['Recent studies provide evidence that inflammation is a feature of the disease process in Osteoarthritis (OA). The clinical significance of P selectin (Ps) in OA has not been adequately studied and the association between Ps level and OA severity remains unknown.', 'We enrolled 120 knee OA subjects and 45 controls. All patients were scored for Kellgren-Lawrence grade (0-4). The Ps in serum and synovial fluid (SF) as well as serum C-reactive protein (CRP) levels were detected.', 'The mean Ps level in OA subjects was markedly increased than that in controls. In OA patients, the SF Ps levels increased with the severity of KL scores and significantly correlated with severity of disease (r=0.546, P<0.001) and serum CRP level (r=0.488, P<0.001). However, the serum Ps level did not show a significant correlation with the severity of OA.'] Is soluble P selectin in synovial fluid level correlated with the radiographic severity of knee osteoarthritis?