Instability of the ankle due to a separate centre of ossification in the lateral malleolus

A case of recurrent instability of the ankle is reported. It was associated with a separate centre of ossification in the lateral malleolus. While such extra ossification centres for both malleoli are recognized, they have not hitherto been incriminated as a cause of instability. The successful treatment of this case is described and the incidence and significance of separate ossification centres for the malleoli are discussed.