The effect of immobilization devices on the load distribution under the foot.

The load distribution under the foot was investigated under various conditions by means of pressure-sensitive transducers. Weight-bearing pressures at the first and third metatarsal heads and at the heel were measured while subjects ambulated barefoot and while wearing numerous immobilization devices. The proportion of body weight imposed on the plantar surface of the foot is dependent on the specific gait pattern displayed during barefoot walking. Maximum reduction of forefoot loads was achieved by means of a short-leg walking cast or an ankle boot cast with a posteriorly placed flat rubber heel. A centrally placed rocker heel leads to increased forefoot loads, especially under the first metatarsal head. Casting devices used in conjunction with cast shoes were not as effective in pressure reduction as the same cast with a posteriorly placed heel, but they were more effective than the rocker heel. The height of the cast and configuration of the sole of the cast shoe had little effect on the observed patterns of force distribution. The wooden-soled post-operative shoe did decrease weight-bearing pressures as compared with barefoot walking and casts with a rocker heel but was less effective than the other devices studied. Peak loads measured at the sole of the foot were dependent on the position of the ankle and subtalar joints at the time of cast application.