OCD Continues To Perplex Researchers And Veterinarians

Although the causes of this condition are not fully understood, medical advances have led to better diagnosis and treatment.

For young horses with bright futures, the best bloodlines, training and attitude are nothing without good legs. Strong legs. Sound legs. A concert of bones, muscles, tendons and joints growing together in rehearsal for real work.

And inside these legs, which even on full-grown horses are no bigger in diameter than a nightclub bouncer’s biceps, any number of problems can arise before a horse enters serious training and strains a tendon on the cross-country field or stumbles in the dressage arena.

Osteochondritis dissecans, a developmental orthopedic disease better known as OCD, is a condition that has perplexed veterinarians for years, not because they can’t or don’t treat it, but because they can’t figure out why exactly it occurs and how exactly it could be prevented.

OCD is an interruption of the normal bone development process. Instead of soft cartilage degenerating and forming bone around joints as the horse grows, horses afflicted with OCD develop lesions. On X-rays, these lesions look like a dent, pit or unevenness in the cartilage or on the underlying bone. When this area of cartilage dies, it dissects itself from the main body in what looks like a flap, signifying OCD.

Those who work with older horses may not witness the development of OCD—if a horse is going to contract it, it will happen before the age of 2—but the aftermath of lameness can last a lifetime. In May, the disorder was the sole subject of a third international symposium in Sweden, where researchers and surgeons discussed questions about OCD that still lack comprehensive answers, such as why some horses essentially “grow out” of lesions while in others they develop into full-blown OCD and then require surgery.

“OCD is a huge problem in sport horses,” said Wayne McIlwraith, a veterinarian from New Zealand who is one of the leading researchers on equine joints and other leg issues. He’s also the director of the Orthopedic Research Center at Colorado State University.

McIlwraith said many people confuse OCD with the similar-sounding osteochondrosis, which relates to all problems of cartilage and bone development. Osteochon-drosis is simply the pathological condition that can lead to osteochondritis dissecans.

OCD is thought to develop after birth during bone development. It can affect any joint, and sometimes it affects the same joint in the opposite leg as well (both hocks, both stifles, etc.).

A Disruption In Natural Growth

In a normal maturation process, McIlwraith explained, joints develop from cartilage, and the bone grows in the center. But in horses with OCD, some of that cartilage that should have turned into bone fails to degenerate and instead stays thick as cartilage. This can cause the cartilage cells to be cut off from the blood supply and hence, from nutrients.

Now weak, the area of cartilage is susceptible to cracks or lesions. If these lesions progress to the point that they die and become flaps hanging off the cartilage or bone, debris from under the flap can float into the joint capsule. In severe cases, the entire flap can detach.