Spatial heterogeneity and age-related differences in calcium content and lacuno-canalicular network in newly formed osteons in human bone

Abstract

Bone quality, influenced by both mineral content and microstructural organization, plays a critical role in skeletal strength and fracture resistance, particularly with advancing age. This thesis aimed to investigate how aging affects the composition and microstructure of recently formed osteons in human cortical bone by analyzing the spatial distribution of calcium content and the osteocyte lacuno-canalicular network (OLCN).

A methodology was developed by combining quantitative backscattered electron imaging (qBEI), which measured calcium content, and confocal laser scanning microscopy (CLSM), which imaged the osteocyte lacuno-canalicular network. This approach enabled the co-registration of structural and compositional data and included a distance mapping and normalization step to allow comparisons across osteons of varying sizes. Canalicular density and calcium content were quantified within subvolumes of 400 µm3 to assess spatial heterogeneity—specifically, how these parameters vary with increasing distance from the Haversian canal—and their interrelation.

The results revealed that osteons from older women exhibited significantly lower canalicular density—with a 56.57 % decrease—than those from younger women, along with reduced network complexity and interconnectivity. These changes occurred without notable alterations in lacunar parameters, suggesting a defect in the formation of the canalicular network itself, rather than in osteoblast incorporation or osteocyte development. In osteons from young women, both calcium content and canalicular density decreased with distance from the Haversian canal, whereas in older women, this spatial organization was often disrupted or absent. A positive correlation between canalicular density and calcium content further supports the hypothesis that the OLCN influences local mineralization dynamics.

These findings highlight early alterations in bone microstructure with age and underscore the importance of the OLCN in maintaining mineral homeostasis and bone quality. This work provides a valuable framework for future studies and may contribute to the development of targeted strategies to enhance bone quality in aging populations.