The Feasability of Reflexive Control in Transfemoral Prostheses

In daily life of a transfemoral amputee (TFA) a stumble or a fall is not uncommon, mainly due to the lack of feedback and control of their prosthesis. Although intelligent knees are now available, proprioceptive feedback and control over the lower leg is needed. Using muscle activity (EMG) as control input and providing artificial feedback is a concept already seen for upper extremity prosthesis, but not for the lower extremity. Ideally this feedback also triggers the reflexes of the prosthetic user, for the prosthesis to become second nature to the user. This article will address the allowed time delays in a system where reflexes and EMG are used to control a transfemoral prosthesis. The response to a kneeunlock was analysed in a modeling study, including the reflex loop and EMG control, to determine the maximal time delays which still allow a stable control of the knee.