Novel knee joint mechanism of transfemoral prosthesis for stair ascent

Abstract

The stability of a transfemoral prosthesis when walking on flat ground has been established by recent advances in knee joint mechanisms and their control methods. It is, however, difficult for users of a transfemoral prosthesis to ascend stairs. This difficulty is mainly due to insufficient generation of extension moment around the knee joint of the prosthesis to lift the body to the next step on the staircase and prevent any unexpected flexion of the knee joint in the stance phase. Only a prosthesis with an actuator has facilitated stair ascent using a step-over-step gait (1 foot is placed per step). However, its use has issues associated with the durability, cost, maintenance, and usage environment. Therefore, the purpose of this research is to develop a novel knee joint mechanism for a prosthesis that generates an extension moment around the knee joint in the stance phase during stair ascent, without the use of any actuators. The proposed mechanism is based on the knowledge that the ground reaction force increases during the stance phase when the knee flexion occurs. Stair ascent experiments with the prosthesis showed that the proposed prosthesis can realize stair ascent without any undesirable knee flexion. In addition, the prosthesis is able to generate a positive knee joint moment power in the stance phase even without any power source.

Mechanisms and component design of prosthetic knees: A review from a biomechanical function perspective

“…In addition to the MPK solutions, the adaptivity can be enhanced only by passive mechanisms. A passive mechanism that acts as a lock axis has been added to a knee device; it locks the knee and generates an extension moment around the knee axis during the stance phase without using any actuators ( Inoue et al, 2013 ). This mechanism enables the knee to adapt to stair ascent, which is based on the knowledge that GRF translates and increases when stance flexion occurs.…”