Midtarsal joint locking: new perspectives on an old paradigm.

We investigated the existence of a midtarsal joint locking mechanism using cadaveric simulations of normal gait. Previous descriptions of this phenomenon led us to hypothesize that non-coupled rotations of the calcaneocuboid and talonavicular (i.e., midtarsal) joints and cubonavicular and talocalcaneal joints occur at heel strike and during weight acceptance, after which joint rotations cease with all bone-to-bone orientations remaining constant during the latter portions of stance phase. Three-dimensional kinematics of the talus, calcaneus, cuboid, and navicular were recorded along with muscle and ground reaction forces. Finite helical axis parameters and joint angles of directly articulating bones were subsequently derived and examined. During weight acceptance, the midtarsal joints everted with obvious changes in the relative orientation of their helical axes. The relative non-parallel orientation of these axes then remained constant until late in stance when these joints inverted and dorsiflexed toward their original pre-stance orientation. The cubonavicular and talocalcaneal joints demonstrated complimentary behavior. Contrary to our hypothesis, the midtarsal joints remained compliant during foot flat and even more so during push-off, despite divergent joint axes. Joint rotations were present after weight acceptance, thereby challenging the concept that midtarsal joint locking produces a rigid lever during push-off.