Despite years of research, no one has a simple answer to this question. Many factors probably cause the initial cartilage damage that sets off the destructive process. It remains a mystery why particular joints are affected by osteoarthritis (OA) if they have not suffered any previous injury or disease.

The aging process clearly can contribute to the breakdown in the joints and cause osteoarthritis, but not all elderly people develop detectable OA. In addition, athletes and laborers often subject their joints to prolonged wear-and-tear, which places them at increased risk of developing arthritis in later years.

Along with continual wear-and-tear, osteoarthritis has been linked with damaging events such as:

• Fractures and infections that can harm the internal tissues of a joint. Individuals who experience repeated knee injuries - such as basketball, football, or soccer players - are much more likely to develop osteoarthritis as they get older.
• In addition, people who overuse their joints by subjecting them to repeated stresses and strains are at increased risk. This is particularly evident in specific occupations such as jackhammer operators, who often develop arthritis of the hands or elbows, and ballet dancers, who develop arthritis of the feet.

Not surprisingly, physical inactivity can be as harmful to the joints as overuse. A lack of exercise or varied movement can weaken the muscles that support the joints and decrease joint flexibility. Eventually, an underused joint may become stiff, painful, dysfunctional, and prone to injury and osteoarthritis.

Heavy individuals are at increased risk of developing arthritis because their joints may be strained by excess weight. This is especially evident in weight-bearing joints such as the knees and hips, which often show the first signs of weight-related strain and injury.

Since being overweight can increase the chances of joint damage and worsen arthritic symptoms, most experts recommend weight-loss programs for overweight people who are at risk for osteoarthritis. Weight gain also should be avoided to help prevent the arthritis that may occur with aging.

Current research suggests that the genes inherited from one's parents may make an individual more likely to develop osteoarthritis than someone who does not have these genes.

Osteoarthritis of the fingers occurs very commonly in families and is most common in women.

In addition, OA is more likely to develop in people who are born with heredity defects that make their joints fit together incorrectly, such as:

• Bow legs
• A hip dislocation
• Laxity (double-jointedness)