Your horse is leaning on the bit, unwilling to bring his hind end up under himself or really use his hindquarters as he moves. When he takes a fence, he doesn't push off with the power you know he has. Is he getting lazy? Regressing in his training? Or is it hock problems?
The hocks are a key part of your horse's hind-end driving mechanism. Actions such as jumping and work at collected gaits, which call for extra hind-end effort, are especially tough on these hard-working joints. So are tight turns and small circles, which load the hocks unevenly and apply twisting force. With time and miles, the joints can start to break down and cause hock problems in horses.
That's the bad news?but there's good news, too. You can take steps to keep your horse working comfortably and extend his career, even when hock problems start to develop. In this article, we'll explain what goes wrong and what you can do.
Hocks, Healthy and Not
The hock links the bones of the lower leg (the cannon bone and the two splint bones alongside) to the tibia, in the upper leg?but it's not a simple joint. It's a complicated assembly of half a dozen bones, built to absorb shock, flex when the horse brings his hind legs under his body, and extend to propel him forward.
Most of the flexion and extension takes place in the upper part of the hock, in the tibiotarsal joint. The end of the tibia has a ridge, running front to back, that fits like the tip of a screwdriver into a groove on the squat, rounded bone below (the talus). ?Slick cartilage coats the working surfaces, and they slide back and forth along the groove as your horse flexes and extends the joint. Behind the talus, the largest hock bone juts up to form the point of the hock (calcaneus), which is roughly equivalent to your heel. It acts as a brace, preventing the joint from overextending.
Below the talus, two small flat bones (the third and central tarsals) are stacked like pancakes on top of the cannon. Other small bones sit behind and to the side, between the calcaneus and the cannon and splint bones. The joints in this lower (distal) part of the hock have limited range of motion. With thick pads of cartilage, they're built to absorb shock. Strong ligaments at the sides keep the whole assembly in line so the hock can't bend to the side?only front to back, like a hinge.
Problems in the hock joints tend to creep up gradually, and early signs can be subtle:
- Your horse may have an on-again off-again lameness, with or without noticeable heat or swelling.
- He may start out stiff but seem to "work out of it" as he warms up.
- He may resist going downhill or backing off the trailer.
- Muscles in his lower back may be sore from working overtime in an effort to spare his hocks.
Often the problem improves with rest but returns when he's back in regular work. Over time the soreness worsens. He takes short, stabbing strides behind or drags his hind toes.
A flexion test can make mild hock lameness easier to spot. For this, enlist a helper to ride or lead your horse. Stand at the hindquarters, facing back, and pick up the lower leg above the fetlock. Raise it as close as you can to the upper leg, flexing the hock, and hold it there for 60 seconds. Then put the foot down and tell your helper to immediately trot the horse straight away. If there's a hock problem, your horse will probably be markedly lamer for a number of strides.
These signs point to trouble, but they don't tell you what (or even exactly where) the problem is. Your veterinarian can do a full lameness exam, take X-rays and perform other tests to see what's going on.
The Prime Suspect: DJD
While several conditions can affect hock joints, for adult horses (especially performance horses) the problem is often degenerative joint disease (DJD), or arthritis. DJD typically develops in the lower joints of the hock, which come under a lot of stress when your horse works. Conformation can contribute. Flaws such as cow hocks and sickle hocks (see below) put uneven pressure on the joints. With upright "post-legged" conformation, the joints flex less to absorb shock, increasing impact and raising the risk of injury.
Within joints, injury or simple wear and tear can set off a destructive chain of events. The inner membrane of the joint, which produces the viscous fluid that fills the joint, becomes inflamed. The fluid, which lubricates the cartilage surfaces, becomes thin and watery. Cartilage is squeezed and starts to wear away, and lumps of new bone growth appear where bones are irritated. This commonly happens first at the inner aspect of the lower hock, where the small tarsal bones are compressed. Bone spavin, as this condition is called, often affects both hocks, but it's usually worse on one side.
Once bone spavin appears, it won't go away. But if you catch the degenerative spiral early, you may be able to manage the condition and slow its progression. The goal is to reduce inflammation in the joint, which in turn reduces pain and joint degeneration. What you do depends on how advanced the condition is, how sore your horse is and how demanding his work is.
Changes in his management and training program can help. Increase his turnout time, so he can move around at will. Cut back on the amount of intense work you do, especially work that stresses the hocks, and give him longer warm-ups. Light activity helps by improving circulation to the hock's soft tissues and by keeping joint fluid moving, which nourishes cartilage. Talk to your vet and farrier about shoeing changes?rockered toes, for instance, where the front part of the shoes are rolled up on an angle, help ease breakover behind. Sometimes it helps to increase hoof angle by raising the heel or shortening the toe. Avoid heel extensions, where the backs of the shoes are extended, and especially outside trailers, where the outside extension turns out. Extensions affect the path and landing of the foot, and that can put uneven pressure on the hocks.
If symptoms flare up, rest and cold hosing (or other cold therapy) can help. So can nonsteroidal anti-inflammatory drugs (NSAIDs) such as phenylbutazone. But soreness often returns when the horse goes back to work, and long-term treatment with NSAIDs may have harmful effects. There are better options, some new and some tried and true.
Joint injection is probably the most widely used and effective treatment for a horse with clearly identified problems in his lower hock joints. The injection puts anti-inflammatory agents directly into the space between the bones of the sore joints.
Corticosteroids and HA: Typically, joint-injection agents are corticosteroids, which have powerful anti-inflammatory effects. They're used alone or in combination with hyaluronic acid (HA), a natural component of cartilage and joint fluid (it's the substance that makes the fluid viscous). Here's what to expect:
- Usually your horse has a couple of days off after the procedure and then eases back into work. It may take two weeks to see the full effects.
- Benefits may last anywhere from weeks to a year or more, depending on how severe the problem is and how hard your horse works. Combining injections with other steps may extend the effects. (Some people have reported longer effects by using the topical anti-inflammatory Surpass?, for example, but there's no clinical data on this.)
- Side effects are rare. Infection is possible but uncommon. (Watch for increased swelling, heat and pain in the joint after the injection.)
- Costs vary. Depending on where you live and how many sites require injection, you'll pay anywhere from less than $300 to more than $700 to have both hocks done.
- Repeated corticosteroid injections have been linked to progressive joint deterioration. The risk is less with some steroids than others and is less in the low-motion joints of the lower hock than in high--motion joints like the stifle; but it's a point to keep in mind. A horse who has a single injection is not likely to have a problem, but injecting routinely every few months could be another matter.
- There's no evidence that injections prevent DJD. It makes sense to inject if the horse has an identified problem; if he doesn't, you may just increase his risks.
IRAP therapy: For a horse who hasn't responded well to traditional joint injections, IRAP injections may be an option. The initials stand for interleukin-1 receptor antagonist protein, a substance derived from the horse's own blood. IRAP targets an inflammatory substance, interleukin-1, that plays a key part in the erosion of cartilage. The therapy has been around only a few years, but it's available at a growing number of clinics. These are the basics:
- The veterinarian draws a sample of your horse's blood using a special syringe containing glass beads. White blood cells bind to the glass beads and start churning out anti-inflammatory proteins. After a 24-hour incubation period, the sample is spun in a centrifuge to separate the serum (the liquid portion of the blood). Then the serum, packed with anti-inflammatory proteins, is injected into the affected joint for three to five weekly treatments.
- Because the serum is derived from your horse's own blood, the risks of side effects are low.
- This treatment isn't for everyone. It costs more than traditional injections?upward of $1,300 for the series of shots. And while there are reports of successful hock treatment, so far it's been used mostly in high-motion joints.
The Whole Horse Option
A second approach delivers medication to the horse's system, with the idea that it will travel to the joints and reduce inflammation there.
Systemic injections: HA (Legend?) is injected intravenously, and polysulfated glycosaminoglycan (Adequan? i.m.) into muscle. Adequan claims a protective effect on cartilage, so it's sometimes the choice when there's evidence of cartilage damage. (Polysulfated glycosaminoglycan, or PSGAG, is a component of cartilage.)
- Many people combine hock injections with systemic Adequan, Legend or both. If your horse has arthritic problems in other joints, not just his hocks, this makes sense because the systemic product may help those joints as well. If only the hocks are involved, injecting those joints directly is probably the best bet.
- Responses vary. Some horses seem to do better on Adequan, some on Legend and some on a regimen that alternates both drugs.
- Shots are usually given on an ongoing basis, at intervals ranging from six weeks to a week or less, depending on your horse's need.
- These medications carry no particular risks. They're not labeled as preventives but are often given with that in mind.
- Adequan lists at about $70 per dose; Legend, about twice that (not including any cost for administering the injections). With a prescription from your vet, you may save substantially by buying from a mail-order supplier.
Nutraceuticals: Dozens of nonprescription powdered, pelleted and liquid joint supplements are available. Many contain glucosamine and/or chondroitin sulfate, which are thought to provide building blocks for cartilage. Other ingredients include hydrolyzed collagen (a processed form of collagen, the protein that forms the framework of bone and cartilage), oral HA, methylsulfonylmethane (MSM contains sulfur; sulfur bonds are essential structural features in all connective tissues), omega fatty acids and more. Keep these points in mind when you shop:
- A supplement alone won't solve severe DJD. These products are most likely to be helpful as preventives in early joint problems and as adjuncts to other treatments. At least, they'll do no harm.
- There's very little research to show which ingredients are helpful for horses or in what quantities. In some studies, a combination of glucosamine and chondroitin sulfate (Cosequin?) seemed to help protect joints from degenerative damage. A recent study at Colorado State showed that avocado and soybean unsaponifiables, which are fractions of the oils of these plants, slowed breakdown of cartilage in horses. Research still needs to be done on other ingredients.
- Unlike drugs, these products don't have to meet licensing standards. Thus the manufacturers don't have to run clinical trials to show that they're effective, and no agency enforces product quality standards. (Makers of products that carry the seal of the National Animal Supplement Council voluntarily agree to meet certain quality-control standards.)
- Expect to spend anywhere from $20 to $80 a month to maintain your horse on one of these supplements.
Your horse doesn't actually need his distal hock joints to use his leg. As DJD advances, the bones sometimes fuse to each other naturally, usually leaving him more comfortable.
As a last resort in an advanced case, you may want to consider a procedure to fuse the affected joints. There are several techniques, some surgical and some involving injections of irritants into the joint, to stimulate new bone growth. Each has pros and cons, so discuss the options with your veterinarian.
Fusion isn't a cure-all. On average about 60 to 80 percent of horses improve with the procedure. When a horse reaches the point where joint injections and other treatments no longer keep him sound, it may make more sense to rethink his career. He may still be comfortable in light work, or he may be ready to retire.
Gary M. Baxter, VMD, MS, DACVS, is a professor of surgery in the department of clinical sciences at the College of Veterinary Medicine at Colorado State University. His particular interests include lameness and performance-horse injuries, developmental bone diseases in young horses and treatment of arthritis.
This article originally appeared in the June 2008 issue of Practical Horseman magazine.