Anatomical considerations of irreducible medial subtalar dislocation.

Irreducible medial subtalar dislocation has been associated with the talar head "buttonholing" through the extensor digitorum brevis (EDB) muscle, entrapment of the talar head in the extensor retinaculum, talonavicular impaction, interpositioning of the EDB muscle between the talus and navicular, and buttonholing of the talar head through the talonavicular ligament and joint capsule. Cadaver analysis of the medial subtalar dislocation in this study supported entrapment of the talar head in the extensor retinaculum and talonavicular impaction as well as impingement of the deep peroneal nerve and associated dorsalis pedis arterial branches between the talus and navicular as causes of irreducible subtalar dislocation. In this study, the talar head was not noted to buttonhole through or entrap the EDB muscle. This is the first report of the deep peroneal nerve implicated as a possible cause of irreducible medial subtalar dislocation.