Separated ossicles of the lateral malleolus.

Sixty ankles of 59 patients with symptomatic ossicles of the lateral malleolus were studied. All patients underwent clinical and radiographic examinations. Stress arthrography was performed on 58, arthroscopy on 48, operative treatment on 52, and histologic examination on 23. The ossicles were classified into 3 sizes (small, medium, and large) and 2 levels (A and B) by location. The relationship between the ossicle and fibular tip was classified into 3 grades according to arthrography results (Grade 1, little inflow [< 1 mm] of the contrast medium; Grade 2, an apparent space [1-2 mm]; Grade 3, a large gap [> 2 mm]) and to operative and arthroscopic findings (Type A, a fibrous union; Type B, a partial continuity; Type C, a lax thin scar tissue; Type D, no continuity). There were significant differences in talar tilt angles on stress radiography between the 3 grades. Chronic symptoms had a tendency to increase from Grade 1 to Grade 3 and from Type A to Type C or D, with instability occurring more than pain. The size and level did not correlate with instability. Acute or chronic inversion forces may act on the connection between the ossicle and fibular tip, and damage to this structure may cause symptoms.