A large bone fragment posterior to talus following medial subtalar dislocation.

To cite: Guler F, Ozyurek S, Turan A, et al. BMJ Case Rep Published online: [please include Day Month Year] doi:10.1136/bcr-2013009262 DESCRIPTION A 24-year-old man admitted to the emergency department due to an ankle sprain during a football game. In clinical examination, the ankle was grossly deformed and medially rotated. The head of the talus was palpable through the overlying skin. Anteroposterior ankle radiograph showed medial subtalar dislocation (figure 1). Under procedural sedation, subtalar dislocation was successfully reduced with traction and pronation of the foot, while the knee was kept in flexion. Postreduction ankle radiographs and multiplanar CT examination were performed. There was a large bone fragment posterior to the talus which is clearly seen in both lateral ankle x-ray (figure 2), sagittal and axial CT images (figure 3). These findings were consistent with the diagnosis of Os trigonum. Plaster cast and symptomatic drug treatment decreased the patient’s complaints significantly. The os trigonum is one of the largest and most common accessory ossicles in the ankle and foot region, located posterior to the lateral tubercle of posterior process of talus, with an estimated prevalence of 1–25%. Fractures of posterior process of talus are rare injuries which result from either direct impingement from the posterior tibial plafond on the