Fracture of the os trigonum: A report of two cases and review of the literature.

We report two cases of acute fractures of the os trigonum. The os trigonum fracture related to the first case was sustained following a hyper-plantar flexion injury during a game of soccer. The second case involved a patient who fell from height and also sustained open fractures of the left distal tibia and lateral malleolus as well as the right calcaneus. In both cases, a preliminary diagnosis of a posterior talar process fracture was made from the initial radiographs of the ankle. The correct diagnosis of an os trigonum fracture rather than a fracture of the posterior talar process was only made following further assessment with CT imaging. Given that the course of treatment is largely determined by imaging findings, CT for further imaging evaluation should be performed in cases of suspected acute bony injuries of the posterior ankle, particularly when the limitations of using radiographs for the assessment of such injuries are expected to be encountered.