Mechanical Gait Analysis of Transfemoral Amputees: SACH Foot Versus the Flex-Foot

Abstract

The purpose of this study was to identify gait mechanics that might explain the physiological benefits found when transfemoral amputees walked over ground using a Flex-Foot® compared to a SACH foot fastened below a hydraulic knee joint. Five active traumatic unilateral transfemoral amputees were videotaped as they walked overground at five controlled speeds ranging from 1.5 to 3.5 mph on a continuous path.

Analysis of the videotape data was conducted on the mean step length, early and late swing and stance phases, and double- and single-support phases for each speed. Since there were no speedby- foot-type statistical interactions, the foot-type comparisons could be made across all speeds. The only significant differences due to foot type were found in the uninvolved double- and uninvolved single-support phases and the late stance-phase ratio (involved late stance phase/uninvolved late stance phase). These differences appear to be caused by a delay in the involved toe-off while using the Flex-Foot.

The Flex-Foot is designed to deform during weight acceptance and reform giving a “pushoff” during late stance. The additional time needed to reform the Flex-Foot could explain the phase differences, and this pushoff mechanism could explain the physiological benefits of walking with the Flex-Foot compared to the SACH foot. With a pushoff, the inertia of the involved limb may be overcome, and the prosthetic limb may be recovered with less upper-body movement and thus less energy would be expended, resulting in a more efficient, symmetrical gait.