Further to our previous article on repository radiographs, we will discuss the common causes of lameness seen in yearlings and 2 years old over the next few weeks. The causes of lameness can be generally divided into developmental and degenerative conditions.

Developmental causes of lameness are largely Osteochondrosis (OCD) and Cystic lesions, which develop during the early stages of a horse's life. Osteochondrosis is a condition where the normal development of bone and cartilage does not occur and loose flaps of this tissue forms at the front or "gliding" aspect of the joint. These tend to occur at predetermined sites in the joint and at certain ages. For instance, most OCD lesions of the fetlock are formed by 5 months of age, whereas most OCD lesions of the stifle do not become evident until at least 6 months of age and can actually heal up to 12 months of age.

Osteochondrosis is a common condition in horses with an incidence of about 5 % in the hock. Thankfully it is a condition that can be readily treated with a good prognosis for soundness in most horses. The common presenting sign for OCD include swelling of the affect joint and mild-moderate lameness. Treatment usually involves arthroscopic removal of the flaps of cartilage and bone with the size and location of the flaps determining the prognosis. With the introduction of repository radiographs most horses that are offered for sale have had the OCD lesions that can be seen on these images removed, and the likelihood of this condition causing a problem after a yearling has been purchased is now less likely. Although a veterinarian viewing repository radiographs at sale may advise you that a horse has had surgery for OCD and they will inform you of the prognosis.

Cystic lesions form in a similar way to OCD but they occur at different locations in the joint. They occur at the weight bearing surface of the joint and for this reason the prognosis for soundness is not as good. There are common sites for cystic lesions, with the fetlock and stifle being the most common. Horses with cystic lesions usually present with moderate lameness and treatment is not as easy as removal of these lesions. In recent times we have been debriding these lesions and then packing them with concentrated bone marrow, which contains large number of stems cells, a bone replacement and a glue to hold all this material together. The interim results for this technique are very promising.

This is an intra-operative image of a hock OCD lesion. The lesion is composed of three pieces which are pointed to by the arrows.

This image shows the area after removal of the lesion. A curette can be seen in the joint.