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Arthritis is a disease characterized by deterioration and inflammation in the joints. There are about 100 different types of arthritis, affecting about 40 million Americans. Osteoarthritis (OA) is the most common kind, affecting about 20 million people. Rheumatoid arthritis is another common form.

OA is a "wear and tear" disease and becomes more common as people get older; indeed, most people develop the condition to some degree in at least one joint by age 60. Bones that meet at joints have soft caps of cartilage at the ends, and years of bending and rubbing can start to wear these caps down. Fingers, knees, and hips are most often affected. The frequency of OA starts to rise after age 50 among men, and after age 40 among women, and symptoms tend to get more severe as people age. Those symptoms can range from mild stiffness to severe pain.

Fortunately, doctors have found that programs of exercise and physical therapy can make a big difference in easing any discomfort. So can judicious use of painkillers such as acetaminophen, use of anti-inflammatory drugs, and injections of medications into the joints. For the most severe cases, joint replacement surgery is often recommended; these operations offer patients major improvements in their quality of life. Finally, people who take an active role in managing their disease can lead long and active lives.

This section has more on:

  • Need-to-know anatomy
  • Causes
  • Risk factors
  • Need-to-know anatomy

    The joints in the body, where two bones come together and need to flex, are designed to make movement easy. The whole joint area is surrounded by a thin covering called the synovial membrane, which releases a lubricating fluid into the joint. The ends of the bones in the joint are lined with slippery cartilage. The whole structure is held together with muscles, tendons, and ligaments. OA can damage any or all of these crucial parts.

    Symptoms start when the protective cartilage stiffens and starts to wear away, often on one side of the joint. As the space in the joint narrows, more cartilage starts rubbing together and eroding. Bits of cartilage fill the joint area, irritating the surrounding membrane, fluid begins to accumulate, and the tendons and ligaments stretch painfully. Knobs of bone, called spurs, begin to grow. This may be felt as joint grinding whenever it moves.


    The causes of osteoarthritis are still not completely clear. While age is one of the factors that contributes to cartilage breakdown, OA is not inevitable and there are many other factors that come into play. Significant trauma to a joint or joint injury may also initiate the process that results in OA many years later. For example, people who have jobs that require repeated bending and strain often get OA in the knee. High school football players who get knee or hip injuries can also develop OA. OA has not, however, been reliably linked to physical exercise, even jogging. In addition to cartilage, there are many other cells and joint parts that become involved, including the bones and the cells lining the joint. All of these act together and release various proteins that accelerate the process, leading to the end result of breakdown of cartilage covering the ends of bones and the formation of new bony spurs.

    Risk factors

    Doctors have identified several major risk factors for developing OA:

    Family history: People with close relatives who have OA tend to be prone to the disease themselves. For example, defects in genes responsible for the formation of collagen, a component of cartilage, make some people more susceptible.

    Advancing age: The older people get, the more frequently OA is found.

    Obesity: Carrying too much weight puts extra stress on certain joints, such as the hips and the knees.

    Overuse or injury to the joint: Athletes and those whose jobs require repetitive bending, for example, may be at higher risk.

    "Malaligned" bones: Conditions such as having knock-knee or being bowlegged increase the chances for wear and tear in the joint.

    Having another form of arthritis, such as rheumatoid arthritis: This can traumatize a joint, also increasing the chances of wear and tear.

    Last reviewed on 7/21/09

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