A polarized light microscopy method for accurate and reliable grading of collagen organization in cartilage repair

Summary Objectives Collagen organization, a feature that is critical for cartilage load bearing and durability, is not adequately assessed in cartilage repair tissue by present histological scoring systems. Our objectives were to develop a new polarized light microscopy (PLM) score for collagen organization and to test its reliability. Design This PLM score uses an ordinal scale of 0–5 to rate the extent that collagen network organization resembles that of young adult hyaline articular cartilage (score of 5) vs a totally disorganized tissue (score of 0). Inter-reader reliability was assessed using Intraclass Correlation Coefficients (ICC) for Agreement, calculated from scores of three trained readers who independently evaluated blinded sections obtained from normal ( n = 4), degraded ( n = 2) and repair ( n = 22) human cartilage biopsies. Results The PLM score succeeded in distinguishing normal, degraded and repair cartilages, where the latter displayed greater complexity in collagen structure. Excellent inter-reader reproducibility was found with ICCs for Agreement of 0.90 [ICC(2,1)] (lower boundary of the 95% confidence interval is 0.83) and 0.96 [ICC(2,3)] (lower boundary of the 95% confidence interval is 0.94), indicating the reliability of a single reader’s scores and the mean of all three readers’ scores, respectively. Conclusion This PLM method offers a novel means for systematically evaluating collagen organization in repair cartilage. We propose that it be used to supplement current gold standard histological scoring systems for a more complete assessment of repair tissue quality.