Influence of bone volume fraction and architecture on computed large-deformation failure mechanisms in human trabecular bone

Orthopaedic Biomechanics Laboratory, University of California, Berkeley, CA, USA.
Bone (Impact Factor: 3.97). 12/2006; 39(6):1218-25. DOI: 10.1016/j.bone.2006.06.016
Source: PubMed


Large-deformation bending and buckling have long been proposed as failure mechanisms by which the strength of trabecular bone can be affected disproportionately to changes in bone density, and thus may represent an important aspect of bone quality. We sought here to quantify the contribution of large-deformation failure mechanisms on strength, to determine the dependence of these effects on bone volume fraction and architecture, and to confirm that the inclusion of large-deformation effects in high-resolution finite element models improves predictions of strength versus experiment. Micro-CT-based finite element models having uniform hard tissue material properties were created from 54 cores of human trabecular bone taken from four anatomic sites (age = 70+/-11; 24 male, 27 female donors), which were subsequently biomechanically tested to failure. Strength predictions were made from the models first including, then excluding, large-deformation failure mechanisms, both for compressive and tensile load cases. As expected, strength predictions versus experimental data for the large-deformation finite element models were significantly improved (p < 0.001) relative to the small deformation models in both tension and compression. Below a volume fraction of about 0.20, large-deformation failure mechanisms decreased trabecular strength from 5-80% for compressive loading, while effects were negligible above this volume fraction. Step-wise nonlinear multiple regression revealed that structure model index (SMI) and volume fraction (BV/TV) were significant predictors of these reductions in strength (R2 = 0.83, p < 0.03). Even so, some low-density specimens having nearly identical volume fraction and SMI exhibited up to fivefold differences in strength reduction. We conclude that within very low-density bone, the potentially important biomechanical effect of large-deformation failure mechanisms on trabecular bone strength is highly heterogeneous and is not well explained by standard architectural metrics.

    • "The key feature for capturing apparent-level behavior is the use of an asymmetric yield criterion (Pugh et al. 1973; Keaveny et al. 1994; Fenech and Keaveny 1999; Niebur et al. 2000), such as Mohr – Coulomb (Wang et al. 2008; Kelly and McGarry 2012), Drucker –Prager (Mercer et al. 2006; Kelly and McGarry 2012), or von Mises with pseudokinematic hardening term (Hernandez et al. 2006; Nawathe et al. 2013). While these models can be calibrated to capture the apparent-level mechanical behavior (Bayraktar et al. 2004b; Morgan et al. 2004; Bevill et al. 2006; Kelly and McGarry 2012), confidence in the predictive ability of modeling requires that they also accurately capture the tissue-level mechanics. Moreover, accurate simulation of tissue mechanics could extend the application of models to predict damage locations (Nagaraja et al. 2005, 2007). "
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    ABSTRACT: Microarchitectural finite element models have become a key tool in the analysis of trabecular bone. Robust, accurate, and validated constitutive models would enhance confidence in predictive applications of these models and in their usefulness as accurate assays of tissue properties. Human trabecular bone specimens from the femoral neck (n = 3), greater trochanter (n = 6), and lumbar vertebra (n = 1) of eight different donors were scanned by μ-CT and converted to voxel-based finite element models. Unconfined uniaxial compression and shear loading were simulated for each of three different constitutive models: a principal strain-based model, Drucker-Lode, and Drucker-Prager. The latter was applied with both infinitesimal and finite kinematics. Apparent yield strains exhibited minimal dependence on the constitutive model, differing by at most 16.1%, with the kinematic formulation being influential in compression loading. At the tissue level, the quantities and locations of yielded tissue were insensitive to the constitutive model, with the exception of the Drucker-Lode model, suggesting that correlation of microdamage with computational models does not improve the ability to discriminate between constitutive laws. Taken together, it is unlikely that a tissue constitutive model can be fully validated from apparent-level experiments alone, as the calculations are too insensitive to identify differences in the outcomes. Rather, any asymmetric criterion with a valid yield surface will likely be suitable for most trabecular bone models.
    No preview · Article · May 2015 · Computer Methods in Biomechanics and Biomedical Engineering
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    • "We used a Poisson's ratio of 0.3, and yield strains of 0.81% in compression and 0.33% in tension, respectively (Bayraktar et al., 2004). For all analyses, kinematic large-deformation geometric non-linearity was included in the constitutive model (Bevill et al., 2006; Stolken and Kinney, 2003). For computational efficiency, the bone tissue in the superior portion of the femoral head was not allowed to fail so as to eliminate spurious stress oscillations near the boundary conditions. "
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    ABSTRACT: The influence of the ductility of bone tissue on whole-bone strength represents a fundamental issue of multi-scale biomechanics. To gain insight, we performed a computational study of 16 human proximal femurs and 12 T9 vertebral bodies, comparing the whole-bone strength for the two hypothetical bounding cases of fully brittle versus fully ductile tissue-level failure behaviors, all other factors, including tissue-level elastic modulus and yield stress, held fixed. For each bone, a finite element model was generated (60-82μm element size; up to 120 million elements) and was virtually loaded in habitual (stance for femur, compression for vertebra) and non-habitual (sideways fall, only for femur) loading modes. Using a geometrically and materially non-linear model, the tissue was assumed to be either fully brittle or fully ductile. We found that, under habitual loading, changing the tissue behavior from fully ductile to fully brittle reduced whole-bone strength by 38.3±2.4% (mean±SD) and 39.4±1.9% for the femur and vertebra, respectively (p=0.39 for site difference). These reductions were remarkably uniform across bones, but (for the femur) were greater for non-habitual (57.1±4.7%) than habitual loading (p<0.001). At overall structural failure, there was 5-10-fold less failed tissue for the fully brittle than fully ductile cases. These theoretical results suggest that the whole-bone strength of the proximal femur and vertebra can vary substantially between fully brittle and fully ductile tissue-level behaviors, an effect that is relatively insensitive to bone morphology but greater for non-habitual loading. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Full-text · Article · Mar 2015 · Journal of Biomechanics
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    • "Due to these limitations, artificial cancellous bones can be used as an alternative to autograft and allograft. However , developing a synthetic cancellous structure that mimics the real cancellous bone architecture is highly very challenging due to their heterogeneous and anisotropic properties [13] [14] [15] [16], as well as the vast microarchitectural variations between skeletal sites [8,17–19]. "
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    ABSTRACT: Artificial bone is a suitable alternative to autografts and allografts, however their use is still limited. Though there were numerous reports on their structural properties, permeability studies of artificial bones were comparably scarce. This study focused on the development of idealised, structured models of artificial cancellous bone and compared their permeability values with bone surface area and porosity. Cancellous bones from fresh bovine femur were extracted and cleaned following an established protocol. The samples were scanned using micro-computed tomography (μCT) and three-dimensional models of the cancellous bones were reconstructed for morphology study. Seven idealised and structured cancellous bone models were then developed and fabricated via rapid prototyping technique. A test-rig was developed and permeability tests were performed on the artificial and real cancellous bones. The results showed a linear correlation between the permeability and the porosity as well as the bone surface area. The plate-like idealised structure showed a similar value of permeability to the real cancellous bones.
    Full-text · Article · Dec 2014 · Medical Engineering & Physics
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