Sub-trabecular strain evolution in human trabecular bone

Abstract

To comprehend the most detrimental characteristics behind bone fractures, it is key to understand the material and tissue level strain limits and their relation to failure sites. The aim of this study was to investigate the three-dimensional strain distribution and its evolution during loading at the subtrabecular level in trabecular bone tissue. 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. Regions without emerging damage were compared to those about to crack. Local strains in close vicinity of developing cracks were higher than previously reported for a whole trabecular structure and similar to those reported for single isolated trabeculae. Early literature on bone fracture strain thresholds at the tissue level seem to underestimate the maximum strain magnitudes in trabecular bone. Furthermore, we found lower strain levels and a reduced ability to capture detailed crack-paths with increased image voxel size. This highlights the dependence between the observed strain levels and the voxel size and that high-resolution is needed to investigate behavior of individual trabeculae. Furthermore, low trabecular thickness appears to be one predictor of developing cracks. In summary, this study investigated the local strains in whole trabecular structure at sub-trabecular resolution in human bone and confirmed the high strain magnitudes reported for single trabeculae under loading and, importantly extends its translation to the whole trabecular structure. Bone can withstand particularly high loads. For example, at the organ level the human proximal femur can endure up to 10 times the bodyweight 1-4. Bone strength is provided both by the material and its heterogeneous hierarchical structure in which each length scale has its important role 5. At the tissue level, the forces are distributed and transferred through the bone based on the relations between the spongy trabecular network and the dense cortical bone. Trabecular bone is metabolically highly active and undergoes remodeling throughout life 6-8. During aging and when affected by metabolic bone diseases such as osteoporosis, the metabolic activity changes as bone turnover is increased 5, 6, 9. These alterations result in net-loss of bone tissue, with decreased structural connectivity and apparent density, which subsequently leads to a weaker structure. To understand the most detrimental characteristics behind bone fractures, it is important to investigate the fracture initiation and find the relationships between failure sites and measurable bone parameters. Many studies utilize computational finite element analysis to investigate the local bone strains during loading 10-12. However, such studies are restricted because of limited experimental data available for validation. The lack of direct experimental measurements of the evolution of strains in bone during loading until failure ...

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“…In general, TMD was always lower in the fracture zone, irrespective of grouping (see Table 3). This finding agrees with Turunen and colleagues, ( 53 ) where TMD was also significantly lower at crack locations in comparison with surrounding trabecular bone. However, Turunen and colleagues ( 53 ) could relate the lower TMD to a significantly lower trabecular thickness in the fracture zone.…”

“…This finding agrees with Turunen and colleagues, ( 53 ) where TMD was also significantly lower at crack locations in comparison with surrounding trabecular bone. However, Turunen and colleagues ( 53 ) could relate the lower TMD to a significantly lower trabecular thickness in the fracture zone. Surprisingly, in the current study trabecular diameter was not different from the nonfracture region.…”

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“…Let us consider the possible application of Equations ( 27)- (30) for predicting struction of a quasi-brittle material under uniaxial compression. The analysis of t of damage rate, acceleration and jerk in the abovementioned example (Figures leads to confidence in the reality of such a possibility.…”