External rotation views in the diagnosis of posterior colliculus fracture of the medial malleolus.

A 25-year-old white man sustained a fracture dislocation of the right ankle with a displaced fracture of the lateral malleolus while playing basketball. He also sustained a fracture of the medial aspect of the distal tibia, in addition to an apparent deltoid ligament injury. The patient underwent open reduction and internal fixation of the lateral malleolus and insertion of a syndesmotic screw. Intraoperatively, external rotation radiographs of the ankle were obtained to determine the origin of the fracture of the medial side of the ankle joint. The radiographs clearly showed a minimally displaced fracture of the posterior colliculus. Posterior colliculus fracture can be occult. This fracture may not be clearly visible on plain antero-posterior or mortise-view radiographs and external rotation is necessary for its diagnosis. This fracture is usually minimally displaced and can be satisfactorily treated conservatively. The patient's leg was placed in a short-leg cast for 6 weeks. Follow-up radiographs revealed healing of the fracture.