Changes in synovitis and bone marrow lesions may not mediate the effect of cartilage loss on joint pain in osteoarthritis

We read with interest the recent article by Bacon et al 1 that used mediation analysis2 to understand the process by which cartilage loss changes joint pain. Given considerable investment in treatments that focus on chondroprotection, this is an important topic and the findings from this study have potential to inform patient management. The authors concluded that a small, non-clinically important effect of cartilage loss on joint pain was mediated by synovitis. To ensure this study accurately informs future research and practice, we ask the authors to clarify the reporting and interpretation of their results. The results presented in tables 3 and 4 do not support the authors conclusion that synovitis mediated the effect of cartilage loss on joint pain. The 95% …