Osteoarthritis (OA), the most common form of arthritis, is a progressive joint disorder characterized by gradual loss of cartilage. Osteoarthritis of the knee afflicts 28 % of adults over age 45 and 37 % of adults over age 65 in the U.S. As a leading cause of disability among noninstitutionalized adults, OA's prevalence, effect on health, and economic consequences are expected to increase dramatically during the next few decades as the population...