Demonstration of a novel method to explore osteon tilt in the human femoral cortex

Osteon tilt, defined as the combination of an osteon's vertical angle and horizontal orientation, remains poorly characterized due to technical limitations in large-scale 3D bone microarchitecture analysis. This study developed a methodology combining traditional serial sectioning using circularly polarized light microscopy with Geographic Information Systems (GIS) to visualize and quantify osteon tilt across the entire femoral cortex. Spatial variation of osteon tilt was analyzed using 1219 osteons across 8 octants and 3 circumferential rings. Vertical osteon angle varied regionally, with acute angles in the anterolateral region and obtuse angles in the posterior region. Osteons demonstrated a general posterior inclination with opposite orientations on the medial and lateral cortices. Vertical angle positively correlated with osteon volume, with the strongest correlation found in the anterior and lateral regions. A paired sample t-test showed no significant difference between serial sections, confirming the preservation of sectional alignment. Osteon tilt patterns may reflect the femur's complex loading environment: smaller, acutely angled osteons predominate in tension-bearing regions, while larger, obtusely angled osteons occur in compression-bearing regions. This GIS-based method enables a quantitative, comprehensive assessment of osteon morphology and provides insights into bone's adaptive remodeling response to biomechanical forces.