Wednesday, March 18, 2009

Joint Disease
by: Les Sellnow

Among the most highly engineered, finely tuned machines built by man are race cars that zip around the Indianapolis 500 track at speeds in excess of 200 miles per hour. However, even the most perfectly constructed car will develop problems from continued competition. It is much the same with the performance horse and his joints. Even with perfect construction or conformation (which is rare), there still is daily wear and tear that destroys parts or joints. The horse's joints are designed to effectively absorb shock, allow for frictionless movement, and effectively bear the weight of a body that often weighs 1,200-1,500 pounds or more.

When equine joint injury occurs, you can turn to sophisticated specialists who have devoted their careers to repairing the damage, just as race car drivers can turn to top mechanics. Unfortunately, the equine specialists do not have the luxury of spare parts.

Veterinary science has provided medical and surgical tools for helping repair equine joints, but there will always be the limitation of having to work with what's there.

In this article about joints and the forces that damage and destroy them, we will examine the types of joints so that we understand the terminology and anatomy. Next we will look at the forces generated by various forms of competition and diagnostics. Finally, we'll look at treatment.

A Look Inside

We begin our discussion with a description of joints. There are three different types or classifications of joints--fibrous, cartilaginous, and synovial.

Fibrous joints are the least likely to be afflicted with disease because they are pretty much immobile. They include joints in the skull and those between the shafts of some long bones.

Cartilaginous joints don't have a high propensity for disease because they, too, have limited movement. These are the joints of the pelvis and vertebrae as well as growth plates, which extend a bone's length during the horse's growing years.

That brings us to synovial joints, the ones most likely to suffer disease and injury because they are the most active joints in the horse's body. They consist of two bone ends covered by articular cartilage. It is this cartilage within the joint that is so smooth and resilient that, when properly lubricated, it allows for frictionless movement of the joint.

Of course, you can't just have two bones covered with smooth, resilient material. You need something to hold the whole thing together and lubricate it. The joint's stability is maintained by a fibrous joint capsule--which attaches to both bones--and collateral ligaments. The collateral ligaments are located on either side of most joints. They are key components of the fetlock, knee, elbow, hock, and stifle joints.

Other ligaments within joints--such as the cruciate ligaments in the stifle--help stabilize some joints.

Ligaments outside the joint capsule also lend support. A prime example is the distal sesamoidean ligaments and suspensory ligaments that, together with the sesamoid bones, make up the suspensory apparatus and hold the fetlock in its correct position.

An enemy of joint health is friction. What is needed to prevent friction? Lubrication. And where does this lubrication within a joint come from? The joint capsule contains an inner lining called the synovial membrane. This lining secretes the synovial fluid that lubricates the joint. A key ingredient in this fluid is hyaluronic acid, also known as sodium hyaluronate or hyaluronan, which lubricates the synovial membrane. Another substance in synovial fluid, a protein called lubricin, is the primary lubricant of the cartilage. In some cases of joint disease there is a depletion of this necessary fluid.


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