Osteoarthritis (OA), also known as Degenerative Joint Disease (DJD), is a very common cause of lameness in horses. Arthritis simply means inflammation in the joints, but OA and DJD refer to a progressive condition wherein the articular cartilage, or padding between the bones, begins to deteriorate at a rate faster than it would normally be repaired. As a result, the bones undergo changes that restrict normal range of motion within the joint. The condition is painful, although it may not be obvious by the time that these degenerative changes have begun to take place. Eventually, the condition can be debilitating. The further the disease progresses, the more difficult it will become to treat.
Articular cartilage is maintained by chondrocytes, cells responsible for producing collagen and proteoglycans which form a highly shock-absorbing and smooth surface over which the bones will glide. During normal wear and tear, this cartilaginous matrix is constantly replenished by the cells, protecting the ends of the bones from damage caused by the stress of everyday activity. Healthy cartilage also maintains accurate tolerances between the bones, determining a specific path in which the joint can flex and extend (normal range of motion).
Degenerative changes allow the rate of cartilage deterioration to surpass the rate of reconstruction. The joint becomes unstable as the shape of the cartilage becomes deformed. Bones respond to increased pressures and joint instability by producing osteophytes, also called bone spurs. These abnormal projections may eventually calcify and harden in an attempt to stabilize the joint, albeit reducing the overall range of motion and being prone to fracture.
Osteoarthritis can occur as a result of an injury, chronic trauma to the joints (heavy exercise demands), congenital limb deformities, and improper shoeing. It can also occur without explanation in an otherwise healthy horse. The disease is very common in geriatric animals. Initial symptoms may be as subtle as a stumble or shorter stamina during a typical activity. As the disease progresses, the owner may notice a shorter stride length, a limp, overall exercise intolerance, one or more swollen joints, heat in the joints, and muscle atrophy (wasting) due to inactivity. Asymmetrical hoof wear may be another sign of OA.
At the earliest signs of arthritis, a complete physical exam should be performed by the veterinarian, who may take x-rays to confirm the arthritic changes within the affected joint. The degree of change on the x-ray is not always proportional to the severity of the animal’s symptoms; nonetheless, it may help the veterinarian determine how aggressive to be with treatment. Horses are good at concealing pain in order to avoid attracting the attention of predators, yet an x-ray may show significant disease. It is also very important to rule out other causes of lameness, especially infectious diseases.
There is no standard protocol for treating OA in horses; and unfortunately, there is no cure. There are numerous drugs, supplements, and therapies that can be employed to try to alleviate pain and slow the progression of the disease. Ideally, these are used in combination to provide multiple modes of action, and early in the onset of OA, in order to achieve the best results for the longest period of time. Below are some of the most common:
NSAIDs:
In many cases, non-steroidal anti-inflammatory drugs (NSAIDs) are chosen as a first approach because of their effectiveness in treating minor pain and swelling. They also have a relatively good margin of safety when dosed properly. Long term use and over-dosage is associated with gastric ulcers, bleeding tendencies, diarrhea, and liver and kidney damage. There are injectable and topical preparations of these drugs, the topicals being safer (but less effective) as they are only minimally absorbed and metabolized.
Corticosteroids:
Corticosteroids are potent anti-inflammatory medications that also suppress immune function. They are very effective for the treatment of OA when injected directly into the inflamed joint (intra-articular injection). They reduce swelling and inhibit white blood cell activity within the joint that is responsible for producing inflammatory enzymes. These drugs may be given systemically as well, but the effectiveness does not usually increase unless arthritis is widespread, and side effects are much more likely when given in this manner. Ill-effects from long term use include adrenal gland and immune suppression, laminitis, gastric ulceration, fungal infections, and liver damage. Side effects seen from steroids injected into a joint would include joint infections (although minimal with good technique).
Polysulfated Glycosaminoglycans (PSGAGs) and Hyaluronic Acid (HA) formulations:
PSGAGs and HA are thought to protect cartilage by inhibiting certain enzymes associated with degradation and increasing the activity of chondrocytes. Available as an intra-articular injection, and as an intramuscular injection, they have few systemic side-effects. Increased bleeding tendency is usually not seen at the recommended dosage but is possible, along with swelling at the injection site, and possible infection when given intra-articularly.
Interleukin-1 Receptor Antagonist Protein (IRAP)
Interleukin-1 is one of the inflammatory enzymes responsible for cartilage deterioration. IRAP intercepts this enzyme before it can bind to joint tissues and cause damage. Rather than a manufactured drug, IRAP is incubated and concentrated in a sample of the arthritic horse’s blood using special equipment. The blood is then centrifuged so that the IRAP-rich serum can be collected and packaged into sterile containers. IRAP serum is administered intra-articularly every 7 to 10 days for 3 treatments.
Oral Supplements and Homeopathic Remedies
There are thousands of over-the-counter supplements on the market for treating arthritis – for horses as well as humans. Many people dose their pets with their own “natural” remedies expecting similar results and margins of safety. There are also famous (and infamous) homeopathic remedies using all sorts of ingredients and incantations. Keep in mind that, while some may really work and really work wonders to relieve arthritic pain, none are regulated or standardized according to quality or quantity of the supposedly contained active ingredients. Glucosamine, chondroitin, hyaluronic acid, methylsulfonylmethane (MSM), and avocado-soybean unsaponifiables (ASU) are all unregulated compounds appearing in numerous supplements that have proven noteworthy in clinical tests when dosed to horses as unadulterated ingredients at therapeutic levels. The problem however, may be finding over-the-counter products that actually contain a significant amount of bio-available ingredients. Many supplements, while apparently safe, pass through the body un-utilized. Then again, some brands seem to work miracles for certain horses. Use discretion when selecting these alternative therapies. Consult a veterinarian if there is any question as to the safety of any product.
In any case, prevention of osteoarthritis is a more lucrative endeavor. Once arthritic change begins within the joints, the best a clinician can do is to attempt to alleviate pain and hopefully slow the progression of joint deterioration. Young animals should be assessed for confirmation abnormalities to prevent the onset of arthritic disease. Proper shoeing is vital, and avoiding repetitive stresses to joints in working and competing animals will help to prevent the onset of progressive degenerative changes to the articular cartilages. When arthritis does occur, early intervention will be much more effective than any treatment protocol instituted once the horse becomes debilitated.