Elevated osteopontin level of synovial fluid and articular cartilage is associated with disease severity in knee osteoarthritis patients

ObjectiveTo investigate osteopontin (OPN) levels in both synovial fluid and articular cartilage of patients with primary knee osteoarthritis (OA) and their relationship with severity of the disease.MethodFifty patients aged 48–81 years with knee OA and 10 healthy controls were enrolled in this study. Anteroposterior knee radiographs or/and Mankin score were taken to determine the disease severity of the affected knee. The radiographic grading of OA in the knee was performed by using the Kellgren-Lawrence criteria. OPN levels in synovial fluid were measured using enzyme-linked immunosorbent assay. OPN levels in articular cartilage were assessed by immunohistochemical methods.ResultsCompared to healthy controls, OA patients had higher OPN concentration in synovial fluid (4519.60±1830.37, 95%CI 3999.42–5039.79 vs 1179.70±303.39, 95%CI 1035.53–1438.74 pg/ml, P<0.001)and articular cartilage(0.6±0.06, 95%CI 0.59–0.62 vs 0.43±0.07, 95%CI 0.38–0.48, P<0.01). In addition, synovial fluid OPN levels showed a positive correlation with articular cartilage OPN levels (r=0.411, 95%CI 0.150–0.619, P=0.003). Subsequent analysis showed that synovial fluid OPN levels significantly correlated with severity of disease (Spearman's ρ=0.581, 95%CI 0.335–0.726, P<0.001). Furthermore, the articular cartilage levels of OPN also correlated with disease severity (Spearman's ρ=0.675, 95%CI 0.500–0.808, P<0.001).ConclusionsOPN in synovial fluid and articular cartilage is associated with progressive joint damage and is likely to be a useful biomarker for determining disease severity and progression in knee OA.