Osteoarthritis in Horses

Happy Monday everyone! 

Osteoarthritis is a common problem that many horse owners deal with on a daily basis.  We've written a brief educational article to highlight different aspects of this disease, as well as management and treatment modalities.  If you have any questions regarding this article feel free to add a comment or send us an email!

Osteoarthritis in Horses

 

Overview:

     Osteoarthritis (OA), which is sometimes referred to as degenerative joint disease (DJD), is a progressive degenerative process that can lead to pain, swelling, and immobility of affected joints. Some studies have shown that OA can be the cause of up to 60% of lamenesses. Osteoarthritis is something that almost every horse owner, especially those with performance horses, will encounter at some point.  Whether it occurs in the 22 year-old trail horse or the 3 year-old reining horse, there is no clear and accurate picture of the typical horse affected with OA. This isn’t just an old horse disease, as we often think of arthritis in people, but has been shown to be the source of lameness in horses as young as 2 years of age.

     OA is a disease process that affects joints; most often joints of the limbs but it can also be seen in the neck, back, and even the jaw. Many factors are involved but the end result is the weakening and destruction of the thin cartilage that lines the ends of bones where they come together to form a joint. Trauma is often the initiating factor, especially in young performance horses, and can be divided into two categories: 1) Abnormal forces on normal cartilage and 2) Normal forces on abnormal cartilage. Abnormal forces include repeated cycles of athletic trauma [even the activity of training or performing] and joint instability due to soft tissue injury or fractures. These forces induce a response that leads to pain and swelling of the joint as well as release of enzymes that damage the normal cartilage. There can also be abnormal cartilage in the joint caused by repeated abnormal forces, developmental bone disease [such as OCD] or the normal aging process. This abnormal cartilage is weaker and more fragile; therefore even the simple forces of walking around the pasture can damage it. Once the cartilage has been damaged the progression of OA has started. There is no cure available for osteoarthritis and once the cartilage has been destroyed there is no way for it to grow back, however there are many options available for management of OA. These options focus on slowing the advancement of cartilage destruction and controlling pain and inflammation; thereby making the horse comfortable enough to perform and have good quality of life.

Clinical Signs:

     Lameness, which is when the horse fails to move in a regular and sound manner, is the most identified clinical sign associated with OA. The degree of lameness can range from very mild to severe crippling pain. What a horse owner may notice can vary as well; sometimes it’s a performance issue or maybe the horse just doesn’t feel right when being ridden, while other times there is a visible limp when walking across the pasture. It is important to know that the sooner a veterinarian can diagnose the source of the lameness the better. This way appropriate therapies can be started to help slow the progression of OA. Another abnormality that can be identified is effusion or swelling of the affected joint. All joints are surrounded by a thick capsule, kind of like a big balloon, and when a joint is inflamed the capsule will swell up with joint fluid. A veterinarian can identify these swollen joints when they examine and palpate the affected joint. Occasionally heat can also be felt as a result of inflammation within the joint.  Another clinical finding that is associated with advanced chronic OA is new bone growth, commonly called bone spurs, around the area of the joint. Bone spurs can also be referred to as osteophytes or enthesophytes depending on where they are located.  Bone spurs are a result of abnormal forces sustained by the joint. The amount of new bone growth is not always associated with the degree of discomfort. Some horses with bone spurs that can only be seen with radiographs can be much more painful than horses with larger spurs that can be felt on palpation.

Diagnosis:

      The process of diagnosing OA can often involve many steps aimed at not only identifying where the disease is present but also eliminating other potential causes of lameness. A lameness exam with nerve and/or joint blocks is most often used to identify the limbs and joints affected. Imaging is the next step in the process and can range from radiographs and ultrasound all the way to advanced imaging like CT, MRI, and nuclear scans. Arthroscopic surgery, which involves putting a small camera into the joint, can also be used to identify and treat diseased cartilage. This procedure typically requires general anesthesia and is commonly used when abnormalities cannot be identified by other means.

Available Therapies:

         NSAIDs-

                  NSAIDs (Non-steroidal Anti-Inflammatory Drugs) are the oldest and likely the most well-known and accessible therapy available today. While phenybutazone (Bute) is often used there are newer products on the market that have a more targeted action and fewer side effects. Equioxx^® is an oral paste marketed for the treatment of pain due to OA and has fewer adverse effects than Bute. Surpass^® is a topical product that is absorbed through the skin and can be applied to the outside of the affected joint.

         Intra-articular Medications-

                  A wide range of medications are available today that can be injected into the diseased joint. Corticosteroids are commonly injected to help decrease inflammation and pain within the joint but caution should be used as some steroids can lead to more cartilage damage down the road. Another commonly used medication is hyaluronic acid, which is a component of healthy joint fluid and provides lubrication to the joint. Lastly there are products called polysulfated glycosaminoglycans (PSGAGs) that can be injected into joints to help protect what cartilage is left.  Examples of these products include Adequan^® and Legend^®.

         Intramuscular PSGAGs-

                  PSGAGs can also be injected into muscles, thereby treating the whole body. This can be helpful when more than one joint is affected and can allow some owners to do treatments at home.

         Regenerative Medicine-

                  This group of therapies represents the most recent advances in OA therapies, the most popular of which is a product called IRAP (Interleukin1-receptor antagonist protein). The product is autologous, meaning a horse’s own blood is used to make it thereby reducing the risk of reactions. Once processed, the resulting liquid, which has a high concentration of a specific protein that can block one of the major causes of joint inflammation and cartilage damage (Interleukin-1), can be injected into affected joints or frozen for later use. This product has proven in several studies to be effective in the early stages of OA as well as in some moderately affected cases. 

Prevention:

     Staring preventative measures early, especially in horses more likely to develop OA, can help delay the onset on clinical signs and slow the progression of the disease. Many different oral supplements are available that contain things like glucosamine and chondroitin sulfate, which can protect cartilage and keep joints healthy. Not all supplements are created equal and you should work with your veterinarian to select a product that is proven and safe. Intra-muscular PSGAGs can also be used as a preventative method to help protect cartilage before it becomes damaged.

     Management changes can also help to keep horses prone to OA comfortable. Low impact exercise like swimming or water treadmills can help keep joints healthy and mobile while reducing the amount of trauma to the cartilage. It is also important to make sure that the horse is physically fit enough for the job that they do. They should also be given appropriate warm-up and cool-down time when undergoing work. Weight management is crucial because a heavier horse can cause more damage to their joints over time and cause existing OA to progress more rapidly, all of which can lead to a more painful horse.

The Long Haul:

     So with all this information in front of you the big question you have to ask is what should you expect once your horse has been diagnosed? Therein lies the million-dollar question for veterinarians and horse owners today. Although our profession has made great strides in the research of why OA occurs and advanced therapy methods, there is still a great deal we don’t know about this disease. What we do know is that this disease is manageable, especially in mild and moderate cases. Even some severe cases can be kept comfortable enough to be used for light riding, breeding, or as nice pasture companion. What needs to be kept in mind is that there is no known cure for this disease and it will continue to progress over the horse’s lifetime.  Starting preventative measures early, diagnosing the issue as soon as possible, and getting appropriate therapies when needed can all help to slow the progress of OA and keep your horse doing what they love for years to come.