Osteoarthritis (sometimes called degenerative arthritis, degenerative joint disease, osteoarthrosis, or hypertrophic osteoarthritis) is a chronic disorder associated with damage to the cartilage and surrounding tissues and characterized by pain, stiffness, and loss of function.
Osteoarthritis, the most common joint disorder, often begins in the 40s and 50s and affects almost all people to some degree by age 80. Before the age of 40, men develop osteoarthritis more often than do women, often because of injury. From age 40 to 70, women develop the disorder more often than do men. After age 70, the disorder develops in both sexes equally.
Normally, joints have such a low friction level that they are protected from wearing out, even after years of use. Osteoarthritis is caused most often by tissue damage. In an attempt to repair a damaged joint, chemicals accumulate in the joint and increase the production of the components of cartilage, such as collagen (a tough, fibrous protein in connective tissue) and proteoglycans (substances that provide resilience). Next, the cartilage may swell because of water retention, become soft, and then develop cracks on the surface. Tiny cavities form in the bone beneath the cartilage, weakening the bone. The attempt of the tissues to repair the damage may lead to new growth of cartilage, bone, and other tissue. Bone can overgrow at the edges of the joint, causing bumps (osteophytes) that can be seen and felt. Ultimately, the smooth, slippery surface of the cartilage becomes rough and pitted, so that the joint can no longer move smoothly and absorb impact. All the components of the joint—bone, joint capsule (tissues that enclose most joints), synovial tissue (tissue lining the joint cavity), tendons, ligaments, and cartilage—fail in various ways, thus altering the function of the joint.
Osteoarthritis is classified as primary (or idiopathic) when the cause is not known (as in the large majority of cases). It is classified as secondary when the cause is another disease or condition, such as an infection, deformity, injury, abnormal use of a joint, metabolic disorder (for example, excess iron in the body [hemochromatosis] or excess copper in the liver [Wilson's disease]), or a disorder that damages joint cartilage (for example, rheumatoid arthritis or gout). Some people who repetitively stress one joint or a group of joints, such as foundry workers, farmers, coal miners, and bus drivers, are particularly at risk. The major risk factor for osteoarthritis of the knee comes from having an occupation that involves bending of the joint. Curiously, long-distance running does not increase the risk of developing the disorder. However, once osteoarthritis develops, this type of exercise often makes the disorder worse. Obesity may be a major factor in the development of osteoarthritis, particularly of the knee and especially in women.
Usually, symptoms develop gradually and affect only one or a few joints at first. Joints of the fingers, base of the thumbs, neck, lower back, big toes, hips, and knees are commonly affected. Pain, often described as a deep ache, is the first symptom and, when in the weight-bearing joints, is usually made worse by activities that involve weight bearing (such as standing. In some people, the joint may be stiff after sleep or some other inactivity, but the stiffness usually subsides within 30 minutes, particularly if the joint is moved.
As the condition causes more symptoms, the joint may become less movable and eventually may not be able to fully straighten or bend. New growth of cartilage, bone, and other tissue can enlarge the joints. The irregular cartilage surfaces cause joints to grind, grate, or crackle when they are moved. Bony growths commonly develop in the joints closest to the fingertips (called Heberden's nodes) or middle of the fingers (called Bouchard's nodes).
In some joints (such as the knee), the ligaments, which surround and support the joint, stretch so that the joint becomes unstable. Alternatively, the hip or knee may become stiff, losing its range of motion. Touching or moving the joint (particularly when standing, climbing stairs, or walking) can be very painful.
Osteoarthritis often affects the spine. Back pain is the most common symptom. Usually, damaged disks or joints in the spine cause only mild pain and stiffness. However, osteoarthritis in the neck or lower back can cause numbness, pain, and weakness in an arm or leg if the overgrowth of bone presses on nerves. The overgrowth of bone may be within the spinal canal in the lower back (lumbar spinal stenosis), pressing on nerves before they exit the canal to go to the legs. This pressure may cause leg pain after walking, suggesting incorrectly that the person has a reduced blood supply to the legs (intermittent claudication—see Peripheral Arterial Disease: Arteries of the Legs and Arms). Rarely, bony growths compress the esophagus, making swallowing difficult.
Osteoarthritis may be stable for many years or may progress very rapidly, but most often it progresses slowly after symptoms develop. Many people develop some degree of disability.
The doctor makes the diagnosis based on the characteristic symptoms, physical examination, and the x-ray appearance of joints (such as bone enlargement and narrowing of the joint space). By age 40, many people have some evidence of osteoarthritis on x-rays, especially in weight-bearing joints such as the hip and knee, but only half of these people have symptoms. However, x-rays are not very useful for detecting osteoarthritis early because they do not show changes in cartilage, which is where the earliest abnormalities occur. Also, changes on the x-ray often correlate poorly with symptoms. For example, an x-ray may show only a minor change in a person who has severe symptoms, or an x-ray may show numerous changes in a person who has very few, if any, symptoms.
Magnetic resonance imaging (MRI) can reveal early changes in cartilage, but it is rarely needed for the diagnosis. Also, MRI is in too short supply to justify routine use. There are no blood tests for the diagnosis of osteoarthritis, although blood tests may help rule out other disorders (such as rheumatoid arthritis—see Joint Disorders: Rheumatoid Arthritis (RA)). If a joint is swollen, a sample of the joint fluid is sometimes withdrawn using a needle and local anesthesia. Analysis of the fluid can help differentiate osteoarthritis from disorders such as infection and gout.
Appropriate exercises—including stretching, strengthening, and postural exercises—help maintain healthy cartilage, increase a joint's range of motion, and strengthen surrounding muscles so that they can absorb stress better. Exercise can sometimes stop or even reverse osteoarthritis of the hip and knee. Stretching exercises should be performed daily. Exercise must be balanced with rest of painful joints, but immobilizing a joint is more likely to worsen the disease than relieve it. Using excessively soft chairs, recliners, mattresses, and car seats may worsen symptoms. Using car seats moved forward, straight-backed chairs with relatively high seats (such as kitchen or dining room chairs), firm mattresses, and bed boards (available at many lumber yards) and wearing wear well-supported shoes or athletic shoes are often recommended.
For osteoarthritis of the spine, specific exercises sometimes help, and back supports or braces may be needed when pain is severe. Exercises should include both muscle-strengthening as well as low-impact aerobic exercises (such as walking, swimming, and bicycle riding). If possible, people should maintain ordinary daily activities and continue to perform their normal activities, such as a hobby or job. However, physical activities may have to be adjusted to avoid bending and thus aggravating the pain of osteoarthritis.
Physical therapy, often with heat therapy (see Rehabilitation: Heat therapy), can be helpful. Range-of-motion exercises performed in warm water are helpful because heat improves muscle function by reducing stiffness and muscle spasm. Cold may be applied to reduce pain from temporary worsening in one joint. Splints or supports (such as a cane, crutch, brace, or even a walker) can protect specific joints during painful activities. Shoe inserts (orthotics) may help reduce pain caused by walking. Massage by trained therapists and deep heat treatment with diathermy or ultrasonography may be useful.
Drugs are used to supplement exercise and physical therapy. Drugs, which may be used in combination or individually, do not directly alter the course of osteoarthritis. They are used to reduce symptoms and thus allow more normal daily activities. A simple pain medicine (analgesic), such as acetaminophen, may be all that is needed for mild to moderate pain. Alternatively, a nonsteroidal anti-inflammatory drug (NSAID) may be taken to lessen pain and swelling. NSAIDs reduce pain and inflammation in joints (see Pain: Nonsteroidal Anti-Inflammatory Drugs). However, they have a higher risk of serious side effects than acetaminophen when used long term. Sometimes other types of pain medicine may be needed. For example, a cream derived from cayenne pepper—the active ingredient is capsaicin—can be applied directly to the skin over the joint.
Muscle relaxants (usually in low doses) occasionally relieve pain caused by muscles straining to support joints affected by osteoarthritis. In older people, however, they tend to cause more side effects than relief.
If a joint suddenly becomes inflamed, swollen, and painful, most of the fluid inside the joint may need to be removed and a special form of cortisone may be injected directly into the joint. This treatment may provide only short-term relief, and a joint treated with cortisone should not be used too often or damage may result. A series of 3 to 5 weekly injections of hyaluronate (similar to a component of normal joint fluid) into the joint may provide significant pain relief in some people for prolonged periods of time (up to a year).
Several nutritional supplements (such as glucosamine sulfate and chondroitin sulfate) are being tested for potential benefit in treating osteoarthritis. So far, results are contradictory, and the potential benefit of glucosamine sulfate and chondroitin sulfate is unclear. There is less evidence that other nutritional supplements work.
Surgical treatment may help when all other treatments fail to relieve pain or improve function. Some joints, most commonly the hip (see Fractures: Hip Fractures) and knee (see Replacing a Knee), can be replaced with an artificial joint. Replacement is usually very successful, almost always improving motion and function and dramatically decreasing pain. Therefore, joint replacement should be considered when pain is unmanageable and function becomes limited. Because the artificial joint does not last forever, the procedure is often delayed as long as possible in young people so the need for repeated replacements can be minimized.
A variety of methods that restore cells inside cartilage have been used in younger people with osteoarthritis (often caused by an injury) to help heal small defects in cartilage. However, such methods have not yet proved valuable when cartilage defects are extensive, as commonly occurs in older people.
Last full review/revision February 2008 by Roy D. Altman, MD