We measured strain in the lateral ligaments of 10 human cadaver ankles while moving the ankle joint and apply ing stress in a variety of ways. We studied the anterior talofibular, calcaneofibular, posterior talofibular, ante rior tibiofibular, and posterior tibiofibular ligaments. Strain measurements in the ligaments were recorded continuously while the ankle was moved from dorsiflex ion into plantar flexion. We then repeated measure ments while applying inversion, eversion, internal rota tion, and external rotation forces.

Strain in the anterior talofibular ligament increased when the ankle was moved into greater degrees of plantar flexion, internal rotation, and inversion. Strain in the calcaneofibular ligament increased as the talus was dorsiflexed and inverted. These findings support the concept that the anterior talofibular and calcaneofibular ligaments function together at all positions of ankle flexion to provide lateral ankle stability. We measured maximum strain in the posterior talofibular ligament when the ankle was dorsiflexed and externally rotated. The strain in the anterior and posterior tibiofibular liga ments increased when the ankle was dorsiflexed. Ex ternal rotation increased strain in the anterior tibiofibular ligament and decreased strain in the posterior tibiofib ular ligament.

Based upon strain measurements in the lateral ankle ligaments in various ankle joint positions, we believe the anterior talofibular ligament is most likely to tear if the ankle is inverted in plantar flexion and internally rotated. Theoretically, the calcaneofibular ligament tears primarily in inversion if the ankle is dorsiflexed;​ the anterior tibiofibular ligament tears in dorsiflexion, especially if combined with external rotation;​ and the posterior tibiofibular ligament tears with extreme dor siflexion.