Incidence, location and classification of 371 third carpal bone fractures in 313 horses.

The medical records and radiographs of all horses with a third carpal bone fracture admitted to The Ohio State University Veterinary Hospital from 1979 to 1987 were reviewed. Three hundred and seventy-one fractures were found in 313 horses; 57 percent were Standardbreds, 41 per cent were Thoroughbreds, and only 1.6 per cent were Quarterhorses. All were young racehorses (average age = 3.1 years). Third carpal fractures occurred more frequently in the right limb (60 percent) than the left limb (40 percent); Thoroughbreds had a greater right-left disparity (67.5 percent R, 27.1 per cent L). Fractures were classified according to their size and anatomical location within the third carpal bone: incomplete fractures of the radial facet (type 1, N = 39), large proximal chip fractures of the radial facet (type 2, N = 140), small proximal chip fractures of the radial facet (type 3, N = 18), medial corner fractures (type 4, N = 13), frontal plane slab fractures of the radial facet (type 5, N = 93), large frontal plane slab fractures involving both the radial and intermediate facets (type 6, N = 35), fractures of the intermediate facet (type 7 N = 13), and sagittal slab fractures (type 8, N = 20). The incidence of each fracture type was significantly different between Standardbreds and Thoroughbreds. Type 1 and 2 fracture were more common in Standardbreds; type 5 and 6 fractures were more common in Thoroughbreds. Differences between these two breeds are related to the different gaits at which they race. The classification more accurately describes the extent of injury and the variation in fractures observed in this study than the traditional division as chips or slabs. A high quality skyline projection is important in correctly identifying these fractures; over 10 percent of the fractures were detected only on this view.