Because ankle inversion trauma can result in persistent isolated subtalar joint instability and can contribute to chronic lateral ankle instability, optimization of subtalar joint ligament injury diagnosis and treatment is essential.

12 fresh-frozen cadaver lower extremities were used. The cradle was a component of a gimbal system that allowed unrestricted inversion/eversion and anterior-posterior and medial-lateral translation of the subtalar joint. The bearing system to which the tibia/fibula were attached allowed unconstrained internal/external rotation and superior-inferior translation. 4N-m inversion/ eversion and internal/external rotational moments and translational forces of 67N were applied. All measurements were performed sequentially in neutral, 10° dorsiflexion and 20° plantarflexion, and were repeated as the cervical, calcaneofibular, and interosseous ligaments were consecutively sectioned in all possible different orders.

In neutral position, inversion increased after sectioning of the cervical (3.7°), interosseous (0.8°), and calcaneofibular (1.9°) ligaments individually. Combined sectioning of all three ligaments showed an increase in inversion of 8.3°, 8.5° and 1.4° in the neutral, plantarflexed, and dorsiflexed positions, respectively, compared to the intact ankle. External rotation also increased in neutral position after sectioning the cervical ligament (2.0°). Combined sectioning of all ligaments showed an increase in external rotation of 3.6° and 5.4° for neutral and dorsiflexion, respectively.

This is the first comprehensive biomechanical cadaver study of the contributions of the cervical, calcaneofibular, and interosseous ligaments to stabilization of the subtalar joint. The surgeon may refer to the findings in both diagnosing and planning treatment of problematic subtalar joint instability