Objectives: Osteocytes play a major role in bone metabolism as mechanosensors, key regulators of osteoblast and osteoclast activity and of the mineral homeostasis. Therefore the assessment of osteocytes characteristics is important to understand bone pathology. We propose to study indirectly the osteocytes by performing quantitative backscattered electron imaging to quantify the sectioned osteocyte lacunae density and size in 2D on bone samples.
Methods: We analysed cortical and cancellous area of transiliac bone biopsy samples from healthy children (n=6; age range from 2 to 9.4 years). Calcium concentration images (pixel resolution 0.9 μm) were obtained by quantitative backscattered electron imaging (Field Emission SEM Supra40, Zeiss, Oberkochen, Germany). Grey-level (value corresponding to 5.2 weight% calcium content) and size (range of 1.55 μm2 to 80 μm2) thresholds were used to obtain binary images of osteocyte lacunae sections (OLS). We measured OLS-density, OLS-porosity and the average value resulting from the frequency distribution of OLS area, perimeter and aspect ratio between major and minor axes (AR).
Results: The OLS-porosity was higher in cortical bone compared to trabecular bone (+24%, P=0.03). It was due to a higher OLS- density (+33%, P=0.03). In contrast there was a trend to smaller osteocyte lacunae in cortical bone (OLS-Area: −6%, ns; OLS-Perimeter: −5%, ns). In general, the size distribution analysis revealed less OLS with large size in cortical bone (6070 μm2 area range: −50%, P=0.03; 3540 μm perimeter range: −28%, P=0.03). The aspect ratio were similar in both bone regions.
Conclusion: Quantitative backscattered electron imaging is sensitive enough to reveal different osteocyte lacunae section density and size between cortical and trabecular bone. This measurement in a healthy children cohort will serve as reference to characterize bone pathologies in children.
Disclosure: The authors declared no competing interests.