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Equine Joint Disease:

Causes and types of joint disease in horses.

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Joint Disease: Causes and Types of Damage

Causes of Joint Problems

Horses have joint problems because we often ask them to do things they weren't designed to do, says Jerry Black, DVM, senior partner and president of the Pioneer Equine Hospital in Oakdale, Calif., and president-elect of the American Association of Equine Practitioners.

After domesticating the horse, man designed competitions for him that put a great deal of additional stress on his joints. Think, for example, of the concussive force on joints of the front legs when a 1,200-pound horse sails over a six-foot jump and lands on his front feet.

Dressage seems like a fairly benign competition as far as placing stress on joints is concerned, but that isn't true. The advanced dressage horse is required to move his center of gravity more to the rear, putting more stress on the hind limbs. Some of the lateral movements, such as the shoulder-in and half-pass, cause high joint stress particularly on the hock. The types of disease and injury that can afflict dressage horses include degenerative joint disease of the hocks, inflammation and degenerative joint disease of the front pasterns, inflammation of the middle knee joint, and degenerative joint disease and inflammation of the fetlock.

Many English show horses also tend to shift their center of gravity to the rear, thus placing more stress on the hind limbs (especially the hock and pastern joints). The goal with some of these show horses is to travel with high front-end action. This is particularly true of the Tennessee Walking Horse in competition. Horses which load more weight on the rear are going to be prone to hock, rear fetlock, and stifle injuries and disease.

With the jumper, there is great stress on the hind limb joints on take-off and on the entire forelimb suspensory apparatus on landing. In addition, the show jumper is often asked to complete one jump, then make a sharp turn to line up for another. This places severe stress on the hocks. Sometimes the stress placed on the joint ligaments of the jumping horse causes inflammation and lameness.

Western horses also are stressed with competition. There is a lot of torque on the rear joints when a cutting horse drops its hindquarters toward the ground and spins a split second before accelerating to stop the movement of the calf it is seeking to hold away from the herd. Some cutting horses are susceptible to injuries and disease involving the hock and stifle joints. The reining horse is asked to run down an arena at speed, slide to a stop, and spin in a circle, with the rear end anchored in place. This produces a great deal of torque on the hind limbs, especially the hocks.

Roping horses also put heavy pressure on their joints. The calf roping horse is asked to slide to a stop as the loop settles over the calf's neck. The sliding stop and the jerk from the calf hitting the end of the rope put stress on the hock and pastern joints.

The header's team roping horse is asked to swing sideways, pulling a steer into position for the heeler to rope the hind feet. The header's horse places added stress on his lower forelimbs, especially the left, while turning the steer.

A barrel racing horse speeding through the cloverleaf course places severe stress on the joints of his front and rear limbs. There is often a compounding of problems with barrel racers, Black says, because in some cases the horses were retired from the racetrack and bring with them problematic front knees, front fetlocks, and front suspensory apparatus.

Western pleasure horses which travel sedately and slowly around the ring might also be prone to joint disease because of their conformation, Black explains. To accentuate a chosen way of going, he says, many Western pleasure horses have been bred and selected to have straighter shoulders and more upright pasterns than horses which perform at speed. This type of conformation can set the stage for poor shock absorption and thus joint disease.

Breeding practices also are implicated in some joint problems of horses which perform at speed. Cutting horse breeders, for example, often line breed to make certain that the horse has "cow sense." This, however, has the potential for compounding genetic joint problems when conformation isn't also taken into account.

And the Problems Arise

When joints suffer trauma, Black says, enzymes and other agents from the joint lining are released that destroy tissue inside the joint, especially articular cartilage (which covers the joint surface of the bone). The result is traumatic arthritis.

"Traumatic arthritis," Black says, "has been defined as the diverse collection of pathological and clinical states which develop after single or repetitive episodes of trauma. The components of traumatic arthritis may include inflammation of the joint lining such as synovitis (inflammation of the synovial membrane) and capsulitis (inflammation of the fibrous joint capsule); injury to the supporting ligaments of the joint (sprain); and fractures to the bones within the joint."

Traumatic arthritis comes in three forms:

Type 1: Synovitis and capsulitis without disturbance of articular cartilage or disruption of major supporting structures. This includes acute synovitis, capsulitis, and most sprains.

Type 2: This is caused by disruptive trauma damaging the articular cartilage or completely rupturing major supporting structures. This includes severe sprains, intra-articular fractures, and meniscal tears. (The meniscus is cartilage that lies between the weight-bearing surfaces of the joint.)

Type 3: Post-traumatic degenerative joint disease occurs when there is residual damage after initial trauma. Type 3 traumatic arthritis can lead to deformity, limited range of motion, or joint instability.

Equine joint disease and associated lamenesses are the most common athletic injuries seen in performance horses today, Black declares . "The pathological effect of trauma on joints is to cause synovitis and capsulitis, which, in turn, creates physical and biochemical damage to the articular cartilage," he says.

Wayne McIlwraith, BVSc, PhD, Dipl. ACVS, of Colorado State University (CSU), president of the American Association of Equine Practitioners adds, "Synovitis and capsulitis cause the release of (the enzymes) metalloproteinases and aggrecanase, prostaglandins, free radicals, and interleukin-1." The resulting tissue inflammation creates pain, effusion, and reduced range of motion.

With some horses, joint injury and disease occur after years of stress. These would be the horses with correct conformation whose joints were strong and supple enough to withstand competitive trauma for a long time before weakening. With others, joint injury and disease might occur after only a single traumatic incident. These might be the horses with conformation anomalies that predispose them to problems.

© Les Sellnow

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