Correlation of bone and cartilage markers in the synovial fluid with the degree of osteoarthritis

In recent years, many biochemical markers were tested with the aim of developing a tool for the early detection and monitoring of osteoarthritis (OA). Apart from chondral markers, we also evaluated osseous markers from the synovial fluid to obtain more comprehensive information, and we compared the levels in relation to the severity of OA. In this prospective, cross-sectional study, synovial fluid samples were obtained from 73 patients with OA of the knee joint prior to operation and after the joint was flushed with 50 ml of normal saline. All patients underwent surgery and were classified in accordance with the Outerbridge and the Noyes classification. The measured biochemical markers included pyridinoline (PD), deoxypyridinoline (DPD), N-telopeptide (NTx), carboxyterminal propeptide of collagen-1 (PICP), matrix metalloproteinases (MMP-1 and MMP-3), and tissue inhibitor of MMPs (TIMP-1). The marker levels were normalized against the total protein content and were compared with the Outerbridge and the Noyes classification. For the majority of markers, the correlation coefficient was below r=0.3, with large 95% confidence intervals. The highest correlation coefficients were obtained from DPD and TIMP-1. In relation to the Outerbridge classification, DPD revealed high values only in stage IV. The overall results indicate that the majority of the tested markers are unspecific with regard to the different stages of OA. The two markers with the highest correlation coefficients showed no major sensitivity to detect OA at an initial stage. However, they might give additional information to clinical and radiological findings with regard to the severity of the disease.