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.