Osteoarthritis: Not Just an Old Horse Disease
There is no need to start panicking about osteoarthritis (OA) the day your foal's feet hit the ground, but its impact should be considered following every footfall thereafter.
When a horse owner says, "My horse has arthritis," the image that often first pops into our heads is an older, wizened, slightly swaybacked, retired horse standing alone in a field slowly plodding along, while his younger counterparts gallop happily past.
"This is simply not an accurate picture of a typical horse with OA," laughs C. Wayne McIlwraith, BVSc, PhD, FRCVS, DSc, Dr. med vet (hc), Dipl. ACVS, Barbara Cox Anthony University Chair and Director of the Orthopaedic Research Center at Colorado State University (CSU).
In fact, the available data show that more than 60% of equine lameness is attributable to OA, and it is widely accepted that OA can affect any horse at any age. However, we have no firm numbers to show exactly which young horses get the disease.
Because there is no cure, the management and prevention of OA continues to be a hot topic for equine practitioners and researchers. Recently, McIlwraith presented an update on OA for his colleagues at the 11th Congress of the World Equine Veterinary Association (WEVA), held in September 2009 in Guarujá, Sao Paulo, Brazil. This article communicates McIlwraith's key points presented at WEVA and relays the most recent research on various treatment modalities to keep young horses with OA functioning as fully as possible.
OA in Younger Horses
Osteoarthritis is a disease of joints with multifactorial causes that results in the progressive degradation and destruction of articular cartilage: the very thin layer of highly specialized connective tissue lining the ends of the long bones where they join. In young horses OA is predominantly trauma-related.
"Trauma can damage joints via a number of ways, but can be categorized into two major pathways: abnormal forces on normal cartilage or normal forces on abnormal (diseased) cartilage," explains McIlwraith.
For example, repeated cycles of athletic trauma, loss of stability or development of joint incongruities (e.g., secondary to fractures, ligament injuries, etc.), and remodeling and microfracture in the bone underlying the articular cartilage can all negatively impact normal articular cartilage. Similarly, normal forces on cartilage damaged via synovitis and capsulitis (i.e., inflammation of the lining of the joint and the capsule overlying the joint, respectively), the normal aging processes, or condi-tions such as osteochondrosis (failure of the bone that underlies articular cartilage to mineralize; can lead to osteochondritis dissecans, or OCD) can equally and negatively affect the cartilage in joints.
"Regardless of the underlying cause, the result is the physical breakdown of articular cartilage culminating in a hot, swollen, painful joint and loss of function," he says.
The Impact of OA
Osteoarthritis continues to be an important topic in equine practice because of its far-reaching impact.
"According to the American Horse Council, the horse industry has a total impact of more than $100 billion on the U.S. gross domestic product," relays David Frisbie, DVM, PhD, Dipl. ACVS, a leading researcher in the field of osteoarthritis who's based at CSU's Gail Holmes Equine Orthopaedic Research Center.
Osteoarthritis resulting in loss not only impacts the horse and owner, but also the more than 4 million people associated with the industry, including trainers, service providers, and associated business owners.
"Treatment costs for OA include those direct out-of-pocket expenses (i.e., treatment- related costs), plus indirect costs such as lost income due to time spent on the affected horse instead of working, lost leisure time, and increased time and expenditures managing the patient with OA," says Frisbie. "Together, these direct and indirect costs can accrue, particularly with horses that develop OA at a very young age."
Osteoarthritis is a progressive disease with no known cure. This means that once a horse develops it, OA will slowly progress for the remainder of the horse's life. Treatment invariably will be necessary at some point during an affected horse's life to manage pain and discomfort, control swelling, prolong the horse's athletic function (which can include competing or simply trail riding), and maximize his lifespan. At present, a multimodal treatment approach is advocated. This includes:
- Pain management via administration of non-steroidal anti-inflammatory drugs (NSAIDs) or corticosteroids;
- Intra-articular medications (hyaluronic acid, polysulfated glycosaminoglycans);
- Intramuscular polysulfated glycosaminoglycans;
- Weight management;
- Non-weight-bearing exercises (e.g., swimming) and physical therapy;
- Dietary modification (adding omega-3 fatty acids); and
- Oral joint health supplements (OJHSs) including glucosamine, chondroitin sulfate, methylsulfonylmethane (MSM), avocado/soybean unsaponifiable extracts (ASU), etc.
Administration of anti-inflammatory drugs--orally, topically, intravenously, or intra-articularly--remains a mainstay in OA management. Non-steroidal anti-inflammatory drugs (NSAIDs), such as phenylbutazone (Bute), are likely the most well-known and accessible treatments; however, clinicians have increasingly recognized safety concerns and encouraged alternatives.
"NSAIDs that inhibit the enzyme cyclooxygenase-2 (COX-2) such as firocoxib are associated with fewer side effects than Bute, which inhibits COX-1," says McIlwraith.
The potential negative side effects from the COX-1 inhibitors spurred the development of topical NSAIDs, including the U.S. Food and Drug Administration (FDA)-approved product containing 1% diclofenac sodium (trade name Surpass). This product, because it is applied topically to the skin overlying one or more joints, does not appear to have the negative side effects seen with some orally administered NSAIDs. Given the low systemic absorption of this product, clinicians expect fewer potential side effects than with orally administered NSAIDs.
"Using an experimental model of OA, the diclofenac cream had both symptom- and disease-modifying effects, meaning that it improved clinical signs of disease and slowed the progression of OA," says Frisbie.
Injecting anti-inflammatory corticosteroids intra-articularly is also an extremely common treatment method. But McIlwraith says not any old steroid will do the trick.
"Marked beneficial effects have been noted after using betamethasone esters (trade name Celestone) and triamcinolone acetonide (trade name Vetalog), and deleterious effects have been identified when methylprednisolone acetate (trade name Depo-Medrol) is injected," he says. "Despite widely relaying this finding, methylprednisolone acetate continues to be an all too commonly used steroid in horses with OA that will ultimately prove to expedite loss of articular cartilage, loss of function, and loss of the horse."
Betamethasone and triamcinolone each can be used alone; however, it is common practice to use a combination of steroid and hyaluronic acid. Frisbie and colleagues revealed in studies that the product used (Hyvisc), injected 14, 21, and 28 days after surgically inducing OA, had disease-modifying effects on OA.
"Similar results were obtained with intra- articular polysulfated glycosaminoglycans, supporting the use of this product as well in horses with OA," notes Frisbie.
Going the Extra Mile
In addition to the above-mentioned approaches, several emerging therapies for equine osteoarthritis are either newly available or on the horizon. The available data regarding these techniques were reviewed by McIlwraith during his presentation at WEVA and are summarized here.
Autologous conditioned serum (ACS) (trade name IRAP, which stands for interleukin-1 receptor antagonist protein) This commercially available tool involves using the horse's own blood to generate "conditioned serum" after incubating the blood sample with specially designed beads. This serum is enriched with growth factors and anti-inflammatory mediators, such as interleukin-1 receptor antagonist (IL-1ra). The clinician then injects the conditioned serum intra-articularly. Investigators performing studies at CSU demonstrated both symptom- and disease-modifying effects. IRAP is also used for soft tissue injuries, but when it comes to joints, it is primarily indicated post- surgically (e.g., after removal of articular chip fractures) or in horses with OA that are no longer responsive to intra-articular injections of hyaluronic acid and Vetalog.
Platelet-rich plasma (PRP) This is a fraction of whole blood that contains a concentrated source of platelets, which are microscopic storage facilities for a variety of growth factors that facilitate healing. This treatment is also commercially availa-ble, but clinicians primarily use it in the management of soft tissue injuries and skin healing. No controlled studies evaluating PRP in OA have been conducted.
Gene therapy with IL-1ra This agent is an inhibitor of the inflammatory mediator IL-1. Frisbie and colleagues have been working on inserting the IL-1ra gene into a virus to deliver high doses of the IL-1 inhibitor into joints with OA.
"We are hoping that this technique, referred to as gene therapy, will effectively arrest OA in the horse and will be a clinical reality in the near future," relays Frisbie.
Extracorporeal shock wave therapy (ESWT) Scientists studied ESWT using an experimental model of osteoarthritis. It appears to be useful in decreasing synovial membrane and joint capsule inflammation, and it improves signs of OA in affected horses.
Physical therapy and rehabilitation While widely recommended and utilized throughout the industry for horses with mus-culoskeletal injuries, little data is available supporting the presumed beneficial impact of physical therapy on OA. To remedy this, a study is currently under way at CSU using an experimental model of OA to assess the effect of underwater treadmill use on OA.
"We anticipate data to be available in the next year," says Frisbie.
Since the exact pathways by which OA develops in horses remain largely ill-defined, preventing OA is challenging.
"In younger, healthy horses with repeat trauma, the focus should be placed on minimizing injury and promptly treating causes of joint instability, such as intra-articular fractures, ligamentous tears, and incongruent joint surfaces (caused by OCD)," suggests McIlwraith. "Early treatment of inflammatory conditions in the joint tissues, such as synovitis or capsulitis, can delay or possibly even prevent OA."
Prophylactic use of IM polysulfated glycosaminoglycans is widespread; but the beneficial effect of this practice remains to be demonstrated in controlled clinical trials.
"Due to the challenges associated with equine experiments, the prophylactic use of PSGAGs is not currently being evaluated," says McIlwraith. "That said, it is agreed that prophylactic intramuscular administration is not likely to be harmful."
Another potential (and possibly more economical) approach to preventing OA is the use of a glucosamine- and chondroitin sulfate-containing oral joint health supplement prior to injury, trauma, or development of OA. According to McIlwraith, unlike studies of polysulfated glycosaminoglycans in horses, research in dogs does support the use of OJHSs prophylactically. Specifically, dogs receiving a glucosamine/chondroitin sulfate combination product for 21 days prior to induction of an experimental acute synovitis had significantly less evidence of joint inflammation than the control group or dogs that were treated after the induction of the synovitis.
McIlwraith explains, "Similar studies evaluating the prophylactic use of OJHSs to prevent OA in horses have not been pub-lished, but OJHSs are widely used for this purpose throughout the equine industry."
It is important to recognize that any horse can develop OA and that each horse owner's and veterinarian's approach to treating or preventing OA will vary. Even though OA is incurable, it does not mean that OA is unmanageable.
"There are some viable options for slowing the progression of OA, particularly in young horses with ambitions to remain athletes for as long as possible," summarizes McIlwraith.
About the Author
Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.
POLL: University Equine Hospitals