Study Links Bone Loss to Proximal Sesamoid Bone Fractures in California Racehorses

A recent study by Sarah Shaffer, International Equine Veterinarian Hall of Fame member Dr. Susan Stover and colleagues at the J.D. Wheat Veterinary Orthopedic Research Laboratory at the UC Davis School of Veterinary Medicine sought to characterize bone abnormalities that precede proximal sesamoid bone (PSB) fractures and determine if pre-existing abnormalities are associated with these fractures. The group retrospectively studied cases from California Thoroughbred racehorses that died from PSB fractures, and controls that died for other reasons, according to a press release issued by UC Davis School of Veterinary Medicine.

The most common fatal injury in racehorses in the United States, PSB fractures account for 45-50% of such injuries in Thoroughbreds, and 37-40% in racing Quarter Horses. The PSBs are two comparatively small bones located in the fetlock that act as part of the suspensory apparatus. Fractures in these bones are likely due to the accumulation of repeated, stress-related processes. This is supported by evidence that racehorses in intensive training are at higher risk for PSB fractures, but the exact causes are not well understood.

Other repetitive overuse injuries in horses are known to be bilateral in nature. With this in mind, the study looked at both the fractured PSB and the intact PSB from the opposing limb of the same horse for all…