New function and passive mechanism of transfemoral prosthetic knee for running safely

Transfemoral amputees who run are required to learn how to control their prosthetic leg motion to avoid falling with unintended prosthetic knee flexion because the function of the existing prosthetic knee for running is likened to a simple hinge joint during stance. However, the risk of falling and injury is a barrier to participation in sports and exercise. We have addressed this concern by developing a passive mechanism for a prosthetic knee; however, the mechanism that locks knee flexion with ground reaction forces (GRFs) could not completely avoid unintended prosthetic knee flexion. The present study aims to reconsider the function of the prosthetic knee for running and propose a new prosthetic knee mechanism. Time is an alternative way to control the lock/unlock of flexion without GRFs; therefore, the new prosthetic knee mechanism should limit flexion after a certain period from the moment that the prosthesis leaves the ground. We developed a rough prototype to confirm the function of the new prosthetic knee and conducted an evaluation experiment. The subject who was attached to the simulated thigh socket and prototype of the new prosthetic knee performed level walking. The results indicated that the new mechanism allowed flexion only during the first half of the swing phase, meaning the subject was able to walk without falling. According to the literature, swing time is approximately constant among different speeds. The new mechanism would appropriately function under actual running conditions. Clinical Relevance-This proposes a new passive prosthetic knee mechanism for above-knee amputees to run safely.