Abstract
Many physiological, biomechanical, evolutionary and clinical studies that explore skeletal structure and function require successful separation of trabecular from cortical compartments of a bone that has been imaged by X-ray micro-computed tomography (micro-CT) prior to analysis. Separation often involves manual subdivision of these two similarly radio-opaque compartments, which can be time-consuming and subjective. We have developed an objective, semi-automated protocol which reduces user bias and enables straightforward, user-friendly segmentation of trabecular from the cortical bone without requiring sophisticated programming expertise. This method can conveniently be used as a ‘recipe’ in commercial programmes (Avizo herein) and applied to a variety of datasets. Here, we characterize and share this recipe, and demonstrate its application to a range of murine and human bone types, including normal and osteoarthritic specimens, and bones with distinct embryonic origins and spanning a range of ages. We validate the method by testing inter-user bias during the scan preparation steps and confirm utility in the architecturally challenging analysis of growing murine epiphyses. We also report details of the recipe, so that other groups can readily re-create a similar method in open access programmes. Our aim is that this method will be adopted widely to create a reproducible and time-efficient method of segmenting trabecular and cortical bone.
Highlights
Biomechanists, bone physiologists, biologists, clinicians and palaeontologists analyse bone structure to answer a myriad of questions [1,2,3,4]
To address the limitations in other segmentation methods, we have developed an objective, semi- 3 automated protocol for segmenting trabecular and cortical bone which was validated in animal and human bone samples and is flexible enough to be applicable across various challenging morphologies
To determine any potential effects of increased cortical porosity on the functionality of our recipe, we examined the outcome when the recipe was applied to the human parietal bone of a five-month-old male and the tibial epiphysis of an eight-week-old STR/Ort mouse; the cortical bone compartment of these immature bones is porous
Summary
Biomechanists, bone physiologists, biologists, clinicians and palaeontologists analyse bone structure to answer a myriad of questions [1,2,3,4]. Trabecular bone can constitute a small fraction of total volume, is more porous on the tissue level, and via its large surface area for remodelling supplies most of the exchangeable calcium pool [8]. This illustrates the differing functions and performance of these structurally diverse compartments, which have been reported to extend to bone type-related differences in osteoblast behaviour even when isolated and maintained in vitro [9]. This approach excludes data from the trabecular regions outside of this volume, making it likely that changes near the cortical boundary would, be missed
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