Intra-Articular Osteochondral Chip Fragments of the Carpus
These are the most common fractures in the carpal joints of racehorses. They occur less commonly in working Quarter horses and sport horses. The primary etiologic factor is trauma, usually associated with fast exercise. Chips may occur on the dorsal aspect of all the carpal bones. In the middle carpal joint, the most frequent site is the distal radial carpal bone, followed by the distal intermediate carpal bone and the proximal third carpal bone. In the antebrachiocarpal joint, the most common location is the proximal intermediate carpal bone, followed by the proximal radial carpal bone, distal medial radius, and the distal lateral radius. The diagnosis is based on clinical signs of synovitis and capsulitis and radiographic demonstration of osteochondral chip fragments. Arthroscopic surgery is the treatment of choice. The overall prognosis is excellent, but the percentage chance of the horse returning to previous performance levels decreases with chronicity and consequent excessive loss of articular cartilage and subchondral bone.
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 fragment of the radial facet of the third carpal bone, followed by fractures of the intermediate facet and both facets of this bone. When a frontal slab fracture of the third carpal bone occurs without joint collapse, it is considered to be “routine.” The treatment is lag screw fixation (done arthroscopically), and many of these horses return to full athletic activity.
Collapsing slab fractures also occur in the carpal bones. The fracture typically involves the third carpal bone, but there is displacement and comminution to the extent that one row of carpal bones tends to collapse. If untreated, the leg progresses to a carpal varus conformation and laminitis develops in the opposite forelimb. Collapsing slab fractures require internal fixation, augmented with cast fixation for up to 6 wk, to minimize later collapse of the joint. Some cases require carpal arthrodesis.
Accessory Carpal Bone Fractures
These are less common than other fractures in the carpus. Lameness generally is seen, and there may be synovial effusion in the carpal canal. Radiographs confirm the diagnosis. These fractures are treated conservatively. Bony union will occur in some cases. Fibrous union may enable a horse to return to athletic activity.
Last full review/revision March 2012 by Stephen B. Adams, DVM, MS, DACVS; Joerg A. Auer, DrMedVet, Dr h c, MS, DACVS, DECVS; James K. Belknap, DVM, PhD, DACVS; Jane C. Boswell, MA, VetMB, CertVA, CertES (Orth), DECVS, MRCVS; Peter Clegg, MA, Vet MB, PhD, CertEO, DECVS, MRCVS; Andrew L. Crawford, BVetMed, CertES (Orth), MRCVS; Jean-Marie Denoix, DVM, PhD, Agregé; Marcus J. Head, BVetMed, MRCVS; C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, DACVS; James Schumacher, DVM, MS, DACVS, MRCVS; John Schumacher, DVM, MS, DACVS, MRCVS; Roger K. W. Smith, MA, VetMB, PhD, DEO, DECVS, MRCVS; Chris Whitton, BVSc, FACVSc, PhD