The Effects of Axial Preload and Dorsiflexion on the Tolerance of the Ankle/Subtalar Joint to Dynamic Inversion and Eversion 2002-22-0013

Forced inversion or eversion of the foot is considered a common mechanism of ankle injury in vehicle crashes. The objective of this study was to model empirically the injury tolerance of the human ankle/subtalar joint to dynamic inversion and eversion under three different loading conditions: neutral flexion with no axial preload, neutral flexion with 2 kN axial preload, and 30° of dorsiflexion with 2 kN axial preload. 44 tests were conducted on cadaveric lower limbs, with injury occurring in 30 specimens. Common injuries included malleolar fractures, osteochondral fractures of the talus, fractures of the lateral process of the talus, and collateral ligament tears, depending on the loading configuration. The time of injury was determined either by the peak ankle moment or by a sudden drop in ankle moment that was accompanied by a burst of acoustic emission. Characteristic moment-angle curves to injury were generated for each loading configuration. Neutrally flexed ankles with no applied axial preload sustained injury at 21 ± 5 Nm and 38° ± 8° in inversion, and 47 ± 21 Nm and 28° ± 4° in eversion. For ankles tested in neutral flexion with 2 kN of axial preload, inversion failure occurred at 77 ± 27 Nm and 40° ± 12°, and eversion failure occurred at 142 ± 100 Nm and 41° ± 14°. Ankles dorsiflexed 30° and axially preloaded to 2 kN sustained inversion injury at 62 ± 31 Nm and 33° ± 4°, and eversion injury at 140 ± 53 Nm and 40° ± 6°. Survival analyses were performed to generate injury risk curves in terms of joint moment and rotation angle.