Fractures of the sesamoid bones of the thumb.

Stability of the thumb metacarpophalangeal joint is provided by the collateral ligament proper, the accessory collateral ligament, the proximal and distal palmar ligaments, and the palmar plate. The adductor pollicis and flexor pollicis brevis muscles also provide soft tissue support and insert on the proximal phalanx of the thumb by way of the sesamoid bones. Fractures of the metacarpophalangeal joint sesamoid bones are uncommon but are often associated with sporting injuries during which the joint is acutely hyperextended. Routine anteroposterior and lateral radiographs may be unremarkable, and oblique views are often necessary to document the fracture. We report eight cases of fracture of the thumb metacarpophalangeal joint sesamoid. Seven were isolated sesamoid fractures, and one was associated with a metacarpophalangeal joint dislocation. None of the fractures were evident on anteroposterior radiographs, but all were seen in the oblique projection. Six fractures were treated with splint or cast immobilization for 2 to 3 weeks, and two were taped. Clinical followup of the seven patients with isolated sesamoid fracture at 6 to 8 weeks revealed pain-free normal function. One patient could not be reached for followup.