Histopathological analyses of murine menisci: implications for joint aging and osteoarthritis

Objective: To establish a standardized protocol for histopathological assessment of murine menisci that can be applied to evaluate transgenic, knock-out/in, and surgically induced OA models. Methods: Knee joints from C57BL/6J mice (6e36 months) as well as from mice with surgically-induced OA were processed and cut into sagittal sections. All sections included the anterior and posterior horns of the menisci and were graded for (1) surface integrity, (2) cellularity, (3) Safranin-O staining distribution and intensity. Articular cartilage in the knee joints was also scored. Results: The new histopathological grading system showed good inter-and intra-class correlation coefficients. The major age-related changes in murine menisci in the absence of OA included decreased Safranin O staining intensity, abnormal cell distribution and the appearance of acellular areas. Menisci from mice with surgically-induced OA showed severe fibrillations, partial/total loss of tissue, and calcifications. Abnormal cell arrangements included both regional hypercellularity and hypocellularity along with hypertrophy and cell clusters. In general, the posterior horns were less affected by age and OA. Conclusion: A new standardized protocol and histopathological grading system has been developed and validated to allow for a comprehensive, systematic evaluation of changes in aging and OA-affected murine menisci. This system was developed to serve as a standardized technique and tool for further studies in murine meniscal pathophysiology models. (C) 2015 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.