Current thought about rheumatoid arthritis focuses on chronic inflammation and the accumulation of structural damage to cartilage and bone. Increasingly, it has become clear that inflammation in RA not only is responsible for signs and symptoms such as pain, stiffness, and swelling, but also is linked to the damage in the joint. The cellular and molecular mechanisms associated with abnormal bone metabolism—osteoimmunology—have been the subject of intense research recently.
http://www.rheumatologynews.com/article/S1541-9800(08)70583-0/fulltextOK..