Protecting Equine Athletes from Osteoarthritis

Since most horses are used for recreational or performance activities, soundness is understandably of vital importance to horse owners. A 2003 study suggested that 60% of lameness problems in horses are related to osteoarthritis, thus stressing the importance of advancements in treating this disease. In humans osteoarthritis is the most common type of arthritis, and in the U.S. alone it afflicts more than 20 million people.

A horse's joints give its skeleton flexibility and allow walking, trotting, running, jumping, and moving its neck and head. The primary factors limiting these activities in the horse are pain and lameness that accompany joint disease. While it can develop in any joint, it is most common in weight-bearing joints, such as the hock, fetlock, pastern, and coffin. Other joints can also be affected as the result of previous injury or from repetitive or abnormal stress.

Osteoarthritis can be considered as a group of disorders marked by progressive deterioration of the articular cartilage (cartilage that covers the surfaces of bones connected at a joint) accompanied by changes in the bone and soft tissues of the joint. This cartilage, which is critical for joints to function normally and alleviates the stress placed on a horse's joints during exercise, coats the ends of the articulating bones and contributes to friction-free motion.

The earliest stage of osteoarthritis (OA), or degenerative joint disease (DJD), occurs when the biochemical components of the articular cartilage (collagen and proteoglycans) start degenerating and the cartilage commences to break down. As the cartilage deteriorates, the body attempts to repair it but is unsuccessful, in part because of the loss of specialized cells called chondrocytes. Because the remaining cells are damaged, they prove unable to produce new cartilage of sufficient quality for effective repair.

Among the contributors to OA are synovitis (inflammation of the soft, pliable membrane lining a joint) and capsulitis (inflammation and thickening of the fibrous tissue enveloping the joint). Other contributors are bone fractures and injury to the bone just beneath the cartilage (subchondral bone). Damage to the subchondral bone not only contributes to degraded articular cartilage and the osteoarthritic process, but is also the first stage in the development of fractures. Soft tissue injuries including disruption of an intraarticular ligament or a meniscus can also lead to OA.

The principal methods for treating OA revolve around the cause of the cartilage breakdown. Treatments for synovitis and capsulitis include physical therapy, intraarticular corticosteroids, intraarticular and intravenous hyaluronan, polysulfated glycosaminoglycans (PSGAG), and new biological therapies, such as gene therapy with interleukin one-receptor antagonist (this protocol has been shown to effectively combat OA but is not yet commercially available), and/or autologous conditioned serum (IRAP).

All are used to try and decrease the inflammation in joints to relieve pain and decrease the cartilage breakdown. All have been shown to be beneficial through research.

Fractures and subchondral bone disease are addressed by arthroscopic surgery, as are meniscal and some ligamentous injuries, while more severe fractures require internal fixation to stabilize the joint. Immediate and correct treatment of these injuries is important to prevent progressive loss of articular cartilage and OA.

Once articular cartilage is lost, restoration of repair tissue is challenging. It is possible that modern medicine, in conjunction with a judicious balance between exercise and rest, might enable a horse to return to some level of activity, usually at a lower level than before the onset of the disease. On the other hand, OA can end a horse's competitive career. Although advances are being made in treatments, such as removing articular cartilage from one location and implanting it in the problem area or transplanting cultured cells, much remains to be learned in order to restore damaged cartilage and joint function.

Even less research has been done on prevention. In Thoroughbred racehorses, poor racetrack surfaces have been implicated in joint injury as well as certain conformation problems. Training techniques for young horses also appear to be important in creating resilient cartilage which can hold up during the rigors of competition.

A number of methods including early exercise, early diagnosis of problems, and thorough evaluation of horses before they go into training have the potential for decreasing the amount of day-to-day and catastrophic injury. Earlier diagnosis is critical as the disease is too advanced when it can be diagnosed with X rays. The new methods include novel imaging techniques, as well as fluid biomarkers. Much of this research is costly and time consuming but is worthwhile for the welfare of the horse and economic health of the industry. More investigation of OA prevention is needed to help our equine athletes.

In a survey of American Association of Equine Practitioners members by the AAEP Foundation in 2003, lameness and arthritis ranked third and fourth, respectively, among diseases/disease categories the veterinarians believed needed additional research. Although studies on osteoarthritis have been funded by the Morris Animal Foundation and Grayson-Jockey Club Research Foundation, additional research to combat this commonly occurring disease is necessary.

The equine veterinary community needs your help in this endeavor. Donations to the Morris Animal Foundation, the Grayson Jockey-Club Research Foundation, the American Quarter Horse Foundation, the American Association of Equine Practitioners Foundation, Inc., or your favorite veterinary school will help support research into the prevention and treatment of osteoarthritis.

Please contact the AAEP Foundation for information about how to make donations for equine research, or call 800/443-0177 (within the U.S.) or at 859/233-0147. This is just one of the many efforts that the AAEP is coordinating on behalf of the industry through the Equine Research Coordination Group (ERCG), which is comprised of researchers and organizations that support equine research. Organized last year with a mission of advancing the health and welfare of horses, the ERCG promotes the discovery and sharing of new knowledge, enhancing awareness of the need for targeted research, educating the public, expanding fundraising opportunities, and facilitating cooperation among funding agencies.

About the Author

C. Wayne Mcllwraith, BVSc, FRCVS, PhD, Dipl. ACVS, Dipl. ECVS

C. Wayne McIlwraith, BVSc, FRCVS, PhD, Dipl. ACVS, Dipl. ECVS, is Director of the Orthopaedic Research Center, Veterinary Teaching Hospital at Colorado State University, and a past president of the American Association of Equine Practitioners.

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