Slab fractures of the fourth and intermediate carpal bones in five horses.

Fractures of the fourth carpal bone were diagnosed in 5 horses; 3 fractures were associated with fracture of the intermediate carpal bone. The diagnosis was delayed in all 5 horses, apparently because of the moderate nature of the clinical signs. Open surgical reduction with lag screw type fixation was used in all horses. Because of delayed treatment, transfixation of carpal bones (necessary for stability), and surgical trauma, degenerative joint disease with osteophyte formation occurred in all 5 horses. None of the 5 horses was able to begin or return successfully to work, although 4 of the 5 were pasture/breeding sound. One horse was euthanatized after being allowed free exercise too early. A mechanical hypothesis is presented for the pathogenesis of these fractures.