Page 112 - 2021 Barrel Stallion Register

EQUINE HEALTH
HOCK INJURIES by Heather Smith Thomas
The hock is one of the largest, most complex and hardest worked joints in the horse’s body so it must be strong and sturdy to avoid injury. The hock is often under great stress because of the activities we ask the horse to do, and it may be injured during high speed performance.
Dr. Olivia Rudolphi of Rudolphi Veterinary Services in Noble, Illinois, says some of these injuries may be due to developmental/congeni- tal lesions such as an OCD (Osteochondritis Dessicans) within the joint—that might not show up until the horse is put into training and doing more exercise. “Lameness causes can vary between the young horse and the more mature horse. In the young horses we may see a puffy hock or a foal with some sort of insult to the joint. As young horses start training, we may see the hock develop swelling if there is some- thing such as an OCD lesion, and there may be lameness,” she says.
Jillian Mills, DVM, DACVSMR (or Dipl. ACVSMR) Presidio Equine Sports Medicine
& Rehabilitation, Encinitas, California, says hock injuries are interesting because this joint is a combination of high and low-motion joints. “These joints can undergo different pathologi- cal changes that can lead to clinically relevant disease,” she explains.
“A lot of times with hocks we will see either acute traumatic injuries, DOD (developmental orthopedic disease) or fatigue-related injuries. Acute injuries often involve fractures which may include the tibia and cannon bones, as well as collateral and intra-articular ligament injuries,” says Mills.
“The upper joint (the high-motion joint) more often has developmental issues such as OCD fragments and subchondral bone cystic lesions. If there is an OCD fragment, the horse may need surgery to have the fragment removed, however this is not always the case,” she says.
“We know that the joint environment is not as healthy as it would be if an OCD lesion was not present. On a pre-purchase exam, osteochondral fragments can be difficult to determine whether surgery may be indicated in the horse’s future. For a young horse that hasn’t had the opportunity to prove itself, if we find an osteochondral fragment in a joint that carries excess fluid, where the horse trots off lame following flexion testing, there’s a higher probability that it will need surgery to remove that chip. The presence of the OCD fragment is an indication that the joint is less healthy, and the horse is more prone to devel- oping arthritis,” says Mills.
By contrast, if the horse is 10 years old and has already proven itself at the buyer’s prospec- tive level of competition, the OCD lesion on
a pre-purchase exam might not be an issue. “With racehorses, however, we are generally dealing with a significantly younger population of horses with a shorter prospective career, so surgery is often recommended.” she says.
“Fatigue-related problems might include subchondral bone disease and a breakdown of the joint’s cartilage. When that happens, we have to manage these horses for arthritis. We sometimes see arthritis in the upper joint, but this is significantly less common than in the lower joints and often results in debilitating lameness. Usually when we’re talking about fatigue-related injuries in the hock we are deal- ing with arthritis in those lower hock joints rather than the upper joint.”
If there are changes in the upper joint, these clinical signs generally include a significant increase in joint fluid which can be appreci- ated as a pronounced swelling. “If there is an osteochondral fragment in there, there is often joint swelling, and the horse may be positive to flexion testing. However, when a horse reacts positively to hock flexion, this is not a specific finding and pain could be originating from ei- ther the high or low motion joints.” says Mills.
The hock is unique because the upper joint is a high-motion joint and the lower joints are low-motion but must endure a lot of concussion.
110 SPEEDHORSE