Arthritis - Description

A joint is a part of the body where two bones connect with each other. A joint consists of many structures. In the simplest form, there are two bones separated from each other by a slight gap called the joint cavity. The end of each bone is covered with cartilage, a tough, elastic material.

The space between bones is covered with a thin membrane called the synovial (pronounced si-NO-vee-uhl) membrane. The synovial membrane secretes (releases) a thin fluid called synovial fluid. The synovial fluid acts like a lubricant in the joint, helping the bones move smoothly against each other.

Arthritis usually involves some form of damage to or destruction of joint parts. In the case of rheumatoid arthritis, the synovial membrane becomes inflamed. The membrane becomes thick and stiff. It is also attacked by white blood cells, which can damage or kill tissue in the joint.

In the case of osteoarthritis, cartilage begins to break down and wear away. It is no longer able to cushion the contact of bones with each other. One bone rubs directly on the other bone. It becomes very painful to move the joint.

Rheumatoid arthritis (RA) and osteoarthritis (OA) are both common disorders. They affect both men and women of all races and ethnic background. In the United States alone, about two million people are thought to have RA. Women are three times more likely to have the condition than men. About 80 percent of patients with RA are diagnosed between the ages of thirty-five and fifty. The condition appears to run in families.

OA is one of the most common causes of disability because of limited joint movement. The condition is much more common among older people than among younger people. Somewhere between 65 and 85 percent of Americans over the age of sixty-five have the condition. Some doctors believe that everyone over the age of sixty is affected to some extent by OA. By contrast, only about 2 percent of Americans under the age of forty-five have OA.