Posterior instability of the talus: an anatomic evaluation.

A cadaver study was conducted to evaluate the role of the posterior tibial margin or posterior malleolus, as well as medial and lateral supporting structures, in providing posterior stability for the talus. Posterior malleolar fractures consisting of approximately 30%, 40%, and 50% of the articular margin on the lateral radiograph were created in specimens that were then subjected to posterior stressing. No posterior talar subluxation was noted in any specimen. Repeat stressing following removal of the medial malleolus again revealed no subluxation in any specimen. The lateral supporting structures, primarily the posterior fibulotalar and fibulocalcaneal ligaments, appeared to be the key structures providing posterior talar stability. If the fibula is stable in an anatomic position, feared posterior instability of the talus would not appear to be an indication for internal fixation of posterior malleolar fractures.