Subtalar instability: a biomechanical cadaver study.

HYPOTHESIS: Subtalar instability is thought to be one of the possible causes for chronic functional instability of the foot and ankle. The purpose of this study was to determine the extent of ligament injury that is followed by subtalar instability and to depict consecutive pathologic joint motion.
METHODS: Twelve fresh human cadaver lower legs were investigated with respect to pathologic motion and mobility of the subtalar joint in a modified spinal column simulator after arthrodesis of the talocrural articulation and selective sectioning of the lateral ligaments of the subtalar joint. In order to simulate several injury mechanisms, ligaments were dissected starting anteriorly in group one (n = 6) and posteriorly in group two (n = 6).
RESULTS: Dissection of the bifurcate ligament in group one resulted in a significant increase in plantar- and dorsiflexion, dissection of the inferior extensor retinaculum resulted in a significant increase in eversion and inversion. Additional dissection of the lateral talocalcaneal ligament resulted in a significant increase in internal and external rotation. Dissection of the calcaneofibular ligament in group two was followed by significant kinematic changes regarding all degrees of motion in the subtalar joint.
CONCLUSIONS: The calcaneofibular ligament plays a key role in lateral stabilisation of the subtalar joint. Therefore, ligaments of the subtalar joint should be included in surgical repair.