The motion responses of thirty fresh-frozen cadaver tibiotalar joints were measured for applied anterior-posterior force, inversion-eversion moment, and internal-external rotary torque. The load-motion response curves obtained after sectioning the anterior talofibular ligament were compared with those for intact specimens in three positions of flexion of the ankle. Laxity of the intact ankle was shown to be dependent on flexion position;​ dorsiflexion was consistently the position of least laxity, reflecting the effects of talar geometry and its articulation with the tibiotalar syndesmosis. Section of the anterior talofibular ligament produced significant increases in laxity for all modes tested. Total anterior-posterior laxity increased by 4.3 millimeters in dorsiflexion, which was the position of maximum change. In contrast, the greatest increases in total inversion-eversion laxity (5.2 degrees) and total internal-external rotation laxity (10.8 degrees) were recorded in plantar flexion.

Clinical Relevance:​ Our measurements demonstrate the importance of the anterior talofibular ligament as a primary stabilizer of the ankle. The greatest increases in laxity after sectioning the anterior talofibular ligament were recorded for ankle positions and loads that correspond to common modes of injury. Contrary to prior studies, we have shown that the antenor talofibular ligament provides significant resistance to varus tilt of the talus in all positions of flexion. Because the increased motions of the talus after sectioning the anterior talofibular ligament are relatively small, many ankles that are chronically symptomatic following ankle injury may have increased talar instability secondary to insufficiency of the anterior talofibular ligament which is undetectable by clinical or radiographic evaluation.