Osteochondral fractures (carpal chip fractures) of the carpal bones are a common cause of lameness in racehorses. The primary etiologic factor is trauma, usually associated with fast exercise. Chips typically occur on the dorsal aspect of the joint. In the middle carpal joint, the most frequent sites are the distal radial carpal bone, proximal third carpal bone, and the distal intermediate carpal bone. In the radiocarpal joint, the most common locations are the proximal intermediate carpal bone, distal lateral radius, proximal radial carpal bone, and the distal medial radius. Diagnosis is based on clinical signs of synovitis and capsulitis and radiographic demonstration of osteochondral chip fragment(s). Arthroscopic surgery is the treatment of choice. The overall prognosis is highly dependent on the degree of articular cartilage damage within the joint identified on arthroscopy.
Carpal Slab Fractures
Slab fractures extend from one articular surface to another articular surface. In the carpus, slab fractures occur in both frontal and sagittal planes. The most common fracture is a frontal slab fracture of the radial facet of the third carpal bone, followed by fractures of the intermediate facet and both facets of this bone. The treatment of choice is lag screw fixation for fractures >10 mm or removal of the fracture fragments if they are thin or not amenable to lag screw fixation.
Accessory Carpal Bone Fractures
These are less common than other fractures in the carpus. Lameness is typically acute and severe, and there may be synovial effusion in the carpal sheath and, less commonly, the radiocarpal joint. Radiographs confirm the diagnosis. These fractures are typically treated conservatively; however, if the fracture is articular and fragmented, surgical removal of the fragments has been performed. Fibrous union may enable a horse to return to athletic activity.