Osteoarthritis (OA) is the most common form of arthritis and a leading cause of disability worldwide. OA affects more women than men and is more common in older age groups. Here are some frequently asked questions about osteoarthritis.
Is OA just the result of aging?
Until the 1980s, OA was considered primarily as a progressive degenerative disorder and a natural occurrence of "wear-and-tear" on joints Recent research is changing this view.
What are the differences between a joint that has osteoarthritis and a normal, aging joint?
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The water content of cartilage in an aging joint does not change significantly. In a joint with OA, the water content increases early in the disease process.
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The biological changes in the cell that occur with OA cause physical, chemical and other changes that are not seen in the aging joint.
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OA causes changes in the bone below cartilage (subchondral bone) that do not occur in an aging joint.
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In an aging joint, fibrillation (fine, rapid contractions or twists of fibers or small groups of fibers) occurs on joint surfaces that don't bear weight. OA occurs primarily in weightbearing joints, like the knees and hips.
What is the major impact of OA?
The primary effect of OA is pain that can lead to disability. The cause of the pain is generally an inflammation or joint incongruity. However, individuals who have the same degree of OA can experience different levels of pain.
How many people in the United States have OA?
In the United States, estimates of arthritis range from as low as 6 percent of the adult population to as high as 90 percent of adults over 40 years of age. According to a 2000 report from the National Center for Health Statistics, up to 32.9 million Americans (about 23 percent of the adult population) reported that their physicians told them that they have some type of arthritis.
Is OA one disease or many?
It's still not clear whether OA is a single disease or many disorders with a similar final outcome. Several areas of study seem to indicate that OA is many distinct entities. Research is continuing to identify several types of risk factors that may contribute to OA.
Does race or ethnicity contribute to OA?
Early studies show conflicting evidence on the development of OA in African-Americans and in Caucasians. Based on a 1999 study by the National Center for Health Statistics, rates for osteoarthritis of the knee, for example, are 2.7 percent of the Caucasian population, 2.1 percent of the African-American population, and 1 percent of people classified in "other" racial categories. Researchers have observed differences in the features of the disease that can be seen on X-rays.
How large a role does heredity play in the development of OA?
Osteoarthritis in all its various forms appears to have a strong genetic connection. Gene mutations may be a factor in predisposing individuals to develop OA. But there are other risk factors as well that can increase a person's risk of developing OA. These include:
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Obesity. Generally, the more weight a person carries, the greater the pressure on weight-bearing joints of the body.
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Aging. As people age, cartilage normally is less able to repair itself.
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Nutrition. Calcium and vitamins C and D are needed to build strong bones. Investigators are researching whether an insufficiency of these vitamins may contribute to developing OA in later life.
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Other diseases and hereditary conditions that affect bones and connective tissues. Among the conditions are Ehlers-Danlos Syndrome, bone dysplasias, and Charcot joints.
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Injury or deformity in a joint. There is an increased risk of developing OA in a joint that is not properly aligned or one that has been injured.
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Occupational factors. Repetitive tasks, overworking the joints and overtiring muscles that protect a joint increase the risk for OA in that joint.