The joints of the evolving foot. Part II. The intrinsic joints.

A description is given of the functional morphology of the intrinsic joints of the foot, with particular reference to the primates, and an attempt is made to define the key human derived features. In the human subtalar joint the compromise axis has become reoriented into a very elevated position and more nearly in line with the functional foot axis than it is in subhuman primates. This provides for torque of the talus, and so the supported body weight, about the axis, during the stance phase of gait. In the subhuman primates the very oblique subtalar axis is important in inverting the foot into a grasping attitude. In subhuman primates the transverse tarsal joint complex plays an important role in supination of the forefoot, which complements inversion at the subtalar joint complex in achieving the ideal grasping position. This movement is only rendered possible by a helical action at the subtalar joint complex. In man the calcaneocuboid joint has been remodelled so as to bring the lamina pedis into a close-packed position during the latter part of the stance phase of gait. The joints between the cuneiforms and the cuboids, and the associated tarsometatarsal joints show significant modifications in man.