Distal metacarpal sequestration in a bison.

A 2-year-old 400-kg female American bison was admitted for evaluation and treatment of an open fracture of the right metacarpal bones 3 and 4. Radiography revealed osteolysis of the distal metaphysis and epiphysis, with extensive bony callus formation along the dorsoproximal and proximomedial aspects extending distally to the proximomedial aspect of the proximal phalanx. Evidence of periosteal or bony proliferation at the fracture site or along the distal segment of the third and fourth metacarpal bones was not visible, suggesting that the distal fracture fragment was becoming a sequestrum. Treatment consisted of soft tissue debridement and placement of the limb in a full-limb cast. The cast was changed every 4 weeks until the sequestrum was removed and the bone healed. It is rare for the distal half of a long bone to sequester following fracture. Additionally, it is remarkable that the sequestrum served as a buttress, which prevented collapse of the bone until the sequestrum was replaced by functional bony callus.