Osteoarthritis is one of the oldest and most common types of arthritis. With the breakdown of cartilage, the part of the joint that cushions the ends of bones, bones rub against each other, causing pain and loss of movement. Often called "wear-and-tear arthritis" or "old person's arthritis," many factors can cause osteoarthritis.
The biologic causes of the disorder are currently unknown. It does not appear to be caused by aging itself, although osteoarthritis generally accompanies aging. Osteoarthritic cartilage is chemically different from normal aged cartilage.
In many cases, certain conditions seem to trigger osteoarthritis. People with joint injuries from sports, work-related activity, or accidents may be at increased risk, and obesity may lead to osteoarthritis of the knees. Individuals with mismatched surfaces on the joints that could be damaged over time by abnormal stress may be prone to osteoarthritis. One study reported that wearing shoes with 2.5 in (6.3 cm) heels or higher may also be a contributing factor. High heels force women to alter the way they normally maintain balance, putting strain on the areas between the kneecap and thigh bone and on the inside of the knee joint.
Demographics
Osteoarthritis is estimated to affect more than 20 million Americans, mostly after age 45. Women are more commonly affected than men.
In the United States about 6% of adults over 30 have osteoarthritis of the knee and about 3% have osteoarthritis of the hip. Prevalence of osteoarthritis in most joints is higher in men than women before age 50, but after this age, more women are affected by osteoarthritis. The occurrence of the disease increases with age. In men, the hip is affected more often while in women, the hands, fingers, and knees are more problematic.
Some forms of osteoarthritis are more prevalent in African-American men and women than in Caucasians, possibly because they have a higher bone mineral density. In the case of knee osteoarthritis, it may be related to occupational and physical demands. African-American women also have a higher risk of developing bilateral knee osteoarthritis and hip osteoarthritis compared to women of other races. This difference may be because African-American women generally have a higher body mass index which puts more stress on the joints.
Osteoarthritis is common worldwide, although risk of osteoarthritis varies among ethnic groups. Caucasians have a higher risk than Asians, and the risk of osteoarthritis in the hips is lower in Asia and some Middle East countries than in the United States. Asians appear to have a higher incidence of osteoarthritis in the knee than Caucasians, however, and an equal risk in the spine. Location of affected joints and inherited forms of the disorder can influence age of onset.
Genetic profile
Genetics plays a role in the development of osteoarthritis, particularly in the hands and hips. One study found that heredity may be involved in 30% of people with osteoarthritic hands and 65% of those with osteoarthritic knees. Another study found a higher correlation of osteoarthritis between parents and children and between siblings than between spouses. Other research has shown that a genetic abnormality may promote a breakdown of the protective structure in cartilage.
Abnormal collagen genes have been identified in some families with osteoarthritis. One recent study found that the type IX collagen gene COL9A1 (6q12-q13) may be a susceptibility locus for female hip osteoarthritis. Other research has suggested that mutations in the COL2A1 gene may be associated with osteoarthritis.
Some evidence also suggests that a female-specific susceptibility gene for idiopathic osteoarthritis is located on 11q. There is some evidence of genetic abnormality at the IL1R1 marker on gene 2q12 in individuals with severe osteoarthritis and Heberden nodes (bony lumps on the end joint of fingers).
Signs and symptoms
Although up to 85% of people over 65 show evidence of osteoarthritis on x ray, only 35-50% experience symptoms. Symptoms range from very mild to very severe, affecting hands and weight-bearing joints such as knees, hips, feet, and the back. The pain of osteoarthritis usually begins gradually and progresses slowly over many years.
Osteoarthritis is commonly identified by aching pain in one or more joints, stiffness, and loss of mobility. The disease can cause significant trouble walking and stair climbing. Inflammation may or may not be present. Extensive use of the joint often exacerbates pain in the joints. Osteoarthritis is often more bothersome at night than in the morning and in humid weather than dry weather. Periods of inactivity, such as sleeping or sitting, may result in stiffness, which can be eased by stretching and exercise. Osteoarthritis pain tends to fade within a year of appearing.
Bony lumps on the end joint of the finger, called Herberden's nodes, and on the middle joint of the finger, called Bouchard's nodes, may also develop.
X rays are used to confirm diagnosis. In people over 60, the disease can often be observed on x ray. An indication of cartilage loss arises if the normal space between the bones in a joint is narrowed, if there is an abnormal increase in bone density, or if bony projections or erosions are evident. Any cysts that might develop in osteoarthritic joints are also detectable by x ray.
Additional tests can be performed if other conditions are suspected or if the diagnosis is uncertain. Blood tests can rule out rheumatoid arthritis or other forms of arthritis.
It is possible to distinguish osteoarthritis from other joint diseases by considering a number of factors together:
Osteoarthritis usually occurs in older people.
It is usually located in only one or a few joints.
The joints are less inflamed than in other arthritic conditions.
Progression of pain is almost always gradual.
A few of the most common disorders that might be confused with osteoarthritis are rheumatoid arthritis, chondrocalcinosis, and Charcot's joints.
Treatment and management
There is no known way to prevent osteoarthritis or slow its progression. Some lifestyle changes can reduce or delay symptoms. Treatment often focuses on decreasing pain and improving joint movement. Prevention and treatment measures may include:
Exercises to maintain joint flexibility and improve muscle strength. By strengthening the supporting muscles, tendons, and ligaments, regular weight-bearing exercise helps protect joints, even possibly stimulating growth of the cartilage.
Joint protection, which prevents strain and stress on painful joints.
Weight control, which prevents extra stress on weight-bearing joints. One study reported that weight loss seemed to reduce the risk for symptomatic osteoarthritis of the knee in women, and in another, women who lost 11 pounds or more cut their risk for developing osteoarthritis in half.
Surgery may be needed to relieve chronic pain in damaged joints. Osteoarthritis is the most common indication for total joint replacement of the hip and knee.
New treatment findings
Studies have found that estrogen may promote healthy joints in women. Hormone replacement therapy may significantly reduce the risk in postmenopausal women, particularly in the knees.
It has been reported that deficiencies in vitamin D in older people may worsen their condition, so individuals with osteoarthritis should strive to get the recommended 400 IU a day. To protect bones, adults should also consume at least 1,000 mg of calcium daily.
Glucosamine and chondroitinsulfate are popular nutritional supplements that may diminish the symptoms of osteoarthritis. According to some reports, a daily dose of 750–1,500 mg of glucosamine and chondroitin sulfate may result in reduced joint pain, stiffness, and swelling, however these supplements are not approved by the Food and Drug Adminstration as effective treatment of osteoarthritis. A person with osteoarthritis should consult with a doctor before using dietary supplements to treat symptoms.
Prognosis
Osteoarthritis is not life threatening, but quality of life can deteriorate significantly due to the pain and loss of mobility that it causes. Advanced osteoarthritis can force the patient to forgo activities, even walking, unless the condition is alleviated by medication or corrected by surgery.
There is no cure for osteoarthritis, and no treatment alters its progression with any certainty. Only heart disease has a greater impact on work, and 5% of those who leave the work force do so because of osteoarthritis.
BOOKS
Grelsamer, Ronald P., and Suzanne Loebl, eds. The Columbia Presbyterian Osteoarthritis Handbook. New York: Macmillan, 1997.
PERIODICALS
Felson, D.T., et al. "Osteoarthritis: New Insights. Part 1: The Disease and Its Risk Factors." Annals of Internal Medicine 133, no. 8 (2000): 635+.
Felson, D.T., et al. "Osteoarthritis: New Insights. Part 2: Treatment Approaches." Annals of Internal Medicine 133, no. 9 (2000): 726+.
McAlindon, Tim. "Glucosamine for Osteoarthritis: Dawn of a New Era?" Lancet 357 (January 27, 2001): 247+.
ORGANIZATIONS
Arthritis Foundation. 1330 West Peachtree St., Atlanta, GA 30309. (800) 283-7800. <http://www.arthritis.org>.
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