Recent Advances: Managing Musculoskeletal Injuries and Arthritis

Wayne McIlwraith, BVSc, PhD, FRCVS, DSc, DrMedVet (hc), Dipl. ACVS, Barbara Cox Anthony Chair and Director of Orthopaedic Research at Colorado State University, spoke on current and new therapeutic options to manage musculoskeletal injuries and osteoarthritis at the AAEP Focus meeting in Ft. Collins, Colo., on July 29.

He reminded the veterinary audience that interleukin-1 (a deleterious cytokine) is at the head of the inflammatory cascade, leading to a breakdown in the cartilage matrix through signaling factors that alter regulation and effect of inflammatory biochemical mediators. The goals of therapeutic intervention focus on returning a joint to normal as quickly as possible, when possible, and to prevent the occurrence and severity of osteoarthritis in an injured joint.

McIlwraith discussed intervention that targets management of capsulitis (joint capsule inflammation) and synovitis (inflammation of the synovial membrane lining the joint), since these tend to occur in advance of degenerative joint disease. One strategy that merits more investigation is physiotherapy, such as swimming or underwater treadmill therapy. This might be cutting-edge therapy, but more research and data is necessary to determine the extent of its value. One point McIlwraith made of great interest is the recent finding that two-thirds of the force across the carpus (knee) at the trot comes from muscle forces, rather than ground reaction forces as previously believed.

McIlwraith mentioned that extracorporeal shock wave therapy (ESWT) significantly reduces lameness and synovial fluid parameters as compared to control horses (those not receiving treatment) in the study; these findings support a pain and inflammatory mechanism of action that elicits lameness.

The clinicians in the panel discussion were also favorably impressed with the use of ESWT, particularly for injuries at a soft tissue and bone interface, such as in the distal (lower) joints of the hock and in the rear third of the heel associated with soft tissue trauma. Back pain was another suggested use of ESWT; however, it was felt if the back could readily be injected, there was no sense in spending the money on repeated shock wave treatments. One clinician said shock wave might be especially useful to apply to capsulitis and soft tissue damage in joints that are not amenable to intra-articular (IA) treatment.

The topic of non-steroidal anti-inflammatory drugs (NSAIDs) has been one of great interest to horse owners because of their value in managing pain and inflammation, yet the well-known adverse effects of gastric ulcer syndrome preclude long-term use of NSAIDs. There has been an in vitro study from some years ago suggesting that phenylbutazone might be injurious to joint cartilage, but McIlwraith noted there is no data or clinical evidence to support this claim in the live horse. With the introduction of a new cyclooxygenase-2 (COX-2, an enzyme that causes inflammation and pain) inhibitory drug (Equioxx) on the market, some information has come to light: If COX-2 mediators are completely suppressed, it is possible to get an up-regulation of interleukin-1, this being counterproductive to managing pain and inflammation. McIlwraith stressed that we should keep an open mind about the advantages of this newly released medication.

Another common joint therapy uses intra-articular (IA) steroid injections. McIlwraith revisited the pros and cons of various corticosteroid drugs, noting that not all of these are created equal in regard to how effective they are and their role in protecting the cartilage. The use of hyaluronic acid (HA) in conjunction with IA steroid treatment has been well-applied in the veterinary world for years. HA is no longer thought to have a primary function as a joint lubricant, since its anti-inflammatory effects are more important. One study mentioned by McIlwraith was that of improvement in lameness of horses injected only with 2 mL of sterile saline, the mechanism as yet undetermined. In moderate to severe cases of osteoarthritis, intra-articular therapy should include both steroids and HA.

Intravenous (IV) treatment with HA labeled for this use (Legend) has had marked favorable effects of decreasing synovial effusion in an injured joint, with therapeutic effects persisting for 44 days following the third weekly treatment. There is common usage of IV HA as a prophylactic medication in normal horses without lameness, and data thus far has not verified this to improve a horse's gait.

McIlwraith reported that oral HA seems to have some positive effect, with some ingredient remaining active in the molecule or fragment of the molecule after it passes through the intestinal tract.

Polysulfated glycosaminoglycans (PSGAGs) are considered to be "disease-modifying osteoarthritic drugs," and although they might be slow acting, they are cartilage modifying. Most of the favorable studies in using Adequan come from its intra-articular use. Studies on IM Adequan have given equivocal effects in one study, yet positive anecdotal reports abound.

A new product called pentosan polysulfate is soon to be licensed in the United States. This substance, made from beechwood hemicelluloses, seems to be a disease-modifying osteoarthritis drug, but it's without any pain-relieving activity such as seen with NSAIDs. Lameness is not improved, but progression of cartilage deterioration might be abated by correcting biologic imbalances in an osteoarthritic joint. Pentosan polysulfate exerts anabolic effects on cartilage precursor cells to decrease erosion of cartilage.

Oral supplements and nutraceuticals have been a hot topic in the horse world for some time. McIlwraith describes these as materials that are fed to heal the lame or make a chronically unsound horse become sound. They are used with the intention of preventing joint problems from occurring. However, McIlwraith points out that if a product is not licensed as a drug, then the manufacturer of such a food product cannot make medical claims as to its efficacy. There are no criteria for licensing these products, and, hence, there is often misrepresentation of advertising. In addition, there is no regulation to ensure the ingredients claimed by the label to be in the bucket are actually present in the bucket.

More specifically, McIlwraith discussed glucosamine salts that in theory are building blocks for articular cartilage. In one Virginia study, he said less than 6% of the material fed was actually bioabsorbed from the intestinal tract. In a Canadian study, following administration of glucosamine via stomach tube, very low levels showed up in the joints. McIlwraith said in one investigative report, fewer than a third of nutraceutical products contained less glucosamine in the container than what was listed on the label. In addition, he asked the audience, how do we even know the correct dose for a horse?

Chondroitin sulfate is absorbed well, but as McIlwraith pointed out, this does not prove effectiveness in the horse. Another study showed a joint-protective effect of a combination of glucosamine and chondroitin sulfate (Cosequin by Nutramax), but no anti-inflammatory effect. Other studies looked at the use of nutraceuticals on joint health, and either the studies did not have sufficient numbers of horses to be scientifically sound, or the data was flawed. When reading the results of studies, it is important to identify who is funding the study, since a company's vested interest could skew the results.

Some research has proven efficacy of the use of omega-3 fatty acids to inhibit enzymes that break down the cartilage matrix. In a three- to four-month period, horses supplemented with omega-3 fatty acids seemed to have less stiffness and pain related to osteoarthritis.

Finally, McIlwraith touched on the supplement with unsaponified avocado and soy, which is thought to somewhat decrease interleukin-1 levels and cartilage disease scores. This might be a useful product to add to a nutraceutical supplement, and more research should be pursued.

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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