SIMULATED LATERAL ANKLE LIGAMENTOUS INJURY - CHANGE IN ANKLE STABILITY

The effect of simulated ankle ligamentous injury on ankle-subtalar joi nt complex laxity was studied. Thirty-six intact ankles were loaded in inversion-eversion and anterior-posterior directions. Motions of the talus and calcaneus were measured with respect to the tibia. Ankles we re tested at neutral, 15 degrees of dorsiflexion, and 15 degrees of pl antar flexion. In all the specimens the anterior talofibular ligament was sectioned and then the calcaneofibular ligament was sectioned; tes ting was then repeated. With sectioning of the anterior talofibular li gament, motion increased primarily in dorsiflexion with both anterior- posterior and inversion-eversion loading. This increase was primarily caused by a large increase in subtalar motion. Additional sectioning o f the calcaneofibular ligament produced little change in ankle subtala r joint motion except in dorsiflexion. Clinically, these findings show that if an anterior-posterior drawer test shows less laxity in dorsif lexion than in neutral and greater laxity than the contralateral asymp tomatic side, then an isolated anterior talofibular ligamentous tear e xists, Similarly, laxity in 15 degrees of dorsiflexion and in neutral suggests calcaneofibular ligament disruption. During inversion-eversio n loading, the increase in ankle-subtalar joint complex rotation with calcaneofibular ligament sectioning occurred primarily in the ankle jo int, implying that the calcaneofibular ligament constrains the talus t hrough the calcaneus. Therefore, a talar tilt on stress radiographs de monstrates a torn calcaneofibular ligament.