Micro-CT-based analysis of the murine osteochondral unit: a review and recommendations for standardized subchondral bone assessment.

Abstract

Micro-CT enables high-resolution, 3D, and non-destructive visualization of bone microarchitecture in small preclinical animal models. It is widely applied to assess mineralized tissues in joints, making it a valuable tool for monitoring disease progression. Murine models are particularly prevalent in joint research due to their cost-effectiveness and disease tunability. Established guidelines for murine bone microstructure assessment provide a standardized framework for morphometric analysis and facilitate cross-study comparisons. However, these recommendations were developed for trabecular and cortical bone in long bones, and may not fully address the unique characteristics of mineralized tissues within joints. This review focuses on murine studies, and aims to: (1) examine reported methodologies for volume of interest selection; (2) outline commonly evaluated parameters; and (3) propose adaptations to expand existing guidelines for quantitative analysis of the osteochondral unit. In the absence of specific guidelines for osteochondral unit analysis, reported volumes of interest vary considerably and are influenced by anatomical differences across strains, sexes, ages, and disease stages. Many studies target the subchondral bone plate (SBP); however, the spatial resolution of desktop microCT is insufficient to distinguish SBP from calcified cartilage; hence, they are measured as 1 entity. To enhance reproducibility and comparability, we recommend standardized volumes of interest that include all mineralized tissues from the articular surface to the growth plate. Given the structural differences between SBP and subchondral trabecular bone, a consistent method for defining their boundary is strongly recommended. Data should be reported using robust, easily implementable metrics such as volume and thickness, with additional parameters (eg, porosity, mineral density) included as appropriate. Commonly used metrics such as SBP thickness and volume should continue to be used. When SBP and calcified cartilage cannot be distinguished, we recommend using the subchondral mineralized plate nomenclature.