Osteoarthritis and Joint Therapies
By Dr. Amanda Wilson
The term "osteoarthritis," or OA, refers to a chronic inflammatory disease of joints that is characterized by degeneration of joint structures and loss of articular cartilage. Also referred to as degenerative joint disease, or DJD, OA is commonly diagnosed and treated in equine veterinary practice. Horses that have had long athletic careers almost always have some degree of OA present in one or multiple joints. Unfortunately, once the disease process has set in, the damage is irreversible. There is good news though: there are many different therapies and treatments available to manage the disease and to help prolong a horse's athletic career by keeping the inflammation and pain to a minimum.
This discussion focuses solely on "synovial" joints, the movable joints within a horse's body that are surrounded by a joint capsule and synovial membrane. Let's take a closer look at the components of synovial joints:
Two ends of bones covered in cartilage sit within a joint capsule, lined with synovium. The synovium secretes synovial fluid. Synovial fluid is a lubricating substance that lives within the joint capsule and protects the ends of the bone from direct contact. Healthy synovial fluid also provides nutrition for the cartilage.
How do horses get OA?
Just like humans, horses get arthritis from repetitive use of certain joints over time. This repetitive use causes a cascade of inflammatory events within the joint that eventually change the physical characteristics of the joint components. The modern athletic horse is asked to do a lot, regardless of discipline. Sharp turns, hard stops, propelling over jumps, and extended trots all create stressful physical forces within joints. These maneuvers can create forces that cause inflammation, leading to a progression of joint disease. Left unchecked, OA can cause significant changes within the bones and other structures that make up a joint.
What are the signs of OA?
The signs of OA can be very subtle in the beginning and only very observant owners may notice them. It is important to keep in mind that there are other diseases that can cause symptoms similar to OA and none of these signs are specific to one disease. The horse may become reluctant to perform a job that they once willingly did. For example, a show jumper may refuse jumps, or a roping horse may balk at going in the box. OA is a painful condition and the horse is simply trying to avoid the pain it knows will come with an athletic maneuver. Some willing horses may never refuse to do their job but owners may see a decline in the horse's ability to do his job as well as he once did.
As the disease progresses, the signs of OA can become more obvious. The horse may develop lameness (alteration in gait due to soreness of one or more limbs and/or other musculoskeletal structures.) Lameness due to OA can range from barely noticeable to very obvious. With lamenesses, it is important that your veterinarian perform a thorough examination and utilize available diagnostic tools to pinpoint the cause of the lameness as there is a huge list of conditions that can cause lameness, OA being one of them.
How does my veterinarian diagnose OA?
A diagnosis of OA is reached after careful examination and diagnostic imaging. The most common complaint that leads to this diagnosis is lameness. The goal with a lameness examination is to narrow down the limb and the area of the limb that the pain is originating from. The veterinarian will observe the horse moving at a walk and trot. Once the affected limb(s) are identified, we perform flexion tests to pinpoint a specific region. Flexion tests are designed to place pressure on a one to two joints for 30-45 seconds then the horse is trotted off. If the lameness worsens after a flexion, it can help narrow down where the pain is coming from. Another tool in the veterinarian's arsenal is "blocking," which refers to the use of local anesthesia (Carbocaine), to temporarily numb regions of a horse's leg and see if the lameness improves.
Once a particular limb and region are identified as the culprit, veterinarians use diagnostic imaging tools such as ultrasound, radiographs, and (less commonly) MRI, to assess the structures within the limb. Radiographs (X-rays) show mostly the skeletal structures and can be used to identify fractures, OCD lesions, arthritis, and other diseases affecting bones. Ultrasound is more helpful at assessing soft-tissue structures such as tendons and ligaments. MRI is typically reserved for those cases in which a diagnosis cannot be made from radiographs and ultrasound but the region of lameness is clear.
It is important to understand that OA can affect multiple joints at the same time. Also, as the horse moves differently to compensate for pain in one area, it can lead to pain in a different region. Your veterinarian may have to tackle several different regions of pain to make the horse comfortable. Sometimes, this can not be done immediately but rather in steps. For example, a horse suffering from coffin joint OA and stifle OA may need to have multiple lameness evaluations and therapies to get him comfortable. Please keep this in mind and allow your veterinarian time to address all causes of lameness. Remember: "Rome wasn't built in a day."
What are options for treatment of OA?
It is important to understand that OA is an irreversible process. Once the inflammatory process sets in, the effects are permanent. The goals of therapy are as follows:
1) Reduce inflammation to prevent further damage to the joint
2) Reduce pain
Once your horse has been diagnosed with osteoarthritis, there are a lot of different options for treatment. You and your vet should work together to determine which therapies your horse will benefit from most. There are several factors to consider such as joints affected, horse's age, discipline, availability of therapies, and cost.
NSAIDs (non-steroidal anti-inflammatory drugs):
NSAIDs such as Bute (phenylbutazone), Banamine (flunixin meglumine), and Equioxx (firocoxib) can help reduce pain and inflammation associated with OA. These should be used with caution and by the direction of a veterinarian because they can have severe side effects with improper use. These may be used in the initial phases of treatment until other therapies have time to take effect.
Joint injections (also called intra-articular injections) involve the injection of medications directly into affected joints. Corticosteroids and hyaluronic acid (HA) are the most common medications used in joint injections. Corticosteroids reduce inflammation. HA is a component of healthy joint fluid and injecting it at the same time as corticosteroids can help make joint fluid more viscous and provide better lubrication for the joint. Joint injections are typically reserved for moderate to severe cases of OA and have to be repeated at regular intervals for effectiveness. Eventually, some cases of OA become too severe for injections to be effective.
Polysulfated glycosaminoglycans (PSGAGs):
Adequan and Pentosan are the PSGAGs available for joint therapy. These are intramuscular medications that are proven to reduce inflammation within the joint and can actually help prevent further destruction of the joint structures when used appropriately. These are usually used for the duration of the horse's athletic career.
There are many oral supplements available for horses with claims that they improve joint health. Each of these supplements has variable amounts of the therapeutic medications. Your veterinarian can help you choose a supplement that is backed by research and is from
a reputable company if you decide to use one.
Although new to the joint therapy game, some biological therapies such as stem cells, interleukin-1 receptor antagonist protein (IRAP), and Platelet-rich plasma (PRP) have shown some promise in treating OA. The key to remember with these therapies are that they are still in the initial phases of research but can potentially help your horse's OA symptoms.
Your veterinarian may choose to use one or a combination of these therapies to treat your horse.
What is the prognosis for OA?
OA is a debilitating disease with irreversible effects. That being said, OA can be managed for long periods of time in performance horses, especially if caught early. Some horses can do very well with careful management. Some eventually have to be retired because the pain from OA is not manageable.
Osteoarthritis can be a difficult disease to manage but with appropriate therapies targeted to the horse's specific needs, we can manage horses with OA for long periods of time. As equine veterinarians, we want to help you succeed with your horse.
What medicines are available to treat this that don't have terrible side effects or that cause ulcers? And how often is treatment necessary to keep them comfortable and rideable?
The treatments listed above are all safe and effective when used appropriately. There are risks and side effects with almost any form of treatment, and your veterinarian is the best resource to determine which therapies to use/how much/how often for your particular horse. The frequency of treatment depends on which treatments are used. NSAIDs are not ideal to use long-term because of their side effects, but rather are used mostly in the early stages of disease, or in the very later stages of disease. Joint injections can vary in frequency too. Ideally, we can get about a year out of injections before we need to do them again. As the disease progresses, frequency may need to be increased. However, we do not recommend doing joint injections in the same joint any more frequent that every 3-4 months. Again, this is determined on a case-by-case basis. PSGAGs are given monthly after the initial loading dose, and continue for the career of the horse.
How can this be accurately diagnosed? And once a horse is affected, how often should x-rays be taken to check on the progression of the disease.
Accurate diagnosis depends on several factors: locating the region causing lameness (by flexions, blocks during a lameness evaluation), and imaging the region (X-rays, ultrasound, MRI.) Ideally, we would obtain radiographs on a regular basis (annually, every two years), but if a horse is getting regularly treated for OA and we know what works, we may not do this as often unless specifically requested by the owner. Again, OA is a permanent diagnosis and we are simply treating the inflammation. Once we know a horse has OA, we can treat them accordingly. If a horse is being treated regularly in one or two joints and develops a lameness from a different joint, then it is prudent to obtain x-rays of that area if they have never been done before.