One of the leading causes of lameness in horses, arthritis is essentially inflammation within a joint. A progressive disease, it can affect performance and pleasure horses of any age or breed. Arthritis occurs as a consequence of traumatic injury or, in most cases, chronic wear and tear, and runs the spectrum from mild discomfort to crippling.

Arthritis pain and stiffness is caused by the wearing down of articular cartilage and even, as it progresses, bone. Poor conformation can contribute due to irregular gaits or uneven loading of limbs, however, “A lot of the sports that horses compete in involve repetitive motions that over time may put more stress on certain joints than others,” explained Dr. Joanna Virgin, equine surgical specialist at Paton & Martin Veterinary Services in Aldergrove, B.C.

What’s in a Joint?

“There are many types of joints that differ in the range of motion and the types of connection between the bones,” said Dr. Virgin. However, she explained, arthritis usually occurs in synovial joints, which consist of an articulation (moving joint) between two bones lined by hyaline cartilage, a supple connective tissue that allows the joint to move without friction, distributes pressure over the joint surface and acts as a shock absorber.

“A fibrous joint capsule surrounds the joint, which is lined by a special type of secretory tissue called synovium,” she said. “The synovium contains the cells that produce the joint fluid, or synovial fluid, that acts as a lubricant. Outside the fibrous joint capsule, or sometimes contained within the walls, may be collateral ligaments that hold the joint together.”

Examples of synovial joints include the knee (which actually contains three joints) and the fetlock, a high-motion joint, which functions as a hinge to flex and extend. The lower hock joints or the pastern joint have very limited motion except for some of rotational or side-to-side movement.

When the joint is damaged in response to one-time or repeated physical stressors, an inflammatory response takes place. “This process is driven by multiple tissues including the synovial lining of the joint and the bone below the articular cartilage, the subchondral bone,” said Dr. Virgin. “This inflammation over time results in irreversible damage to the cartilage and eventually changes to the subchondral bone as well.”

Inklings of Equine Arthritis

Clinical signs of arthritis include reduced range of motion of the joint, pain, swelling, lameness and changes in performance such as shortness of stride, stiffness, uneven gaits, difficulty picking up or maintaining canter leads, reluctance to engage in work they had previously done comfortably. Arthritis can occur in any joint but, depending on what the horse does for a living, or how it’s built, occur in predictable locations. “The lower joints of the hocks are often frequently affected by arthritis in both English and western horses despite having a very limited range of motion,” said Dr. Virgin. “Other high-motion joints such as the coffin joint, fetlock joint or stifle joint may be affected by arthritis.”

If an owner suspects their horse has arthritis, they should consult a veterinarian for a diagnosis and treatment strategy. Early intervention can help control inflammation and slow the cycle of damage.

The veterinarian will first watch the horse move, either in-hand, on the lunge or under saddle. They will usually perform a lameness evaluation, flexion tests and often also do nerve and joint blocks to isolate localized pain. Sometimes arthritic changes can be felt physically. Dr. Virgin used the example of pastern ringbone. “Your veterinarian may be able to see and feel the excessive bone production occurring around the pastern joint in advanced cases.”

Arthritis is Incurable but Treatable

A definitive diagnosis is usually based on radiographs (x-rays). Remodeling – or replacement of old bone tissue by new tissue – around a joint and narrowing of the joint space are common signs, said Dr. Virgin. However, she added, arthritis isn’t always easy to diagnose, even with x-rays, especially if the horse doesn’t indicate pain or resistance to flexion or lameness exams. If an owner suspects arthritis due to performance or behavioural changes, there are further options to explore.

Other imaging technologies such as ultrasound, nuclear scintigraphy and thermography can also aid in the diagnostic process and help direct the course of treatment, but they may be cost-prohibitive and, in most cases, can only be carried out at an equine clinic or hospital.

Arthroscopic evaluation via insertion of an endoscope through small incisions is the only diagnostic tool that gives vets a good look at the articular cartilage, but in many equine joints we have a limited view of the joint, said Dr. Virgin. Arthroscopy can identify problems in the joint that may result in arthritis down the road, such as a chip or cartilage damage.

Arthritis is incurable, but treatment with the goal of slowing the disease’s progression can be successful and usually requires a combination of measures. These could be as straightforward as balanced nutrition and weight control to reduce forces on the joints and muscles, consistent, gentle exercise, and maintaining well-balanced hooves through regular farrier visits. Some horses may benefit from massage, acupuncture, chiropractic and other touch therapies.

Oral or injected non-steroidal anti-inflammatory drugs (NSAIDs), such as phenylbutazone (bute), as well as flunixin meglumine (better known by its brand name Banamine®) can reduce pain, swelling and stiffness, but aren’t suggested for long-term use due to their major side effects such as ulcers, kidney damage and colic. Although the newer-generation NSAIDs firocoxib and meloxicam are generally easier on the gastrointestinal system, they still are to be used short-term. The topical cream, diclofenac sodium, penetrates through the skin and is easily applied.

Joint Injectables for Horses

Injectable substances such as hyaluronic acid (HA), polysulfated glycosaminoglycan (PSGAG), and pentosan polysulfate (PPS) are intended to provide pain relief, stimulate cartilage repair, and reduce friction and inflammation.

However, said Dr. Virgin, there is “mixed evidence” to support the use of some of these medications. “We have not been able to show that long-term they can prevent arthritis and evidence for disease-modifying effects [stopping, slowing or reversing the disease] within a joint has been somewhat inconsistent. Some of these products may be useful in treating symptoms of arthritis when they are injected directly into the affected joint rather than given to the horse intravenously or intramuscularly. There is a bit more evidence to support the positive effects of polysulfated glycosaminoglycan and hyaluronic acid when injected directly into the joint.”

She calls corticosteroid joint injections “the classic therapy for arthritis treatment.” Inexpensive and fast-acting, they “are potent anti-inflammatories that are going to suppress the production of inflammatory mediators in the joint that are driving further inflammation and damage. Corticosteroids will also reduce pain associated with the arthritis. Like all things, they must be used judiciously and only at your veterinarian’s directive.” As with any intra-articular shots, there is the potential risk (albeit low) of bacteria being inserted into the joint and a very slight risk of laminitis.

The newest treatments, regenerative therapies, use the horse’s own blood or bone marrow to produce an anti-inflammatory product that is injected directly into the joint, said Dr. Virgin, citing Interleukin-1 receptor antagonist protein (IRAP), platelet-rich plasma (PRP), stem cells and Pro-Stride – a combo IRAP/PRP product.

These therapies, she said, “Provide growth factors that help change the cellular environment in the joint, which we hope can help facilitate repair of damaged cartilage and soft tissue structures in the joint. There is still a lot of research going on in these areas to determine their influence on cartilage repair, but we do know that most of these therapies seem to have a positive symptom modifying effect.”

Human-horse Arthritis Connection

Prevention is the key to eluding equine arthritis. Ensure your horse maintains a healthy weight, receives routine attention from a qualified farrier, is provided high-quality feed and is exercised and conditioned carefully and regularly.

“The best way to prevent wear-and-tear injuries to joints in the horse is probably similar to how you would prevent them in people, said Dr. Virgin. “Avoid repetitive stress injuries and vary your horse’s routine and workout, cross-train when applicable and maintain steady physical activity, such as providing turn out. If we knew the magic bullet to prevent arthritis, it would be world-breaking news. Unfortunately, researchers and scientists haven’t figured out how to do that in humans let alone horses.”

Research into equine arthritis usually serves a double purpose, as the horse is an ideal model for the disease in humans. Cartilage changes that occur in the horse mirror what happens in people. Investigations continue into gene therapy – using genes to treat or prevent the degenerative process. Results of a 2014 study out of Texas A&M College of Veterinary Medicine & Biomedical Sciences indicate gene therapy, still in its infancy in equine medicine, combined with stem cells, which are widely used in treating injuries, could reduce the progression of early-stage arthritis. Also interesting is the further understanding of biomarkers for arthritis. Biomarkers are measurable indicators or signals – cellular, biochemical or molecular – of a disease process in the body. Detecting biomarkers would allow identification of arthritis at a very early stage, facilitating changes to the horse’s management that may mitigate joint damage.

Although the understanding of arthritis’s mechanisms is ever expanding, we may not yet be able to permanently cure our horses (or ourselves) of the disease or prevent it altogether, but with improved and newer generation treatments, along with the old standbys, we can now do more than ever before to keep them comfortable and active as long as possible.