Os Subtibiale Displacement Secondary to Pronation-External Rotation Ankle Injury

Os subtibiale is a rare accessory ossicle of the ankle, not considered to be clinically significant. However, its presence in trauma patients may cause a misdiagnosis such as malleolar fracture and over-treatment. Because the ossicle is attached to the deltoid ligament, ankle trauma that causes a medial compartment injury may detach the os subtibiale from the medial malleolus. In these situations, magnetic resonance imaging may help to diagnose the deltoid injury, demonstrate the features of the ossicle, and guide the treatment process.