Multiscale Biomechanics Group

Introduction

Our group’s research is dedicated to simulate aspects of bone in its multiple scales. The temporal scales range from milliseconds (10^-3s) for fracture whole bone fracture to several years (10⁷s) for bone architecture changes, as in the case of osteoporosis. The spatial scale on the other hand ranges from a few micrometers (10^-5m), which isthe size of a single trabecula to several centimeters (10^-2m), for an entire vertebra. Our research covers and combines biomechanics in the range of all these scales. We investigate multiscale biological models with computer simulations and develop experimental methods for their validation.  ↑Top↑

Bone failure projects (milliseconds)

Bone failure projects lay in the milliseconds temporal scale. Customarily, we further differentiate these projects by their spatial scale.

Failure prediction in human bone using high-resolution imaging (whole organ)

Today, a patient's risk for osteoporotic fractures is estimated using DXA. In research, high-resolution quantitative computed tomography, such as HR-pQCT, is used to investigate bone quality. The aim of this project is to establish alternative assessments based on large-scale FE simulations and HR-pQCT. Ideally, this project will allow better understanding of the underlying changes in the osteopenic bone.

In the course of this project, a parallel linear FE solver ParFE is extended to account for large deformations and nonlinear material properties. It remains to be evaluated if and to what extent nonlinear simulations will allow a more accurate prediction of patient specific fracture risk.

Microstructural failure of trabecular networks (organ microstructure)

On a micro-architectural level we are investigating networks of trabecular bone.  Linear elastic FE solvers are the tool we use  to predict apparent stiffness of a trabecular network. Some of the apparent limitations are the the ability to define fracture relevant parameters, such as the ultimate strength or the local failure of a trabecular network. Within this project, we explore different methods to enhance the predictability of failures in trabecular networks.

Inelastic tissue properties of trabeculae (single microstructure)

Nonlinear post-elastic mechanical properties of trabecular bone tissue play a key role in understanding fracture onset. This project aims to overcome the small-sample limitations in mechanical testing by using a novel micro-bending setup adapted to a single trabecula. The combination of fluorescence microscopy and FE simulation permits the measurement of characteristic load-displacement curves and the indirect modeling of material tissue properties in the plastic region. After a first validation study, this approach will allow a better insight into the material fracture mechanism, as well as into the role of collagen and calcium density in fracture.
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Bone remodeling projects (weeks and years)

A larger time scale is used to simulate architectural changes of bone during a lifetime. Bone remodeling projects simulate different biological and biomechanical effects on the microstructure of whole bones. Depending on the species, the size of the investigated whole bone samples varies from a few millimeters to several centimeters.

Simulation of vertebroplasty (years)

In the recent years, bone remodeling algorithms based on theoretical bone adaptation models have been developed to simulate the process in bone and its microstructure. However, restricted computational possibilities have limited such simulations in size, resolution and timescale. Taking advantage of the high computational power of recently developed parallel computer tools we hope to overcome these limitations. With the simulation of bone adaptation of whole human vertebrae at high resolutions we cross a border and model the long term microstructural changes of the whole bone due to osteoporosis.

Furthermore, bone adaptation simulations are expanded to simulate long term effects of clinical interventions. Vertebroplasty is a minimally invasive technique to stabilize fractured vertebra during which the vertebral body is being filled with bone cement. Efforts are made to simulate the bone behavior under the changed mechanical conditions. Finally, the anabolic or catabolic effect of signal agents is modeled in the bone adaptation simulations.

Simulation of mouse model (weeks)

Although a promising method, in silico modeling of the bone adaptation currently lacks experimental validation and is mostly dismissed as a supplement for the investigations of the existing biological theories. Further development of the simulation algorithm, and most importantly its validation against experimental data, can help establish in silico modeling as a self-standing technique, thus reducing the number of animal studies, as well as opening a new window of possible applications in the clinics. With this project we attempt to validate in silico simulations of the effects of aging, disease (osteoporosis) and associated treatments with in vivo experimental studies conducted in mice. We thus hope to establish this technique as a reliable computational model of bone adaptation.

Methods

Our group focuses on the development of  computational and experimental methods. We have established a physics-based in silicoframework for the simulation of bone remodeling, as well as a nonlinear FE code for predicting failure onset. For the model validation  we have constructed a  mechanical setup, which allows the examination of tissue properties and study of bone failure behavior. Finally, standard post-processing of the experimental data has been further improved with an image-based algorithm, which allows determination of the 3D strains based on micro-CT images.

Non-linear FE

The aim of this work is to develop a nonlinear finite element (FE) solver, which is based on the existing parallel FE package ParFE, introduced earlier at ETH Zurich (http://sourceforge.net/projects/parfe). ParFE is using the Trilinos framework (http://trilinos.sandia.gov/) and the CG solver AztecOO in combination with a smoothed aggregation based algebraic multigrid preconditioner. Specifically, changes to the simulation code will involve the implementation of a Newton-Raphson (NR) nonlinear solving scheme using the routines of ParFE for the individual linear solves. This resembles the approach of modern commercial FE solvers used for example in structural mechanics. However, a special-purpose FE solver had to be developed in order to handle the large number of elements (order of billions) and for efficient use of very large number of processors. Previous findings suggest that nonlinear geometrical effects in combination with complex tissue properties play an important role in the mechanical failure of the bone microstructure. Although the best material model for bone still has to be determined, we strongly believe that micro-FE simulations could be significantly improved in their accuracy by incorporating nonlinear effects.

Strain mapping as a quantitative approach to image guided failure assessment

Using mechanical testing in combination with high-resolution 3D imaging allows the observation of potential failure mechanisms of the bone microstructure. Additionally, strain mapping with deformable image registration allows determination of local displacements and strains, thus enabling a quantitative assessment of the relevant failure modes.

The current validation study suggests that the precision of the deformable image registration is roughly four-fold better than the voxel size (7 µm and 30 µm, respectively). A validation of the computed strains is underway.

Physics based in Silico Biology

Bone microstructure is often studied with the help of high-resolution three-dimensional computer tomography scans. The biophysical models are implemented into flexible simulation tools that allow easy adaptation and exchange of the underlying theoretical principles. The simulation tools are based on advection equations and micro FE analysis (ParFE). In order to handle large input data sets and extensive computation steps the simulations are performed at the Swiss National Supercomputing Center,which allows parallel computation.

Experiments to determine material properties

In vitro testing of single trabeculae

We have selected a bending test method to measure the mechanical properties of single trabecula. To facilitate such experiments a prototype micro bending machine was designed. The micromechanical measurements are carried out under direct visual observation using a light microscope.

Image guided failure assessment of trabecular networks

Networks of trabecular bone are investigated with a combination of a micro-compression device and synchrotron radiation computer tomography (Swiss Light Source, SLS). This procedure, known as Image Guided Failure Assessment (IGFA), is planned for the investigation of 3D failure mechanisms in human vertebral bone specimens. Apart from obvious mechanical and biological relevance, we hope that this data will allow validation of our mechanical simulation models.


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Group Members

Müller, Ralph
Lorenzetti, Silvio
Badilatti, Sandro
Carretta, Roberto
Christen, David
Levchuk, Alina
Li, Zihui
Ruffoni, Davide
Rickenbacher Dominik
Schulte Friederike
Zwahlen, Alexander

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Recent Publications

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20 records found

Title	Author(s)	Year
Strain-adaptive in silico modeling of bone adaptation - A computer simulation validated by in vivo micro-computed tomography data	Schulte, F. A.; Zwahlen, A.; Lambers, F. M.; Kuhn, G.; Ruffoni, D.; Betts, D.; Webster, D. J.; Müller, R.	2013
Strain-adaptive in silico modeling of bone adaptation - A computer simulation validated by in vivo micro-computed tomography data Type   Journal Article Author   Schulte, F. A.; Zwahlen, A.; Lambers, F. M.; Kuhn, G.; Ruffoni, D.; Betts, D.; Webster, D. J.; Müller, R. Year   2013 Journal   Bone Abstract   Computational models are an invaluable tool to test different mechanobiological theories and, if validated properly, for predicting changes in individuals over time. Concise validation of in silico models, however, has been a bottleneck in the past due to a lack of appropriate reference data. Here, we present a strain-adaptive in silico algorithm which is validated by means of experimental in vivo loading data as well as by an in vivo ovariectomy experiment in the mouse. The maximum prediction error following four weeks of loading resulted in 2.4% in bone volume fraction (BV/TV) and 8.4% in other bone structural parameters. Bone formation and resorption rate did not differ significantly between experiment and simulation. The spatial distribution of formation and resorption sites matched in 55.4% of the surface voxels. Bone loss was simulated with a maximum prediction error of 12.1% in BV/TV and other bone morphometric indices, including a saturation level after a few weeks. Dynamic rates were more difficult to be accurately predicted, showing evidence for significant differences between simulation and experiment (p<0.05). The spatial agreement still amounted to 47.6%. In conclusion, we propose a computational model which was validated by means of experimental in vivo data. The predictive value of an in silico model may become of major importance if the computational model should be applied in clinical settings to predict bone changes due to disease and test the efficacy of potential pharmacological interventions. Pages   485-92 Volume   52 Issue   1 Author Address   Institute for Biomechanics, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland. Electronic address: fschulte@ethz.ch. Edition   2012/09/19 Date   Jan ISSN   1873-2763 (Electronic) 1873-2763 (Linking) Accession Number   22985889 Electronic Resource Number   10.1016/j.bone.2012.09.008 S8756-3282(12)01232-X [pii] Notes   Schulte, Friederike A Zwahlen, Alexander Lambers, Floor M Kuhn, Gisela Ruffoni, Davide Betts, Duncan Webster, Duncan J Muller, Ralph United States Bone Bone. 2013 Jan;52(1):485-92. doi: 10.1016/j.bone.2012.09.008. Epub 2012 Sep 14. Language   eng URL   Link to Website / File       Export: EndNote XML · BibTex
In vivo validation of predictive models for bone remodeling and mechanobiology	Levchuk, A.; Müller, R.	2013
In vivo validation of predictive models for bone remodeling and mechanobiology Type   Edited Book Editor   Levchuk, A.; Müller, R. Year   2013 Publisher   Springer Science + Business Media Series Editor   Holzapfel, G.A.; Kuhl, E. City   Dordrecht Electronic Resource Number   10.1007/978-94-007-5464-5_27       Export: EndNote XML · BibTex
Strain-adaptive in silico modeling of bone adaptation - A computer simulation validated by in vivo micro-computed tomography data	Schulte, F. A.; Zwahlen, A.; Lambers, F. M.; Kuhn, G.; Ruffoni, D.; Betts, D.; Webster, D. J.; Müller, R.	2012
Strain-adaptive in silico modeling of bone adaptation - A computer simulation validated by in vivo micro-computed tomography data Type   Journal Article Author   Schulte, F. A.; Zwahlen, A.; Lambers, F. M.; Kuhn, G.; Ruffoni, D.; Betts, D.; Webster, D. J.; Müller, R. Year   2012 Journal   Bone Abstract   Computational models are an invaluable tool to test different mechanobiological theories and, if validated properly, for predicting changes in individuals over time. Concise validation of in silico models, however, has been a bottleneck in the past due to a lack of appropriate reference data. Here, we present a strain-adaptive in silico algorithm which is validated by means of experimental in vivo loading data as well as by an in vivo ovariectomy experiment in the mouse. The maximum prediction error following four weeks of loading resulted in 2.4% in bone volume fraction (BV/TV) and 8.4% in other bone structural parameters. Bone formation and resorption rate did not differ significantly between experiment and simulation. The spatial distribution of formation and resorption sites matched in 55.4% of the surface voxels. Bone loss was simulated with a maximum prediction error of 12.1% in BV/TV and other bone morphometric indices, including a saturation level after a few weeks. Dynamic rates were more difficult to be accurately predicted, showing evidence for significant differences between simulation and experiment (p<0.05). The spatial agreement still amounted to 47.6%. In conclusion, we propose a computational model which was validated by means of experimental in vivo data. The predictive value of an in silico model may become of major importance if the computational model should be applied in clinical settings to predict bone changes due to disease and test the efficacy of potential pharmacological interventions. Author Address   Institute for Biomechanics, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland. Electronic address: fschulte@ethz.ch. Edition   2012/09/19 Date   Sep 14 ISSN   1873-2763 (Electronic) 1873-2763 (Linking) Accession Number   22985889 Electronic Resource Number   S8756-3282(12)01232-X [pii] 10.1016/j.bone.2012.09.008 Notes   Schulte, Friederike A Zwahlen, Alexander Lambers, Floor M Kuhn, Gisela Ruffoni, Davide Betts, Duncan Webster, Duncan J Muller, Ralph Journal article Bone Bone. 2012 Sep 14. pii: S8756-3282(12)01232-X. doi: 10.1016/j.bone.2012.09.008. Language   Eng URL   Link to Website / File       Export: EndNote XML · BibTex
Imaging of cellular spread on a three-dimensional scaffold by means of a novel cell-labeling technique for high-resolution computed tomography	Thimm, B. W.; Hofmann, S.; Schneider, P.; Carretta, R.; Müller, R.	2012
Imaging of cellular spread on a three-dimensional scaffold by means of a novel cell-labeling technique for high-resolution computed tomography Type   Journal Article Author   Thimm, B. W.; Hofmann, S.; Schneider, P.; Carretta, R.; Müller, R. Year   2012 Journal   Tissue Eng Part C Methods Abstract   Computed tomography (CT) represents a truly three-dimensional (3D) imaging technique that can provide high-resolution images on the cellular level. Thus, one approach to detect single cells is X-ray absorption-based CT, where cells are labeled with a dense, opaque material providing the required contrast for CT imaging. Within the present work, a novel cell-labeling method has been developed showing the feasibility of labeling fixed cells with iron oxide (FeO) particles for subsequent CT imaging and quantitative morphometry. A biotin-streptavidin detection system was exploited to bind FeO particles to its target endothelial cells. The binding of the particles was predominantly close to the cell centers on 2D surfaces as shown by light microscopy, scanning electron microscopy, and CT. When cells were cultured on porous, 3D polyurethane surfaces, significantly more FeO particles were detected compared with surfaces without cells and FeO particle labeling using CT. Here, we report on the implementation and evaluation of a novel cell detection method based on high-resolution CT. This system has potential in cell tracking for 3D in vitro imaging in the future. Pages   167-75 Volume   18 Issue   3 Author Address   Department for Mechanical and Process Engineering, Institute for Biomechanics , ETH Zurich, Zurich, Switzerland . Edition   2011/09/29 Date   Mar ISSN   1937-3392 (Electronic) 1937-3384 (Linking) Accession Number   21951168 Electronic Resource Number   10.1089/ten.TEC.2011.0262 Notes   Thimm, Benjamin W Hofmann, Sandra Schneider, Philipp Carretta, Roberto Muller, Ralph United States Tissue engineering. Part C, Methods Tissue Eng Part C Methods. 2012 Mar;18(3):167-75. Epub 2011 Nov 21. Language   eng URL   Link to Website / File       Export: EndNote XML · BibTex
Increased marrow adiposity in premenopausal women with idiopathic osteoporosis	Cohen, A.; Dempster, D. W.; Stein, E. M.; Nickolas, T. L.; Zhou, H.; McMahon, D. J.; Müller, R.; Kohler, T.; Zwahlen, A.; Lappe, J. M.; Young, P.; Recker, R. R.; Shane, E.	2012
Increased marrow adiposity in premenopausal women with idiopathic osteoporosis Type   Journal Article Author   Cohen, A.; Dempster, D. W.; Stein, E. M.; Nickolas, T. L.; Zhou, H.; McMahon, D. J.; Müller, R.; Kohler, T.; Zwahlen, A.; Lappe, J. M.; Young, P.; Recker, R. R.; Shane, E. Year   2012 Journal   J Clin Endocrinol Metab Abstract   Context: We have previously reported that premenopausal women with idiopathic osteoporosis based on fractures (IOP) or idiopathic low bone mineral density (ILBMD) exhibit markedly reduced bone mass, profoundly abnormal trabecular microstructure, and significant deficits in trabecular bone stiffness. Bone remodeling was heterogeneous. Those with low bone turnover had evidence of osteoblast dysfunction and the most marked deficits in microstructure and stiffness. Objective: Because osteoblasts and marrow adipocytes derive from a common mesenchymal precursor and excess marrow fat has been implicated in the pathogenesis of bone fragility in anorexia nervosa, glucocorticoid excess, and thiazolidinedione exposure, we hypothesized that marrow adiposity would be higher in affected women and inversely related to bone mass, microarchitecture, bone formation rate, and osteoblast number. Design: We analyzed tetracycline-labeled transiliac biopsy specimens in 64 premenopausal women with IOP or ILBMD and 40 controls by three-dimensional micro-computed tomography and two-dimensional quantitative histomorphometry to assess marrow adipocyte number, perimeter, and area. Results: IOP and ILBMD subjects did not differ with regard to any adipocyte parameter, and thus results were combined. Subjects had substantially higher adipocyte number (by 22%), size (by 24%), and volume (by 26%) than controls (P<0.0001 for all). Results remained significant after adjusting for age, body mass index, and bone volume. Controls demonstrated expected direct associations between marrow adiposity and age and inverse relationships between marrow adiposity and bone formation, volume, and microstructure measures. No such relationships were observed in the subjects. Conclusions: Higher marrow adiposity and the absence of expected relationships between marrow adiposity and bone microstructure and remodeling in women with IOP or ILBMD suggest that the relationships between fat and bone are abnormal; excess marrow fat may not arise from a switch from the osteoblast to the adipocyte lineage in this disorder. Whether excess marrow fat contributes to the pathogenesis of this disorder remains unclear. Pages   2782-91 Volume   97 Issue   8 Author Address   M.H.S., Columbia University, College of Physicians and Surgeons, Department of Medicine, PH8-864, 630 West 168th Street, New York, New York 10032. ac1044@columbia.edu. Edition   2012/06/16 Date   Aug ISSN   1945-7197 (Electronic) 0021-972X (Linking) Accession Number   22701013 Electronic Resource Number   jc.2012-1477 [pii] 10.1210/jc.2012-1477 Notes   Cohen, Adi Dempster, David W Stein, Emily M Nickolas, Thomas L Zhou, Hua McMahon, Donald J Muller, Ralph Kohler, Thomas Zwahlen, Alexander Lappe, Joan M Young, Polly Recker, Robert R Shane, Elizabeth United States The Journal of clinical endocrinology and metabolism J Clin Endocrinol Metab. 2012 Aug;97(8):2782-91. Epub 2012 Jun 14. Language   eng Custom 2   3410269 URL   Link to Website / File       Export: EndNote XML · BibTex
Deformable image registration and 3D strain mapping for the quantitative assessment of cortical bone microdamage	Christen, D.; Levchuk, A.; Schori, S.; Schneider, P.; Boyd, S. K.; Müller, R.	2012
Deformable image registration and 3D strain mapping for the quantitative assessment of cortical bone microdamage Type   Journal Article Author   Christen, D.; Levchuk, A.; Schori, S.; Schneider, P.; Boyd, S. K.; Müller, R. Year   2012 Keywords   Animals; Biomechanics; Female; Femur/*pathology/radiography; Imaging, Three-Dimensional/*methods; Mice; Reproducibility of Results; *Stress, Mechanical; Time Factors; Tomography, X-Ray Computed Journal   J Mech Behav Biomed Mater Abstract   The resistance to forming microcracks is a key factor for bone to withstand critical loads without fracturing. In this study, we investigated the initiation and propagation of microcracks in murine cortical bone by combining three-dimensional images from synchrotron radiation-based computed tomography and time-lapsed biomechanical testing to observe microdamage accumulation over time. Furthermore, a novel deformable image registration procedure utilizing digital volume correlation and demons image registration was introduced to compute 3D strain maps allowing characterization of the mechanical environment of the microcracks. The displacement and strain maps were validated in a priori tests. At an image resolution of 740 nm the spatial resolution of the strain maps was 10 mum (MTF), while the errors of the displacements and strains were 130 nm and 0.013, respectively. The strain maps revealed a complex interaction of the propagating microcracks with the bone microstructure. In particular, we could show that osteocyte lacunae play a dual role as stress concentrating features reducing bone strength, while at the same time contributing to the bone toughness by blunting the crack tip. We conclude that time-lapsed biomechanical imaging in combination with three-dimensional strain mapping is suitable for the investigation of crack initiation and propagation in many porous materials under various loading scenarios. Pages   184-93 Volume   8 Author Address   Institute for Biomechanics, ETH Zurich, Zurich, Switzerland. dchristen@ethz.ch Edition   2012/03/10 Date   Apr ISSN   1878-0180 (Electronic) 1878-0180 (Linking) Accession Number   22402165 Electronic Resource Number   S1751-6161(11)00310-9 [pii] 10.1016/j.jmbbm.2011.12.009 Notes   Christen, David Levchuk, Alina Schori, Stefan Schneider, Philipp Boyd, Steven K Muller, Ralph Research Support, Non-U.S. Gov't Netherlands Journal of the mechanical behavior of biomedical materials J Mech Behav Biomed Mater. 2012 Apr;8:184-93. Epub 2012 Jan 8. Language   eng URL   Link to Website / File       Export: EndNote XML · BibTex
Towards patient‐specific material modeling of trabecular bone post‐yield behavior	Carretta, R.; Lorenzetti, S.; Müller, R.	2012
Towards patient‐specific material modeling of trabecular bone post‐yield behavior Type   Journal Article Author   Carretta, R.; Lorenzetti, S.; Müller, R. Year   2012 Journal   International Journal for Numerical Methods in Biomedical Engineering ISSN   2040-7947       Export: EndNote XML · BibTex
Abnormal bone microarchitecture and evidence of osteoblast dysfunction in premenopausal women with idiopathic osteoporosis	Cohen, A.; Dempster, D. W.; Recker, R. R.; Stein, E. M.; Lappe, J. M.; Zhou, H.; Wirth, A. J.; van Lenthe, G. H.; Kohler, T.; Zwahlen, A.; Müller, R.; Rosen, C. J.; Cremers, S.; Nickolas, T. L.; McMahon, D. J.; Rogers, H.; Staron, R. B.; Lemaster, J.; Shane, E.	2011
Abnormal bone microarchitecture and evidence of osteoblast dysfunction in premenopausal women with idiopathic osteoporosis Type   Journal Article Author   Cohen, A.; Dempster, D. W.; Recker, R. R.; Stein, E. M.; Lappe, J. M.; Zhou, H.; Wirth, A. J.; van Lenthe, G. H.; Kohler, T.; Zwahlen, A.; Müller, R.; Rosen, C. J.; Cremers, S.; Nickolas, T. L.; McMahon, D. J.; Rogers, H.; Staron, R. B.; Lemaster, J.; Shane, E. Year   2011 Journal   J Clin Endocrinol Metab Abstract   Context: Idiopathic osteoporosis (IOP) in premenopausal women is an uncommon disorder of uncertain pathogenesis in which fragility fractures occur in otherwise healthy women with intact gonadal function. It is unclear whether women with idiopathic low bone mineral density and no history of fragility fractures have osteoporosis. Objective: The objective of the study was to elucidate the microarchitectural and remodeling features of premenopausal women with IOP. Design: We performed transiliac biopsies after tetracycline labeling in 104 women: 45 with fragility fractures (IOP), 19 with idiopathic low bone mineral density (Z score</=-2.0) and 40 controls. Biopsies were analyzed by two-dimensional quantitative histomorphometry and three-dimensional microcomputed tomography. Bone stiffness was estimated using finite element analysis. Results: Compared with controls, affected women had thinner cortices; fewer, thinner, more widely separated, and heterogeneously distributed trabeculae; reduced stiffness; and lower osteoid width and mean wall width. All parameters were indistinguishable between women with IOP and idiopathic low bone mineral density. Although there were no group differences in dynamic histomorphometric remodeling parameters, serum calciotropic hormones, bone turnover markers, or IGF-I, subjects in the lowest tertile of bone formation rate had significantly lower osteoid and wall width, more severely disrupted microarchitecture, lower stiffness, and higher serum IGF-I than those in the upper two tertiles, suggesting that women with low turnover IOP have osteoblast dysfunction with resistance to IGF-I. Subjects with high bone turnover had significantly higher serum 1,25 dihydroxyvitamin D levels and a nonsignificant trend toward higher serum PTH and urinary calcium excretion. Conclusions: These results suggest that the diagnosis of IOP should not require a history of fracture. Women with IOP may have high, normal or low bone turnover; those with low bone turnover have the most marked deficits in microarchitecture and stiffness. These results also suggest that the pathogenesis of idiopathic osteoporosis is heterogeneous and may differ according to remodeling activity. Pages   3095-105 Volume   96 Issue   10 Author Address   M.H.S., Columbia University, College of Physicians and Surgeons, Department of Medicine, PH8-864, 630 West 168th Street, New York, New York 10032. ac1044@columbia.edu. Edition   2011/08/13 Date   Oct ISSN   1945-7197 (Electronic) 0021-972X (Linking) Accession Number   21832117 Electronic Resource Number   jc.2011-1387 [pii] 10.1210/jc.2011-1387 Notes   Cohen, Adi Dempster, David W Recker, Robert R Stein, Emily M Lappe, Joan M Zhou, Hua Wirth, Andreas J van Lenthe, G Harry Kohler, Thomas Zwahlen, Alexander Muller, Ralph Rosen, Clifford J Cremers, Serge Nickolas, Thomas L McMahon, Donald J Rogers, Halley Staron, Ronald B Lemaster, Jeanette Shane, Elizabeth United States The Journal of clinical endocrinology and metabolism J Clin Endocrinol Metab. 2011 Oct;96(10):3095-105. Epub 2011 Aug 10. Language   eng Custom 2   3200255 URL   Link to Website / File       Export: EndNote XML · BibTex
Computational finite element bone mechanics accurately predicts mechanical competence in the human radius of an elderly population	Mueller, T. L.; Christen, D.; Sandercott, S.; Boyd, S. K.; van Rietbergen, B.; Eckstein, F.; Lochmuller, E. M.; Müller, R.; van Lenthe, G. H.	2011
Computational finite element bone mechanics accurately predicts mechanical competence in the human radius of an elderly population Type   Journal Article Author   Mueller, T. L.; Christen, D.; Sandercott, S.; Boyd, S. K.; van Rietbergen, B.; Eckstein, F.; Lochmuller, E. M.; Müller, R.; van Lenthe, G. H. Year   2011 Journal   Bone Abstract   High-resolution peripheral quantitative computed tomography (HR-pQCT) is clinically available today and provides a non-invasive measure of 3D bone geometry and micro-architecture with unprecedented detail. In combination with microarchitectural finite element (muFE) models it can be used to determine bone strength using a strain-based failure criterion. Yet, images from only a relatively small part of the radius are acquired and it is not known whether the region recommended for clinical measurements does predict forearm fracture load best. Furthermore, it is questionable whether the currently used failure criterion is optimal because of improvements in image resolution, changes in the clinically measured volume of interest, and because the failure criterion depends on the amount of bone present. Hence, we hypothesized that bone strength estimates would improve by measuring a region closer to the subchondral plate, and by defining a failure criterion that would be independent of the measured volume of interest. To answer our hypotheses, 20% of the distal forearm length from 100 cadaveric but intact human forearms was measured using HR-pQCT. muFE bone strength was analyzed for different subvolumes, as well as for the entire 20% of the distal radius length. Specifically, failure criteria were developed that provided accurate estimates of bone strength as assessed experimentally. It was shown that distal volumes were better in predicting bone strength than more proximal ones. Clinically speaking, this would argue to move the volume of interest for the HR-pQCT measurements even more distally than currently recommended by the manufacturer. Furthermore, new parameter settings using the strain-based failure criterion are presented providing better accuracy for bone strength estimates. Pages   1232-8 Volume   48 Issue   6 Author Address   Institute for Biomechanics, ETH Zurich, Zurich, Switzerland. Edition   2011/03/08 Date   Jun 1 ISSN   1873-2763 (Electronic) 1873-2763 (Linking) Accession Number   21376150 Electronic Resource Number   S8756-3282(11)00074-3 [pii] 10.1016/j.bone.2011.02.022 Notes   Mueller, Thomas L Christen, David Sandercott, Steve Boyd, Steven K van Rietbergen, Bert Eckstein, Felix Lochmuller, Eva-Maria Muller, Ralph van Lenthe, G Harry United States Bone Bone. 2011 Jun 1;48(6):1232-8. Epub 2011 Mar 2. Language   eng URL   Link to Website / File       Export: EndNote XML · BibTex
Towards validation of computational analyses of peri-implant displacements by means of experimentally obtained displacement maps	Basler, S. E.; Mueller, T. L.; Christen, D.; Wirth, A. J.; Müller, R.; van Lenthe, G. H.	2011
Towards validation of computational analyses of peri-implant displacements by means of experimentally obtained displacement maps Type   Journal Article Author   Basler, S. E.; Mueller, T. L.; Christen, D.; Wirth, A. J.; Müller, R.; van Lenthe, G. H. Year   2011 Journal   Comput Methods Biomech Biomed Engin Abstract   Micro-finite element (muFE) analysis has recently been introduced for the detailed quantification of the mechanical interaction between bone and implant. The technique has been validated at an apparent level. The aim of this study was to address the accuracy of muFE analysis at the trabecular level. Experimental displacement fields were obtained by deformable image registration, also known as strain mapping (SM), of dynamic hip screws implanted in three human femoral heads. In addition, displacement fields were calculated using muFE analysis. On a voxel-by-voxel basis, the coefficients of determination (R(2)) between experimental and muFE-calculated displacements ranged from 0.67 to 0.92. Linear regression of the mean displacements over nine volumes of interest yielded R(2) between 0.81 and 0.84. The lowest R(2) values were found in regions of very small displacements. In conclusion, we found that peri-implant bone displacements calculated with muFE analysis correlated well with displacements obtained from experimental SM. Pages   165-74 Volume   14 Issue   2 Author Address   Institute for Biomechanics, ETH Zurich, Zurich, Switzerland. Edition   2010/12/21 Date   Feb ISSN   1476-8259 (Electronic) 1025-5842 (Linking) Accession Number   21170767 Electronic Resource Number   931324019 [pii] 10.1080/10255842.2010.537263 Notes   Basler, S E Mueller, T L Christen, D Wirth, A J Muller, R van Lenthe, G H England Computer methods in biomechanics and biomedical engineering Comput Methods Biomech Biomed Engin. 2011 Feb;14(2):165-74. Language   eng URL   Link to Website / File       Export: EndNote XML · BibTex

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