Abstract

Os trigonum as one of the most common accessory ossicles of foot,  may have a fibrocartilaginous articulation with posterior process of talus. This  articulation may be misdiagnosed as a fracture of the posterior  process of talus. Despite well known chronic injuries of athletes, acute fracture of the os trigonum is rare. Hyperplantarflexion and invertion of the ankle is the mechanism of injury. We report a case of an acute fracture of the os trigonum with a fibrocartilaginous articulation diagnosed with computerized tomography which highlights the importance of considering such injuries in patients with acute posterior ankle pain and ‘nut cracker’ sign positivity and obtaining advanced imaging modalities in ankle sprains.

Key words: Os trigonum, talus, fracture, ankle sprain, accessory ossicle, foot.