Passive prosthetic ankle-foot mechanism for automatic adaptation to sloped surfaces

This article describes the development of a prototype prosthetic ankle-foot system that passively adapts to surface slopes on each step of walking. Engineering analyses were performed to design the cam clutch and clutch engagement and disengagement mechanism. The prototype was tested by a veteran with a unilateral transtibial amputation. Kinematic and kinetic data were recorded while the subject walked on a treadmill at slopes ranging from 10 to +10 degrees. After each slope condition, the subject rated his level of exertion and socket comfort. The subject reported increased comfort and reduced exertion for downhill slopes when using the prototype compared with his usual prosthesis. The subject also expressed that when walking downhill on the prototype, it was the most comfortable he had ever been in a prosthesis. The prosthetic ankle torque-angle relationship shifted toward dorsiflexion for uphill and toward plantar flexion for downhill slopes when using the prototype, indicating slope adaptation, but this effect did not occur when the subject walked with his usual prosthesis. The prototype also demonstrated late-stance plantar flexion, suggesting the potential for storing and returning more energy than standard lower-limb prostheses.