Hock Injuries

By Heather Smith Thomas.....................................................................................................................................................................................................................................................................................................................................................................

he 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—especially if a horse must stop and turn quickly.

Duncan Peters DVM, DACVSMR, ISELP Certified Member, East-West Equine Sports Medicine, Lexington, Kentucky says we often see hock soreness in performance horses due to strain and stress. “In young horses (weanlings, yearlings) we may see Developmental Orthopedic Disease (DOD), such as OCD or bone cysts, in the hock joints. These defects are usually discovered early on, and many are taken care of surgically. Occasionally some of those are not evident until the young horse starts training and then gets a little osteochondral fragment (usually in the tibial tarsal joint) and associated swelling and lameness within the joint,” he says.

“Most of those chips in the joint will occur early in their training or when they start racing or athletic performance. The horse has to stop training and have the chip removed surgically. Some of those horses can get back to work and training within 90 days or so and don’t miss very much time,” says Peters. If the problem is discovered early and taken care of, the outcome is usually good.

“More commonly, the hock problems we see in young horses are just a soreness. As the horse starts working and being asked to do more, the hock joints get sore, just because of the mechanics of that area of the leg. 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. Those lower joints are held together with many small ligaments—holding those two rows of small bones together.” The hock has seven bones and is similar to the human ankle.

If there is too much strain on the hock, there will be inflammation associated with the ligaments holding those small bones together, as well as inflammation within the joint itself--which causes synovitis in the joint. “Depending on what we find, it may require a different course of treatment,” says Peters.

“The other thing we might see in some of these young horses coming into racing and performance is bone soreness related to concussion in the lower joints. This may depend on the surfaces they work on, the level of activity, and the maturity and quality of the bone.” Some of these horses will get some bone bruising and bone soreness.

Synovitis and bone trauma can lead to arthritis in those lower joints. “This can progress and become serious if not taken care of early on. Usually for treatment we use some injections in those joints (steroids, hyaluronic acid, IRAP, stem cells, platelet rich plasma, amnionic fluid isolates, etc.) in an effort to reduce the inflammation and curb the development of arthritis. We’ll also back off on the exer-

cise and training for a while. If there is bone soreness and trauma—perhaps some micro-fractures associated with the T bone bruising—this may take 4 to 6 months of rest before the horse can go back to work, and some people don’t like to miss that much time in training and performance events.” This is time and money lost. “If the joint has synovitis, many of those horses will respond favorably if we change their routine a little, backing off on the level of work, and treating the joints themselves with injections. Those horses may only lose 2 to 4 weeks of work and then can get right back to it,” says Peters. Proper diagnosis is very important. Several of these problems may show up with similar signs, but may need a completely different course of treatment and a different length of time off, in terms of how they respond. “Another thing that’s interesting about the hock is that there is sometimes some involvement with the proximal suspensory ligament. There may be some pain-causing damage to that ligament where it originates at the back of the hock. This may actually be the primary problem that leads to secondary hock problems. We find this on MRIs more than with any other type of diagnostic tool,” he says. “These horses won’t be performing well; they have a soft-tissue problem related to the origin of the suspensory ligament, either at the back of the cannon bone (just below the hock) or even into the plantar ligament—since some of those fibers attach up into the plantar ligament at the back of the hock,” he explains. “That whole area functions as one unit. There may be general hock soreness that includes a soft tissue component. The high suspensory area may need to be addressed or explored to make sure we are taking care of all the problems that are causing the soreness,” says Peters. There are also some unusual aspects that are occasionally encountered with hock joint soreness. “There may be collateral ligament injuries. These are interesting because the hock has 2 sets of collateral ligaments. One set is under tension during flexion and the other set is under tension during extension of the hock joint. Occasionally we see some ligament damage in one or the other set, depending on what kind of trauma occurred. Collateral ligament injury can certainly occur.” Basically the things that can happen to the hock joints in a young horse are osteochondral fragments (chips) in the upper tibial tarsal joint, inflammation in any of the three joints for a variety of reasons (generally related to exercise), associated soreness of the proximal suspensory apparatus (as part of the functioning unit of the hock) and collateral ligament injuries. Some of these injuries may be due to the horse’s conformation (putting more stress on certain parts of the joint) or just to an occasional bad step or excessive trauma. Dr. Olivia Rudolphi (Rudolphi Veterinary Services, in

By Heather Smith Thomas.....................................................................................................................................................................................................................................................................................................................................................................

Noble, Illinois) says some injuries may be due to a simple blunt trauma or perhaps a puncture if the horse runs into something while running around the pasture. “In older horses with hock changes we may see a narrowing of the joint due to arthritic changes. Some of this could be due to how they were used as a young horse (how much stress on the joints in an athletic career). If those early problems are not seen and addressed, there may be some cartilage weakening later on and arthritic changes later in life,” she says.

Some hock problems may be due to conformation, and how straight or angled the hind leg is, and which stresses are put on the hock joint. “Poor hoof management and shoeing can also have repercussions on up the leg.