Historically plain radiography has been the primary investigative tool by which structure in osteoarthritis is measured. Magnetic resonance imaging (MRI) is widely used in medical diagnosis for its various advantageous features, such as high-resolution capability, the ability to produce an arbitrary anatomic cross-sectional image, and wide range of available tissue contrast. Its ability to image features such as the subchondral bone, cartilage and soft tissue structures means that its application in knee osteoarthritis (OA) raises hope of improving our understanding of structural associations of pain and function in OA joints, previously based on conventional radiography. Additionally, MRI has the potential for assessing the effect of risk factors for epidemiologic investigation and the effectiveness of therapeutic interventions in OA clinical trials.