To compare the 3-dimensional (3D) orientation of the tibiotalar, tibiocalcaneal, and intertarsal joints in cadaveric specimens following structural weakening to predetermined ligaments in the peritalar region and medial ankle tendons under axial loads and simulated calcaneal valgus deformity.
Eight fresh-frozen, unembalmed human lower leg and foot specimens were placed in a materials testing machine. The mid-stance period of gait was simulated and the 3D orientation of the tibiotalar, tibiocalcaneal, and intertarsal joints was measured using an electromagnetic motion analysis system. Specimens were then axially loaded at 840 N for 5400 cycles with the calcaneus in its initial orientation and under simulated valgus conditions using a heel wedge following attenuation (multiple stab incisions) of selected ligaments (tibionavicular, anterior tibiotalar and tibiocalcaneal portions of the medial deltoid ligament, the inferior calcaneonavicular ligament, and the superomedial calcaneonavicular ligament) or tendons (tibialis posterior, flexor digitorum longus, and flexor hallucis longus). The joint orientation measurements were then repeated and compared with baseline intact measurements.
Pes planovalgus was observed in 6/8 specimens following testing. The tibiotalar, tibiocalcaneal, talonavicular, and calcaneocuboid joints were more dorsiflexed, everted, and externally rotated following either ligament or tendon compromise. The changes in orientation were small but showed consistent patterns with the smallest changes (typically < 1 degrees ) for the transverse plane and largest (up to 3.5 degrees ) for the frontal plane. The magnitude of change was similar for the tibiotalar and tibiocalcaneal joints, largest for the talonavicular joint, and smallest for the calcaneocuboid joint for both ligament and tendon compromise. The orientation of the talocalcaneal joint was more plantarflexed and everted relative to baseline, for both the ligament and tendon compromise with < 1 degrees of change in orientation about the transverse plane. Under simulated valgus heel conditions, joint orientation was further increased especially about the frontal plane in the direction of eversion. The smallest changes were noted for the calcaneocuboid joint (approximately 1 degrees ), similar change (approximately 2-3 degrees ) for the tibiotalar, tibiocalcaneal and talocalcaneal joints, and the largest changes (> 3 degrees ) for the talonavicular joint. There were no observed differences in the magnitude of change between ligament or tendon condition.
Selective attenuation to either the ligaments supporting the tibiotalar, talocalcaneal, and talonavicular joints or the medial ankle tendons followed by cyclic loading results in small but important changes in the orientation of the tarsal bones consistent with the development of pes planovalgus.