Bone Abstracts

Spatial distributions of major and minor chemical elements are supposed to change during tissue maturation and due to bone diseases. Previous studies suggested that osteocytes have the ability to interact with the bone matrix of their environment. For this interaction osteocytes make use of the big inner surface of the osteocyte lacuno-canalicular network (OLCN) in which they are accommodated. The aim of this study was to quantify spatial correlations between the elemental composition of bone with the appearance of the OLCN to observe the possible impact of the network on the mineralized bone matrix.

To visualize and classify the OLCN structure, confocal laser-scanning microscopy (CLSM) was used after staining samples of human compact bone (children and adults, femoral midshaft) with rhodamine-6G. The analysis of the elemental composition of bone was performed using a scanning electron microscope equipped with an energy dispersive X-ray analysis (EDX) detector. Local concentrations of Ca, P, Mg and Na were evaluated and quantified in regions of 40×30 μm² selected based on differences in OLCN characteristics.

Regions of interstitial bone without any accessible OLCN showed the highest values of the Ca content (11.5–13 at %Ca). In contrast, regions of osteonal bone with an intact network had lower Ca content with values down to 8 at %Ca. While the Na concentration increased with increasing Ca this relation was not observed for Mg. Also in the comparison between children and adults these elements behaved differently with Na higher in adults and Mg higher in children. The Ca/P ratio increased slightly from 1.6 to 1.8 (theoretical value for hydroxyapatite equals 1.67) with the Ca content. Variations in the chemical compositions of human cortical bone were found depending on i) Ca content (interpretable as tissue age), ii) individual age and iii) canalicular network.