Discover how a young horse with persistently puffy hocks but no lameness was diagnosed with and treated for a medial malleolus lesion to set him on the course for a sound, productive life

As a retired professor of equine surgery at Kansas State University College of Veterinary Medicine, Elizabeth Santschi, DVM, Dipl. ACVS, has seen thousands of young horses with osteochondritis dissecans (OCD). The common and typically temporary condition is characterized by loose cartilage and/or bone fragments in the joint.

Osteochondritis dissecans is more likely to occur in the hock than in other joints. The most common locations are the distal intermediate (lower central) ridge of the tibia (the long bone that stretches from stifle to hock), the lateral (outer) trochlear ridge of the talus (the largest bone in the hock joint), the medial malleolus (the bony protrusion at the top and inside of the hock), and the medial trochlear ridge of the talus (TheHorse.com/154331). It is less common to find OCDs in the stifle and fetlock. While OCDs can develop in all breeds, they’re most prevalent in Warmbloods, Thoroughbreds, and Standardbreds.

“We can argue that these breeds are the most frequently radiographed horses,” says Santschi. “That might be why we see it in those breeds more than others. There may be a genetic component but no gene associated with OCDs. My opinion is that while high-protein feed and rapid growth may contribute to OCDs, they are not the primary cause of the joint disease.”

In some young horses the lesions resolve themselves, but most cases require surgery to reduce the risk of lameness or arthritis later in life. Lameness and joint effusion (fluid swelling) are typical indicators of many types of OCD—in particular lesions in the tarsocrural (the biggest hock joint, at the distal end of the tibia and the trochlear of the talus, where all movement occurs) joint. However, that is not always the case.

Santschi uses the case of a 6-month-old Warmblood to highlight this point. The colt presented with an effusion on the left hock but no soreness. The client restricted the colt’s paddock size, cold-hosed the joint, and administered a short course of phenylbutazone (Bute) orally for three days. When the swelling didn’t go down, the client scheduled a veterinary examination.

“The horse had no pain on palpation, and no lameness was detected,” says Santschi. “His temperature, pulse, and respiration was normal. Looking at how puffy it was, radiographs of both hocks were ­recommended.”

The radiograph of the left hock revealed a normal distal intermediate ridge of the tibia, a small area of irregularity at the distal end of the lateral trochlear ridge, and loose cartilage on the axial aspect of the medial malleolus (the flat groove of the tibia). Radiographs of the right hock were within normal limits, she says.

Again, medial malleolar OCD is a less common manifestation of hock OCD than lesions on the distal intermediate ridge of the tibia. It can also be difficult to diagnose because the lesions are small and sometimes subtle. Occasionally, vets only stumble across these lesions during exploratory arthroscopy (inserting an arthroscope into a small incision to view a joint)