Stance Phase Characteristics of Above-Knee Prostheses

Abstract

The design of mechanisms claimed to afford improved function to the amputee while the prosthesis is weight-bearing has generally been carried out in an intuitive fashion. This paper reports the findings of a preliminary investigation into the objective assessment of various types of devices with a view to ascertaining whether or not the amputee is able to use the theoretical advantage they offer him.

During the stance phase of gait, the prosthesis is required to be stable from heel contact until the time of initiation of knee flexion preparatory to swing through. The voluntary use of hip extensors and flexors together with body contact eg. ischial seat, will in some way meet these requirements. By measuring this anterior-posterior hip moment as the amputee performs various activities; walking, climbing stairs and ramps, stepping over objects etc., the influence of a knee mechanism can be evaluated. 

The anterior-posterior hip moment was calculated on the basis of the force actions as measured by an instrumented pylon in the shank of the prostheses, and the limb configuration defined by the segment lengths and the knee angle. All the instrumentation was therefore incorporated in the prosthesis, allowing the amputee a greater degree of freedom than would be possible with a force platform technique.