Post-hoc analysis of a randomized clinical trial of 109 patients with knee osteoarthritis shows that pain at rest and pain on movement are associated with different profiles of proinflammatory biomarkers, indicating that these pain characteristics might originate from different mechanisms. IL-6 and IL-8 concentrations in the synovial fluid were significantly associated with self-reported pain on movement but not pain at rest (when measured on the Likert scale), whereas TNF concentration was significantly associated with both.