Contributions of active and passive toe flexion to forefoot loading

Toe flexion during terminal stance has an active component contributed by t he muscles that flex the toes and a passive component contributed by the pl antar fascia. This study examined the relative importance of these two mech anisms in maintaining proper force sharing between the toes and forefoot. T hirteen nonpaired cadaver feet were tested in a dynamic gait stimulator, wh ich reproduces the kinematics and kinetics of the foot, ankle, and tibia by applying physiologic muscle forces and proximal tibial kinematics. The dis tribution of plantar pressure beneath the foot was measured at the terminal stance phase of gait under normal extrinsic muscle activity with an intact plantar fascia, in the absence of extrinsic toe flexor activity (no flexor hallucis longus or flexor digitorum longus) with an intact plantar fascia, and after complete fasciotomy with normal extrinsic toe flexor activity. I n the absence of the toe flexor muscles or after plantar fasciotomy the con tact area decreased beneath the toes and contact force shifted from the toe s to the metatarsal heads. In addition, pressure distribution beneath the m etatarsal heads after fasciotomy shifted laterally and posteriorly, indicat ing that the plantar fascia enables more efficient force transmission throu gh the high gear axis during locomotion. The plantar fascia enables the toe s to provide plantar-directed force and bear high loads during push-off.