Description and validation of a simple histological nerve tissue scoring system for nerve allografts

Background: In nerve allograft development, currently used subjective histological scoring systems to evaluate nerve structure in experimental studies are not uniform and have not been validated. The aim of this study was to describe and validate a simple, fast and inexpensive method to compare structural properties of nerve allografts on a histological level. Materials and methods: A total of 113 histological sections of rat (sciatic nerves) and human peripheral nerve segments (thoracodorsal and long thoracic nerve for motor and sural for sensory nerve) treated with various decellularization protocols were analyzed. Slides were stained with Hematoxylin & Eosin (H&E), Toluidine Blue and Laminin. A subjective scoring system using a 5-point scale was used to score each nerve section by four independent researchers. For validation of this score both inter- and intra-rater reliability were calculated using the Intraclass Correlation Coefficient (ICC). Results: Overall, an excellent correlation between the different observers was found for the Toluidine Blue (ICC = 0.919, 95% CI: 0.891–0.941), H&E (ICC = 0.9, 95% CI: 0.865–0.927) and Laminin staining (ICC = 0.897, 95% CI: 0.860–0.926). Intra-rater reliability was good for all three staining techniques (ICC >0.8). Conclusion: This study demonstrates the validity of this simple scoring system to evaluate nerve structure after different processing protocols. All three evaluated staining techniques can reliably be used for both rat and human nerve tissue. We believe this method is suitable to compare different processing techniques to create processed nerve allografts, especially when the average scores of multiple raters are used.