Human cartilage glycoprotein 39--biomarker of joint damage in knee osteoarthritis.

Human glycoprotein of cartilage (YKL-40) synthesizes chondrocytes and synovial cells in inflammatory conditions or remodels the outer cell matrix in osteoarthritis. The aim of this study was to conduct a parallel analysis between thickness of cartilage and length of osteophytes, ultrasound indicators of joint destruction, with levels of YKL-40 in serum in patients with primary osteoarthritis. Ultrasound findings and concentration of YKL-40(ng/ml) were examined in 88 patients. The average value cartilage thickness measured on medial condyles of the femur was 1.30 +/- 0.23 mm and on lateral was 1.39 +/- 0.27 mm. Median YKL-40 in patients with shorter osteophytes was 62.0 (44.5-90) ng/ml, and with longer osteophytes was 119 (range 80-171) ng/ml (p = 0.000). YKL-40 can be a marker for the appearance of longer osteophytes (sensitivity = 79.1%; specificity = 61.9%; cut off = 75.0 ng/ml). The duration of illness is very much connected to values of YKL-40 (r = 0.651, p = 0.000). After an illness duration of five years, the concentration of YKL-40 was 83.68 +/- 33.65 ng/ml, after ten years it was 138.22 +/- 48.88 ng/ml, and after 15 and 20 years it was 209.30 +/- 79.36 ng/ml and 218.50 +/- 106.51 ng/ml, respectively. Higher concentrations of YKL-40 indicate the level of cartilage destruction and can be used for assessment of destruction.