Targeting the synovial tissue for treating osteoarthritis (OA): where is the evidence?

Osteoarthritis (OA) is often a progressive and disabling disease, which occurs in the setting of a variety of risk factors--such as advancing age, obesity and trauma--that collude to incite a cascade of pathophysiological events within joint tissues. An important emerging theme in OA is a broadening of focus from a disease of cartilage to one of the 'whole joint.' The synovium, bone and cartilage are each involved in pathological processes that lead to progressive joint degeneration. Additional themes that have emerged over the past decade are novel mechanisms of cartilage degradation and repair, the relationship between biomechanics and biochemical pathways, the importance of inflammation and the role of genetics. In this article, we review the molecular, clinical and imaging evidence that synovitis is not an 'incidental finding of OA', but plays a significant role in disease pathogenesis, and could therefore represent a target for future treatments.