Institute of Lightweight Design and Structural Biomechanics

Vienna, Austria

Institute of Lightweight Design and Structural Biomechanics

Vienna, Austria
SEARCH FILTERS
Time filter
Source Type

Chevalier Y.,Ludwig Maximilians University of Munich | Chevalier Y.,Institute of Lightweight Design and Structural Biomechanics | Zysset P.K.,University of Bern | Zysset P.K.,Institute of Lightweight Design and Structural Biomechanics
Journal of Biomechanical Engineering | Year: 2012

In most finite element (FE) studies of vertebral bodies, axial compression is the loading mode of choice to investigate structural properties, but this might not adequately reflect the various loads to which the spine is subjected during daily activities or the increased fracture risk associated with shearing or bending loads. This work aims at proposing a patient-specific computer tomography (CT)-based methodology, using the currently most advanced, clinically applicable finite element approach to perform a structural investigation of the vertebral body by calculation of its full six dimensional (6D) stiffness matrix. FE models were created from voxel images after smoothing of the peripheral voxels and extrusion of a cortical shell, with material laws describing heterogeneous, anisotropic elasticity for trabecular bone, isotropic elasticity for the cortex based on experimental data. Validated against experimental axial stiffness, these models were loaded in the six canonical modes and their 6D stiffness matrix calculated. Results show that, on average, the major vertebral rigidities correlated well or excellently with the axial rigidity but that weaker correlations were observed for the minor coupling rigidities and for the imagebased density measurements. This suggests that axial rigidity is representative of the overall stiffness of the vertebral body and that finite element analysis brings more insight in vertebral fragility than densitometric approaches. Finally, this extended patientspecific FE methodology provides a more complete quantification of structural properties for clinical studies at the spine. © 2012 by ASME.


PubMed | Ecole Polytechnique Federale de Lausanne, Institute for Surgical Technology and Biomechanics and Institute of Lightweight Design and Structural Biomechanics
Type: Journal Article | Journal: Journal of biomechanics | Year: 2016

Current homogenized finite element (hFE) models of the patella lack a validated material law and mostly overlook trabecular anisotropy. The objective of this study was to identify the elastic constants of patellar trabecular bone. Using CT scans of 20 fresh-frozen cadaveric patellae, we virtually extracted 200 trabecular cubes (5.3mm side length). Bone volume fraction and fabric tensor were measured. The elastic constants were identified from six independent load cases using micro finite element (FE) analyses. Both anisotropic and isotropic material laws were considered. The elastic constants were validated by comparing stiffness, strain and stress between hFE and FE predictions of 18 patellar sections and six load cases. The hFE section models were built from CT (anisotropic law) and CT (isotropic law) scans. The homogenized anisotropic model induced less error (135%) in the global stiffness prediction than the isotropic one (186%), and less error in the prediction of local apparent strain, stress, and strain energy, compared to the isotropic one. This validated hFE model could be used for future applications, either with the anisotropic constants, or with the isotropic ones when the trabecular fabric is unavailable.


Chevalier Y.,Institute of Lightweight Design and Structural Biomechanics | Quek E.,University of California at San Francisco | Borah B.,Procter and Gamble | Gross G.,Procter and Gamble | And 3 more authors.
Bone | Year: 2010

Previous antiresorptive treatment may influence the anabolic response to teriparatide. The OPTAMISE (Open-label Study to Determine How Prior Therapy with Alendronate or Risedronate in Postmenopausal Women with Osteoporosis Influences the Clinical Effectiveness of Teriparatide) study reported greater increases in biochemical markers of bone turnover and volumetric bone mineral density (BMD) when 12 months of teriparatide treatment was preceded by 2 years or more of risedronate versus alendronate treatment. The objective of this study was to use quantitative computed tomography (CT)-based nonlinear finite element modeling to evaluate how prior therapy with alendronate or risedronate in postmenopausal women with osteoporosis influences the biomechanical effectiveness of teriparatide. Finite element models of the L1 vertebra were created from quantitative CT scans, acquired before and after 12 months of therapy with teriparatide, from 171 patients from the OPTAMISE study. These models were subjected to uniaxial compression. Total BMD-derived bone volume fraction (BV/TVd, i.e., bone volume [BV]/total volume [TV]), estimated from quantitative CT-based volumetric BMD, vertebral stiffness, and failure load (strength) were calculated for each time measurement point. The results of this study demonstrated that 12 months of treatment with teriparatide following prior treatment with either risedronate or alendronate increased BMD-derived BV/TVd, the predicted vertebral stiffness, and failure load. However, the effects of teriparatide were more pronounced in patients treated previously with risedronate, which is consistent with the findings of the OPTAMISE study. The mean (± standard error) increase in stiffness was greater in the prior risedronate group than the prior alendronate group (24.6 ± 3.2% versus 14.4 ± 2.8%, respectively; p = 0.0073). Similarly, vertebral failure load increased by 27.2 ± 3.5% in the prior risedronate group versus 15.3 ± 3.1% in the prior alendronate group (p = 0.0042). The mechanical variables increased in greater proportion than BV/TVd, which increased by 6.9 ± 0.9% versus 4.6 ± 0.8% in the prior-risedronate and prior-alendronate groups, respectively (p = 0.0290). Our finding indicated that while teriparatide can be used with success on patients who have previously undergone treatment with risedronate and alendronate, it demonstrated greater anabolic effect on biomechanical properties in prior-risedronate patients in the first year of teriparatide treatment. © 2009 Elsevier Inc. All rights reserved.


Gross T.,Institute of Lightweight Design and Structural Biomechanics | Pahr D.H.,Institute of Lightweight Design and Structural Biomechanics | Peyrin F.,European Synchrotron Radiation Facility | Zysset P.K.,Institute of Lightweight Design and Structural Biomechanics
Computer Methods in Biomechanics and Biomedical Engineering | Year: 2012

At the tissue level, the local material properties of human cancellous bone are heterogeneous due to constant remodelling. Since standard high-resolution computed tomography scanning methods are unable to capture this heterogeneity in detail, local differences in mineralisation are normally not incorporated in computational models. To investigate the effects of heterogeneous mineral distribution on the apparent elastic properties, 40 cancellous bone samples from the human femoral neck were scanned by means of synchrotron radiation microcomputed tomography (SRμCT). SRμCT-based micromechanical finite element models that accounted for mineral heterogeneity were compared with homogeneous models. Evaluation of the apparent stiffness tensor of both model types revealed that homogeneous models led to a minor but significant (p < 0.05) overestimation of the elastic properties of heterogeneous models by 2.18 ± 1.89%. Variation of modelling parameters did not affect the overestimation to a great extent. It was concluded that the heterogeneous mineralisation has only a minor influence on the apparent elastic properties of human cancellous bone. © 2012 Copyright Taylor and Francis Group, LLC.


Pahr D.H.,Institute of Lightweight Design and Structural Biomechanics | Dall'Ara E.,Institute of Lightweight Design and Structural Biomechanics | Varga P.,Institute of Lightweight Design and Structural Biomechanics | Zysset P.K.,Institute of Lightweight Design and Structural Biomechanics
Computer Methods in Biomechanics and Biomedical Engineering | Year: 2012

This study validated two different high-resolution peripheral quantitative computer tomography (HR-pQCT)-based finite element (FE) approaches, enhanced homogenised continuum-level (hFE) and micro-finite element (μFE) models, by comparing them with compression test results of vertebral body sections. Thirty-five vertebral body sections were prepared by removing endplates and posterior elements, scanned with HR-pQCT and tested in compression up to failure. Linear hFE and μFE models were created from segmented and grey-level CT images, and apparent model stiffness values were compared with experimental stiffness as well as strength results. Experimental and numerical apparent elastic properties based on grey-level/segmented CT images (N = 35) correlated well for μFE (r 2=0.748/0.842) and hFE models (r 2=0.741/0.864). Vertebral section stiffness values from the linear μFE/hFE models estimated experimental ultimate apparent strength very well (r 2=0.920/0.927). Calibrated hFE models were able to predict quantitatively apparent stiffness with the same accuracy as μFE models. However, hFE models needed no back-calculation of a tissue modulus or any kind of fitting and were computationally much cheaper. © 2012 Copyright Taylor and Francis Group, LLC.


Previous antiresorptive treatment may influence the anabolic response to teriparatide. The OPTAMISE (Open-label Study to Determine How Prior Therapy with Alendronate or Risedronate in Postmenopausal Women with Osteoporosis Influences the Clinical Effectiveness of Teriparatide) study reported greater increases in biochemical markers of bone turnover and volumetric bone mineral density (BMD) when 12 months of teriparatide treatment was preceded by 2 years or more of risedronate versus alendronate treatment. The objective of this study was to use quantitative computed tomography (CT)-based nonlinear finite element modeling to evaluate how prior therapy with alendronate or risedronate in postmenopausal women with osteoporosis influences the biomechanical effectiveness of teriparatide. Finite element models of the L1 vertebra were created from quantitative CT scans, acquired before and after 12 months of therapy with teriparatide, from 171 patients from the OPTAMISE study. These models were subjected to uniaxial compression. Total BMD-derived bone volume fraction (BV/TV(d), i.e., bone volume [BV]/total volume [TV]), estimated from quantitative CT-based volumetric BMD, vertebral stiffness, and failure load (strength) were calculated for each time measurement point. The results of this study demonstrated that 12 months of treatment with teriparatide following prior treatment with either risedronate or alendronate increased BMD-derived BV/TV(d), the predicted vertebral stiffness, and failure load. However, the effects of teriparatide were more pronounced in patients treated previously with risedronate, which is consistent with the findings of the OPTAMISE study. The mean (+/-standard error) increase in stiffness was greater in the prior risedronate group than the prior alendronate group (24.6+/-3.2% versus 14.4+/-2.8%, respectively; p=0.0073). Similarly, vertebral failure load increased by 27.2+/-3.5% in the prior risedronate group versus 15.3+/-3.1% in the prior alendronate group (p=0.0042). The mechanical variables increased in greater proportion than BV/TV(d), which increased by 6.9+/-0.9% versus 4.6+/-0.8% in the prior-risedronate and prior-alendronate groups, respectively (p=0.0290). Our finding indicated that while teriparatide can be used with success on patients who have previously undergone treatment with risedronate and alendronate, it demonstrated greater anabolic effect on biomechanical properties in prior-risedronate patients in the first year of teriparatide treatment.

Loading Institute of Lightweight Design and Structural Biomechanics collaborators
Loading Institute of Lightweight Design and Structural Biomechanics collaborators