Osteoarthritis is the most common form of arthritis. The condition is characterised by loss or failure of the functional and/or biochemical integrity of the joint. The clinical symptoms include joint stiffness, pain and dysfunction, but the principal problem for the majority of patients is the pain. Although there are no pain receptors in the cartilage, the origin of the pain is thought to be due to stimulation of the A delta mechanoreceptors and the C polymodal nerve endings in the synovium and surrounding tissues. However, some of the pain experienced in and around the joints is referred pain or sympathetic efferent pain. In addition, there is a poor correlation of clinical symptoms with radiological or imaging appearance. This lack of correlation of clinical evaluation and imaging makes attempts at treatment difficult and compromises attempts to design studies and to evaluate the outcome of osteoarthritis in clinical trials.