Mechanical stability of the subtalar joint after lateral ligament sectioning and ankle brace application: a biomechanical experimental study.

BACKGROUND: The roles of each ligament supporting the subtalar joint have not been clarified despite several biomechanical studies. The effects of ankle braces on subtalar instability have not been shown.

HYPOTHESIS: The ankle brace has a partial effect on restricting excessive motion of the subtalar joint.

STUDY DESIGN: Controlled laboratory study.

METHODS: Ten normal fresh-frozen cadaveric specimens were used. The angular motions of the talus were measured via a magnetic tracking system. The specimens were tested while inversion and eversion forces, as well as internal and external rotation torques, were applied. The calcaneofibular ligament, cervical ligament, and interosseous talocalcaneal ligament were sectioned sequentially, and the roles of each ligament, as well as the stabilizing effects of the ankle brace, were examined.

RESULTS: Complete sectioning of the ligaments increased the angle between the talus and calcaneus in the frontal plane to 51.7 degrees + or - 11.8 degrees compared with 35.7 degrees + or - 6.0 degrees in the intact state when inversion force was applied. There was a statistically significant difference in the angles between complete sectioning of the ligaments and after application of the brace (34.1 degrees + or - 7.3 degrees ) when inversion force was applied. On the other hand, significant differences in subtalar rotation were not found between complete sectioning of the ligaments and application of the brace when internal and external rotational torques were applied.

CONCLUSION: The ankle brace limited inversion of the subtalar joint, but it did not restrict motion after application of internal or external rotational torques.

CLINICAL RELEVANCE: In cases of severe ankle sprains involving the calcaneofibular ligament, cervical ligament, and interosseous talocalcaneal ligament injuries, application of an ankle brace might be less effective in limiting internal-external rotational instabilities than in cases of inversion instabilities in the subtalar joint. An improvement in the design of the brace is needed to restore better rotational stability in the subtalar joint.