BlueCross BlueShield of Tennessee Medical Policy Manual

Microprocessor-Controlled Prostheses for the Lower Limb


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 individuals who have the capability to maneuver on uneven terrain and with a variable gait.

More than one hundred different prosthetic knee designs are currently available (e.g. Intelligent Prosthesis, Adaptive, Rheo Knee®, C-Leg®, Genium™ Bionic Prosthetic System, Seattle Power Knees; 3 models include Single Axis, 4-bar, and Fusion).  The choice of the most appropriate design depends on the individual’s activity level. 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. Hydraulic prostheses are heavier than other options and require gait training; for these reasons, these prostheses are generally prescribed for athletic or fit individuals.

Microprocessor-controlled ankle-foot prostheses are being developed for transtibial amputees, (e.g. Proprio Foot®, iPED, Endolite élan, Kinnex, Raize, Triton Smart Ankle, emPOWER). 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.

Currently in the launch phase in the U.S. are lower-limb powered prostheses that are designed to replace the muscle activity of the quadriceps. It uses artificial proprioception with sensors in order to bend and straighten the prosthetic joint and respond to the appropriate movement required for the next step, (e.g. Power Knee [Ossur], PowerFoot BiOM ®).





Microprocessor-controlled prostheses are categorized as Class I, exempt devices.  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.

Medicare uses the following functional ability levels when determining medical necessity:

Level 0. Does not have the ability or potential to ambulate or transfer safely with or without assistance and a prosthesis does not enhance their quality of life or mobility.

Level 1. Has the ability or potential to use a prosthesis for transfers or ambulation on level surfaces at fixed cadence. Typical of the limited and unlimited household ambulatory.

Level 2. Has the ability or potential for ambulation with the ability to traverse low level environmental barriers such as curbs, stairs, or uneven surfaces. Typical of the limited community ambulatory.

Level 3. Has the ability or potential for ambulation 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.

Level 4. Has the ability or potential for prosthetic ambulation that exceeds basic ambulation skills, exhibiting high impact, stress, or energy levels. Typical of the prosthetic demand of the child, active adult, or athlete.

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


Alimusaj, M., Laetitia,F.,  Braatz, F., Gerner, H.,  and Wolf, S. (2009). Kinematics and kinetics with an adaptive ankle foot system during stair ambulation of transtibial amputees. Gait & Posture, 30, 356-363. (Level 4 evidence)

BlueCross BlueShield Association. Evidence Positioning System. (4:2018). Microprocessor-controlled prostheses for the lower limb (1.04.05). Retrieved November 16, 2018 from (26 articles and/or guidelines reviewed)

Cherelle, P., Grosu, V., Cestari, M., Vanderborght, B., and Lefeber, D. (2016) The AMPFoot 3, new generationpropulsive prosthetic feet with explosive motion characteristics: design and validation.BioMedical Engineering, 15(3), 145-163. (Level 4 evidence) Center for Medicare & Medicaid Services, CGS Administrators, LLC. (2018, November) Lower limb prostheses (LCD ID: L33787). Retrieved November 16, 2018 from

Delussu, A.,  Brunelli, S.,  Paradisi, F.,  Iosa, M.,  Pellegrini, R.,  Zenardi, D., et al. (2013, March).  Assessment of the effects of carbon fiber and bionic foot during overground and treadmill walking in transtibial amputees. Gait & Posture, e-published ahead of print (Level 5 evidence)

Fradet, L., Alimusaj, M.,  Braatz, F., and Wolf, S. (2010, April). Biomechanical analysis of ramp ambulation of transtibial amputees with an adaptive ankle foot system. Gait & Posture, e-published ahead of print doi:10.1016/j. gaitpost.2010.04.011. (Level 5 evidence)

Gailey, R., Gaunaurd, I., Agrawal, V., Finnieston, A., O’Toole, C., and Tolchin, R. (2012). Application of self-report and performance-based outcome measures todetermine functional differences between four categories of prosthetic feet. Journal of Rehabilitation, Research and Development (JRRD), 49(4), 597-612. (Level 4 evidence)

Kannenberg, A., Zacharias, D., & Pröbsting, E. (2014). Benefits of microprocessor-controlled prosthetic knees to limited community ambulators: systematic review. Journal of Rehabilitation Research & Development, 51, (10), 1469-1496. (Level 1 evidence)

Rosenblatt, N., Bauer, A., Rotter, D., and Grabiner, M. (2014).  Active dorsiflexing prostheses may reduce trip-related fall risk in people with transtibial amputation. Journal of Rehabilitation Research & Development (JRRD), 51 (8), 1229-1242. (Level 4 evidence)

Struchkov, V. and Buckley, J. (2015, November). Biomechanics of ramp descent in unilateral trans-tibial amputees: Comparison of a microprocessor controlled foot with conventional ankle–foot mechanisms. Clinical Biomechanics, 32 (2016), 164-170. (Level 4 evidence)

Theeven, P., Hemmen, B., Brink, P., Smeets, R., & Seelen, H. (2013). Measures and procedures utilized to determine the added value of microprocessor-controlled prosthetic knee joints: a systematic review. BMC Musculoskeletal Disorders, 14:333. (Level 1 evidence)

U.S. Food and Drug Administration. (1999, July). Center for Devices and Radiological health. 510(k) Premarket Notification Database. K991590. Retrieved January 24, 2017 from

Wolf, S.,  Alimusaj, M., Fradet, L., Siegel, J., and Braatz, F. (2009) Pressure characteristics at the stump/socket interface in transtibial amputees using an adaptive prosthetic foot. Clinical Biomechanics, e-published (Level 4 evidence)




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