Imaging the painful osteoarthritic knee joint: what have we learned?

Pain in the peripheral joints is an increasingly common problem, resulting in significant patient disability and health-care expenditure. Osteoarthritis (OA), a syndrome of joint pain with associated structural changes, is the most prevalent joint disease, yet the etiology of pain in OA is not entirely clear. Traditional assessment of the structure-pain relationship in knee OA has relied on conventional radiography, which has several limitations, not least the discrepancy between symptoms and radiographic findings. MRI has the capability to visualize all the structures within the knee joint, and there is a growing body of work using MRI to examine the correlation between structural findings and symptoms. In large cohort studies, synovial hypertrophy, synovial effusions, and abnormalities in the subchondral bone have been associated with knee pain. Advances in our understanding of the etiology of pain in OA will assist in the identification of further targets for treatment of this common and painful disease.