The symptomatic os subfibulare. Avulsion fracture of the fibula associated with recurrent instability of the ankle.

Four adults who had symptomatic instability of the ankle had an associated os subfibulare. Operative exploration revealed the ossicle to represent a non-union of an avulsion fracture of the anterior talofibular ligament. These findings suggest that an os subfibulare represents an avulsion fracture that may or may not be associated with laxity of the anterior talofibular ligament, rather than being a normal variant.