Sources of pain in osteoarthritis: implications for therapy

Osteoarthritis is the leading musculoskeletal cause of disability in western society. Despite this, it is stilldifficult to gain a precise definition of what osteoarthritis actually is. It is well known that there is amodest correlation between x-ray changes and pain. However, for knee joint structure there is largelyconsistent evidence that bone marrow lesions, synovitis/effusions and cartilage defects are associatedwith knee pain and cartilage loss. In addition, muscle strength and obesity predict pain even in the absenceof structural knee pathology. Finally, the pain system itself is involved with both pain processing andgenetic factors implicated in recent studies. These improvements in basic science have greatly enhancedour understanding that osteoarthritis is an umbrella term for a number of pathways leading to very similarpain and structural outcomes; these outcomes are leading to lesion-specific therapies, which indicate theimportance of trying to pinpoint causes of pain in the individual.