Equine Joints and Arthritis: An Overview
For most horse owners we buy horses in order to have fun and partake in different athletic activities, whether that’s a sedate hack around the block or heading off and competing at Badminton, we all want our horses to do something.
Unfortunately, lameness is a relatively common problem affecting horses of all types and occupations, and one of the most common causes of lameness is joint disease.
The terms degenerative joint disease (DJD), osteoarthritis (OA), and arthritis are used in the equine world somewhat interchangeably and they all have similar meanings. The literal meaning of arthritis is inflammation of the joint, whereas osteoarthritis refers to inflammation of both bone and joint, DJD is a more general term denoting degenerative changes in a joint over time. As you can see one of the key concepts when we talk about joint disease is inflammation, most of the time this is initiated by traumatic injury, infection, degenerative processes or ‘wear and tear’. Once inflammation is started it may become self-perpetuating, where by the tissue damage caused by the inflammation actually goes on to cause more inflammation. When tissue is damaged the body releases chemical messengers that cause increased blood flow to that area, increased permeability of the blood vessels, pain, and swelling. Once inflammation is started, white blood cells and other blood products leave the circulation and focus on the region of injury, in this case the inside of the joint.
Equine joints normally contain a relatively thick viscous fluid called synovial fluid, which plays many important roles in the health of the joint including nourishing cartilage, waste elimination, hydrostatic stabilization, and lubrication. With inflammation, the volume of fluid within the joint will often increase, as protein and plasma from the circulation diffuses into the joint and is added to the synovial fluid. White blood cells then move into the joint, where they release damaging enzymes, free radicals, and pro-inflammatory chemical messengers.
Although inflammation is a normal part of the healing processes and is required to occur for healing to take place properly, it is when these stages occur at a level that is unacceptable that we see problems and we must take steps to try and ensure the inflammation is kept under control. The alteration of the normal internal environment of the joint, the changes in the synovial fluid and the cartilage, and the actions of the white blood cells lead to cumulative and potentially irreversible damage to the tissues of the joint. The synovial fluid becomes less viscous and nourishing, the cartilage loses its resiliency, the soft tissues lining and supporting the joint become thickened and stiff, and the bone beneath the cartilage becomes abnormal, sometimes even collapsing or changing shape. These processes result in impaired joint function and pain.
So while traumatic injury or “wear and tear” may be involved in causing joint disease, it is the body’s own reaction to these injuries in the form of inflammation which can exacerbate or perpetuate the injury leading to chronic osteoarthritis. A fundamental concept in treating this problem is reducing this inflammatory response, and many of the treatment options currently used in equine veterinary medicine are used in pursuit of this goal.
The best way to control DJD is to prevent it. Unfortunately, because this disease is often secondary to a traumatic incident, prevention is difficult. However, several areas of care can help reduce the possibility of developing DJD from an injury. A diet with balanced vitamins and minerals plus the correct ratio of roughage to grain should be formulated to help with the proper development of cartilage. As a foal, the conformation of the limbs will greatly influence the way the joint will wear as the horse matures.
When proper alignment is missing, abnormal wear may lead to premature DJD of the joint. Hoof care is an area that is often overlooked but has a lot to do with the proper alignment of the lower pastern region. Adequate trimming and shoeing can help maintain alignment. Finally, the training regime must be reasonable for the animal. It is important that the training ground is level and that the surface is not too hard or too soft. Each animal should have a work schedule tailored to its unique fitness level and injury status. Adequate muscling will help reduce the likelihood for injury and reduce the chances for DJD.
Treatment of the degenerative equine joint disease is generally limited to reducing joint pain and stiffness. Nonsteroidal anti-inflammatory drugs (for example, firocoxib, ketoprofen, and phenylbutazone) or corticosteroids may provide relief.
Chronic use of many of these agents can decrease or suppress chondrocyte metabolism and cause further degradation of the cartilage matrix by the inhibition of normal collagen and proteoglycans synthesis. Some NSAlDs can cause gastrointestinal ulceration and hemorrhage. The problems and limitations of NSAlDs and steroidal anti-inflammatory agents have recently led to a search for agents that relieve pain and inflammation and limit or reverse cartilage degeneration side effects. Physical therapy may prove helpful. In advanced cases, surgical fusion may be performed on selected joints. Some horses return to athletic soundness following surgical fusion of the pastern or tarsal joints.
While systemic treatment is an important component in the prevention of equine joint disease and in managing affected horses, local treatment of arthritis joints provides a method for targeted, highly effective treatment. In many cases, systemic medication alone is not sufficient to alleviate the pain of joint disease, and joint injection is needed in order to have the best chance of returning the horse to full function for a period of time.
Corticosteroids are an important group of medications, which have been and continue to be a mainstay in our options for treatment of joint disease. They are our most potent anti-inflammatory medications. There are different corticosteroid types used for joint injection, which differ in strength, time of onset, and duration of action. Not all are equal in their efficacy, and some may have detrimental side effects systemically and/or within the joint. Recent research examining the effects of triamcinolone has shown that this corticosteroid is particularly effective, and can have both symptomatic and protective benefits. The combined injection of corticosteroids and hyaluronate into arthritic joints seems to have a synergistic effect.
Recent research and development in the treatment of equine joint disease has led to the addition of biologically-based treatments to our range of options. These biologic treatment options use tissue from the horse such as blood, serum, bone marrow, or other tissues in the development of novel therapies.
Within the inflamed joint, a protein chemical messenger called interleukin-1 (IL-1) is one of the main signals for the propagation of inflammation. Another protein chemical messenger called interleukin-1 receptor antagonist (IRAP) acts to oppose the actions of IL-1 by blocking its cell surface receptor, which has a potent anti-inflammatory effect. This new treatment option can be used in horses that respond poorly to cortisone injections, or as an alternative treatment option.
Over the last several years there has been a high level of interest in medical circles and the media regarding the use of stem cells for medical procedures. The general concept of a stem cell is a cell type that is relatively undifferentiated and which has the ability to divide and produce more cells of this type. These cells can then differentiate into more specialized or specific cell lines, such as muscle cells, cartilage cells, tendon cells, etc. We can obtain these cells from the tissues of the adult horse (primarily bone marrow), and grow them in the laboratory as tissue cultures. In theory, the introduction of these cells in regions of injury could provide superior healing through tissue regeneration rather than tissue repair through scar tissue formation.
While this is an appealing theory, at this point there is a lack of evidence to show that this is what actually happens. However, despite gaps in our knowledge, there are some promising experiments and clinical studies on the use of bone marrow-derived stem cell cultures in the treatment of equine joints disease. These studies suggest that this treatment may modify the degenerative equine joints disease process and improve the health of the joint, although not in ways predicted by our theory of regeneration. It appears that these cultured cells may act to influence the overall cellular environment within the equine joint through inter-cell signaling mechanisms, reducing the cycle of inflammation and degeneration. While much is yet to be discovered about this type of treatment, it does show promise as an additional option for equine joint disease treatment in certain situations.
In our perpetual pursuit of higher, faster, stronger, it is important to recognise the price that our equine companions pay for our competitive aspirations. The harder we push for success, the greater the chance for injury. Responsible horse ownership should include recognising the risk factors for injury, understanding the options and methods for reducing risk and dealing with an injury, and taking action. Comprehensive prevention and management of equine joint disease in the equine athlete are affected by many factors; genetics, nutrition, training, fitness level, foot care, and veterinary care all play a role. By paying careful attention to all these factors, we can hope to reduce the impact of equine joint disease and have healthier, happier horses.