Osteochondritis Dissecan

(Photo courtesy of Lanna Mills)

By Lauren Lamb

Osteochondrosis is a disease in which the cartilage and subchondral bone in the joints fail to develop normally. The cartilage and subchondral bone play a major role in keeping a joint healthy and preventing the development of osteoarthritis.

When a fragment of abnormal cartilage and subchondral bone become dislodged, the disease is renamed to osteochondritis dissecan. These free floating fragments can become lodged between two opposing articular surfaces within the joint. If the osteochondritis dissecan fragment gets lodged between articular surfaces, significant damage to the cartilage can occur along with severe lameness. For the purpose of this paper, Osteochondrosis and osteochondritis dissecan will be referred to as OCD.

OCDs are seen predominately in young horses less than two years of age. A lot of times the horse will have an OCD at the age of six months, but it is not diagnosed until the horse is put into training as a yearling or two-year-old. OCDs can be seen in all breeds of horses, but some breeds like Warmbloods and Standardbreds are more predisposed. The fetlocks, hocks and stifles are the most commonly affected joints; however, any joint can be affected. A horse with an OCD will frequently have bilateral joints affected, meaning both the left and right leg will be affected.

Despite extensive time and funds dedicated to research, the cause of OCDs has not been defined. This is largely due to the multiple variables and risk factors that can play a role in a horse developing an OCD. The risk factors for OCDs can be broken down into environmental and genetic. Genetic factors are thought to account for 25 to 50 percent of the disease risk. Some research has shown that large body size, which can also be linked to genetics, can be a risk factor for OCDs. Environmental factors that can increase the risk of OCDs include copper deficiency, high phosphorus intake relative to calcium intake and irregular/intense exercise.

The best way to reduce the risk of your horse developing an OCD is to make sure it is being fed a well-balanced diet with sufficient copper, low phosphorous and high calcium levels. Foals need to have daily exercise so the cartilage and subchondral bone in the joint can properly develop. They should be allowed free turnout exercise in a paddock with even footing. Forced exercise should be avoided for the first six to nine months of life. During the first few months of life, the cartilage and subchondral bone in a foal’s joints are developing. This, coincidentally, is also the time when most OCD lesions develop.

Despite taking all the precautions mentioned to eliminate the environmental risk factors, some foals will still develop OCDs secondary to genetic predisposition. With that being said, you can have full sibling offspring with one foal having OCDs and the other not having any OCDs. This just re-iterates the challenges faced by scientist as they attempt to fully understand the cause of OCDs.

Joint effusion, excess fluid in the joint, with an OCD is the most common clinical sign. Often, this joint effusion will be seen after the foal has been exercised or turned out. The effusion may go away with stall rest, but many times it does not. Rarely is a lameness noted, except in case with a loose fragment of cartilage and subchondral bone that gets stuck between articular surfaces. If a loose fragment gets stuck in an articular surface, the foal will usually display a severe lameness.

Read the August issue to learn more!