Conventional wisdom has held that osteoarthritis (OA) is solely a wearing out of your joint cartilage, while rheumatoid arthritis (RA) is caused by inflammation, an errant immune response. However, OA and RA may have more in common than once believed. New evidence points to an inflammatory component of OA, and it suggests that obesity not only places undue stress on your knees and hips, but also may damage all of your joints more insidiously, at a cellular level. In addition, researchers are recognizing the vital role of the bone underneath the cartilage, prompting a closer look at the whole joint as it relates to OA. Experts hope this new understanding will translate into new strategies to prevent and treat OA, the most common form of arthritis and a disease with limited medical treatments.