Active plantar-flexion above-knee prosthesis: concept and preliminary design.

Lower limb prostheses produced so far do not replace the function of the musculature, which provides the necessary amount and the proper distribution of energy to the ambulatory mechanism. Provision of external power to lower limb prostheses has been hindered by the fact that the large amount of energy needed at a lower limb necessitates the use of external power sources of unacceptably high mass and volume. Self energized mechanisms offer a promising alternative to the problem. Normally a large part of energy output during locomotion appears at the ankle joint. It seems therefore desirable to develop an above-knee prosthesis featuring active plantar-flexion at the ankle. Energy may be offered by a self energized system. The system, described here, accumulates energy during the passive movements of the knee and ankle joints and stores it for later use at the ankle.