Accessory ossification patterns and injuries of the malleoli.

An accessory, distal focus of epiphyseal ossification may develop in either malleolus. These foci are not anatomically separate entities, even though they appear to be radiographically. They usually are asymptomatic. However, they may be injured, either acutely or chronically. The diagnosis of such injury by conventional radiography is limited. Bone scintigraphy may be positive if there is a stress fracture. The fracture pattern, a type 7 growth mechanism injury, extends through a segment of the malleolus. An ossicle may also be avulsed as a ligament failure analogue, similar to a sleeve fracture of the patella. This is more common in the lateral than in the medial malleolus. These avulsions, if not adequately diagnosed and treated, may progress to delayed union, nonunion, or a chronically painful ankle.