Simulated Lateral Ankle Ligamentous Injury

The effect of simulated ankle ligamentous injury on ankle-subtalar joint 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 were tested at neutral, 15° of dorsiflexion, and 15° of plantar flexion. In all the specimens the anterior talofibular ligament was sectioned and then the calca neofibular ligament was sectioned; testing was then re peated. With sectioning of the anterior talofibular liga ment, 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 of the calca neofibular ligament produced little change in ankle sub talar joint motion except in dorsiflexion. Clinically, these findings show that if an anterior-posterior drawer test shows less laxity in dorsiflexion than in neutral and greater laxity than the contralateral asymptomatic side, then an isolated anterior talofibular ligamentous tear ex ists. Similarly, laxity in 15° of dorsiflexion and in neutral suggests calcaneofibular ligament disruption. During inversion-eversion loading, the increase in ankle- subtalar joint complex rotation with calcaneofibular liga ment sectioning occurred primarily in the ankle joint, implying that the calcaneofibular ligament constrains the talus through the calcaneus. Therefore, a talar tilt on stress radiographs demonstrates a torn calcaneofibular ligament.