A Retrospective Study of Catastrophic Pelvic Fractures in California Thoroughbred Racehorses.

Here, we describe and characterize catastrophic pelvic fractures in Thoroughbred racehorses in California. We reviewed retrospectively racehorse autopsy reports from horses that died spontaneously or were euthanized because of complete pelvic fractures in California between 1992 and 2018. The exercise history of affected horses was compared with eventmatched control horses. Catastrophic pelvic fractures were sustained by 133 horses. Pelvic fractures were 2.7% of all musculoskeletal fatalities. Pelvic fractures occurred during training (48.0%), racing (35.0%), and non-exercise (17.0%). Horses ≤4-y-old were affected most frequently (73.5%); horses ≥5-y-old were affected less frequently (26.5%). Fractures were more common in females (68.1%) than in geldings (23.1%) and intact males (8.8%). Bilateral fracture occurred in 46.9% of horses. The ilium was fractured alone or with other pelvic bones in 90.3% of horses; 28.4% of these cases included bilateral iliac wing fractures. Preexisting periosteal calluses associated with the catastrophic fracture line were observed in 31.9% of horses with pelvic fractures. Calluses were frequently associated with ilial fractures (88.9%). Of horses with complete pelvic fracture, 25.7% died spontaneously, and 89.6% of those deaths were a consequence of massive internal bleeding from lacerated blood vessels. The horses with pelvic fractures had fewer races (spaced farther apart), exercised less intensely throughout their career, and had more lay-ups than control horses. They also had 31% less exercise time and 40% fewer events since the last lay-up than control horses. Factors associated with these events, such as preexisting injuries, should be identified to enable recommendations for diagnosis, treatment, and prevention of catastrophic pelvic fractures.