In the neutral position, the anterior talofibular ligament can check posterior movement of the leg on the tarsus and external rotation of the leg on the tarsus because it is directed forward and medially. With the foot in plantar flexion, the anterior talofibular ligament becomes more vertically oriented and is in a position to check inversion of the talus in the mortise. This ligament is the most commonly injured of the ligaments of the ankle, the mechanism of injury usually being a combined plantar flexion–inversion strain.