Article Medically Reviewed By:
David T. Felson, MD
Chief of the Boston University Clinical Epidemiology Research Training Unit Professor of Medicine, Boston University School of Medicine (BUSM) Professor of Public Health, Boston University School of Public Health (BUSPH) Boston, MA
Overview
What Is It?
Osteoarthritis affects structures throughout the joint. The cartilage, the slippery tissue that covers the ends of bones in a joint, begins to break down and wear away. This allows bones to rub together, eventually causing inflammation and pain.
There are more than 100 kinds of arthritis, which literally means joint inflammation. According to the Centers for Disease Control and Prevention (CDC), about 46 million Americans (one in five adults) are afflicted, and more than 21 million have osteoarthritis, by far the most common form, especially among older people. Sometimes called degenerative joint disease, osteoarthritis affects more than 12 percent of U.S. adults. Osteoarthritis accounts for most of the hip and knee replacement surgeries performed in the United States. As with other types of arthritis, women are at higher risk than men for the condition.
Osteoarthritis affects structures throughout the joint. Among them the cartilage, the slippery tissue that covers the ends of bones in a joint, is usually affected. 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, which allows bones under the cartilage to rub together. This causes bone remodeling and change in boney shape and loss of motion of the joint. Over time, the joint loses its normal shape. Also, bone spurs—small growths called osteophytes—may grow on the edges of the joint. By the time a person has symptoms from osteoarthritis, it is no longer just a disease of cartilage. Bone has changed, muscles across the joint have often weakened and there is occasionally inflammation in the lining of the joint.
Unlike some other forms of arthritis, osteoarthritis only affects joints, not internal organs. Rheumatoid arthritis—the second most common form of arthritis—affects other parts of the body besides the joints. It begins earlier than osteoarthritis, causes inflammation and may make people feel sick, tired and sometimes feverish, among other symptoms.
Some younger people get osteoarthritis from a joint injury, but osteoarthritis most often occurs in people over 40. In fact, at least 80 percent of people over age 55 have x-ray evidence of osteoarthritis in at least one joint, and approximately one-third have symptoms of the disease. Since the number of older Americans is increasing, so is the number of people with osteoarthritis. Before age 45, more men have the condition (often the result of a sports or work injury), while after age 45, osteoarthritis is more common in women.
Osteoarthritis affects each person differently. In some peo...
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