A comparison of passive and quasi-passive prosthetic ankles over varying speeds and terrains

Quasi-passive (QP) prosthetic ankle-foot devices can provide functional benefits over passive prostheses without the complexity, weight, and cost of fully powered devices. However, research examining how to best design QP ankles to optimize patient outcomes is limited. This randomized, repeated measures crossover trial compares two different QP prosthetic ankles (variable stiffness, variable damping) against two energy-storage-and-return (ESR) ankles in seven individuals with unilateral transtibial amputation over eight distinct walking tasks (3 level-ground speeds, figure-8 overground pattern, 5° incline and decline, stair ascent and descent). Subject feedback is collected for every ankle on each walking task, and five tasks are biomechanically instrumented using motion capture and force plates. Results show that variable damping is on average the least preferred across all walking tasks, both from subject feedback and biomechanical metrics. For level-ground walking, the remaining three ankles receive similar subject feedback scores, although biomechanical results indicate that the ESR ankles produce higher peak power and center-of-mass push-off work at faster speeds. The variable-stiffness ankle is preferred by subjects over the ESR ankles on decline walking, though no significant difference is seen in the measured biomechanical metrics. These results demonstrate that a QP variable-stiffness prosthesis can achieve similar level-ground walking performance to ESR ankles at slow and moderate speeds, and shows promise in adaptability for walking tasks on sloped terrain.