Artikel
A micro-CT study on trabecular transformation of mineralized architecture in normal postnatal spine growth in mice
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Veröffentlicht: | 23. Oktober 2017 |
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Gliederung
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Objectives: Bone is a dynamic architectural structure, central to locomotion in all mammals. During physiological growth bone structurally responds to mechanical strain and changing musculoskeletal demands. This is true for both cortical and trabecular bone, with the latter heavily studied to understand fracture healing and pathology like osteoporosis. Especially mice have become a widespread animal model for investigating a host of orthopedically-important questions. We hypothesize that the forming trabecular bone architecture is rather well organized and that the main structural motifs develop in well defined, timed stages. We use high resolution micro-computed tomography (μCT) to quantify and report architectural transformation that constitutes cornerstones of normal bone formation in a well-established mouse model.
Methods: Lumbar spine segments of 19 female C57BL/6 mice pups between 1 and 14 days post-partum were investigated. Samples were extensively studied by μCT augmented by conventional histology. Careful considerations and pretests were made to ensure a high comparability of these different density samples in the μCT. 3D data was obtained with an isotropic voxel size of 2.5 μm. Geometric, volumetric, as well as bone mineral density (BMD) measurements were determined. Qualitative and quantitative analysis was performed in 2D and 3D using software based on ImageJ/FIJI and the BoneJ plugin.
Results and Conclusion: Figure 1 [Fig. 1]. Within the first 14 days of life the mineralized lumbar spine undergoes extensive morphological transitions. The first-formed spongy template becomes a highly oriented cancellous bone structure, well-fitting to serve as a load bearing structure.
While the vertebral bodies grow, a decrease in bone volume fraction and trabecular number takes place. As expected, the formation of cancellous bone occurs in distinct phases: An initial spicular template consolidates and rearranges then establishes a preferentially vertical-horizontal configuration as a result of highly-oriented spatial expansion. By 14 days of age, the young lumbar vertebra shows all anatomical landmarks of an adult spine. BMD calibrated histograms show a maturation of material properties. Our analysis allowed to directly compare growing samples of different size and mineral density in novel high resolution data, supported by conventional histology.
Understanding the principles of normal bone formation in the spine provides a basis for predicting the dynamics of cancellous bone architecture, which strongly determines the structure's mechanical properties. Our study makes it possible to benchmark treatment, pathology or the interaction of bone with implanted biomaterials.