The OARSI histopathology initiative - recommendations for histological assessments of osteoarthritis in the mouse.

Aim: To describe a histologic scoring system for murine osteoarthritis (OA) that can be applied universally to instability, enzymatic, transgenic and spontaneous OA models.

Methods: Scientists with expertise in assessing murine OA histopathology reviewed the merits and drawbacks of methods described in the literature. A semi-quantitative scoring system that could reasonably be employed in any basic cartilage histology laboratory was proposed. This scoring system was applied to a set of 10 images of the medial tibial plateau and femoral condyle to yield 20 scores. These images were scored twice by four experienced scorers (CL, SG, MC, TA), with a minimum time interval of 1 week between scores to obtain intra-observer variability. An additional three novice scorers (CR, CL and MM) with no previous experience evaluated the images to determine the ease of use and reproducibility across laboratories.

Results: The semi-quantitative scoring system was relatively easy to apply for both experienced and novice scorers and the results had low inter- and intra-scorer variability. The variation in scores across both the experienced and novice scorers was low for both tibia and femur, with the tibia always having greater consistency.

Conclusions: The semi-quantitative scoring system recommended here is simple to apply and required no specialized equipment. Scoring of the tibial plateaus was highly reproducible and more consistent than that of the femur due to the much thinner femoral cartilage. This scoring system may be a useful tool for both new and experienced scorers to sensitively evaluate models and OA mechanisms, and also provide a common paradigm for comparative evaluation across the many groups performing these analyses.