Sub-Trabecular Strain Evolution and Fracture Criteria in Human Trabecular Bone

To understand the most detrimental characteristics behind bone fractures, it is key to understand the local strain limits and its relation to failure sites locally and globally. Digital volume correlation is an emerging technique to study strains in the trabecular bone structure under loading. The aim of this study was to investigate the three-dimensional strain distributions as well as damage criterion at the sub-trabecular level in trabecular bone tissue using different image resolutions. Human cadaver trabecular bone samples were compressed in situ until failure, while imaging with high-resolution synchrotron radiation X-ray tomography. Digital volume correlation was used to determine the strains inside the trabeculae in cracking (where fractures are about to occur) and non-cracking regions. Bone tissue was found to withstand locally very high compressive or tensile strains (~10%) without immediately resulting in a fracture. Thus, local strains in close vicinity of developing cracks were higher than previously reported for a whole trabecular structure and similar as reported for single isolated trabeculae. Current literature investigating bone fractures at the tissue level seem to underestimate the maximum strain magnitudes in trabecular bone. We similarly report lower strains when downscaling our images (reducing the resolution); this suggests that the observed strains are dependent on the resolution at which they are investigated. Furthermore, the local strain magnitudes at the crack regions correlate with global parameters (global yield strain, average tissue mineral density and bone volume fraction). The trabecular thickness appears to be an important predictor for where the structure will break, as it fails at the weakest link. In summary, this first study to investigate the local strains in a trabecular structure at sub-trabecula resolution in human bone confirms the high strain magnitudes reported for single trabeculae under loading and more importantly extends the translation to the whole trabecular structure.