Osteoarthritis is a progressive, chronic disease that causes the degeneration of joints, resulting in pain, stiffness and lameness in performance and pleasure horses of any age.
This leading cause of equine lameness mainly affects the leg joints – hock, fetlock, pastern, coffin, stifle and knee – but can also involve the back and neck. It can result from a single traumatic incident, but it is more likely to be brought about by repetitive injurious incidents or mechanical strain. Essentially, osteoarthritis is a breakdown in the cartilage of a synovial joint (i.e. a freely-moving joint).
Anatomy of a Joint
A synovial joint consists of the ends of two bones that are covered by smooth, supple articular cartilage, a connective tissue that allows the joint to move without friction while distributing pressure over the joint surface and acting as a shock absorber. The joint is covered by the capsule, a hard outer layer that connects the bones and provides
protection. The interior lining of the joint capsule, the synovial membrane, produces synovial fluid that fills the joint capsule to provide lubrication and nutrients to the joint.
When Disease Strikes
Because articular cartilage has no blood or nerve supply, it is unable to heal or regenerate. It is also susceptible to breakdown under increases in joint stress. When cartilage begins to break down, inflammation sets in as a natural healing response. The synovial fluid alters in composition as a result, and excess fluids enter the joint. Without its normal lubrication, the cartilage degenerates even further. The bone eventually is exposed, becomes damaged and tries to heal itself by producing more bone. The ends become thickened and the joint deforms.
While the horse generally doesn’t experience symptoms in the early stages of joint degeneration, by the time the bony
changes become visible, the osteoarthritis processes are already underway. But, said Dr. Sheila Laverty, chief of Equine Surgery at the University of Montreal’s Faculty of Veterinary Medicine and an osteoarthritis research specialist, “It’s the pain associated with the disease process that is the problem.”
If an owner suspects osteoarthritis in a joint, a veterinarian must be consulted to make a diagnosis and plan a treatment strategy. The vet will first do a lameness evaluation that could include observing the horse at a walk and trot on a lunge line, in-hand or under saddle, flexion tests as well as nerve and joint blocks, in which a local anaesthetic is injected to desensitize an area and isolate localized pain.
Radiographs (x-rays) are a first-line tool to diagnose osteoarthritis. They can’t pick up on the disease’s onset or its early stages because cartilage does not show up on x-rays; however, changes to the bone do appear. Laverty added, “The x-rays don’t always correlate with the level of pain. The role of pain in this disease is fascinating. Usually, when it’s very advanced, you will have pain. But in the early stages, you might have changes that might look like osteoarthritis on an x-ray, but the horse might be perfectly sound.”
The evolution of other diagnostic imaging technologies have enabled veterinarians to obtain more detailed evidence of osteoarthritis and can indicate its development at that critical early stage.
Ultrasound detects fluid in the joint and can also be used to evaluate some bone changes. It’s now possible to detect articular cartilage changes on magnetic resonance imaging (MRI), however, referral to a specialized centre is necessary. Nuclear scintigraphy (bone scans) can pinpoint the joint involved, but will not provide specific information on the disease stage or joint damage. Computer tomography (CT) scans can provide information on the bone changes and this technology is being assessed to evaluate cartilage. Arthroscopic evaluation of the joint provides a valuable assessment of the articular cartilage surface. However, general anesthesia is required and it is an invasive process.
The main treatment goals are pain reduction and the minimization or prevention of further deterioration by controlling inflammation. They are most effective when implemented early in the onset of osteoarthritis. “Probably the most important thing is weight control,” said Dr. Wendy Pearson, a University of Guelph instructor, who specializes in the research of medicinal plants and nutraceuticals for horses, has been exploring the possibility that mint could help reduce joint inflammation in osteoarthritic horses.
In Pearson’s experiments, mint is put through an artificial digestion procedure that mimics upper gastrointestinal tract digestion and metabolism by the liver. “We use the resulting extract to condition cartilage pieces – usually from pigs – that are stimulated to produce inflammatory chemicals in a tissue culture environment,” explained Pearson. “We then measure the amount of inflammatory chemicals the cartilage produces to see if there is less inflammation in the presence of the mint digest.”
The tested mint was developed by Dr. Laima Kott from the Department of Plant Agriculture at Guelph. It is bred to contain high amounts of rosmarinic acid, an anti-inflammatory substance. “The plant is strongly anti-inflammatory in the cartilage experiments and was able to reduce inflammation in live horses to a similar degree,” said Pearson. Studies are also set to take place that will investigate how mint might help humans who suffer from the disease.
Laverty said, “If a horse is overweight, there are [many] more forces going down the limb.” Also, she said, exercise has been repeatedly shown in human studies to decrease pain, especially before the disease is advanced and this is likely to apply to horses too. “So, rather than locking your horse up in the early stages, it’s much better to give the horse gentle exercise. Keep the horse moving,” she recommended.
Depending on the situation, other therapies can include hydrotherapy (cold water/ice packs), corrective shoeing, surgery and a host of medications.
Non-steroidal anti-inflammatory drugs (NSAIDs) such as the old standby phenylbutazone (bute), as well as flunixin meglumine, ketoprofen, naproxen and carprofen, have been used for decades to reduce the pain, swelling and stiffness of osteoarthritis. They are most commonly administered orally or by injection. Over time, their use can cause major side effects, however, including ulcers, kidney damage and colic, particularly in older horses.
Although more expensive, some of the newer NSAIDs show promise in providing the benefits without as many side effects of more traditional products. Firocoxib directly targets COX-2, an enzyme that is responsible for pain and inflammation. This targeted action is said to help reduce systemic side effects. Available as an oral paste in the US, firocoxib is prescribed in Canada in a pill format called Previcox.
Another option for localized osteoarthritis is the topical cream, diclofenac sodium (brand name Voltaren), which penetrates through the skin into the joint and can be applied by the horse owner themselves on a daily basis, if necessary.
Other treatments are administered directly into the affected joint – or intra-articularly. They must be given by an experienced veterinarian in a sterile environment.
IRAP, the acronym for interleukin-1 receptor antagonist protein, is a treatment that’s actually derived from the horse itself. Interleukin-1 is secreted by many types of cells to attack other damaged cells and infection. It can sometimes be detrimental to joint healing because it promotes inflammation and deterioration of joint tissues. IRAP blocks interleukin-1 from causing this damage. To obtain the serum, blood is drawn with a commercial syringe containing glass beads that stimulate production of IRAP and other proteins. It is then incubated and processed for 24 hours before injection.
Because IRAP is produced by the horse, and isn’t officially a “medication,” its use is popular among competitors seeking drugs that can’t be detected. But, at about $600 per joint/treatment, it’s an expensive option. (See Is a Pain-free Future Possible? for more on “regenerative therapies” like IRAP that use elements of the horse’s own body to provide relief – and perhaps even someday a cure.)
Another intra-articular treatment, hyaluronic acid (HA) has been used in horses for around 30 years. It is a natural component of synovial fluid, which lubricates articular cartilage. With HA treatment, a gel-like substance is injected to decrease friction within the joint, reducing pain and inflammation. It has also been shown to be effective when administered intravenously, which is particularly beneficial when more than one joint is affected.
Corticosteroids are fast-acting, long-lasting anti-inflammatories that have been used for about 50 years to treat joint problems. They remain one of the most commonly used osteoarthritis drugs and are the least expensive. Yet, controversy in the veterinary world has said that that some corticosteroids can actually cause the loss of structural compounds from joint cartilage. “Intra-articular corticosteroids have been much maligned,” said Laverty. “But they are the most potent antiinflammatories we’ve got and they help alleviate joint pain effectively.”
She calls them “valuable medication to keep horses functioning,” but said the dose needs to be tailored by a veterinarian to the situation.“They need to be used judiciously, so, in my opinion, they should be reserved for more advanced cases where the pain wasn’t controlled with intra-articular injections of hyaluronic acid or IRAP.”
Polysulfated glycosaminoglycan (PSGAG), probably better known by its commercial name, Adequan, used to be given intra-articularly, but now is often administered in the muscle. It is similar to compounds found in cartilage and has been shown to reduce inflammation.
Oral Joint Supplements
There are hundreds of nutritional supplements, or nutraceuticals, geared toward managing osteoarthritis. Some of the more prevalent ingredients in these blends are: glucosamine, chondroitin sulfate and methylsulfonylmethane (MSM). Other mixes include omega 3 fatty acids, avocado-soybean unsaponifiable extracts, yucca, devil’s claw, garlic, vitamin C…the list goes on.
Still hotly debated as to their efficacy, nutraceuticals remain unregulated. Laverty warns horse owners should be wary of false claims made by manufacturers, especially on the internet. For example, an unpublished study she undertook in her laboratory because she was “frustrated” by the type of advertising being made about glucosamine for use in humans and horses showed that some products claiming to contain the ingredient didn’t have glucosamine in them at all.
She advises using products from reputable companies, looking for a certificate that states that the contents have been analyzed. Dr. Wendy Pearson, a sessional instructor in the University of Guelph’s Animal and Poultry Science department, has researched medicinal plants and nutraceuticals for horses for about 15 years. She agrees that it’s a buyer beware environment. “The most important thing to recognize is that the industry is in a juvenile state and there are many products out there that would not meet a minimum standard for safety or efficacy,” said Pearson.
“The most solid protection the consumer has to ensure they are buying quality products is to purchase from companies with transparent accountability standards and to buy from companies that support their products with objective third-party research on safety and efficacy. Find a company that supports their products with research, can provide certificates of analysis for ingredients and products and manufacture to a well-established quality benchmark.”
Preventing osteoarthritis from occurring in the first place is critical. Despite common beliefs, not every older horse has the disease and even foals as young as six months can develop osteoarthritis. Consider some of the following tips to help avert osteoarthritis.
• Keep the horse moving, ensuring turnout and exercise are done carefully and appropriate to the horse’s condition.
• During exercise, warm-up slowly and cool down properly.
• Ice or hose limbs and joints after a hard workout.
• Regularly note any limb changes such as swelling or heat.
• Breed horses for optimum conformation – i.e. angular limb deformities can predispose horses to the disease.
• Provide young horses with ample turnout and exercise to develop strong joints as they grow.
• Ensure a qualified farrier shoes/trims your horse – incorrect balance can cause stress, particularly on the lower leg joints.
• Create a balanced nutritional plan for your horse to avoid obesity.
Any horse can develop osteoarthritis. But, with dedicated management – and help from a knowledgeable veterinarian – a horse can remain comfortable, happy and productive for many years.