Improved ankle-foot system for above-knee amputees

Abstract

Above-knee amputees were studied while wearing a prosthesis containing either a standard or a modified single axis foot. The modified foot allowed 12-15 degrees of dorsiflexion and reduced stiffness in the area of the metatarsal-phalangeal (MTP) joint. The amputees were allowed to vary the stiffness at the two joints to obtain what "felt best." The amputees agreed that in comparison to the standard single-axis foot, the modified foot: a) offered a more comfortable gait while walking on level ground; b) made walking up inclines easier; c) affected knee stability while walking on declines; and d) made foot placement on stairs and ladders more critical due to potential knee instability. As well as qualitative reactions, changes in the gait cycle were measured quantitatively for different speeds and inclinations of walking on a treadmill. Measurements from normal subjects matched by age and sex were used for control purposes. All participants wore soft-soled shoes. The amputees selected a stiffness that allowed a degree of dorsiflexion which precisely matched on average that of the normal subjects. In contrast, they selected a stiffness at the MTP joint which allowed very little flexion of the toes. Significant changes also occurred in the pattern of hip movements, so that they became much more symmetrical on the two sides, although substantial differences remained between the hip movements of the amputees and the normal subjects. If modifications in the ankle joint can be coupled with improvements in the knee joint to prevent potential instability, a much improved gait should be possible for above-knee amputees.