Correlation between systemic markers of inflammation and local synovitis in knee osteoarthritis

Background: In the elderly population joint swelling, effusion and pain indicate local synovitis and the presence of inflammation. At present, no serum marker has been shown linking to knee synovitis in KOA. With regard to serum high sensitive C-reactive protein (hsCRP) as a measure of inflammation, this study aimed to determine the association of systemic inflammation with local synovitis, as well as with pain and muscle strength in KOA. Methods: The study population was selected consecutively among patients with KOA presented to Ayatollah Rouhani Hospital Rheumatology Clinic with knee joint synovitis. The diagnosis of KOA was confirmed according to the American College of Rheumatology diagnostic criteria. Data regarding radiographic, demographic and biochemical characteristics were provided and IL-17, IL-10, TGF-ß and hsCRP in serum and synovial fluid (SF) were measured in all patients. Stepwse linear regression models were used to determine the correlation between SF- hsCRP as a measure of local inflammation with other systemic or local markers of inflammation. Results: A total of 40 patients (women 65%) with mean age 65.6+8.9 (49-86) years, mean BMI 27.7+3.7 (22-38) kg/m2, were analyzed. SF-hsCRP was positively correlated with serum hsCRP as well as serum and SF cytokines. Knee pain was positively associated with BMI and radiographic severity and negatively with quadriceps muscle strength (QMS) (r=-0.350, p=0.029). In stepwise linear regression analysis the SF-hsCRP was positively correlated with serum hs-CRP (r=0.769, p=0.001), SF-IL-17 (r=0.428, p=0.001) and negatvely with serum IL-10 (r=-0.316, p=0.002). Conclusion: These findings indicate that systemic markers of inflammation such as serum hsCRP, and IL-17 are associated with local inflamation in KOA.