A new histology scoring system for the assessment of the quality of human cartilage repair: ICRS II.

BACKGROUND: A reliable and reproducible method is needed to assess cartilage repair.
PURPOSE: This study was undertaken to test the reproducibility of 2 established histological scoring systems, the Modified O'Driscoll Scale (MODS) and International Cartilage Research Society (ICRS) Visual Assessment Scale (ICRS I), and subsequently to develop and evaluate a new grading system for cartilage repair. STUDY
DESIGN: Cohort study; Level of evidence, 2.
METHODS: A total of 107 cartilage biopsy specimens were graded using MODS and ICRS I, and the reader variability was measured. The new grading system, ICRS II, was developed and the inter- and intrareader variability determined by 3 independent readers. Collagen type II deposition was assessed immunohistochemically.
RESULTS: The MODS and ICRS I demonstrated high interreader variability, with MODS also showing high intrareader variability. A new histological scoring system, ICRS II, was developed comprising 14 criteria to assess parameters related to chondrocyte phenotype and tissue structure. The ICRS II demonstrated lower inter- and intrareader variability compared with MODS or ICRS I. The overall assessment and matrix staining scores had the best correlation coefficients for inter- and intrareader variability (r = .81 and .82, respectively). The extent of collagen type II in cartilage, considered a marker of differentiation toward hyaline cartilage, could represent a measure of good cartilage repair. A correlation coefficient of .56 was obtained between the extent of collagen type II staining and the overall assessment score.
CONCLUSION: The ICRS II represents an improvement over current histological cartilage repair grading systems in terms of reader reproducibility. The clinical relevance and its ability to predict long-term repair durability will be assessed once long-term clinical data become available.