A Review of Fatal Fetlock Injuries in California Racehorses

When a racehorse breaks down on the track, you're not only faced with the devastating loss of a horse, but also economic loss and, potentially, an injured jockey. One of the most common sites of catastrophic injuries in Thoroughbred racehorses is the fetlock and its surrounding structures.

To try to prevent more of these injuries from happening, four veterinarians involved with the California Horse Racing Board and University of California (UC), Davis, Racing Injury Prevention Program recently studied past breakdowns and their causes. Erin McKerney, DVM, a veterinarian at the UC Davis J.D. Wheat Veterinary Orthopedic Research Laboratory, presented the team's findings at the 2013 American Association of Equine Practitioners' convention, held Dec. 7-11 in Nashville, Tenn.

"Fetlock injuries comprise over half of fatal musculoskeletal injuries among California racehorses," McKerney said. "Repetitive loading and fetlock hyperextension associated with training and racing subject fetlock-supporting musculoskeletal structures to degenerative and adaptive changes. These changes can weaken key structures, thus predisposing the fetlock region to catastrophic fracture."

This is fairly common knowledge among sport- and racehorse practitioners. The problem is pinpointing which pre-existing lesions put these horses as most risk for breakdown and how to detect them before the worst happens.

In their retrospective study, McKerney and her team analyzed post-mortem examination records of 358 California racehorses (Thoroughbreds, Quarter Horses, and one Arabian) that sustained catastrophic injuries between July 2011 and July 2013. Of these, she said 185 (52%) incurred fatal fetlock injuries. The team then categorized the 185 cases according to injury site, fracture configuration, and pre-existing lesions and compared horses' age, breed, gender, limb injured, and the track surface the animals raced on.

"Proximal sesamoid bone (PSB) fracture was the most common cause of fetlock injury, followed by cannon bone (MC3) fracture, soft tissue injury, and long pastern bone (P1) fracture," McKerney said. "Eighty-eight percent of fetlock injuries included visible evidence of a pre-existing lesion, with visibly discrete lesions observed in 65% of fractured PSBs. The most common lesion was subchondral bone discoloration and porosity at the abaxial (outward facing) aspect of the medial (inner) PSB."

She said the identification of this pre-existing lesion in the bone beneath the joint surface is a new finding that, with further investigation, could lead to ways to detect affected horses before catastrophic fetlock injury occurs.

McKerney listed other findings of note, including:

  • Horses older than 5 years were more likely to sustain soft tissue injuries;
  • Most fatal fetlock injuries, particularly sesamoid and cannon bone fractures, had evidence of pre-existing lesions;
  • Both sesamoid bones in the fetlock are usually fractured;
  • Cannon bone fractures most commonly affected the lateral (outside) condyle;
  • Rupture of the ligaments that connect the sesamoid bones to the pastern was the most common soft tissue injury;
  • Sesamoid bone fracture was also the most common Quarter Horse injury; 
  • Ligament injuries were more common in Thoroughbreds than Quarter Horses;
  • Fetlock injuries usually occurred in the front limbs;
  • Injuries did not differ among track surfaces; and
  • Most pastern bone fractures occurred during training while most soft tissue injuries occurred during racing.

In conclusion, McKerney said, veterinarians and researchers can use these observations about fracture configuration and pre-existing lesions associated with fetlock breakdown injuries to identify patterns that could help them detect and prevent more breakdowns from happening.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.