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Microprocessor-controlled prostheses use feedback from sensors to adjust joint movement on a real-time as-needed basis. Active joint control is intended to improve safety and function, particularly for patients who have the capability to maneuver on uneven terrain and with variable gait.
More than 100 different prosthetic ankle-foot and knee designs are currently available. The choice of the most appropriate design may depend on the patient’s underlying activity level. For example, the requirements of a prosthetic knee in an elderly, largely homebound individual will be quite different than a younger active person. In general, key elements of a prosthetic knee design involve providing stability during both the stance and swing phase of the gait. Prosthetic knees also vary in their ability to alter the cadence of the gait, or the ability to walk on rough or uneven surfaces. In contrast to more simple prostheses, which are designed to function optimally at one walking cadence, fluid and hydraulic-controlled devices are designed to allow amputees to vary their walking speed by matching the movement of the shin portion of the prosthesis to the movement of the upper leg. For example, the rate at which the knee flexes after “toe-off” and then extends before the heel strike depends in part on the mechanical characteristics of the prosthetic knee joint. If the resistance to flexion and extension of the joint does not vary with gait speed, the prosthetic knee extends too quickly or too slowly relative to the heel strike if the cadence is altered. When properly controlled, hydraulic or pneumatic swing phase controls allow the prosthetist to set a pace that is adjusted to the individual amputee from very slow to a race walking pace. Hydraulic prostheses are heavier than other options and require gait training; for these reasons these prostheses are generally prescribed for athletic or fit individuals. Other design features include multiple centers of rotation, referred to as “polycentric knees.” The mechanical complexity of these devices allows engineers to optimize selected stance and swing phase features.
Microprocessor-Controlled Prosthetic Knees
Microprocessor-controlled prosthetic knees have been developed, including the Intelligent Prosthesis (IP) (Blatchford, United Kingdom), the Adaptive (Endolite, England), the Rheo (Ossur, Iceland), the C-Leg®, Genium Bionic Prosthetic System, and the X2 and X3 prostheses (Otto Bock Orthopedic Industry, Minneapolis, MN) and Seattle Power Knees (3 models include Single Axis, 4-bar and Fusion, from Seattle Systems). These devices are equipped with a sensor that detects when the knee is in full extension and adjusts the swing phase automatically, permitting a more natural walking pattern of varying speeds. For example, the prosthetist can specify several different optimal adjustments that the computer later selects and applies according to the pace of ambulation. In addition, these devices (with the exception of the Intelligent Prosthesis) use microprocessor control in both the swing and stance phases of gait. (The C-Leg Compact provides only stance control.) By improving stance control, they may provide increased safety, stability, and function; for example, the sensors are designed to recognize a stumble and stiffen the knee, thus avoiding a fall. Other potential benefits of microprocessor-controlled knee prostheses are improved ability to navigate stairs, slopes, and uneven terrain, and reduction in energy expenditure and concentration required for ambulation. The C-Leg® was cleared for marketing in 1999 through the 510(k) process of the U.S. Food and Drug Administration (FDA, K991590). Next-generation devices such as the Genium Bionic Prosthetic system and the X2 and X3 prostheses utilize additional environmental input (eg, 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 Otto Bock as part of the Military Amputee Research Program.
Microprocessor-Controlled Ankle-Foot Prostheses
Microprocessor-controlled ankle-foot prostheses are being developed for transtibial amputees. These include the Proprio Foot® (Ossur), the iPED (developed by Martin Bionics LLC and licensed to College Park Industries), and the Elan Foot (Endolite). With sensors in the feet that determine the direction and speed of the foot’s movement, a microprocessor controls the flexion angle of the ankle, allowing the foot to lift during the swing phase and potentially adjust to changes in force, speed, and terrain during the step phase. The intent of the technology is to make ambulation more efficient and prevent falls in patients ranging from the young active amputee to the elderly diabetic patient. The Proprio Foot™ and Elan Foot are microprocessor-controlled foot 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 Ossur Web site indicates use of the Proprio Foot™ for low to moderate impact for transtibial amputees who are classified as level K3 (i.e., community ambulatory, with the ability or potential for ambulation with variable cadence).
In development are lower-limb prostheses that also replace muscle activity in order to bend and straighten the prosthetic joint. For example, the Power Foot BiOM® (developed at the Massachusetts Institute of Technology and licensed to iWalk) is a myoelectric prosthesis for transtibial amputees that uses muscle activity from the remaining limb for the control of ankle movement. This prosthesis is designed to propel the foot forward as it pushes off the ground during the gait cycle, which in addition to improving efficiency, has the potential to reduce hip and back problems arising from an unnatural gait with use of a passive prosthesis. This technology is limited by the size and the weight required for a motor and batteries in the prosthesis.
The Power Knee (Ossur), which is designed to replace muscle activity of the quadriceps, uses artificial proprioception with sensors similar to the Proprio Foot in order to anticipate and respond with the appropriate movement required for the next step. The Power Knee is currently in the initial launch phase in the United States.
Manufacturers must register prostheses with the restorative devices branch of FDA and keep a record of any complaints, but do not have to undergo a full FDA review.
A microprocessor-controlled knee may be considered medically necessary in amputees who meet the following requirements:
A microprocessor-controlled knee is considered not medically necessary in individuals who do not meet these criteria.
A powered knee is considered investigational.
A microprocessor-controlled or powered foot is considered investigational.
Federal Employee Program (FEP) may dictate that all devices, drugs or biologics approved by the FDA may not be considered investigational and thus, these devices may be assessed only on the basis of their medical necessity.
Decisions about the potential benefits of microprocessor-knees involve multiple factors including activity levels as well as the patient's physical and cognitive ability. A patient's need for daily ambulation of at least 400 continuous yards, daily and frequent ambulation at variable cadence or on uneven terrain (e.g., gravel, grass, curbs), and daily and frequent use of ramps and/or stairs (especially stair descent) should be considered as part of the decision. Typically, daily and frequent need of two or more of these activities would be needed to show benefit.
For patients in whom the potential benefits of the microprocessor knees are uncertain, patients may first be fitted with standard prosthesis to determine their level of function with the standard device.
The coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member's specific benefit plan language.
7/27/2006: Approved by Medical Policy Advisory Committee (MPAC)
7/20/2007: Policy reviewed, description updated. Policy statement revised; microprocessor-controlled knee prosthesis changed from investigational to may be considered medically necessary in amputees who meet criteria as outlined in policy. Non-covered codes table removed. Covered codes table added. HCPCS L5856, L5857, and L5858 moved to covered. ICD-9 codes 897.2-897.7 and V43.65 added
11/15/2007: Revised policy approved by MPAC
4/27/2010: Title changed from "Prosthetic Knees" to "Prostheses for the Lower Limb." Description section revised to include ankle-foot prostheses information. Policy statement section was revised to add two new policy statements regarding ankle-foot and powered knee prostheses; these are considered investigational. FEP verbiage was added to the Policy Exceptions section. Code Reference section was revised to add the following language: "*Some covered procedure codes may have multiple descriptions. Coverage will only be made for covered codes when used for services outlined within the policy statement."
04/20/2011: Policy reviewed; no changes.
04/26/2012: Policy reviewed; no changes.
12/21/2012: Added the following new 2013 CPT code to the Code Reference section: L5859.
04/19/2013: Policy reviewed; no changes.
04/24/2014: Policy reviewed; description updated regarding available devices for microprocessor-controlled prosthetic knees and ankle-foot prostheses. Policy statement unchanged.
Blue Cross Blue Shield Association Policy # 1.04.05
This may not be a comprehensive list of procedur codes applicable to this policy.
The code(s) listed below are ONLY medically necessary if the procedure is performed according to the "Policy" section of this document.