Correlation between protein YKL-40 and ultrasonographic findings in active knee osteoarthritis

The aim of our study was to analyze the level of the glycoprotein YKL-40 in patients with active knee osteoarthritis (OA) and to search possible correlations with local inflammation and ultrasound (US) findings.

A prospective study with fifty consecutive patients with active knee OA (diagnosed based on the American College of Rheumatology criteria for OA with radiographic confirmation) was performed. Concentrations of YKL-40 in serum and synovial fluid were measured by ELISA. US examinations - Gray scale (GS) US and Power Doppler (PD) US - of the knee was performed according to international guidelines. The suprapatellar, medial and lateral parapatellar recesses were scanned in each knee to evaluate synovial hypertrophy and vascularization.

Forty women (mean age 61.50±11.33 years old) and 10 men (aged 68.50±6.60 years old) were enrolled. We found that the synovial level of the glycoprotein (237.80±104.08 ng/ml) was significantly higher compared to the serum concentration (112.83±60.61 ng/ml, p<0.001). The serum concentration in OA patients was higher comparing with age-matched healthy controls (84.19±11.39 ng/ml) (p<0.05). A statistically significant association between YKL- 40 in synovial fluid and serum levels was shown. We determined a moderately positive linear relationship between the synovial level of the glycoprotein and the serum concentration. No association between the levels of inflammatory markers - erythrocyte sedimentation rate and C-reactive protein - and YKL-40 concentrations was detected. Our study revealed a strong relationship between YKL-40 in synovial fluid and GS US and feeble with PD US. YKL-40 correlated with inflammatory activity in knee joints and neovascularization detected by US.

YKL-40 is involved in the pathogenesis of OA synovitis. Evaluation of YKL-40 levels in parallel with US might provide more sensitive and reliable information for the diagnosis and understanding of OA.