Walking pattern of midfoot and ankle disarticulation amputees.

Measurements of the vertical component of ground reaction force (ORF) and dynamic center of pressure (COP) were recorded for five subjects with midfoot level amputations and six with Syme's ankle disarticulation amputations. All of the subjects underwent amputation surgery as a consequence of peripheral vascular disease and diabetes. GRF measurement was accomplished with the F-Scan system (Tekscan, Boston, MA). Each group exhibited a consistent, reproducible pattern of gait. Subjects with Syme's ankle disarticulation initiated initial loading response, i.e., heel strike, with a concentration of GRF in the center of the anatomic heel. COP progressed along the midline to the center of the anatomic forefoot, where GRF was concentrated at push-off. Midfoot amputees initiated loading at the lateral-posterior heel. COP progressed medially 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 concentration of GRF occurred at push-off, similar to the normal foot. These findings explain the decreased magnitude of propulsion seen in midfoot level amputees and may explain the seemingly paradoxical increased metabolic cost of walking observed in midfoot amputees as compared with Syme's ankle disarticulation amputees.