Osteoarthritis, also known as degenerative joint disease, involves a progressive breakdown of cartilage and other joint tissues. It starts with softening of the smooth cartilage surface, which then becomes pitted and frayed. Unlike most of the body’s tissues, which are able to regrow when damaged, cartilage has a very limited blood supply, which hampers its ability to repair itself.
Over time, sections of cartilage start to break down faster than they are repaired and, eventually, they wear away completely. Without this cushion, the bones rub together, making movement difficult and painful (see "How Osteoarthritis Weakens Your Joints" ). The friction can also cause bony outgrowths called osteophytes, or “spurs,” which can add to the discomfort.
Osteoarthritis is the most common form of arthritis and one of the most common causes of physical disability in adults. As noted previously, an estimated 27 million people in the United States have the condition. According to the National Arthritis Data Group, some signs of osteoarthritis can often be seen on X-rays by age 25. Typically, however, symptoms of pain and stiffness usually don’t start until later in life.
As cartilage continues to break down, the joints lose their normal shape and osteophytes (spurs) may form. Bits of bone or cartilage often break off into the joint space, causing more pain and joint damage. The cartilage breakdown may cause inflammation of the synovial membrane, which in turn leads to production of enzymes and cytokines (inflammatory proteins) that cause further cartilage damage. The quality of hyaluronic acid, a substance in the synovial fluid, also may change, and this can reduce its protective effects.
Osteoarthritis occurs most often in the knees, hips, spine, small joints of the fingers and base of the thumb and big toe, although it can affect any joint. When severe osteoarthritis affects the knees, hips and spine, it may significantly limit activity and diminish a person’s quality of life.
The good news: Osteoarthritis generally has little or no effect on longevity—in other words, it won’t shorten your life.