Injections are becoming more and more common in all Equestrian disciplines. While they can be helpful in restoring proper joint movement and relieving pain, are injections really the best option for your horse?
As a horse is ridden, normal wear and tear on the joints, tendons and ligaments is expected. More damage is done to the horse’s body as he ages, and the training becomes more difficult. A horse’s joint is made up of synovial fluid, surrounding the space where the two bones meet (Fig. 1). The cartilage that surrounds the ends of the bones allows them to slide against each other as the horse moves. Osteoarthritis can occur when the cartilage becomes damaged and erodes. It is extremely difficult for cartilage to regenerate so the body creates pain and inflammation to keep the horse from using that joint to allow time for it to heal. Once a horse loses too much cartilage, the bone underneath will be exposed and begin to re-model. At that point it’s too late to fix; the damage is irreversible.
Knowing that almost all horses end up with arthritis as they age, it is in the rider’s best interest to prevent as much damage as possible to keep his horse happy and sound. There are several oral supplements that can help keep joints in good shape. Methylsulfonylmethane, better known as MSM, supports collagen production and has anti-inflammatory properties. Chondroitin Sulfate occurs naturally in the horse’s body in bones, tendons and ligaments and cartilage and can be used to replace the sulfate that has been lost. Glucosamine is a sugar compound that also exists in the horse’s body and can help to build more cartilage in greater quantities. However, studies have shown that glucosamine doesn’t always work as an oral supplement and should be given intravenously for the best results.
When a joint in a horse’s body becomes painful and inflamed, many riders turn to injections to “fix” the problem. Hock and coffin injections are the most common because of the strain any discipline puts on those joints. Corticosteroids are injected into the joints to reduce pain and prevent inflammation. There are several types: triamcinolone and methylprednisolone acetate, more commonly known as Vetlog and Depo-Medrol. Corticosteroids are a group of hormones that already exist in the body. They are produced by two adrenal glands close to the kidneys and they help to regulate inflammation. When injected into a joint, corticosteroids act as long-lasting anti-inflammatory agents by activating glucocorticoid receptors (GR) to regulate the transcription of target genes. Once activated, the GR are transported to the nucleus, where they bind to DNA at specific sequences in the corticosteroid-responsive genes called the glucocorticoid response elements (GRE). When two GR bind to negative GRE, there is an increase in the suppression of genes that encode the synthesis of inflammatory proteins. In this manner, corticosteroids inhibit the tissues within the joint from releasing chemical mediators that cause heat, swelling, fluid and pain.
Problems with Corticosteroids:
There are several issues with corticosteroid injections, the worst of which include potentially deadly infections. As with any injection, there is always a risk that an infection can be introduced to the body. Some veterinarians even prescribe antibiotics when they inject a horse, just in case some bacteria slipped into the injection site. There is also a positive correlation between corticosteroid injections and laminitis. Many horses have suffered from laminitis and some have even foundered after joint injections.
Although a great way to improve a horse’s well-being and prevent pain, corticosteroid injections can do more harm than good. The corticosteroids only block the pain and inflammation in a joint; they are not a cure for any underlying issues. When a horse is uncomfortable or lame because of a joint issue, the problem is likely the breakdown of cartilage between the bones (refer to the Biomechanics section). By blocking the pain and inflammation, a corticosteroid injection seems like a miracle because the horse is sound and comfortable within a few days. The rider, seeing no soundness problems, continues riding and training, all the while causing more trauma to the already damaged cartilage (Fig. 2).
Injections can offer months of relief, but as the cortisone levels in the joint diminish, another injection is needed, and the cycle continues. Once the cartilage is damaged, Polysulfated Glycosaminoglycans (PSAGs) like Adequan are used to try and repair it, but the results vary.
Corticosteroids also get in the way of normal tissue metabolism. This means that when tissues are damaged, the corticosteroids prevent the tissues from repairing themselves and they begin to die off. This seems to be more of an issue with horses that already have mild arthritis, but studies have shown that excessive amounts of corticosteroids can block tissue metabolism of a healthy horse too.
A molecule known as Hyaluronate occurs naturally within the cartilage and synovial fluid and is responsible for the lubrication of articular cartilage. Vets often inject HA in addition to the corticosteroid injections to support the lubricating qualities of synovial fluid and cartilage resilience. The most common HA injection is known as Legend. Injecting HA helps to maintain cartilage thickness and surface area smoothness, although it cannot restore the full properties of the Hyaluronate.
If injections are needed, they should be used as little as possible, and definitely not as a preventative measure. Remember, injections may help quiet joint inflammation and pain, but they are not a cure! Discuss all the options with your vet to make sure you do what is best for your horse.