Management of Osteoarthritis in the Equine Athlete

There are many options for management of OA

I have already reviewed normal joint function and the ways osteoarthritis (OA) can develop and progress in our equine companions. While there is no cure for OA, we are lucky to have many tools available to manage the associated clinical signs and slow the progression of the disease.

Because OA is a progressive disease, treatment will likely become necessary at some point in an affected horse’s life to manage pain and inflammation, prolong athletic activity, and improve quality of life. Given the many treatment options available today, owners commonly choose a combination of systemic therapy, supplements, intra-articular medication, and careful rest and rehabilitation.

Systemic Therapies for Management of OA

Oral non-steroidal anti-inflammatory drugs (NSAIDs), such as phenylbutazone (Bute) have been a mainstay of OA treatment for years. These medications are easily administered and effectively reduce the pain and inflammation of osteoarthritis. Bute is often well tolerated, but serious and potentially life-threatening complications, such as gastric ulcers, kidney dysfunction, and right dorsal colitis, can occur. Risks are increased with high doses and prolonged administration; however, individual tolerance is variable, and some horses will experience adverse events even with a few doses. Therefore, traditional NSAIDs alone are not an ideal long-term solution for management of OA.

COX-2 Selective NSAIDs were developed due to concerns over the adverse effects seen with traditional NSAIDs. While traditional NSAIDs inhibit enzymes cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2), COX-2 selective NSAIDs, as their name implies, inhibit only one part of the inflammatory pathway targeted by NSAIDs. These COX-2 selective NSAIDs, such a firocoxib, are associated with fewer side effects than traditional NSAIDs like Bute. Because of the lower risk of adverse effects, firocoxib may be a better option for horses requiring an NSAID for long-term pain management.

Topical NSAIDs were developed in response to risks associated with systemic NSAID use. Diclofenac sodium (trade name Surpass) is formulated for topical application to the skin overlying one or more joints. The low systemic absorption means there are fewer potential side effects expected than with orally administered NSAIDs.

Polysulfated glycosaminoglycans (PSGAGs) and Hyaluronan (HA) are integral constituents of synovial fluid and cartilage within the normal, healthy joint. Formulations of PSGAGs and HA are available for systemic administration, either intramuscularly or intravenously, as well as intra-articularly. These formulations are intended to supplement or replace the naturally produced compounds that may be lacking in an arthritic joint. Studies have shown that these administered compounds are relatively short-lived. However, additional anti-inflammatory effect through interactions with the inflammatory cascades associated with OA have been theorized to provide additional benefit. Although somewhat costly, these treatments have been increasing in popularity due to relative ease of administration and few adverse effects.

Intra-articular Medications for Management of OA

Joint injections remain a mainstay of treatment for OA, with increasingly more products available for use by equine practitioners. Duration of effect, mechanism, side effects, and cost vary greatly among treatment options. For this reason, an individualized plan should be developed for each case, with consideration given to the degree of OA present, goals for future athletic use, and budget. Regardless of medication administered, joint injections carry inherent risk of joint inflammation (“flare”) or infection. Careful adherence to aseptic technique by the equine practitioner and close adherence to recommendations for stall rest and gradual return to exercise is critical to reduce these risks.

Corticosteroids are powerful anti-inflammatory agents that work by affecting the body’s natural immune response. They work at multiple levels to block the inflammatory cascade and prevent downstream effects. Early studies showed negative effects on cartilage health, with decreased chondrocyte size, loss of GAGs, and degeneration of articular cartilage with local bone necrosis. However, it is now believed that these effects were exacerbated by the high doses used in the early studies, and more recent studies using lower, more physiologic, doses show beneficial effects.

The three most commonly used corticosteroids are:

• Methylprednisolone acetate (Depo-medrol): long acting, dose-depended deleterious effects on articular cartilage. Physiologic dose inhibits inflammation while preserving normal joint environment
• Triamcinolone acetate (Vetalog/Kenalog): medium duration of action, fewer negative effects on articular cartilage and joint health. Higher risk of inducing laminitis than other corticosteroids
• Betamethasone (Betavet): intermediate- to long-acting glucocorticoid, no identified deleterious side effects on articular cartilage health.

Hyaluronan is produced by synovial cells and is found in joint fluid and articular cartilage, where it provides lubrication and shock absorption within the joint. HA also interacts with the inflammatory response within the joint by affecting the migration of cells and inflammatory compounds within the joint. Exogenous HA supplementation by intra-articular injection is thought to replace or augment the function of HA produced by the body. The physical presence of HA within the joint following injection is short-lived, but the anti-inflammatory effects may play a larger role in the improvement of lameness than providing physical lubrication alone.

Polysulfated glycosaminoglycans are also available for either intra-articular or intramuscular administration. These disease-modifying OA drugs have been known to alter progression of OA by supporting the natural healing functions of the joint and inhibiting detrimental effects of inflammatory molecules on cartilage. Although less useful for treating acute inflammation, these drugs are meant to prevent ongoing cartilage damage.

As you can see, there are many options to choose from when creating a plan for management of OA in the equine athlete. The veterinarian and horse owner working together as a team can design a treatment plan that is well suited to the horse, the condition, and the goal – whether that be high level competition or leisurely pleasure riding.

Research is ongoing to create and validate new treatment modalities to prolong the career and improve the comfort of our equine athletes and companions. In the next blog post, I will cover some of these more sophisticated treatment options.

—Rebecca Bishop, DVM