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Comparison between two ICRS histology scoring systems for cartilage repair

The histological quality of cartilage is considered to be one of the most important outcome tools to objectify success of different treatment modalities in regenerative orthopedics and tissue engineering. The aim of this pilot study was to compare the applicability of two International Cartilage Research Society (ICRS) visual histological assessment scales, ICRS I and ICRS II in the analysis of cartilage restoration after treatment with genetically modified autologous bone marrow clots. Chondral defects in 28 skeletally mature sheep which were randomly assigned to 4 different groups ; TGF group (TGF-β1 gene transduced bone marrow clot), GFP group (Green fluorescent protein transduced bone marrow clot), BMC group (untransduced bone marrow clot) and NC group (negative control, no treatment) were treated accordingly. After 6 months animals were sacrificed and osteochondral explants were analyzed. For histological assessment, slides were stained with hematoxylin - eosin and Safranin O. Two independent evaluators examined 112 slides blinded, 4 slides for each specimen using assessment scale ICRS I then ICRS II. Significant period of time passed between first and second examination, so the possibility of a bias with the respect to the first examination has been avoided entirely. ICRS I assesses 6 features that are graded with grades from 0 to 3. With ICRS II 14 features are evaluated on a visual analogue scale. Each parameter is scored on a scale from 0 to 100%. The ICRS I demonstrated lower inter-reader variability compared with ICRS II. Results yielded with ICRS I assessment scale were 98.7% coincident between two observers while those obtained with ICRS II assessment scale varied greatly. Subchondral bone and overall assessment scores had the best correlation coefficients for inter-reader variability (r = 0.82 and 0.76, respectively). ICRS I score revealed statistical significant difference in cell distribution between TGF and NC group (p=0.002). ICRS II showed statistical significant difference in surface and matrix staining score between TGF and NC group (p=0.009 and 0.007, respectively). ICRS II enabled better discrimination of scoring parameters but it is more suited for evaluators with strong background in cartilage histopathology. ICRS I remains easy to use for less experienced evaluators.

ICRS II histological assessment scale; cartilage repair

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