Jesse Tyma, DVM, Dipl. ACVS, joined us to talk about OCD in horses. During the episode, she discussed risk factors, clinical signs, treatment options, and more.
What Is OCD?
Osteochondritis dissecans, or OCD, refers to a discernible osteochondral fragment separate from the parent bone that occurs due to inflammation within the joint environment.
“OCD has been described in every diarthrodial joint in the horse,” Tyma said. However, she noted lesions are most common in the tarsocrural joint of the hock, femoropatellar joint of the stifle, and the front and hind fetlock joints.
Within each of these joints, there are also predilection sites. Tyma said for the tarsocrural joint, the distal intermediate ridge of the tibia, often abbreviated as the DIRT area, is the most common site by far. For the femoropatellar joint of the stifle, the lateral trochlear ridge of the femur is the most common site. True OCD lesions in the fetlocks occur in the dorsal sagittal ridge. However, Tyma noted some developmental lesions of the fetlocks are not technically OCDs based on their histologic appearance but are lumped into the OCD category because management is the same.
What Types of Horses Are at Risk for OCD?
OCD is a disease of juvenile horses, Tyma explained. The condition is most common in Warmbloods and Standardbreds and slightly less common in Thoroughbreds, Quarter Horses, and Arabians. “We don’t have evidence that it is as prevalent in other breeds, but they also haven’t been studied as extensively,” Tyma said. “Warmbloods and Standardbreds and Thoroughbreds have probably been studied the most.”
OCD lesions are rarely seen in ponies or feral horses, which suggests selective breeding and management styles are key factors in the development of this process.
How Does OCD Occur?
Tyma said OCD is caused by an interplay of factors, and isolating them is tricky. The disease itself stems from alterations in the process of endochondral ossification and vascular changes causing focal necrosis or abnormal structure of the subarticular cartilage. This disturbance is called osteochondrosis (OC), and genetics, environmental effects, and biomechanical factors all play a role in causing it.
Tyma said the role of genetics is complicated. Researchers have identified a locus associated with the process of endochondral ossification on about 2/3 of the horse’s chromosomes. The disease also seems to be specific to athletic breeds with selected breeding practices. “It’s clear that genetics certainly play a part, but we still have a lot more to learn in that realm, and it’s not the whole story,” Tyma said.
As far as environmental factors, the balance of trace minerals and dietary energy level have both been implicated as contributing to osteochondrosis. Specifically, researchers have found copper to have a positive effect on healing OC lesions, and there is some mixed evidence to support copper supplementation in gestating mares, Tyma explained.
Very high phosphorous levels are associated with a pathogenesis of osteochondrosis, but Tyma said this is uncommon. She said dietary energy levels—specifically, easily digestible carbohydrates—have been associated with a higher incidence of osteochondrosis.
“Those juvenile horses that are going through rapid growth spurts and are all of a sudden lanky and tall at the withers a few days later are often common offenders,” Tyma said. “Horses exhibiting these changes are ones that we recommend cutting back on their carb intake.”
Tyma said biomechanical factors play a large role in the development of OCD based on the fact we see common predilection sites within joints. Biomechanical loading is related to exercise regimens, foal conformation, the firmness and unevenness of the ground foals are exercising on, and other variables.
Tyma continued by emphasizing that osteochondrosis is a dynamic condition. “So many lesions that are present very early in life regress and heal without intervention in that early juvenile stage,” she said. In the tarsocrural joint of the hock, lesions can spontaneously regress until the horse is 5 or 6 months old. In the femoral patellar joint, the lesions can be dynamic until the foal is 8 or 9 months old.
Tyma said horses are most likely to develop OCDs by the time they are early yearlings.
Clinical Signs of OCD
The most common sign of OCD is acute onset of joint effusion, usually with no lameness present. This often occurs in late weanlings and early yearlings. Many horses with OCD present with no clinical signs at all. Rather, the lesions appear on survey radiographs.
Tyma said it’s common in the Thoroughbred and Standardbred industries to screen horses for OCD in their late weanling to early yearling stage ahead of the yearling sales. Tyma said screening is wise for horses intended for athletic pursuits so any lesions can be managed early in the disease process to optimize long-term joint health.
Surgical Treatment for OCD
Tyma described three categories of patients with OCDs: patients with both clinical and radiographic signs, patients with clinical signs but no radiographically evident signs, and patients with radiographic evidence but no clinical signs.
For the first category of horses, Tyma recommended arthroscopic debridement and fragment removal. For the second category, Tyma often recommends surgical treatment, as well. “You have a horse that’s in that age category that’s presenting with acute effusion of one of our high-motion joints that has a predilection for these, there’s a lesion in there that warrants evaluation debridement,” she explained. “Even if we can’t see it on radiographs, we know where to look once we’re in there.”
For asymptomatic patients with radiographic lesions, surgery is also indicated to obtain a horse without joint effusion or lameness when it’s time to be athletic.
For mature horses in training that are already performing at the desired level, Tyma said conservative rather than surgical management is often possible.
Postoperative Management and Outcomes
“Postoperative management is a bit patient- and site-specific, but in general these surgeries are well-tolerated elective procedures in young and systemically healthy horses, and their recovery is pretty quick,” Tyma said.
The surgical incisions are tiny, and the surgeon closes the instrument and scope portals. They bandage the surgical site, and the horse remains bandaged for a couple of weeks, possibly longer if they had a lot of joint effusion. Tyma typically keeps horses on stall rest with hand-walking for a couple of weeks, then small paddock turnout for a couple of weeks, and back to full turnout and light training at the four-week mark. Horses can usually return to full training by six weeks.
Horses will be on non-steroidal anti-inflammatories for a few days and possibly postoperative antibiotics, which Tyma said is not necessarily supported by the literature but can be industry-driven at times. She often treats joints with a course of hyaluronic acid postoperatively in yearlings heading for sales. She stays away from corticosteroids as a blanket recommendation postoperatively, but she will reach for them in persistently abusive cases for a cosmetic outcome on a certain timeline.
Overall, Tyma said the prognosis for recovery to soundness and general future athleticism for patients with typical OCDs is good to excellent. Some lesions have a lower prognosis, such as large lesions in the stifle on the lateral trochlear ridge and lesions in the shoulder. If an OCD becomes loose in the joint and bounces around before settling somewhere, it can cause articular cartilage damage and inflammation in the joint, which will cause effusion to persist longer postoperatively and might warrant more ongoing support.
“The beauty of arthroscopy is that we can visually evaluate the health of the joint while we’re managing the OCD lesion and then make decisions based on what we’re seeing in there tailored to that patient specifically,” Tyma said.
About Dr. Jesse Tyma
Jesse Tyma, DVM, Dipl. ACVS, is an accomplished equine surgeon with experience in orthopedic, soft tissue, and emergency surgery; sports medicine; and advanced diagnostic imaging on a robust Thoroughbred and Standardbred racehorse and mixed sport horse population. Her clinical interests include gastrointestinal and soft tissue surgery, wound management, sports medicine, and back disorders.
Tyma grew up in New Hope, Pennsylvania, and attended Amherst College for her undergraduate education followed by Cornell University’s College of Veterinary Medicine. She completed a rotating internship at Rhinebeck Equine followed by a large animal surgical residency at the University of Georgia and then became a diplomate of the American College of Veterinary Surgeons (large animal). She returned to the Hudson Valley of New York to join the Rhinebeck Equine team. Tyma is a member of the AAEP Internship Sub-Committee of the Sustainability Mission and is both a Decade One member and a Starting Gate group facilitator. She is passionate about providing dedicated mentorship for intern veterinarians and building a strong sense of community and collaboration through her practice.
