Section 5. Bone, Joint, and Muscle Disorders

Chapter 66. Osteoarthritis

Topic: Osteoarthritis

Osteoarthritis

Osteoarthritis (previously called degenerative arthritis, degenerative joint disease) is a chronic disorder of joint cartilage and surrounding tissues that is characterized by pain, stiffness, and loss of function.

Osteoarthritis, the most common joint disorder, affects most people to some degree by age 70. Before the age of 40, men develop osteoarthritis more often than do women, 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. Osteoarthritis also occurs in almost all animals with a backbone--including fish, amphibians, and birds. Because the disorder is so widespread in the animal kingdom, some authorities believe that osteoarthritis may have evolved from an ancient method of cartilage repair.

Many myths about osteoarthritis persist--for example, that it is an inevitable part of aging, like gray hair and skin changes; that it results in little disability; and that treatment is not effective. Although osteoarthritis is more common in older people, it is not caused simply by the wear and tear that occurs with years of use. Instead, microscopic changes in the structure and composition of cartilage appear to be responsible. Most people who have the disorder, especially younger people, have few if any symptoms; however, some older people develop significant disabilities.

Causes

Normally, joints have such a low friction level that they are protected from wearing out, even after years of use. Osteoarthritis probably begins most often with an abnormality of the cells that synthesize 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. Bone can overgrow at the edges of the joint, producing 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), tendons, ligaments, and cartilage--fail in various ways, thus altering the joint.

Osteoarthritis is classified as primary (or idiopathic) when the cause is not known (the large majority of cases). It is classified as secondary when the cause is another disease or condition, such as Paget's disease (see Section 5, Chapter 61), an infection, deformity, injury, or overuse of a joint. Some people who repetitively stress one joint or a group of joints, such as foundry workers, coal miners, and bus drivers, are particularly at risk. Much of the risk for osteoarthritis of the knee comes from occupations that involve bending of the joint. Curiously, long-distance running champions appear not to be at higher 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.

Symptoms

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, usually made worse by activities that involve weight bearing (such as standing), is the first symptom. In some people, the joint may be stiff after sleep or some other inactivity, but the stiffness usually subsides within 30 minutes of moving the joint.

As the condition causes more symptoms, the joint may become less movable and eventually may not be able to fully straighten or bend. The attempt of the tissues to repair may lead to new growth of cartilage, bone, and other tissue, which 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 at the ends or middle of the fingers (called Heberden's or 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, pressing on nerves before they exit the canal to go to the legs. This may cause leg pain after walking, suggesting incorrectly that the person has a reduced blood supply to the legs (intermittent claudication (see Section 3, Chapter 34)). 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.

See the sidebar How to Live With Osteoarthritis.

Diagnosis

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 correlate poorly with symptoms. For example, an x-ray may show only a minor change while the person is having severe symptoms, or an x-ray may show numerous changes while the person is having 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 too expensive 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 Section 5, Chapter 67)).

Treatment

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 shock better. Exercise must be balanced with rest of painful joints, but immobilizing a joint is more likely to worsen osteoarthritis than to improve 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) is 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, the person should maintain ordinary daily activities and continue to perform his or her 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 Section 1, Chapter 7), can be helpful. Heat improves muscle function by reducing stiffness and muscle spasm. Cold may be applied to reduce pain. 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 from walking. Massage by trained therapists, traction (see Section 5, Chapter 62), and deep heat treatment with diathermy or ultrasound 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 appropriate exercise. A simple pain medicine (analgesic), such as acetaminophen, may be all that is needed. Alternatively, a nonsteroidal anti-inflammatory drug (NSAID) may be taken to lessen pain and swelling. NSAIDs reduce pain and inflammation in joints (see Section 6, Chapter 78). The cyclooxygenase-2 (COX-2) inhibitors (coxibs) provide relief equivalent to the other NSAIDs but may have fewer gastrointestinal side effects (see Section 6, Chapter 78). People at risk for gastrointestinal problems may prefer them. Sometimes other types of pain medicine may be needed, such as a skin cream derived from cayenne pepper--the active ingredient is capsaicin--which is applied directly to the skin over the joint.

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 injections of hyaluronate (a component of normal joint fluid) into the joint may provide significant pain relief in some people for prolonged periods of time. Several nutritional supplements (such as glucosamine and chondroitin sulfate) are being tested for potential benefit in osteoarthritis.

See the figure Replacing a Knee.

Surgery may help when all other treatments fail to relieve pain. Some joints, most commonly the hip and knee, can be replaced with an artificial joint (see Section 5, Chapter 62 and Section 5, Chapter 66); replacement is usually very successful, almost always improving motion and function and dramatically decreasing pain. Therefore, joint replacement should be considered when function becomes limited. Because the artificial joint does not last forever, such surgery 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 to help heal small defects in cartilage. However, such methods have not yet been proven valuable when cartilage defects are extensive, as commonly occurs in older people.