What's new in osteoarthritis pathogenesis?

Osteoarthritis is the leading musculoskeletal cause of disability in the Western society. Despite this, it is still difficult to gain a precise definition of what osteoarthritis actually is. The methods used for the study are narrative review and viewpoint focussing on the knee. It is well known that there is a modest correlation between X-ray changes and pain. Improvements in imaging have shown that osteoarthritis should be regarded as an umbrella term for a number of pathophysiological processes leading to pain and/or cartilage loss. If these are inside the joint (such as bone marrow lesions, cartilage defects or meniscal tear) then they can be considered osteoarthritis, while those outside the joint (such as obesity, weak muscles and vitamin D deficiency) could be considered the osteoarthritis syndrome. These improvements in basic science are leading to lesion-specific therapies indicating the importance of trying to pinpoint causes of pain in the individual.