Separate centre of ossification of the lateral malleolus with instability of the ankle joint.

Four cases of recurrent instability of the ankle joint are reported. The instability was associated with a separate centre of ossification of the lateral malleolus and abnormal movement between the ossicle and the distal fibula. All patients were successfully treated by surgery: two underwent internal fixation and ligamentous reconstruction and two, ligamentous reconstruction after removal of the ossicle.