WALKING PATTERN OF MIDFOOT AND ANKLE DISARTICULATION AMPUTEES

Measurements of the vertical component of ground reaction force (GRF) and dynamic center of pressure (COP) were recorded for five subjects w ith midfoot level amputations and six with Syme's ankle disarticulatio n amputations, All of the subjects underwent amputation surgery as a c onsequence of peripheral vascular disease and diabetes. GRF measuremen t was accomplished with the F-Scan system (Tekscan, Boston, MA). Each group exhibited a consistent, reproducible pattern of gait. Subjects w ith Syme's ankle disarticulation initiated initial loading response, i .e., heel strike, with a concentration of GRF in the center of the ana tomic heel. COP progressed along the midline to the center of the anat omic forefoot, where GRF was concentrated at push-off. Midfoot amputee s initiated loading at the lateral-posterior heel. COP progressed medi ally to the midline, where it progressed distally to the level of the distal residual limb (proximal metatarsal metaphyses). It then shifted medially under the base of the first metatarsal, where a small concen tration of GRF occurred at push-off, similar to the normal foot. These findings explain the decreased magnitude of propulsion seen in midfoo t level amputees and may explain the seemingly paradoxical increased m etabolic cost of walking observed in midfoot amputees as compared with Syme's ankle disarticulation amputees.