Diagnosing and treating equine osteoarthritis (OA) is a top priority for many equine practitioners. The disease causes lameness and can lead to the debilitating, premature end of a race or working horse’s career.
Clinical signs such as swelling, heat over the joint, pain, loss of flexion, evidence of fibrosis and loss of joint space in radiographs means damage has already occurred to the horse’s articular cartilage.
“About half of all horse farms have at least one horse with OA or a lameness issue,” says Allison Stewart, DVM, Dipl. ACVS, an associate professor at the University of Illinois.
“The use of ultrasound (for stifle and possible foot damage or laminitis secondary to OA), arthroscopy, radiographs and MRIs all contribute the making an OA diagnosis. Radiographs are most cost effective, but MRIs show more detail such as bone changes like bone anemia/sclerosis and reduced or increased signal in cartilage.”
Testing synovial fluid for an increased mononuclear cell count increase can evaluate for differential cellular counts, pH, total protein concentration and mucin precipitate quality, says Dr. Stewart. A more invasive method of detection is arthroscopy, possibly in chorus with an MRI, to definitively identify fibrillation on cartilage, other irregularity or loss of cartilage.
“Isolating the lameness area and identifying its cause is the first step in a treatment plan,” Stewart says. “Sometimes a diagnosis route is determined by the client’s budget. If the client has limited funds, I allocate the money for use in treatment more heavily than additional diagnostics.”
While many veterinarians are content with methods of definitively diagnosing OA, they’d like a more scientific way to prevent disease onset altogether.
Unlike predictions made in treating canine OA, specific horse breeds aren’t predicted to be at a higher risk or predisposition to the disease. Training regimen or work load is a more precise indicator of the likelihood of a horse developing OA–and at what age and which limbs will be affected.
“Training, conformation, track surface and genetics can all contribute to OA,” Stewart says. “Thoroughbred horses are likely to have forelimb problems while standard-bred horses present with OA in hind limbs. Typically the repetitive stress on a joint causes the disease.”
Horses age 20 and older typically have more than one joint affected by OA, but those diagnosed with the disease at a young age will require lifelong treatment and are often require a repurposed role.
“Sixty percent of athletic horses are retired because of OA,” says C. Wayne McIlwraith, BVSc, PhD, FRCUS, DSc, DrMedVet (hc), Dipl. ACVS, a professor of surgery and director of orthopedic research at Colorado State University. “Sometimes horses present with such severe OA that there’s not much else to do but fuse the joints.”
Joint fusion is a final effort by veterinarians to allow the horse to retain limb function. There are many treatment options available before fusion, although some horses are presenting with OA as early as age 2, and need decades of leg use.
“To combat joint disease or osteoarthritis in horses, veterinarians use autologous conditioned serum (ACS), also called by the product name IRAP ( interleukin-1 receptor antagonist protein),” Stewart says. “Corticosteroids alone or with hyaluronate sodium (Legend) can be an effective drug therapy, but stem cell therapy is promising. Right now stem cells are used more in tendon injuries. It’s hard to affect the cartilage surface, but stifle joints may show a response.”
Non-steroidal anti-inflammatory drugs such as phenylbutazone and firocoxib are commonly used to treat OA, says Alicia Bertone, DVM, PhD, Dipl. ACVS, the Trueman Chair in Equine Clinical Medicine and Surgery at Ohio State University.
“Polysulfated glycosaminoglycan (Adequan) intramuscular injection has anti-inflammatory effects, which treat symptoms and the degenerative disease process,” Dr. Bertone says. “Any of the chosen treatments can be used with supplements. Although not proven effective, they certainly can’t cause any harm.”
Educating owners and stressing the importance of a good diet, which is the building block for cartilage, are basic ways to advise clients on preventing OA, says Bertone.
“Keep in mind that from the knee down in the front and from the hock down in the rear, horses don’t have muscle,” Bertone says. “This is why joints in the lower leg are more likely to have OA. In addition to a good diet, owners can wrap legs prior to a workout to prevent an accident.”
Ann Rashmir-Raven, DVM, MS, Dipl. ACVS, of the University of Michigan, says not to underestimate the power of ice.
“Icing joints after exercise and workouts can prevent injury,” Dr. Rashmir-Raven says. “Just as with human athletes, icing gives fresh legs for afternoon training after a hard morning workout. Icing the joints isn’t simply strapping on some bags of ice, though. The entire joint has to have surface contact. Using ice boots that place icy water all over the joint is best.
“The old-timers used to put horses in a cold river to prevent laminitis,” she notes. “Horses have a tremendous ability to circulate blood, so there’s little concern for frost bite.”
Rashmir-Raven says horses can wear grooves in their stalls, which means over time an uneven floor develops.
“Horses should be standing on an even surface when in their stalls,” Rashmir-Raven says. “Making sure a horse is properly shod will prevent injury, laminitis and OA. Dogs can go three-legged, horses can’t. Horses’ sheer size makes lameness a big problem, but horses with OA shouldn’t just be stuck in a pasture. They need to be worked out.”
Experts say although treatment options are better now than ever, they’re hopeful a better way to prevent and treat OA will be developed–perhaps through a combination of dietary benefits known today and biologic treatment still being unraveled.
“The wave of the future is more preventive in nature,” Stewart says. “I don’t know if supplements will play a role, but it would be ideal and more scientific to inject supplements because we know it will be better absorbed than if taken orally.”
Some researchers hope that comparing biomarkers in equine blood samples can predict whether an individual animal is at risk of developing a bone or joint disorder, such as OA. If such a test becomes marketed, blood screening would permit preselection for breeding and give a heads–up to clients wanting to treat the disease preventively.
“The biotherapeutic use of the blood product platelet rich plasma (PRP) releases healing proteins called growth factors when activated in the body,” Bertone says. “There are many growth factors with varying responsibilities, but they do accelerate tissue and wound healing. This is a normal, natural way for the body to regrow cartilage in the joint. This is a very active area of research.”
McIlwraith uses more PRP now than just six months ago, based on positive results seen in his laboratory.
“Stem cell therapy has been more effective for us than other treatments,” McIlwraith says. “I remain very hopeful about stem cell therapies. We feel we need to devise a better, faster, more efficient way to treat OA because, unfortunately, this is a disease that can lead to euthanasia of an animal.
“It’s always weighed not only if the owner can financially pay to treat the OA, but if they are willing to treat a horse that may no longer be of use for them in the way they want it to be.”
Bertone rates OA as the No. 1 morbidity factor in horses.
“There’s not good data available, but I bet if you examined 20-year-old horses, they’d all have some level of OA. A great study would be to test a group of horses at age 5, 10, 15, 20, etc., and see how many have OA. Data would provide an excellent way for owners to plan how they can use their horses and what they can expect from them.”
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