Osteoarthritis

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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 people, it progresses quickly; in others, the symptoms develop slowly and may be stable for many years. Researchers do not yet know what causes the disease, but they suspect a combination of factors in the body and in the environment. Diet, weight and stresses on the joints from certain jobs, hobbies or other activities may affect the disease and how a person reacts to it.

Usually, osteoarthritis develops slowly. Early in the course of the disease, joints may ache after physical work or exercise. Osteoarthritis can occur in any joint, but most often occurs at the joints in the hands, hips and knees.

• Hands: Osteoarthritis of the fingers is the one type of the disease that seems to be hereditary. More women than men have it, and risk increases after menopause. Small, bony knobs appear on the end joints of the fingers. They are called Heberden's nodules. Similar knobs (called Bouchard's nodules) can appear on the middle joints of the fingers. Fingers can become enlarged and gnarled, and may ache or be stiff and numb. The base of the thumb joint is also commonly affected by osteoarthritis. This kind of osteoarthritis can be helped by medications, splints or heat treatment.

• Knees: The knees are among the body's main weight-bearing joints. They are also among the joints most commonly affected by osteoarthritis. An afflicted knee may be stiff, swollen and painful, making it hard to walk, climb or get in and out of chairs and bathtubs. If not treated, osteoarthritis in the knee can lead to disability. However, even with treatment, osteoarthritis may progress. Medications, losing weight, exercise and walking aids can reduce pain and disability. In severe cases, knee replacement surgery may be required. Research studies show that being overweight increases the risk of developing osteoarthritis of the knees.

• Hips: Osteoarthritis in the hip can cause pain, stiffness and severe disability. People may feel the pain in their hips, groin, inner thighs or knees. Walking aids, such as canes or walkers, can reduce stress on the hip. Osteoarthritis in the hip may limit moving and bending. This can make daily activities such as dressing and foot care a challenge. Walking aids, medication and exercise can help relieve pain and improve motion. A health care professional may recommend hip replacement if the pain is severe and not helped by other methods.

Researchers suspect that genes play a role in 40 percent to 65 percent or more of hand osteoarthritis cases, 50 percent of the risk of osteoarthritis of the hip, and 70 percent of the risk of osteoarthritis of the spine. Scientists are looking for genetic mutations that may be involved in osteoarthritis. In the future, a test to determine who carries the genetic defect (or defects) could help people reduce their risk for osteoarthritis with lifestyle adjustments.