Fracture of the os trigonum: a case report.

The os trigonum is an inconsistently present accessory bone of the foot situated at the posterolateral aspect of the talus. It may be radiographically confused with fractures of the posterior process of the talus. Fracture of the os trigonum per se is extremely rare. Hyperplantarflexion of the ankle is the mechanism of injury in which the os trigonum is compressed between the posterior malleolus of the tibia and the tuber calcaneus. Computed tomography is the choice of imaging modality in cases where fractures of posterior talus structures, including the os trigonum, are suspected. A high index of suspicion is necessary to diagnose a fracture of the os trigonum after a severe plantarflexion injury to the ankle. Conservative treatment is usually successful. We report a case of a fracture of the os trigonum, its clinical features, treatment and significance.