F ractures of the carpal bones have been extensively documented in racehorses and predominantly involve osteochondral chip and slab fractures of the dorsal surfaces of these bones. Fractures of the distal aspect of the radius and of the radial, intermediate, and third carpal bones are the most common and are thought to be related to chronic cyclic loading and superimposed acute compressive forces. 1-4 Progressive subchondral bone sclerosis induced by repetitive trauma predisposes to fracture of these bones. The inflammatory response that follows results in synovi- tis and capsulitis and, if left untreated, osteoarthritis and recalcitrant lameness. Comminuted or crush frac- tures of the carpal bones, with subsequent severe lameness and instability of the carpal joint, have also been documented. 5 Fracture of the accessory carpal bone is an uncommon, although well-recognized, fracture that is reported to occur predominantly as a result of a fall during racing over fences. 6-8 Both hyperextension (bowstring effect) and compression between the radius and third carpal bone (nutcracker effect) have been proposed as possible etiologic mechanisms. Fractures of the palmar surfaces of the carpal bones, however, are rarely described in the literature. 9 A single case report 10 describes fragment removal in a horse with a fracture of the palmar aspect of the inter- mediate carpal bone, and little other information is available on the pathogenesis of these fractures or on the clinical and radiographic signs in and outcome of affected horses. The purpose of the study reported here, therefore, was to determine clinical and radio- graphic findings, treatment, and outcome of horses with fractures of the palmar aspect of the radial carpal bone, with or without concurrent fractures of the pal- mar surfaces of the other carpal bones. Criteria for Selection of Cases Medical records of horses with forelimb lameness and subsequent radiographic evidence of a fracture of the palmar aspect of the carpal bones examined between 1984 and 2000 at the Cornell University Veterinary Medical Teaching Hospital, the Edisto Equine Clinic, or the Rochester Equine Veterinary Clinic were reviewed. Horses that had radiographic evidence of crushed carpal bones and carpal collapse were excluded. Procedures Medical record analysis—Signalment, history, clinical findings, results of diagnostic testing (includ- ing lameness examination, diagnostic intra-articular anesthesia, and radiography), surgical and necropsy findings, treatment, and outcome were obtained from medical records. Follow-up information was gathered from referring veterinarians and owners by means of a detailed questionnaire and telephone interviews. Nonsurgical treatment—Treatment for horses that did not undergo surgical removal of fracture fragments consisted of stall rest and, in some instances, applica- tion of a cast or bandage to the injured limb. Some horses also received injections of hyaluronan into the antebrachiocarpal joint or IM injections of polysulfat- ed glycosaminoglycan (PSGAG). Physiotherapy, con- sisting of passive flexion of the carpal joint, was also performed in some horses. JAVMA, Vol 219, No. 6, September 15, 2001 Scientific Reports: Retrospective Study 801 EQUINE Fractures of the palmar aspect of the carpal bones in horses: 10 cases (1984–2000) Markus Wilke, Dr med vet; Alan J. Nixon, BVSc, MS, DACVS; John Malark, DVM, DACVS; Grant Myhre, DVM Objective—To determine clinical and radiographic findings, treatment, and outcome of horses with frac- tures of the palmar aspect of the radial carpal bone, with or without concurrent fractures of the palmar surfaces of the other carpal bones. Design—Retrospective study. Animals—10 horses. Procedure—Medical records were reviewed to obtain information on history, signalment, clinical and radiographic findings, treatment, and outcome. Follow-up information was gathered from owners and referring veterinarians. Results—7 horses became lame after recovery from general anesthesia for treatment of an unrelated problem. The remaining 3 horses developed a fore- limb lameness after falling (1 horse) or being turned out in a pasture (2 horses). Fractures involved the pal- mar surface of the radial carpal bone in all 10 horses; in addition, the ulnar carpal bone was affected in 2 horses, the intermediate carpal bone in 2 horses, and the distal aspect of the radius in 4 horses. None of the 4 horses treated nonsurgically returned to work, and 3 were euthanatized because of recalcitrant lameness. In the other 6 horses, fragments were removed surgically. Two were euthanatized because of continued lameness, 1 was euthanatized for other reasons, 2 were sound enough for light work, and 1 returned to athletic work. Conclusions and Clinical Relevance—Results sug- gest that fractures of the palmar aspect of the carpal bones are uncommon in horses. The prognosis appears to be poor for affected horses but may be better for horses that undergo arthroscopic removal of intra-articular fragments. (J Am Vet Med Assoc 2001;219:801–804) From the Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853 (Wilke, Nixon); the Edisto Equine Clinic, 7796 White Point Rd, Yonges Island, SC 29449 (Malark); and the Rochester Equine Veterinary Clinic, 10 Rod Rd, Rochester, NH 03867 (Myhre). Address correspondence to Dr. Nixon.