A person who has severe knee pain and extensive radiographic evidence of osteoarthritis is thought to have an “obvious” explanation for the pain. Some people, however, may have severe radiographic damage (Kellgren-Lawrence grade 41) with no pain, or vice versa.2 Such discordances, which are also seen in rheumatoid arthritis,3 have been the subject of much interest for clinicians and researchers. Some researchers have suggested that little or no relation exists between the “illness” of joint pain and the “disease” of radiographic osteoarthritis.

In the linked study (doi:10.1136/bmj.b2844), Neogi and colleagues assess the association between knee pain and radiographic osteoarthritis in people whose knees were discordant for pain.4 The study design was a within person, knee matched case-control study that examined 696 people from the Multicenter Osteoarthritis Study (MOST) and 336 from Framingham. Odds ratios were 151 (95% confidence interval 43 …