Correlation of imaging semi-quantification with biochemical assessment of proteoglycans content in trypsinized articular cartilage

In order to validate an ultrasound cartilage elastography system developed by one of the authors for predicting pathological changes of articular cartilage (AC), it is necessary to established an in vitro model to study AC proteoglycans (PGs) degradation after trypsin digestion. AC of eight intact fresh bovine femur condyles were used for trypsin digestion with a concentration of 1 mg/ml. Full-thickness AC cylinders of 3 mm in diameter were harvested at a time interval of 0.5, 1, 2, and 3 hours after starting trypsin digestion. AC cylinder was then cut into two symmetric parts, one half for histomorphometric measurements of the Safranin O stained area fraction on histological sections and another half for validation of imaging method via conventional biochemical analysis by measuring uronic acid content. Results showed that PGs in the AC was significantly decreased with time of trypsin digestion both histologically and biochemically. There was a significant correlation between the histomorphometric measurements of Safranin O stained area fraction and uronic acid content (r=0.502, p<0.001). Results of this study suggested that the established in vitro PGs degradation model and histomorphometric measurements could be used for validation of the ultrasound cartilage elastography system in prediction of early AC pathological changes