A retrospective study of radial fractures in racehorses in California, 2006-2022.

Radial fractures are relatively uncommon (0-1%) injuries in postmortem studies of racehorses, and few cases have been published. We describe here a series of 42 cases of radial fractures observed in California racehorses. Autopsy findings from all racehorses submitted for postmortem examination between 2006 July 1 and 2022 June 30 that had a recorded radial fracture were evaluated. We included 42 horses (30 Thoroughbreds, 12 Quarter Horses), most of which were 3-5-y-old. Catastrophic radial fracture was observed in 30 (71%) horses; in the remaining 12 (29%) horses, the fracture of the radius was considered an incidental finding. All of the catastrophic radial fractures were complete, displaced, and comminuted; 70% were articular and 30% were non-articular; 61% were open and 39% were closed; 83% were diaphyseal to distal epiphyseal and 17% were proximal epiphyseal. Nine of the 30 horses with catastrophic fracture had a preexisting periosteal callus associated with the main line of fracture. Among Quarter Horse racehorses, the frequency of callus in radial fractures tended to be higher (p = 0.083) in 3-y-olds compared with other ages. In 6 of these 9 cases, the callus was located along the cranial aspect of the distal third of the diaphysis. All incidental cases consisted of osteochondral fragmentations, which occurred most frequently on the cranial border of the intermediate facet of the distal articular surface of the radius. Knowledge of the common sites of stress fractures or osteochondral stress remodeling in the radius can help to focus autopsies and to improve the characterization and interpretation of those lesions.