Study Examines Osteoarthritis Formation after Fetlock Injury

A recent study carried out by a team of equine orthopedic researchers at the University of Guelph Comparative Orthopedic Research Laboratory took a closer look at post-traumatic osteoarthritis in horses. Specifically, the team evaluated whether or not single impact injury to the fetlock could progress to post-traumatic osteoarthritis or osteochondral disease in horses.

According to previous research, the fetlock is the site of more traumatic and degenerative lesions on racehorses than any other joint. In fact, another study published by the same group indicated as many as 70% of 2- and 3-year-old racehorses could suffer from some form of osteoarthritis. The effects of osteoarthritis on articular cartilage have been studied more extensively than its effects on the subchondral bone (which is located under the bone surface within a joint), and the study's authors wanted to learn more about the disease mechanism there.

Study authors Antonio Cruz, DVM, MVM, MSc, DrMedVet, Dipl. ACVS, ECVS, said the bone and cartilage structure can be thought of as a mattress and box spring.

"This is a study to investigate the mechanism of disease pertaining post-traumatic osteoarthritis," he explained. "Is it a disease that originates initially from damage to cartilage or from damage to bone or from simultaneous damage to both? How do they relate? Is the mattress (cartilage) damaged first or the spring box (bone underneath)? This is important for horse's health because our primary focus in dealing with osteoarthritis has been the cartilage and may be we need to think more about the bone."

Using 12 horses, the researchers created a typical impact lesion on the back of the fetlock, toward the inside of the leg (an area called the medial metacarpal condyle), in one randomly chosen leg on each animal; the opposite limb served as a control. The team then implemented a low to moderate intensity exercise routine for the horses.

Horses underwent regular lameness examinations and radiographs were taken at both the beginning and end of the study. Horses were euthanized at one (three horses), four (four horses), and eight to 10 (five horses) months after the start of the study and evaluated closely at necropsy.

At the study's conclusion, the team found that there was a wide variety in the extent and depth of the lesions in the horses' medial metacarpal condyles. The mild to moderate lameness the animals had experienced since the initial injury gradually reduced over the course of about two months, but the damage to their cartilage and, eventually bone, did not improve.

The team also found that the impact of the initial injury did not result in generalized osteoarthritis in the joint during the course of the study, but they could not rule out the possibility that a return to high-impact exercise could result in a spread beyond the original injury site.

When it comes to reducing the incidence of osteoarthritis, Cruz said there are a variety of factors for owners to consider: "Proper genetic stock, conformation, adequate conditioning, competition schedule, warming up and cool down, shoes and trimming, nutrition, riding; in one word, horsemanship."

The study, "Evaluation of experimental impact injury for inducing post-traumatic osteoarthritis in the metacarpophalangeal joints of horses," appeared in October in the American Journal of Veterinary Research. The abstract is available online.


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