RELATIONSHIP BETWEEN SERUM CARTILAGE OLIGOMERIC MATRIX PROTEIN-LEVELSAND DISEASE PROGRESSION IN OSTEOARTHRITIS OF THE KNEE-JOINT

The value of serum cartilage oligomeric matrix protein (COMP) as a mar ker of disease progression was investigated in 81 hospital out-patient s with clinical knee osteoarthritis (OA). Progressing patients were de fined by a decrease of greater than or equal to 2 mm in joint space on X-ray or requiring knee surgery during the 5 yr of follow-up. Of the 57 patients for whom full data were available, 20 progressed and 37 di d not progress. Serum COMP levels increased during the first year in t hose who progressed (mean 6.42 mu g/ml) (S.D. 6.64) compared to those who did not progress [mean 0.07 mu g/ml (S.D. 4.99); P < 0.001]. Chang es in COMP during the first year were related to baseline COMP (r = -0 .672, P < 0.001) and weight-to-height ratio (r = 0.272, P = 0.47). Aft er allowing for these variables, serum COMP increased during the first year in progressive patients by 5.04 mu g/ml [95% confidence interval (CI): (2.61, 7.46)] more than in non-progressive patients. Discrimina nt analysis gave a sensitivity of 70% and specificity of 78% at a cut- off value of 3.17 mu g/ml. Baseline serum COMP levels did not differ b etween the groups but were related to late phase scintigraphy scan abn ormalities. These observations suggest that the changes in serum COMP may have prognostic significance and are consistent with a model of OA in which early signs of episodic clinical progression can be found in the cartilage as well as in subchondral bone.