With some estimates relating as much as 60 percent of equine lameness problems to osteoarthritis, it’s no wonder every tack store you enter and horse supply catalog you flip through is crammed with supplements touting miraculous results in the treatment of degenerative joint disease.

A host of other therapeutic options exist when bringing your veterinarian’s arsenal into play. There are few rules writ in stone when it comes to treating or preventing osteoarthritis; it’s a very individual process that should be approached with your veterinarian’s guidance, taking your horse’s individual needs into consideration.

Osteoarthritis can stem from a variety of disorders, but the end result is the same: pain and dysfunction resulting from the progressive deterioration of the articular cartilage (that covers the ends of the bones in joints to dissipate shock and help them move freely against each other) and the accompanying changes to the bone and soft tissues in the joint.

A synovial joint is a joint like the knee or hock that has a space in between the interacting bones. The joint is surrounded by a tough joint capsule, which is lined by the synovial membrane. This fragile membrane secretes the slippery egg white-like synovial fluid that works with the articular cartilage to let the joint move easily. Because the cartilage doesn’t have its own blood supply, the synovial fluid is also responsible for carrying nutrients into the cartilage from the highly vascular synovial membrane. The synovial membrane also clears waste products within the joint capsule.

When things go wrong in the joint, the disease progression is a vicious cycle. Regular daily wear and tear can cause inflammation of the synovial membrane and fibrous capsule (synovitis and capsulitis, respectively), and this inflammation causes the release of enzymes and other agents that are believed to contribute to the degradation of the articular cartilage. As cartilage is broken down, some of the products from that process stimulate the synovial membrane to release even more catabolic products that further erode the cartilage.

When the cartilage is damaged, it compromises its abilities to spread out concussive forces to the underlying bones and to allow the joints to move easily, eventually resulting in damage to the bone. Therefore, joint inflammation not only causes uncomfortable pain and swelling from the primary insult, but also starts into motion a cycle of damage that leads to osteoarthritis.

Acute, traumatic joint injuries are another, more direct path to osteoarthritis.

Cartilage can be damaged directly by large concussive forces to the joint, as you might see in a race horse’s knees. This damage could be brought on directly by the heavy pounding itself or as a result of bone fractures in the joint that cause cartilage loss.

When treating joint disease, timely surgical intervention may be required to repair injuries involving bone chips or fractures and ligament damage.

Medical treatments can help address joint inflammation, with the goal of ending discomfort, returning the horse to work, and halting production of the nasty inflammatory products that bring about osteoarthritis.

Breaking The Cascade

Your doctor wants you to eat more salmon and walnuts and ease up on the margarine and baked goods. The reason behind that recommendation, oddly enough, could relate directly to your horse’s stiff hocks. It’s all about the fatty acids.

Fish oil and flax provide the highly touted beneficial omega-3 fatty acids, while brownies harbor omega-6s. Both of these fatty acids are broken down by the body into various products that affect all sorts of bodily functions.

Omega-6 fatty acids aren’t inherently evil, but their breakdown, via a chain of events called the arachidonic cascade, results in pro-inflammatory metabolites. These products serve a function, but when the body produces them faster than it uses them, it can result in heart disease and other disorders.

The omega-3s “compete” with the omega-6s to be broken down, so the more omega-3s in your diet, the greater the dampening effect on inflammation.

This doesn’t mean that you should switch your horse’s training aids from sugar cubes to sardines, but it will help to explain how some of these drug therapies work.

“NSAIDs [non-steroidal anti-inflammatory drugs] inhibit an enzyme called cyclooxygenase that’s part of the arachidonic cascade. Basically, they inhibit the production of prostaglandin E2, PGE2. PGE2 not only potentiates pain, making the nerve endings in the synovial membranes more sensitive—because pain’s an important part of the disease process—but PGE2 also causes the breakdown of proteoglycans and collagen in the cartilage matrix,” explained C. Wayne McIlwraith, BVSc, PhD, professor of surgery and director of the Orthopedic Research Center at Colorado State University.

There are two forms of cyclooxygenase (COX), COX-1 and COX-2. COX-1 plays a role in protecting the GI tract and other organs; the latter has been mainly associated with “bad” inflammatory events. NSAIDs like phenylbutazone non-selectively inhibit both COX-1 and COX-2, thus they have the potential for causing ulcers and kidney damage in cases of overdose or long-term use.

COX-2 specific inhibitors, such as carprofen, have been developed that show promise for horses that don’t tolerate bute well. This class of drugs has recently gained attention in the news and court systems–think Vioxx and Celebrex–for their link to increased risk of heart attack and stroke in humans, rare conditions in the horse.

“COX-2 inhibitors are going to be useful to the veterinarian when the patient is not tolerating phenylbutazone well,” predicted McIlwraith in his 2005 Frank J. Milne State-of-the-Art Lecture at the American Association of Equine Practitioners Annual Meeting.

Surpass, a recently licensed topical NSAID cream, has also shown promising results in a clinical field trial for relief of joint inflammation in horses and would theoretically reduce adverse systemic effects.

The heavy hitters in treating joint inflammation are corticosteroids.

“Steroids work higher up the arachidonic cascade than NSAIDs do. Non-steroidals are usually the first line of treatment because they can be given orally, and they all inhibit a certain level of pain. If you’ve got a persistence in clinical signs, which include excess fluids in the joint, plus or minus lameness, then you’ve got to go to an intraarticular corticosteroid,” said McIlwraith. “You’ve got a number of choices for intraarticular therapy, but the most potent are corticosteroids.

“In the old days, all corticosteroids were lumped together, and they were all ‘bad.’ We now know that ones such as beta-methasone and triamcinolone acetonide, available as Vetalog, have positive effects and they don’t cause damage to the cartilage,” he continued. “Depo-Medrol, or methyl prodnisolone acetate, at higher doses and with frequent use, will cause damage to articular cartilage.”

Because Depo-Medrol is the most powerful, longest-lasting corticosteroid used, it’s still used.

“Some clinicians feel that with keeping the dose low and not using it too often, they can get away with not causing damage,” said McIlwraith. “It’s probably used more in distal hock joints than anywhere, and the rationale for using it there is that it’s a low-motion joint, and we don’t have to worry about saving the cartilage. Yes, it’s a low-motion joint and probably not as harmful in that joint, but on the other hand, we always want to preserve cartilage, and I think it’s a mistake to say, ‘We don’t need it.’ “

HA—No Laughing Matter

Hyaluronan, a.k.a. hyaluronic acid or sodium hyaluronate, is a big, flexible water-loving molecule found throughout the horse’s body tissue. Sometimes referred to as “nature’s moisturizer,” it makes skin supple, keeps heart valves pliable, and, combined with water, is the primary component of synovial fluid.

Hyaluronic acid has mild analgesic and moderate anti-inflammatory effects, making it a useful tool against less severe cases of synovitis.

“On a scale of zero to 10, you’ll get a potential 10 with corticosteroids, more like a five with NSAIDs. HA is like a three,” noted McIlwraith.

Hyaluronic acid is often administered intraacticularly (into the joint) in conjunction with corticosteroids.

“Some people feel that used together, you get a better result, and certainly we know that it doesn’t cause any harm,” he said. “I don’t see using it alone intraarticularly—the effect is pretty low-grade.”

McIlwraith primarily uses hyaluronic acid in its intravenous form, marketed by Bayer as Legend. Much of the osteoarthritis research performed in his lab is done on a model of osteoarthritis, where they create chip fractures in the knee joint.

“We’ve shown that intravenous HA works in our model,” he said. “Clinically, a lot of people use it prophylactic, almost like keeping your oil changed. It has a low-grade anti-inflammatory effect for a horse that’s in heavy competition, so quite a lot use it on a regular basis. When they get a particularly acute problem, they’ll go ahead and use intraarticular corticosteroids on top of it, and that’s a good way to use it, I think.”

Hyaluronic acid is also available in oral supplement form, such as Kinetic Technologies’ Conquer. As with all nutraceuticals, they are unregulated and lack any definitive proof as to their efficacy, but there is positive anecdotal support for their use.

Polysulfated glycosaminoglycan, known commercially as Adequan, is referred to as a slow-acting disease-modifying osteoarthritic drug. It’s traditionally intended for use in cases where cartilage damage is detected, rather than merely inflammation, and is intended to prevent further cartilage degeneration.

Adequan is available in intramuscular and intraarticular forms. “I mainly use I.A. Adequan, or prescribe it, after I’ve done arthroscopic surgery and I’ve got significant cartilage damage. I think it’s a great drug for that,” said McIlwraith. “There have been some positive effects with intramuscular use, but the results are not nearly as much as with intraarticular.”

Adequan I.M. was unveiled and its use bolstered after a study done by McIlwraith’s team showed an increased risk of infection following use of the drug intraarticularly.

“A lot of veterinarians shy away from using it intraarticularly in the U.S. In the study we did, we also showed you can eliminate any risk of infection with half a ml of amikacin [an antibiotic] given at the same time,” said McIlwraith. “I think if you use multiple [intramuscular] injections, you will benefit horses, but it takes a lot longer to see the effects.”

Treatment strategies depend upon the stage of disease, what’s causing it, and your horse’s job, so work with your veterinarian to develop a plan of attack that suits your situation.

Awaiting A Scientific Study And Proof

A huge array of unlicensed, unproven oral supplements boast joint-saving claims of varying descriptions, but the facts regarding their efficacy, and in some cases safety, remain indeterminate.

Because there are no licensing requirements, no one company will be eager to shell out the big bucks required for a legitimate scientific study. Negative results mean negative profits, and positive results would be eagerly cited by every other similar supplement manufacturer that didn’t have to lay out the dough for the study.

That being said, two of the most common joint nutraceutical ingredients are glucosamine and chondroitin sulfate.

Chondroitin sulfate is the major component of aggrecan, which occupies the spaces in between the collagen fibers in articular cartilage and allows it to remain stiff when compressed.

In vitro testing (not done in a body) has shown favorable results, but there’s no clear proof of efficacy in the body. There’s a big question mark when it comes to whether these ingredients can be effectively absorbed by the GI tract and utilized by the horse.

Anecdotal support and non-scientific studies into various nutraceuticals abound. In December 2005, the Horse Journal published a summary of their joint supplement field trials that began in the late 1990s.

“Although pain relief is slower to occur with glucosamine than the new combination products, it remains an excellent economical option. Glucosamine doesn’t have a significant effect on active inflammatory processes, so this must be dealt with separately in acutely inflamed joints. However, regular continued use can inhibit future inflammation,” read the article.

“Acutely inflamed joints are a special problem, where HA excels. Results with liquids and gels were clearly superior to the powders in quieting down hot, swollen joints,” it continued.

In February of this year, the National Institutes of Health released the results of their $12.5 million clinical study on the efficacy of glucosamine and chondroitin sulfate for osteoarthritis pain relief in humans. The four-year, 16-site study was the first of its kind in the United States and followed nearly 1,600 participants, who received 24 weeks of one of five treatments: glucosamine alone, chondroitin sulfate alone, the two together, a placebo, or celecoxib (Celebrex).

Those receiving celecoxib were the only overall group of participants to experience statistically significant pain relief versus the placebo.

In the moderate-to-mild pain subgroup, glucosamine combined with chondroitin sulfate provided statistically significant pain relief–about 79 percent had 20 percent or greater pain reduction compared to 54 percent for the placebo group. There were no other significant differences noted between treatments. Because the subgroup that did see a benefit was small in number, the findings are only considered preliminary.

If it took the NIH $12.5 million and four years to determine a potential benefit to some participants, it’s no wonder horse owners are in the dark. And regardless of proven efficacy or not in other species, there’s no guarantee that what holds true for humans goes for horses.

While we await proof and/or determine the usefulness of these products in our own horses, there are other medical treatment options on the horizon.

C. Wayne McIlwraith, BVSc, PhD, professor of surgery and director of the Orthopedic Research Center at Colorado State University, noted exciting positive results in their chip model studying the effects of an oral product, containing soy and avocado, that’s available in France. He’s also seen scientifically documented benefits from PPS (pentosan polysulfate sodium), a disease-modifying osteoarthritic drug licensed in Australasia for horses as Pentosan Equine Injection.

In a study his lab performed comparing extracorporeal shock wave therapy (ESWT) to Adequan I.M. and a placebo treatment, ESWT outperformed both of the other treatments.