Synovial fluid pro-inflammatory profile differs according to the characteristics of knee pain

Abstract Objective The role of inflammation and pain in osteoarthritis (OA) is not fully understood. We evaluated the association between pro-inflammatory biomarkers and pain. Methods We used baseline data and samples from a randomized controlled trial of colchicine for symptomatic knee OA. Severity of pain of the more symptomatic knee was assessed by NHANES-I criterion and WOMAC pain index. Pains on movement and at rest were self-reported on an 11-point Likert scale. Severity of radiographic tibiofemoral OA was assessed by Kellgren and Lawrence (KL) grade. Concentrations of synovial fluid (sf) IL-1β, IL-6, IL8, TNFα, CTXI and CTXII, as well as urinary (u) CTXII were measured. Results Of the 109 patients enrolled in the study, 70 patients (70% women) with synovial fluid obtained by direct aspiration were included for analysis. The mean ± SD age and body mass index (BMI) of the patients were 57.6 ± 8.3 years and 28.8 ± 5.2 kg/m2 . After adjustment for age, sex, and BMI, Sf IL-6 and IL-8 were statistically significantly associated with 11- point pain on movement, but not with pain at rest. No significant associations were observed with WOMAC pain scores. Sf IL-1β (analyzed as detectable/ non-detectable) was inversely associated with pain. In contrast, after adjustment, Sf TNFα was associated with WOMAC total pain and both pain on movement and at rest. Sf/u CTXII was associated with radiographic severity, but not with knee pain. Conclusions This study provides indication that OA pain mechanisms may differ according to the characteristics of the pain