Procollagen IIC-peptide as a marker for assessing mechanical risk factors of knee osteoarthritis: Effect of obesity and varus alignment

Objective - To ascertain by cross sectional examination whether the concentration of procollagen IIC-peptide in joint fluid significantly correlates with mechanical risk factors of knee osteoarthritis (OA), such as obesity (body mass index) and varus alignment (lateral femorotibial angle). Methods - The concentrations of procollagen IIC-propeptide in synovial fluid were measured by a sandwich enzyme immunoassay of 65 patients with the same radiological stage of primary knee OA - that is, Ahlbak stage I. The relations between procollagen IIC-peptide and body mass index and lateral femorotibial angle were examined using simple regression analysis and multiple regression analysis. Results - Significant positive correlations were found between procollagen IIC-propeptide concentrations and body mass index (r=0.479, p<0.0001), and between procollagen IIC-propeptide concentrations and lateral femorotibial angle (r=0.375, p=0.0021). Significant correlations were also found by multiple regression analysis. The multiple correlation coefficient of body mass index and femorotibial lateral angle to the procollagen IIC-propeptide concentrations was 0.547 (p<0.0001). Conclusions - The findings suggest that synthesis of type II collagen by chondrocytes is enhanced by abnormal mechanical stress, in this case obesity and varus alignment. It is concluded that procollagen IIC-propeptide concentrations in joint fluid are a useful marker of early OA.