential to unload and decrease stress on remaining limb;

m. Potential to return to an active lifestyle.

3. Physical and Functional Fitting Criteria for New Amputees:

a. New amputees may be considered if they meet certain criteria as outlined above;

b. Premorbid and current functional assessment important determinant;

c. Requires stable wound and ability to fit socket;

d. Immediate postoperative fit is possible;

e. Must have potential to return to active lifestyle.

Summary of Evidence

Microprocessor-controlled prostheses use feedback from sensors to adjust joint movement on a real-time as-needed basis. The literature consists of a number of small within-subject comparisons of microprocessor-controlled knees versus hydraulic knee joints. For K3- and K4-level amputees, studies show an objective improvement in function on some outcome measures and a strong patient preference for microprocessor-controlled prosthetic knees. Benefits include a more normal gait, an increase in stability, a decrease in falls, and a decrease in the cognitive burden associated with monitoring the prosthesis. It is concluded that a microprocessor-controlled knee may provide incremental benefit for these 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.

Evidence is insufficient to permit conclusions regarding the effect of a microprocessor-controlled prosthesis on health outcomes in limited community ambulators. Evidence is also insufficient to permit conclusions regarding the effect of a next-generation microprocessor-controlled prosthesis on health outcomes.

The limited evidence available to date does not support an improvement in functional outcomes with a microprocessor-controlled or powered foot-ankle prostheses compared with standard prostheses.

Despite the few studies available addressing post-hip disarticulation followed by prosthetic utilization, evidence is sufficient to support improvement in functional outcomes with patient use of hip hydraulic prostheses. Key elements to successful patient acceptance of the device is correct prosthetic device selection, in addition to training, fitting, and device features.


Each benefit plan, summary plan description or contract defines which services are covered, which services are excluded, and which services are subject to dollar caps or other limitations, conditions or exclusions. Members and their providers have the responsibility for consulting the member's benefit plan, summary plan description or contract to determine if there are any exclusions or other benefit limitations applicable to this service or supply. If there is a discrepancy between a Medical Policy and a member's benefit plan, summary plan description or contract, the benefit plan, summary plan description or contract will govern.


There is no specific coverage policy on microprocessor-controlled knee prosthesis, in part because there is no specific HCPCS code describing this prosthesis.

Generally, coverage will include supplies necessary for effective use of a covered prosthesis, as well as adjustments, repairs, and replacements that are necessary to make the equipment functional for as long as the equipment continues to be medically necessary.

Shoes (a pair) may be covered when one or both shoes are an integral part of the artificial limb(s). Check the member’s contract.

HCPCS codes:

L5856 Swing and stance phase microprocessor knees,

L5857 Swing phase only microprocessor knees,

L5858 Stance phase only microprocessor knees,

L5961 Hydraulic/pneumatic hip (e.g., Helix3DHip® Joint),

L5973 Microprocessor foot/ankle.


Disclaimer for coding information on Medical Policies

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.

The presence or absence of procedure, service, supply, device or diagnosis codes in a Medical Policy document has no relevance for determination of benefit coverage for members or reimbursement for providers. Only the written coverage position in a medical policy should be used for such determinations.

Benefit coverage determinations based on written Medical Policy coverage positions must include review of the member’s benefit contract or Summary Plan Description (SPD) for defined coverage vs. non-coverage, benefit exclusions, and benefit limitations such as dollar or duration caps.


The following codes may be applicable to this Medical policy and may not be all inclusive.

CPT Codes

97110, 97112, 97116, 97761, 97762, 97763


L5000, L5010, L5020, L5050, L5060, L5100, L5105, L5150, L5160, L5200, L5210, L5220, L5230, L5250, L5270, L5280, L5301, L5312, L5321, L5331, L5341, L5400, L5410, L5420, L5430, L5450, L5460, L5500, L5505, L5510, L5520, L5530, L5535, L5540, L5560, L5570, L5580, L5585, L5590, L5595, L5600, L5610, L5611, L5613, L5614, L5616, L5617, L5618, L5620, L5622, L5624, L5626, L5628, L5629, L5630, L5631, L5632, L5634, L5636, L5637, L5638, L5639, L5640, L5642, L5643, L5644, L5645, L5646, L5647, L5648, L5649, L5650, L5651, L5652, L5653, L5654, L5655, L5656, L5658, L5661, L5665, L5666, L5668, L5670, L5671, L5672, L5673, L5676, L5677, L5678, L5679, L5680, L5681, L5682, L5683, L5684, L5685, L5686, L5688, L5690, L5692, L5694, L5695, L5696, L5697, L5698, L5699, L5700, L5701, L5702, L5703, L5704, L5705, L5706, L5707, L5710, L5711, L5712, L5714, L5716, L5718, L5722, L5724, L5726, L5728, L5780, L5781, L5782, L5785, L5790, L5795, L5810, L5811, L5812, L5814, L5816, L5818, L5822, L5824, L5826, L5828, L5830, L5840, L5845, L5848, L5850, L5855, L5856, L5857, L5858, L5859, L5910, L5920, L5925, L5930, L5940, L5950, L5960, L5961, L5962, L5964, L5966, L5968, L5969, L5970, L5971, L5972, L5973, L5974, L5975, L5976, L5978, L5979, L5980, L5981, L5982, L5984, L5985, L5986, L5987, L5988, L5990, L5999, L7360, L7362, L7367, L7368, L7500, L7510, L7520, L7600, L7700, L8400, L8410, L8415, L8417, L8420, L8430, L8435, L8440, L8460, L8465, L8470, L8480, L8485, L8499

ICD-9 Diagnosis Codes

Refer to the ICD-9-CM manual

ICD-9 Procedure Codes

Refer to the ICD-9-CM manual

ICD-10 Diagnosis Codes

Refer to the ICD-10-CM manual

ICD-10 Procedure Codes

Refer to the ICD-10-CM manual

Medicare Coverage:

The information contained in this section is for informational purposes only. HCSC makes no representation as to the accuracy of this information. It is not to be used for claims adjudication for HCSC Plans.

The Centers for Medicare and Medicaid Services (CMS) does not have a national Medicare coverage position. Coverage may be subject to local carrier discretion.

A national coverage position for Medicare may have been developed since this medical policy document was written. See Medicare's National Coverage at <>.


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14. 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

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43. Microprocessor-Controlled Prosthetic Knees. Chicago, Illinois: Blue Cross Blue Shield Association Medical Policy Reference Manual (2015 April) Durable Medical Equipment 1.04.05.

Policy History:

Date Reason
10/15/2017 Document updated with literature review. Coverage unchanged. The following was added to the beginning of coverage section, “ALERT: Health Care Services Corporation (HCSC) no longer maintains a Hanger Inc. Prosthetics & Orthotics Patient Assessment Validation Evaluation Tool (PAVET™) Evaluation for Microprocessor Knee (K-PAVET™) form on any of our web sites. To utilized the K-PAVET™ form for Microprocessor and Powered Knees, refer to the Hanger Inc., web site at ‘’.”
4/15/2015 Document updated with literature review. Coverage unchanged. Rationale was substantially revised.
1/1/2015 Reviewed. No changes.
12/15/2013 Document updated with literature review. No changes to Coverage. “Êlan ® (Endolite)” was added as an example of a microprocessor-controlled foot/ankle.
12/1/2011 Document updated with literature review. The following was added to Coverage: 1) The Genium™ Bionic Prosthetic System microprocessor knee and a powered knee are considered experimental, investigational and unproven; 2) A four-axis, hydraulic or pneumatic hip joint (e.g., Helix 3D Hip® [OttoBock]) may be considered medically necessary when the patient has an overall score of 50 or higher, and cadence score 15 or higher on the PAVET Evaluation, and the Helix 3D Hip will be used in conjunction with the OttoBock C-Leg.
1/1/2009 Revised/updated entire document
7/15/2007 CPT /HCPCS code(s) updated
5/15/2007 Revised/updated entire document
6/15/2006 New medical document

Archived Document(s):

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