Foot Clearance during Free Swing of a Transfemoral Prosthetic Leg: Four-Bar Knee vs. Ankle Dorsiflexion

Polycentric knees are frequently used in transfemoral prostheses because they provide added stability in stance phase and relative ankle dorsiflexion in swing phase. Despite this relative ankle dorsiflexion, patients still complain of inadequate toe clearance even with polycentric knees. We hypothesize that active ankle dorsiflexion via a knee-ankle coupling provides more toe clearance than provided by polycentric knees during midswing the most critical phase of toe clearance. This hypothesis was evaluated by examining toe clearance of kinematic knee models processed on data from existing able-bodied data. A knee with active ankle dorsiflexion achieved larger toe clearance (3.01 cm) than the polycentric knee (3.89 cm) during midswing. Knee designs with active ankle dorsiflexion should be reconsidered for improved toe clearance in the gait of amputees.