Aging. OA becomes more common as people age. It usually begins after age 45, and it is most common in people over age 65. While the association between OA and aging is strong, the reason for the association is unclear. One theory is that the cells involved in cartilage repair dwindle in number as people age.

Gender. OA affects both men and women. Up to about age 50, OA is more common in men. After age 50, it’s more common in women. Women also experience faster progression of hip OA than men.

Excess body weight. Obesity plays more than just a mechanical role in OA development. Being overweight or obese is a strong risk factor for development of OA, particularly of the knees, and contributes to more severe symptoms and impact of OA. In addition, recent research suggests that excess body fat produces chemicals that may fuel joint inflammation.

Joint injury. Traumatic injury to a joint, whether from sports or a car wreck, is another strong risk factor for development of OA. Among people with a prior knee injury, the lifetime risk of OA is 57 percent. Researchers are studying the ways in which cells’ abnormal response to injury and inadequate repair contribute to the disease.

Genetic factors. Your genes can play a role in OA risk, particularly of the hands. For example, a person whose mother has or had OA of the hands may be at greater risk for also developing OA of the hands.

Occupation. A job, or any long-term activity, that requires repeated, forceful or excessive knee bending; kneeling or twisting; lifting or carrying heavy loads; or working while standing may cause recurrent “little injuries,” putting people at a higher risk for knee or hip OA over time.