Arthritis of the knee is most often osteoarthritis. In this disease, the cartilage in the joint gradually wears away. In rheumatoid arthritis, which can also affect the knees, the joint becomes inflamed and cartilage may be destroyed. Arthritis not only affects joints; it can also affect supporting structures such as muscles, tendons, and ligaments.Osteoarthritis may be caused by excess stress on the joint from deformity, repeated injury, or excess weight. It most often affects middle-aged and older people. A young person who develops osteoarthritis may have an inherited form of the disease or may have experienced continuous irritation from an unrepaired torn meniscus or other injury. Rheumatoid arthritis often affects people at an earlier age than osteoarthritis.

Signs and Diagnosis
Someone who has arthritis of the knee may experience pain, swelling, and a decrease in knee motion. A common symptom is morning stiffness that lessens as the person moves around. Sometimes the joint locks or clicks when the knee is bent and straightened, but these signs may occur in other knee disorders as well. The doctor may confirm the diagnosis by performing a physical examination and examining x rays, which typically show a loss of joint space. Blood tests may be helpful for diagnosing rheumatoid arthritis, but other tests may be needed too. Analyzing fluid from the knee joint may be helpful in diagnosing some kinds of arthritis. The doctor may use arthroscopy to directly see damage to cartilage, tendons, and ligaments and to confirm a diagnosis, but arthroscopy is usually done only if a repair procedure is to be performed.

Treatment
Most often osteoarthritis of the knee is treated with pain-reducing medicines, such as aspirin or acetaminophen (Tylenol); nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (Motrin, Nuprin, Advil); and exercises to restore joint movement and strengthen the knee. Losing excess weight can also help people with osteoarthritis.Rheumatoid arthritis of the knee may require physical therapy and more powerful medications. In people with arthritis of the knee, a seriously damaged joint may need to be replaced with an artificial one. (A new procedure designed to stimulate the growth of cartilage by using a patient's own cartilage cells is being used experimentally to repair cartilage injuries at the end of the femur at the knee. It is not, however, a treatment for arthritis.)Source: National Institute of Arthritis and Musculoskeletal and Skin DiseasesReviewed: May 2001Brand names included in this booklet are provided as examples only, and their inclusion does not mean that these products are endorsed by the National Institutes of Health or any other Government agency. Also, if a particular brand name is not mentioned, this does not mean or imply that the product is unsatisfactory.