Horse Care – Joints in Jeopardy

A closer look at osteochondritis dissecans

story by Hope Ellis-Ashburn

While the presence of osteochondritis dissecans (OCD) can be off-putting, successful treatment of this fairly common condition is just as commonly achieved and has no negative effect on a horse’s future performance. Liz Elzer, VMD, DACVS-LA, a surgeon with Rood & Riddle Equine Hospital in Saratoga Springs, N.Y., explains how top veterinarians deal with the condition in racehorses.

Osteochondritis Dissecans Defined

Dr. Elzer describes osteochondritis dissecans as a failure of normal bone formation at very specific spots on the joints. Today, the condition is more commonly known as osteochondrosis.

“We’ve come to understand that it is a broader disease process than was originally thought,” Dr. Elzer said of the new nomenclature.

“The normal process by which bone, cartilage and joints are formed is called endochondral ossification, which is a specific way that bones grow at their ends. When something in that process is interrupted, an OCD is formed,” Dr. Elzer explained.

There are various theories as to what this interruption might be, including an interruption to the blood supply or possibly trauma. Regardless, that piece of bone does not ossify normally, from the cartilage precursor, which results in an island of abnormal bone in a joint rather than the bone being contiguous and strong along the entire weight-bearing surface, Dr. Elzer said.

Some OCDs can be innocuous, but others almost always require treatment. Those requiring treatment are usually those where cartilage in the weight-bearing portion of the joint is affected or a piece of bone becomes loose in the joint, requiring removal. Many diagnostic methods exist, but Dr. Elzer said that typically an OCD is found upon x-ray of a joint with clinical signs of the disease, such as a joint with fluid distension sometimes accompanied by lameness. OCDs usually become clinically evident in weanlings and yearlings.

No Single Cause

Dr. Elzer explained that the most important thing to understand about OCD is that it can be caused by any number of factors. There are likely some genetic components, but nutrition, exercise and rapid growth also play roles.

“There is some evidence that there is a breed predilection, which suggests a genetic basis, but it’s not the entire story,” she said.

Nutritional mineral imbalances, especially with copper, along with diets containing an overload of energy or calories are known to contribute to OCD. Evidence suggests that rapid growth may also be brought on during times of the year when grass is particularly rich.

Finally, the mineral composition of soil affects the nutritional value of the pasture grass and hay raised on it. Too much of or not enough minerals such as calcium, selenium, zinc and phosphorus can contribute to the formation of an OCD.

Dr. Elzer advises working with your veterinarian or an equine nutritionist to help determine the best diet for your young horses. County extension agents can help with soil testing to ensure that the forage-based portion of your horses’ diet satisfies their nutritional needs.

While these recommendations always apply, they are especially important if your farm is experiencing a higher incidence of OCD than normal. Appropriate nutrition at the appropriate time is key.

In exercise, just as with nutrition, balance is essential.

“Bone requires stimulation to form normally,” Dr. Elzer explained. “You want young growing bones to have the stimulation of normal exercise, but you certainly don’t want an excessive amount at a young age.”

Just as with too much exercise, you can also have not enough.

Unless the horses have an issue with their limbs, Dr. Elzer advises that normal turnout for them provides an appropriate amount of exercise. Trauma can occur from excessive running during turnout, but being out on pasture is a far better option than being confined to a stall.

Treatment

An OCD that presents clinically from weanling to around six months of age will typically be monitored.

“Some of those heal [on their own] and some don’t,” Dr. Elzer said.

Injections, either intramuscularly or directly into the joint, of polysulfated glycosaminoglycans or hyaluronic acid in conjunction with rest and a re-evaluation of the horse’s diet is one approach that, depending upon the severity of the condition, may be taken. Interleukin-1 Receptor Antagonist Protein (IRAP®) and stem cell therapies are still other treatment options.

However, Dr. Elzer advises that if a joint is symptomatic enough to need injections, it is probably wise to remove the OCD. Normally, any OCD determined to be detrimental to long-term soundness is removed, she said.

“The most common time to remove an OCD is when a horse is a yearling. We’ve waited until the OCD has fully declared itself and we know that it’s probably not going to heal,” she said. The OCD is removed via an arthroscopic procedure before the horse goes to work, as leaving it in place could potentially damage the joint.

An untreated OCD that is shedding bony debris into the joint can eventually lead to degenerative joint disease. However, it is a judgment call whether to surgically remove an asymptomatic OCD that is unlikely to cause unsoundness.

Some small OCDs that do not show clinical signs may never affect the horse and can often be left alone. Nonetheless, many breeders opt to remove these too for horses intended for sale so that there can be no question as to their significance.

If surgical treatment is deemed necessary, it should be performed promptly. Dr. Elzer advises that treatment of a symptomatic yearling is very different than of a 3- or 4-year-old horse as, by this age, the joint has likely begun to form arthritis.

Outcomes

Successful treatment depends entirely on the size of the OCD, where it is, and whether it is located on a non-critical part of the joint. Common sites for the development of an OCD are the fetlock, hock and stifle, with specific predilection sites in each of these joints.

“There are some locations on the joint that are more forgiving than others,” Dr. Elzer explained. “You can have a relatively large OCD that can be removed and, as long as it’s not shedding debris into the joint anymore, it will be just fine.”

But she says there are other places where horses can have OCDs that are located on important weight-bearing surfaces of the joint which can be very detrimental to soundness. “Surgery, for example, on the femoral condyle in the stifle can be a challenging place to get a good outcome,” she said.

However, all is not lost on horses that do not achieve the desired outcome.

“Being a racehorse is probably the most strenuous, athletic pursuit that any of these horses would be doing,” Dr. Elzer said. “There are certain situations where we have a horse that we think might not quite be able to be a racehorse, but could be a riding horse or some type of sport horse.”

How the development of an OCD affects a horse can be extremely variable and range from virtually harmless to career-limiting. However, once removed, many OCDs have no effect whatsoever on the horse’s long-term soundness or career opportunities.

Full Disclosure

Because the condition is fairly common, Dr. Elzer explained that in Thoroughbreds it is very customary for any yearling going through a sale to have a full set of radiographs taken. These radiographs are then available for viewing in a repository accessible to anyone. But she says that Standardbreds may not be x-rayed until after they are sold, which sometimes means a slightly later diagnosis and removal.

While certainly a consideration, treatment for—or even the removal of—an OCD is not always reflective of a horse’s future success. HB

Hope Ellis-Ashburn is a freelance writer living in Tennessee. To comment on this story, email us at readerforum@ustrotting.com.