Working horses are commonly diagnosed with, and are treated for, acute or chronic joint inflammation. For many decades, intra-articular (IA) injections of corticosteroids have been used to treat these conditions. However, considering how popular these injections are and the fact other treatment options exist, there is little consensus on questions regarding the “best” corticosteroid, how often such injections can be used, and how ultimately deleterious they are to joint cartilage.
Corticosteroid injections are one of the most commonly prescribed treatments for joint pain and inflammation resulting from osteoarthritis. Arthritis, of course, is inflammation of a joint. Uncontrolled, osteoarthritis is thought to lead to chronic changes in the cartilage and underlying subchondral bone. The cycle of inflammation, cartilage and bone damage, pain, and further cartilage and/or bone damage from ongoing inflammation can result in horses that are unable to perform for their intended use, or worse, are chronically lame and in pain.
Corticosteroids are injected into joints in an effort to decrease inflammation. While the drugs are not directly pain-relieving, reducing joint inflammation can help interrupt the joint-inflammation cycle, thereby reducing pain. By decreasing pain and inflammation, horses are able to move more normally.
Commonly used corticosteroids
Three long-acting corticosteroids are commonly used in the treatment of equine joint inflammation. They are:
- methylprednisolone acetate (MPA);
- triamcinolone acetate (TCA); and
For as long and as often as these drugs have been used, it’s actually fairly remarkable there is so much left to be learned about them. As such, they are the subject of a considerable amount of controversy.
Comparative benefits and detrimental effects
Simply stated, there is little data to indicate one corticosteroid is better than another when it comes to IA administration. Further, there are no established doses. In fact, one can support just about any position one wants when it comes to the use of a particular intra-articular corticosteroids. For example:
- Whereas research in the 1980s suggested the “best” corticosteroid to use in joints was betamethasone, work in human medicine suggests this drug is the most deleterious corticosteroid for joint cartilage.
- Whereas research with large, repeated doses of MPA led some to conclude this drug should not be used in horse joints, research at lower doses has shown it is chondroprotective. In fact, MPA has been shown to have beneficial effects on the proteoglycan metabolism of interleukin-1-treated equine chondrocytes in vitro.
- Whereas some may use TCA in the belief it is most likely to be chondroprotective and the least likely to cause harm, it has been shown to also have deleterious effects on cartilage, and specifically in horses.
These confounding results should not be unexpected. The effects of various corticosteroids on cartilage metabolism differ between normal and inflamed joints. In addition, there is no evidence to indicate any one corticosteroid for intra-articular use is fundamentally much different from another. In other words, there is no evidence individual medications work at different receptors or have different mechanisms of action. In fact, the only demonstrable differences between the various corticosteroid drugs seem to be in bioavailability and potency (i.e. in terms of the biological effect per mole of drug).
How often between injections?
In human medicine, most clinicians wait a minimum of three months between injections. Further, they remove joint fluid before injection to confirm the needle’s placement in the joint. Doing so also appears to enhance the therapeutic benefit. It is also common practice to include a one percent lidocaine with corticosteroid injections to provide immediate pain relief. In horses, an ideal interval for injections has not been established. However, equine studies indicate the effects from a single IA corticosteroid injection can be expected to last approximately two months.
Whatever the beneficial or detrimental effects of individual corticosteroids or dosing regiments, IA corticosteroids alone should not be considered as the sole management strategy for osteoarthritis. As with any incurable conditions, there are many treatment options that may have more or less evidence for their effectiveness. Effective interventions may include:
- Systemic nonsteroidal anti-inflammatory agents: Several are available and all have shown some efficacy and side effects.
- Maintaining a healthy weight: Obesity appears to be a significant problem in many horses. In other species, reducing weight has been shown to be helpful in the management of arthritis. The rationale is obvious; less weight means less force applied to a joint. For example, in humans, there is a direct relationship between weight and force applied to joints. Every pound of body weight causes an additional four pounds of weight on a joint. In dogs with hip osteoarthritis, weight management has been shown to be the single most effective nonpharmacological management tool. One study found that following a body weight loss of 11 to 18 percent, dogs with osteoarthritis were less lame.
- Movement: Other management techniques that could help horses with osteoarthritis include daily access to turnout and getting regular, daily exercise. If horses must be temporarily housed in a box stall (e.g. at a competition), frequent hand-walking and allowing ample time for a slow warm-up might help.
Osteoarthritis is an incurable condition for which many treatments exist. Corticosteroid injections are among the most commonly prescribed of those options. At higher doses, all corticosteroids have been associated with gross cartilage damage and chondrocyte toxicity, in both in vitro and in vivo work. The detrimental effects on articular cartilage appear to be both time- and dose-dependent. Beneficial effects tend to occur at low doses and for shorter durations of treatments, while detrimental effects are seen at higher doses and more frequent durations. Thus, while IA corticosteroids are important tools to help control joint inflammation in horses, the lowest effective dose and the longest possible dosing intervals should be the goal of equine veterinarians.
David W. Ramey, DVM, is a Southern California equine practitioner who limits his practice to the care of performance and pleasure horses. Visit his website at doctorramey.com. Columnists’ opinions do not necessarily reflect those of Veterinary Practice News.