Osteochondrosis Dissecans (OCD)
OCD is an abbreviation for "Osteochondrosis Dissecans". It is one of the 5 primary manifestations of developmental orthopaedic disease (DOD).
Osteochondrosis Dissecans occurs as a result of a defect in the process of endochondral ossification. Endochondral ossification is a process through which bone grows during the developmental stage of life. On the ends of the bones, there exist a layer of cartilage. As the bone grows, the cartilage layer provides a "scaffolding" or "meshwork" into which osteoblasts (bone cells) can attach themselves. As the bone cells are laid down on the cartilage matrix, the cartilage eventually develops into bone. This process is called endochondral ossification, or mineralization of cartilage. Meanwhile, a new layer of cartilage is forming on the newly-formed end of the bone. And the process continues until the bones have reach their predetermined length.
For a variety of reasons, some of which are known and some of which are unknown, there may occur a defect in the process of endochondral ossification. This especially occurs in bones that are growing very rapidly. The faster the bone grows, the more "finely tuned" this process must be in order for normal ossification of the cartilage to occur.
In some cases, the cartilage matrix does not completely ossify before the new layer of cartilage is formed overtop. What is left is something in-between cartilage and bone that resides underneath the new layer of cartilage. This cartilage-bone substance is not as strong as normal subchondral bone, and usually results in a visible defect or incongruency within the layer of cartilage that overlays the site. In some cases, a piece of abnormal subchondral bone and cartilage can break or "dissect" off of the end of the bone, resulting in an osteochondral (bone + cartilage) chip fragment. This type of fragment is known as osteochondrosis dissecans or "OCD".
The presence of an osteochondritic lesion within the joint can result in incongruency of the articular surface of the joint, which in turn results in joint instability. Unstable joints become inflamed (causing synovitis or arthritis). As you know, a common consequence of joint inflammation is swelling, pain and lameness.
Some OCD lesions are more intimidating then others in regard to prognosis for future performance.
Prognosis will depend on primarily three things:
1) The joint involved. The higher-motion and higher-weightbearing the nature of the joint the more significant a cartilage defect becomes.
2) The location of the lesion within the joint. Some areas of the joint are not highly-articulating (i.e. they are not in direct contact with another bone) or are not directly involved in bearing weight. These areas of the joint are not considered to be as important as those which articulate and/or accommodate weightbearing stress. For example, there may be an osteochondral defect "off to the side" which doesn't interfere with normal motion or weightbearing of the joint. It is unlikely that this type of lesion would have a large impact on joint stability. Therefore a horse with this type of OCD carries a better prognosis than a horse with a lesion directly involved with joint motion and/or weightbearing.
3) The size of the lesion. The larger the lesion (i.e. the larger the defect), the greater the amount of incongruency along the articular (joint) surface. Increased articular incongruency translates into increased joint instability. Increased instability would predispose the horse to more severe arthritis and lameness.
Since osteochondrosis is a developmental disease, clinical signs usually manifest by the age of 2-3 years in the horse. Classic symptoms include joint swelling and/or lameness in the absence of any injury.
Diagnosis is easliy confirmed via the use of diagnostic imaging (such as radiography or ultrasonography).
Treatment generally warrants surgical intervention in the form of diagnostic/ surgical arthroscopy. OCD fragments are removed through a comparably-sized incision into the joint and the underlying defect(s) are debrided and cleaned.
To learn more about ARTHROSCOPIC SURGERY for the treatment of osteochondrosis dissecans in the horse, please click HERE.
Occasionally, conservative arthrotherapy is elected in cases of OCD. Click the icon below to learn more about these strategies of joint treatment in the horse.
Stifle OCD in the Young Horse
Veterinarians commonly diagnose OCD in aclinical (i.e. sound) weanlings during Thoroughbred yearling sales. Once the lesion(s) have been discovered, many horse owners pursue surgical intervention with the intention of addressing the pathology before clinical signs manifest (a process known as preemptive surgery).
Recent research suggests that preemptive surgery for stifle OCD may not always be the best therapeutic strategy. Arthroscopic removal of OCD fragmentation is not an innocuous procedure, and there is evidence that the fragments can reattach during the first 12 months of age.
Juvenile Thoroughbreds undergoing surgery for OCD lesions of the stifle had significantly decreased performance as racehorses compared to control horses.
A recent study followed 37 juvenile Thoroughbreds with stifle OCD, 35 juveniles with hock OCD, and a cohort of age- and sex-matched controls with no evidence of OCD (Russell, et.al.).
Juveniles with stifle OCD that underwent surgery had significantly lower total earnings, fewer total starts and fewer first place finishes compared to control horses. Russell and colleagues concluded that juvenile Thoroughbreds undergoing surgery for OCD lesions of the stifle had significantly decreased performance as racehorses. They therefore recommend that delaying surgery might benefit some of these animals.
It is for this reason that The Atlanta Equine Clinic recommends waiting until horses are at least 12-18 months of age before considering arthroscopic removal of osteochondritic lesions within stifle joints not exhibiting signs of arthritis or pain. Exercise restriction and serial imaging of the lesions is implemented during the first year of the animal's life.