Three-dimensional imaging of crack propagation mechanisms in human cortical bone on three paired anatomical locations
Résumé
The comprehension of crack propagation mechanisms in human cortical bone is of great importance for the improvement of fracture risk prediction. It is known that crack advance can be slowed down by toughening mechanisms, such as micro-damage formation near the crack tip. These mechanisms are thought to be related to bone microstructure. Recent results showed that under low loading rate, the radius diaphysis resisted better to crack propagation than the femoral diaphysis or neck (Gauthier et al., JMBBM, 2017). X-Ray CT imaging at the microscopic scale (µCT) is a standard method for the assessment of human cortical bone architecture but the assessment of micro-damage requires sub-micrometric spatial resolution. The aim of the current study is to investigate the microstructure and micro-damages of paired anatomical locations subjected to toughness experiments. We assessed the microstructure of human cortical bone of 8 paired radius diaphysis, femoral diaphysis and femoral necks (female, 50 - 91 y.o.) using Synchrotron Radiation (SR)-µCT in absorption and phase modes (voxel size of 0.7 µm). Image acquisition was performed on two different volumes of interest in each sample: the first one corresponds to a region where no particular mechanical stress was applied, in order to investigate structural differences between the locations; the second one, to a damaged region where three-point bending toughness tests were performed under a quasi-static strain rate (10-4 s-1), to evaluate structural changes, as micro-damages formation, due to crack propagation. Phase µCT allows the enhancement of the visibility of osteons, that might play a major role in crack propagation mechanisms as illustrated on Figure 1. After acquisition, we designed an image processing workflow to extract quantitative information on bone structural elements, such as Haversian canals, osteons or lacunae. Cracks and micro-damages were also segmented and quantified to investigate their relationships with human cortical bone toughness.