DYNAMIC SUPPORT OF THE HUMAN LONGITUDINAL ARCH - A BIOMECHANICAL EVALUATION

This study was designed to evaluate the dynamic support provided to th e human longitudinal arch by the leg muscles active in the stance phas e of gait and by the plantar aponeurosis. Ten fresh adult cadaveric sp ecimens were mounted in a materials testing machine. The tendons of th e posterior tibialis, flexor digitorum longus, flexor hallucis longus, peroneus longus, peroneus brevis, and Achilles tendon were attached t o force transducers. Plantar loads of 0, 350 and 700 N were applied, a nd the tendons were tensioned individually. The Achilles tendon was te nsioned an amount equal to the plantar load; the posterior tibialis, f lexor digitorum longus, flexor hallucis tongus, peroneus longus, and p eroneus brevis were tensioned a fractional amount (depending on the pr oportion of the cross-sectional area to the gastrocsoleus complex). Th e angular relationships between the first metatarsal, navicular, and t alus were recorded using a 3-dimensional movement analysis system. An additional series of measurements was obtained by positioning the ankl e plantarflexed 10 degrees under a plantar load of 350 N. Dorsiflexing the toes with the ankle in and 700 N permitted an evaluation of the e ffect of the plantar aponeurosis. The plantar aponeurosis, via dorsifl exion of the toes, contributed the most significant arch support in th e sagittal plane with a 3.6 degrees between the first metatarsal and t alus at 350 N and a 2.3 degrees increase at 700 N. The posterior tibia lis tendon consistently provided arch support at plantar loads of 350 N acid 700 N. The peroneus longus consistently abducted the forefoot i n the transverse plane at 350-N and 700-N load levels. The study provi des further insight into the dynamic supporting and deforming forces o f the longitudinal arch.