Arthritis is an unwelcome diagnosis for any horse, regardless of his discipline or occupation. Whether the condition appears suddenly after trauma or gradually with worsening stiffness, it means the same thing: Chronic inflammation has led to permanent degradation of the cartilage in a horse's joints.
And the damage is irreversible: "The reality is that you're not going to fix the joint or cure arthritis," says Margaret Brosnahan, DVM, Assistant Professor of Equine Medicine at Midwestern University College of Veterinary Medicine. "Your goal is to reduce the inflammation, pain and further damage."
Dire as that sounds, however, current research is yielding new treatments and investigating management techniques that can help horses work longer and live more comfortably with arthritis. Here's an overview of how arthritis develops, how it can be managed and the treatments available for it.
A Cascade Effect
A horse's knees, hocks and pasterns are designed to flex, compress and extend hundreds or thousands of times each day, for years on end--all while supporting his weight and enduring concussive forces.
Joints have several components: collateral ligaments, which prevent lateral movements of the bones; synovial fluid, which fills the space between the bones and provides lubrication and nourishment to the cartilage; the joint capsule, which stabilizes the joint; the synovial membrane, which regulates the joint fluids; and the articular cartilage, the soft structural tissue that covers and cushions the ends of the bones where they meet.
The cartilage is a framework of tissue made up of collagen fibers, which give the structure its strength. The collagen is interlaced with proteoglycans--long, protein-based molecules with negative charges that trap water within the matrix. As the joint flexes, the cartilage compresses and expands, forcing water in and out of the spaces, which helps to provide a shock-absorbing effect.
"Collagen is like the cotton in your clothes," says David Frisbie, DVM, PhD, DACVS, DACVSMR, a professor of equine surgery at the Colorado State University Orthopedic Research Center. "Take a wad of intricately laced cotton, put it in water, and it will soak it up like a sponge. Press down and it will expunge it out and then refill again. That's how cartilage works. The collagen is the framework, and the proteoglycans are stuck in the collagen to keep the sponge full and the water interspersed."
As a horse moves, the flexing and compression can produce minute damage within the joint structures that triggers mild inflammatory responses to make the repairs. Normally, the body's own defenses control inflammation and the joint remains healthy and sound.
Sometimes, however, the inflammatory process overwhelms the body's ability to contain it, either from a single acute injury or from many years of use. At that point, a cascade of events begins: The inflammatory enzymes break down the lubricating synovial fluid, which gets thinner. Proteoglycans are lost and the collagen fibers lose integrity, which diminishes the cartilage's ability to retain lubricating water. This damage stimulates even more inflammation, which fills the joint capsule with fluids, leading to pressure, pain and stiffness. The buildup of inflammatory enzymes further breaks down the synovial fluid, which leads to more damage to the cartilage.
"Left unchecked, a lot more degeneration can occur because the inflammatory response keeps triggering a loss of proteoglycans and collagen. It's a bad cycle at work," says Frisbie. "This is how an acute injury can cause progressive damage." Eventually, the cartilage can tear or erode away entirely, leaving the exposed ends of hardened bone to rub against each other. This is a painful, advanced case of osteoarthritis, also called degenerative joint disease.
The Challenge of Diagnosis
The key to helping a horse live comfortably with arthritis is to catch it early and get the inflammation under control to stop the cycle of damage. But in most cases, by the time a horse is lame, the arthritis is already advanced.
That's why it's important to investigate even minor discomfort. Some horses show early signs of arthritis in their way of going: They'll move stiffly until they've warmed up, or they may be perpetually short-strided. Others may be reluctant to move only on one lead, or in one direction, or at a certain gait--signs that are especially significant if these movements were previously performed with ease. Sometimes developing arthritis causes a sour attitude or resistance to rider aids.
A veterinarian will begin the diagnostic process with a hands-on examination to look for heat and swelling in a horse's joints, followed by a full lameness exam, including flexion tests. Nuclear scintigraphy can detect subtle early changes that indicate injury within the bones; X rays will show the more significant changes associated with more advanced arthritis. Arthroscopy--the insertion of a fiber-optic "camera" directly into the interior of the joint--is the best way to diagnose lesions in the cartilage.
It's not possible to cure arthritis at this time, but treatments can halt or slow the cycle of inflammation that brings further damage, ease pain and stiffness, and/or support the regeneration of cartilage as much as is possible.
The right treatments for an individual case of arthritis depend in part on the causes as well as severity of the problem. Your veterinarian is the best judge of what is most likely to work for your horse. Fortunately, there is a growing number of options to choose from.
These medications are effective at reducing inflammation and the associated swelling and pain. Inexpensive and easy to administer, phenylbutazone (bute) has long been a staple in most barns, but it is not the best choice for long-term use in all horses because it can damage the lining of the gastrointestinal tract. However, bute may be prescribed for arthritis flare-ups lasting a week or two.
Another type of NSAID, firocoxib, is available in a new oral paste product (Equioxx). Clinical trials have shown that firocoxib is as effective as bute in reducing lameness associated with arthritis and it may facilitate greater improvement in some areas, such as range of motion. Because firocoxib is a COX-2 inhibitor, it may be less irritating to the gastrointestinal tract.
Also available is a topical cream (Surpass) containing diclofenac sodium, which is applied directly to the skin over the affected joint. Commonly prescribed for acute injuries, this product has been shown to have protective effects in joints, says Frisbie.
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Oral nutraceuticals. Currently, there are more than 80 supplements formulated to support equine joint health on the market. Many contain glucosamine, chondroitin sulfate and/or hyaluronan, substances found naturally in joints: Glucosamine is believed to play a role in the formation and repair of cartilage, chondroitin sulfate helps give cartilage its elasticity, and hyaluronan helps lubricate joints and form the matrix of articular cartilage. Some newer supplements contain soybean and avocado unsaponifiables (ASU), which studies suggest may reduce inflammation and protect cartilage.
Nutraceuticals are not required to meet the same standard for Food and Drug Administration approval as drugs are, and so their efficacy has not been studied as extensively. However, equine and human research suggests that some of these substances have protective effects. Your veterinarian can help you decide what's best for your horse.
Corticosteroid injections. In use since the 1950s, the injection of corticosteroids directly into the synovial fluid has been well documented to halt inflammation within a joint. "There are very few cases where I don't start by using steroids," says Frisbie. "They are potent, relatively inexpensive and symptom-modifying and disease-modifying, meaning they alleviate pain and can slow the progression of deterioration. The arthritis cases I see tend to have been going on for a while, and steroids combined with hyaluronic acid is usually the first line of treatment."
The frequency of steroid administration varies, but Tracy Turner, DVM, of Turner Equine Sports Medicine and Surgery in Minnesota, says that he typically administers this treatment every six to 12 months. "That's not to say the drug works for six months, but it takes the inflammation out of the joint and the horse gets a range of motion back," he says. "Then the owner can apply other treatments or management to maintain the horse."
Hyaluronic acid injections. Hyaluronic acid (HA) is a normal component of synovial fluid as well as articular cartilage. It has been injected directly into the arthritic joints of horses since the 1970s, and an intravenous injection (Legend) has been available since the 1980s. Both injectable forms have an anti-inflammatory effect, and they also seem to stimulate the body to produce more HA, which thickens the synovial fluid and increases its cushioning ability within the joint.
The prophylactic effect of Legend has been studied in racehorses. Research suggests that HA-treated horses raced longer before requiring their first joint injection and had a better speed index, a higher average number of starts and earned more money than horses treated with a placebo.
HA injection protocols vary by product, but many veterinarians give one dose a week for three weeks. "If I'm treating a horse for inflammation, I may use HA," says Turner. "In a horse that has cartilage damage or has had surgery, I'll more likely use polysulfated glycosaminoglycans."
Polysulfated glycosaminoglycans (PSGAGs) and related polysaccharides are, like HA, among the naturally occurring compounds found in the articular cartilage matrix. PSGAGs have been used in both intra-articular and intramuscular injections. They have an anti-inflammatory effect, and are believed to stimulate the production of synovial fluid as well as prevent further degradation and facilitate repair of the cartilage itself.
The PSGAG most frequently used (Adequan) is injected into the muscle every four days over 28 days. "We just did a study of Adequan and its disease-modifying activities," says Frisbie, "and we found that it improved the health of articular cartilage."
IRAP Interleukin-1 receptor antagonist protein (IRAP) blocks interleukin-1, a protein that can accelerate joint damage. IRAP is produced naturally in the body, but researchers have found ways to bolster the amounts available.
The most widely used type of IRAP therapy involves taking blood from the arthritic horse and stimulating the production of IRAP as well as other undefined beneficial mediators from the white blood cells. The resulting serum, called autologous conditioned serum (ACS), is then injected into the same horse's inflamed joints in three treatments once a week.
The use of IRAP therapy has so far been limited to horses with advanced arthritis. "It's not the first line of defense," says Turner, "but it shows a lot of promise. And a lot of clinics are starting to use it." At a cost of around $1,200 to $1,500, IRAP is expensive compared to prices of $100 to $150 per treatment for other joint injections. However, Frisbie points out that "it may be cheaper to inject one joint every six months than it is to feed a supplement every day--so consider the cost ratio."
Extracorporeal shock wave therapy (ESWT). ESWT, which involves directing a beam of energy waves at a target site, has shown promise as a treatment for osteoarthritis in horses. In one study, ESWT-treated horses showed significant improvement in clinical lameness as well as in the concentrations of certain biochemical markers of the disease. However, further research is needed to fully demonstrate the efficacy of ESWT.
In severe cases, where there is no other way to alleviate pain, a surgeon may want to fuse a joint. Either by chemical, laser or physical surgery, the veterinarian destroys remaining cartilage, enabling the two exposed bone ends to grow together into a single, immobile structure. With the source of friction removed, the pain diminishes. In some cases, depending on which joints are affected, the horse may be sound enough for riding.
With careful management, many horses can live comfortably with arthritis for years. The goals are to keep them as active as possible, in order to stimulate circulation, while minimizing the risks of overuse and the inflammation it brings. Each horse's exact needs will vary, depending on the severity of his case; your veterinarian will help you plan a regimen that strikes the right balance for your horse. But here are the general guidelines:
Keep riding, if possible. Moderate exercise helps keep joints healthy by stimulating the production of synovial fluid and by strengthening the muscles that help stabilize the joints. "We recommend light work as long as it is in the horse's comfort zone," says Brosnahan. "You don't want to work a horse to the point of lameness."
Optimize turnout. Moving around in a pasture also provides exercise that reduces stiffness and allows the horse to move at his own pace. "For some horses, walking around a pasture and grazing is enough," says Brosnahan, "and anything more than that is too much." Keep an eye on herd dynamics, though. You don't want an arthritic horse to be chased to the point of exhaustion. Turnout in a smaller area with one or two quiet companions might be a better option. If turnout isn't available, make sure that horses confined to stalls get some form of daily exercise. If you can't ride or turn out the horse, take him for walks, as you would a dog.
Choose appropriate footing. Whether for riding or for turnout, choose footing that provides some cushioning without being too soft. Hard surfaces subject the joints to pounding, concussive forces, while ground that is too soft or deep can cause strains. Also avoid steep hillsides, rocky or uneven terrain, or other areas that invite overwork or missteps.
Have hooves trimmed regularly. Timely hoof care is important for all horses but especially so for those with arthritis, because regular trimming minimizes joint strain. "When the feet get long, there's more risk of torque and twist, especially when the feet crack and start to break up," says Turner. "You can also talk to your farrier about providing your horse with a more forgiving breakover."
Manage your horse's weight. As a horse's activity levels diminish, his weight is likely to go up, and additional pounds place more stress on joints. Evaluate your horse's diet to consider whether it's meeting his nutritional needs and is matched to his caloric needs. Consult your veterinarian or an equine nutritionist with any questions.
With modern treatment strategies as well as time-honored methods, horses with arthritis can live comfortable, almost normal, lives. But it's best to catch it in its earliest stages, before much damage has been done. And that means paying close attention to your horse's bumps, swellings and idiosyncrasies, especially as he reaches his mid-teens.
"By the time they reach the age of 15 or 18 or so, most horses experience some hock pain due to arthritis," says Frisbie. "The big question is, 'How well do we perceive it in our horses?' If you determine the horse is sore, you can decrease inflammation and get a more normal cellular environment. That, along with good conditioning to strengthen the area and protect against injury, gives the horse the therapeutic benefit he needs."
This article originally appeared in the July 2008 issue of EQUUS magazine.