Rationale for HOCK INJECTIONS
There are many options when it comes to treating equine arthritis. Many topical, oral, systemic, and local medications have been shown to alleviate clinical signs of joint pain.
So why are veterinarians often so quick to recommend hock injections for the treatment of distal tarsitis in the horse?
This is a common concern for many horse owners. For the most part, the concern lies with the infusion of corticosteroid(s) into the joint. The deleterious effects of steroids on joint health have been documented. Heavy abuse of steroids at racetracks have earned them a poor reputation among the equine industry.
Although steroids can certainly have deleterious effects in the joint, we should consider the whole picture:
Let's say we don't infuse steroid into the joint. The inflammatory cells will persist in the joint. As a result, the following consequences will occur:
The presence of the inflammatory cells within the joint will increase the hydrostatic pressure within the joint causing the influx of fluid. Increased synovial fluid in the joint (called effusion) results in distension of the joint and stretching of the joint capsule (which houses nerve endings). Stretching of the joint capsule results in pain. So the horse's lameness will persist.
The inflammatory cells release degradative enzymes (called lysozymes) and other chemical mediators that break down hyaluronan (HA) within the synovial fluid. The primary function of HA is to protect the cartilage (i.e. chondroprotection) and provide a smooth, slippery surface on which the joint can function. HA breakdown results in low-viscosity synovial fluid. The fluid becomes very thin and watery, thereby losing its ability to protect the cartilage. Consequently, erosion of the cartilage ensues. The articular surface loses its congruency which in turn causes increased joint instability. Loss of joint stability triggers more inflammation, which further accelerates the cycle of degradation.
In other words, persistent inflammation is not healthy for a joint!
Let's say we infuse steroid into the joint. The presence of steroid will reduce inflammation within the synovial environment. As a result, the hydrostatic pressure will decrease, fluid will leave, the joint will decompress. The horse will be more comfortable and therefore more sound.
Furthermore, there will be less degradation within the joint due to the absence of the inflammatory enzymes and mediators. Therefore, in one sense, steroids are helping us to IMPROVE synovial integrity. On the other hand steroids also result in breakdown of HA which, as we previously discussed, is chondroprotective (protects the cartilage). Therefore, we must weigh both sides. The factors that determine if intraarticular injection using steroid is indicated include:
How important is the integrity of this joint in regard to the soundness of the horse?
Is it a high-motion joint?
Is it a high-weightbearing joint?
In this case we are dealing with the distal tarsal (hock) joints. These are extremely low-motion joints. They are so low-motion in fact, that we would not be able to observe a difference in the horse's gait if the distal tarsal joints did not exist! In horses that are refractory to antiinflammatory therapy, we often elect to surgically or chemically fuse
(i.e. eliminate) these joints altogether. There is no compromise to the horse's performance as a result. Because the distal hock joints do exist, however, they can become unstable and a source of pain and lameness for the horse. This problem is referred to as "distal tarsitis". From a veterinary standpoint, we are not very concerned about keeping the distal tarsal joints happy and healthy. The horse doesn't even need them! We are more concerned about alleviating the pain that can negatively affect the horse's performance.
In higher-motion (and therefore more important) joints, we need to maintain good synovial integrity and a healthly environment. In this type of joint, therefore, we need to really think about whether or not steroids are indicated.
How much inflammation is present? Inflammatory changes can eventually become irreversible. This leads to greater joint disease and further inflammation. The deleterious effects of inflammation may outweigh those that occur pursuant to steroid injection. In many cases of joint disease, intraarticular steroids are HEALTHIER for the joint than a lack of steroids. In other words, the benefit of steroids outweighs the deleterious side effects.
When it comes to the distal hock joints, the combination of the low-motion nature of the joints coupled with the presence of moderate to severe inflammation usually prompts us to treat them via intraarticular injection(s).
To learn more about DISTAL TARSITIS please click HERE.