Background: Cortical bone is a dynamic, living tissue that has a hierarchically organised microstructure which is able to repair itself and adapt to dynamic mechanical loading. Bones adaptation to changes in its mechanical environment is controlled at the cellular level. Osteocytes, the primary mechanosensory cells, reside in osteocyte lacunae. Variations in the dimensions of osteocyte lacunae have been reported; however, the role of these variations in bones adaptive response is unknown. The aim of this study was to explore potential variations in osteocyte lacunar size and shape in bone following mechanical loading.
Methods: A fibula of a C57Bl/6J male mouse was subjected to 2-week in-vivo mechanical loading utilising the noninvasive murine tibia loading model (three times per week, 16.5N, 40 pulses, 10s interval; ethical approval had been obtained). The contralateral fibula served as internal control. Both fibula were scanned nondestructively using a conventional desktop micro-CT (Skyscan 1172) at 5 μm resolution. Subsequently, 1.4 mm of the proximal part of the loaded fibula was rescanned at a nominal resolution of 700 nanometer. After reconstruction and segmentation channels and lacunae were visualized and quantified.
Results: In the loaded fibula, substantial periosteal bone formation had occurred at the periosteal surface of the proximal region; this was not seen in the contralateral fibula. The new bone showed a disorganised woven-bone-like pattern. The newly formed bone exhibited higher lacunar density and variations in shape and size. Mean lacunar volume (593 μm3) at the border of pre-existing cortical bone and newly formed bone was nearly twice as high as in the midcortical regions (306 μm3).
Discussion: Osteocyte lacunae formed in rapidly forming bone have a morphology that differs from spatially closely-related osteocytes. NanoCT protocols may offer 3D insight into bone microstructure and its regulation by mechanical loading.
Disclosure: The authors declared no competing interests. This research was funded by the European Commission through MOVE-AGE, an Erasmus Mundus Joint Doctorate programme (2011-0015) and also supported by PhD Fellowships and G.0858.11 from the Research Foundation Flanders (FWO Vlaanderen), OT/09/035 from KU Leuven and the Clinical Research Funds of the University Hospitals Leuven.