Evaluation of the Polycentric above Knee Prosthesis

The optimal design of human lower limb prostheses, in particular of knee devices, is fundamental in order to restore the lost functionality and aesthetic aspect of the amputee’s locomotion. Among all knee devices, the four-bar linkage is still the most widespread mechanism, since, despite its simplicity, it allows the prosthesis to be sufficiently stable and, at the same time, to replicate the natural motion of the joint with a sufficient accuracy. This paper presents an optimization procedure for the synthesis of a four-bar linkage for knee prosthesis. Starting from an experimental reference motion and given some patient-specific requirements related to his capacity to control and to stabilize the prosthesis, the procedure identifies the four-bar linkage that best-fits the experimental motion, at the same time respecting the given specifications. During optimization procedure a set of four bar knee configurations are evaluated to allow a more normal gait to be achieved. Geometry of these new designs increases stability while allowing swing flexion, thereby rendering a locking feature unnecessary. Simulation shows that increase in instant center will be apple advantage for the user and also minimize the energy consumption. Extra toe clearance as compared to single axis knee is also providing a more natural gait.