Correlation of a novel matrix protein with the degree of cartilage degradation

Cartilage-derived retinoic acid-sensitive protein (CD-RAP), also referred to as melanoma-inhibiting activity (MIA), is detected physiologically only in cartilage tissue and pathologically in malignant melanoma. Recent studies indicated that this protein might be useful as a marker for altered joint metabolism or damage. The purpose of this study was to evaluate whether there is any correlation between the degree of cartilage degradation and levels of this protein. In a prospective cross-sectional study, synovial fluid samples were obtained from 67 consecutive patients undergoing surgery of the knee joint. The degree of cartilage degradation was determined intraoperatively using the Outerbridge and Noyes classifications. MIA/CD-RAP was measured by a commercially available enzyme-linked immunosorbent assay (ELISA). The marker levels were compared against the Outerbridge and Noyes classifications and the correlation coefficients were calculated. At advanced stages of cartilage degradation, there were decreased synovial fluid levels of MIA/CD-RAP. The correlation coefficients were -0.449 and -0.418 for the Outerbridge and Noyes classifications, respectively, with large 95% confidence intervals. While the physiological function of MIA/CD-RAP is still unclear, the results indicate that MIA/CD-RAP levels depend on the degree of cartilage degradation. Despite the high interindividual variations, MIA/CD-RAP might be useful as a marker to monitor degenerative joint lesions.