Torsion-transmitting properties of the hind foot

The torsion-transmitting capacity of the hind foot was studied experimentally in ten cadaver specimens. An average of 0.44 degrees of outward rotation of the tibia occurred for every degree of supination of the foot. The relationship was linear. There was less transmission of torsion during dorsal extension than during plantar flexion of the ankle. The joint complex of the hind foot somewhat resembles a universal joint except that the distal fork of the universal joint changes its configuration through its range of motion. This distal fork, consisting of the calcaneus, the cuboid, and the navicular, together with the central piece, the talus, constitutes a three-arm link system, which explains the configurational change. The process of balance when standing on one leg and when walking on uneven surfaces, when the torsion-transmitting effect plays a central role, can be controlled as rotations in the hip joint. This torsion-transmitting model helps to elucidate the trauma mechanisms of various ankle fractures. It also may explain why anterior knee pain due to malalignment can be relieved with supinating foot supports.