Arthritis literally means joint inflammation and the term is used to describe the pain, stiffness, and/or swelling in the joints of the body where one or more bones are joined by tendons and muscles. An arthritic joint is one that may have varying degrees of inflammation and possibly destruction of the joint cartilage, which normally provides a smooth surface enabling adjacent bones to move and glide on each other during normal motion.

The most common type of arthritis is called osteoarthritis and is more common with advancing age. People with osteoarthritis usually have joint pain and limited movement. Unlike some other forms of arthritis, osteoarthritis affects only the joints. This condition is sometimes called degenerative joint disease or osteoarthrosis. Osteoarthritis primarily affects the joint cartilage, or the slippery tissue that covers the ends of bones in a joint. Healthy cartilage allows bones to glide over one another and absorbs energy from the shock of physical movement. In osteoarthritis, the surface layer of cartilage breaks down and wears away. This allows the bony surface under the cartilage to rub together, causing, pain, swelling, and loss of motion of the joint. Over time, affected joints may lose their normal shape. Also, bone spurs—small growths called osteophytes—may grow on the edges of the joint. Bits of bone or cartilage can break off and float inside the joint space, causing more pain and possible damage.

The second most common form of arthritis - rheumatoid arthritis— may affect not only the joints, but organs of the body as well. Rheumatoid arthritis is recognized as a systemic disease that involves responses of the immune system that play a role in the inflammation that affects joints and other organs. Rheumatoid arthritis may begin at a younger age than does osteoarthritis. Often patients with rheumatoid arthritis will require medications not only to treat the pain of arthritis, but drugs which modulate the immune system to control inflammation at other parts of the body.

Osteoarthritis is one of the most frequent causes of physical disability among adults. It is estimated that by 2030, 20 percent of Americans who are over the age of 65 years—about 70 million people—will be at risk for osteoarthritis.