A horse’s fetlock is the crossroads of its mechanical universe on each limb. A hinge joint must operate smoothly back and forth, and a system of tendons and ligaments must operate that hinge from the muscles above; some even continue past the joint to affect the mechanics of the pastern and coffin joints.

But in the horse moving at speed, it is the fetlock joint–or the bones that create it–that often fail. Nowhere is this seen more graphically, or more tragically, that on the racetrack. Fetlock injuries accounted for more than half the catastrophic injuries to California racehorses, according to a 2013 study reported at the American Association of Equine Practitioners.

This winter, racing authorities in New York compiled statistics of Thoroughbred racing fatalities in that state. A review of the New York State Gaming Commission – Cornell University postmortem examinations over the last three years revealed that nearly half of the horses (45 percent) that died while racing experienced fatal musculoskeletal injuries of the fetlock joint.

This high prevalence of injury to a specific joint motivated the publication of advice to Thoroughbred trainers on the possible prevention of fetlock injuries. As it happens, this advice is pertinent to all athletic horses in training. Moreover, since so many former racehorses are transitioning to new careers in sport or as pleasure horses, it’s important to understand the stress that these horses’ joints have been under, and what possible pre-existing injuries may have affected them.

• Step 1: Be vigilant. The fetlock joints of all horses under your care should be examined and flexed on a regular basis. Horses should be jogged on a hard macadam surface before going out to breeze. Horses with lameness in both front or hind legs often don’t have an obvious head nod or hip hike; they may just appear uncomfortable or have a shortened stride. Horses exhibiting these characteristics should not be breezed. If heat, pain or swelling in the fetlock joint is noticed, a veterinarian should perform a lameness examination.
• Step 2: Obtain an accurate diagnosis. Lameness is a symptom, not a disease. Treating lameness with brief periods of rest and anti-inflammatory therapy (NSAIDs and/or corticosteroid injections) but without an actual diagnosis may not solve the underlying problem. Symptomatic therapy may reduce or eliminate the lameness in some cases. However, in other cases, such as pathologic changes that develop within the cannon and proximal sesamoid bones, the lameness simply returns when training resumes. Training horses with recurrent lameness can lead to fatal musculoskeletal injuries.
• Step 3. Use diagnostic imaging. Radiograph the fetlock joints of horses with persistent joint inflammation, particularly those with decreased range of motion. Pathologic changes in the cannon bone and in the proximal sesamoid bones occur over time, are progressive, and may require adjustment of the training schedule. If radiographs are normal and lameness persists, use advanced imaging (scintigraphy, CT or MRI) to determine the cause. Conduct ultrasound examination on suspensory ligaments if they are enlarged or tender to the touch. Failure of the suspensory apparatus can also result in catastrophic fetlock breakdown injuries.
• Step 4: Treat the underlying condition. Follow the instructions provided by veterinarians and don’t resume training until a follow-up examination indicates that the underlying cause of lameness has resolved.

The importance of fetlock injury prevention is underscored by countless studies in the United States and Great Britain, and including both flat racing and jump racing horses. In addition, a California study of fatal injuries in racing Quarter horses from 1990 to 2007 revealed that the most common fatal musculoskeletal injuries were metacarpophalangeal and metatarsophalangeal joint (fetlock) support injuries (40%).

In Oklahoma in 2013, the highest musculo-skeletal site of injury in fatalities of all racing breeds was tied, attributed to either the knee or the fetlock, each with 33 percent of injuries.

Injuries to sport horses, on the other hand, tend to be classified simply as that, rather than as a cause of death, so a larger set of injuries shows up in the few studies that actually count the structures injured by sport. It is also difficult to compare sport horses to racehorses since racehorses tend to be younger and are all of the same breed, whereas sport horses may range in age by ten or more years between subjects, and be of almost any breed or combination of breeds. Thoroughbreds, however, are making inroads in sport as second-career sport horses after their racing careers are overs.

A 2006 study led by Rachel Murray at the Animal Health Trust in England classified injuries by specific soft tissues, such as the suspensory ligament, pelvis, or coffin joint. 

Murray found that elite show jumpers, event horses and dressage horses most frequently injured their suspensory ligaments. Elite show jumpers also injured distal portions of their deep digital flexor tendons; non-elite show jumpers had a second place injury category of the navicular bone or navicular ligaments.

In dressage horses, both elite and non-elite horses in Murray’s study group were likely to injury their hind suspensories. Elite dressage horses were further at risk for injury to their hocks, while non-elite dressage horses might more likely injure their navicular bones or navicular ligaments.

With combined training for eventing, both elite and non-elite horses likewise tended to injure their suspensories, followed by the navicular bone or navicular ligaments, but the elite horses injured a third structure–the superficial digital flexor tendon–six times more frequently than nonelite horses did. 

The hock was the site of the most frequent injury in endurance horses.

Racehorses are certainly easier to study and the fact that their injuries are usually recorded in databases allows researchers to compile numbers that associate injuries with different racetracks or surfaces, as well as the types of injuries, when racehorses suffer a catastrophic injury. 

In spite of all we hear about career-ending injuries in horses, the facts about what the ill-fated horses had in common is rarely discussed, and even injuries to currently racing horses are often not accurately or completely described. Making the threat of injury real in the minds of trainers and caregivers is an important mental precursor to taking steps to preventing a similar problem in a horse.

Fetlock injuries often occur when the joint extends beyond its normal range of motion (hyperextension). Understanding how the horse loads its limb and what the effect of the racetrack surface are are critical to protecting the fetlock and insuring its proper function, just as are early intervention in injury to the fetlock, evaluating the health of the joint’s surfaces and the cartilage’s repair rate.

Without four healthy and functional fetlocks, a horse moving at speed may be risking its life. In addition, a horse that isn’t fully functional on all four legs might exhibit behavior or balance changes that increase other risks, no matter what sport it performs. 

To read more:

McKerney, E., E. Collar, and S. M. Stover. “Fatal musculoskeletal injuries of the metacarpophalangeal and metatarsophalangeal (fetlock) joints in California racehorses: one hundred thirty-nine cases.” Proceedings of the 59th Annual Convention of the American Association of Equine Practitioners, Nashville, Tennessee, USA, 7-11 December 2013. American Association of Equine Practitioners (AAEP), 2013.

Sarrafian, Tiffany L., et al. “Fatal musculoskeletal injuries of Quarter Horse racehorses: 314 cases (1990–2007).” Journal of the American Veterinary Medical Association 241.7 (2012): 935-942.

Murray, R. C., et al. “Association of type of sport and performance level with anatomical site of orthopaedic injury diagnosis.” EQUINE VETERINARY JOURNAL-SUPPLEMENT- 36 (2006): 411.