The disease can be hereditary, but genes don't tell the whole story. Researchers still are not sure when and why genes influence development of the disorder. It is most likely tied to hormonal differences in some way as well as to body structure. Osteoarthritis is the most common form of arthritis and is usually the result of damage to joints over time, as the cartilage covering bones breaks down and allows them to rub against each other. It may occur more in women because their bodies are built to accommodate childbearing with hips spaced farther apart, increasing strain on the knees, researchers say.
Women are twice as likely as men to have arthritic knees.
But scientists also point to a reduction in estrogen levels as women age, and many physicians prescribe hormone-replacement therapy to protect against the wearing down of bone and cartilage. Other, so-called autoimmune, types of arthritis such as lupus often flare up during pregnancy. Rheumatoid arthritis, another autoimmune form, usually dissipates during pregnancy but roars back after a few months. Estrogen can rise to 100 times its normal level during pregnancy, and investigators are exploring whether changes in hormonal levels during pregnancy might influence the course of autoimmune forms of arthritis. A landmark study in the 1930s revealed that levels of a substance produced by the adrenal gland, cortisone, rise during pregnancy and may help alleviate rheumatoid arthritis symptoms.