Cortical Bone Microelasticity Assessed with Scanning Acoustic Microscopy: Relationship to Nanostructural Characteristics across a Human Osteon

Abstract

Objective :Scanning acoustic microscopy derived impedance (Z) of cortical bone osteons shows a bimodal lamellar pattern of alternating high and low Z values. The goal of this study was to assess the relationship of osteon level impedance variation to the orientation and size of mineral (hydroxyapatite) platelet at one micron resolution. Methods : Data were acquired on a human femoral cross-section using 900-MHz SAM, synchrotron radiation micro-computed tomography (SR-μCT to measure the local variation of HA content) and small angle X-ray scattering (SAXS). SAXS provides the relative variation of HA platelet orientation and changes in mean thickness from the analysis of the integrated SAXS intensity and pattern, respectively. Results : While SR-μCT images showed a constant level of mineral, both SAM and SAXS images displayed the lamellar level modulation related to the modulation of microelasticity, orientation and thickness of the platelets. Z was strongly correlated with the SAXS intensity (R2=0.91, p<0.0001) but much lower correlated with the platelets thickness (R2=0.35, p<0.0001). Conclusions : Our study is the first one that combines SAXS, SR-μCT and SAM to elucidate the impact of mineral platelets orientation and mean thickness on microelasticity. Our results suggest that the main factor contributing to microelasticity variations is the platelet orientation reflected in modulations of the integrated SAXS intensity.