More Than Wear And Tear - Osteoarthritis: Arthritis

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More than wear and tear

Osteoarthritis is virtually unheard of in children and is rare in young adults. But it's common among older people. Almost everyone over age 65 has some cartilage and bone changes typical of the disorder. For this reason, osteoarthritis was long considered a natural product of aging, reflecting everyday wear and tear on cartilage. Although this attitude still prevails among many physicians, experts now believe the cause is much more complex. External factors, such as injuries, are important initiators, but the rate of progression is probably also affected by genetic and environmental traits.

While it's true that one's risk of developing osteoarthritis symptoms increases with age, many people whose x-ray films indicate joint changes typical of osteoarthritis have no symptoms. The severity of osteoarthritis symptoms depends on many factors, including how people use their joints. That's why taking the time to protect your joints is so important (see "Joint protection strategies").

The first signs of osteoarthritis are microscopic pits and fissures in the surface of the cartilage in your joints (see Figure 5). These fissures indicate that biochemical changes are gradually making the cartilage less resilient. Cartilage cells themselves produce enzymes that damage the molecules making up the structure of the cartilage, and tiny pieces of cartilage may flake off into the joint cavity. This changes the shape of the cartilage lining the bone, causing further damage as the altered surfaces move against each other.

As cartilage degenerates, patches of exposed bone appear. Just as a damaged gasket leads to metal-on-metal contact in a machine, your bones experience mechanical friction and irritation. They try to repair themselves, but the repair is disorderly. As a result, the surface thickens and osteophytes (bone spurs) form.

Once your cartilage is damaged, the resulting abnormalities can irritate surrounding soft tissues and cause inflammation. People with severely damaged joints sometimes have episodes of joint swelling from synovitis (inflammation of the joint's lining); however, this inflammation tends to be much milder than in rheumatoid arthritis or other inflammatory joint diseases. The damaged cartilage, bone rubbing on bone, and the inflammation combine to make movement painful.

Doctors sometimes refer to osteoarthritis as noninflammatory to distinguish it from other rheumatic diseases. But many people with osteoarthritis experience low-grade inflammation. It may arise when the articular cartilage in your joint fails to recover fully from an injury. In addition, inflammation may reflect an attempt by the joint to repair damage, or it may be due to genetic or metabolic factors that predispose you to joint degeneration.

Last updated:	September 05, 2008