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).

Making a Treatment Plan

For this case Santschi prescribed her go-to treatment for a medial malleolus lesion with effusion but no pain: reducing the horse’s exercise, monitoring the hock for increased effusion, and following up with radiographs in two months.

At the next visit the effusion was unchanged, and radiographs revealed a 4-by-2-millimeter lucency (an area that appears less “white” than the surrounding structures, indicating decreased bone density) on the inside of the medial malleolus of the tibia, with a small bone fragment about the size of a pencil tip (2-3 millimeters) within the lucency. Santschi recommended surgery due to the persisting puffiness and diminishing likelihood the lesion would heal ­spontaneously.

During the arthroscopic surgery she removed the fragment on the medial malleolus and debrided the soft bone in the area to remove damaged tissue and allow for healing.

The goal with this procedure is to remove the bone fragments and weakened bone tissue to reduce effusion and support cartilage health. Persistent effusion degrades the cartilage, making it more susceptible to damage from normal forces. Surgery for OCDs is minimally invasive and low risk, but medial malleolar surgery can be challenging due to the hock’s anatomy.

Postop Recovery

Because this colt experienced no side effects during or after surgery, he was sent home after 24 hours of postoperative monitoring by Santschi’s team at the university’s medical center with instructions to remain on stall rest. The sutures were removed 10 to 14 days later.

“I didn’t inject the tarsocrural joint at this point, due to my experiences with hock joint flares at suture removal,” says Santschi. “However, many veterinarians would inject hyaluronic acid or orthobiologics such as IRAP (interleukin-1 receptor antagonist protein) or PRP (platelet-rich plasma) for inflammation control.”

For the first month she recommended the horse be confined to a small paddock with turnout restrictions lifted two months post-surgery. At 60 days she injected the tarsocrural joint with IRAP. Because a small amount of effusion persisted after the injection, the colt was confined to a stall for three days and then allowed regular turnout.

Orthobiologics such as PRP, IRAP, and α-2 macroglobulin are substances vets can create by harvesting the horse’s own blood and concentrating factors that can promote cell growth or reduce inflammation. Commercial and some scientific literature claim these therapies enhance the delivery of specific growth factors or encourage superior anti-inflammatory activity. It is unclear if the purported benefits make a clinical difference, says Santschi, and vets choose products based on their experience, client desires, and available equipment. She says she used IRAP in this case due to its anti-inflammatory and growth factor effects.

Long-Term Prognosis

When Santschi examined the horse at 12 months old, the treated joint showed no residual puffiness. A small amount of thickening in the joint remained, but Santschi predicts it will not limit his future performance. “Cosmetically, there may be a small thickening at the joint capsule, but it is quite subtle,” she says. “For most purposes, the horse will pass a vet check and perform just fine.”