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Research Papers

Experimental Validation of Finite Element Analysis of Human Vertebral Collapse Under Large Compressive Strains

[+] Author and Article Information
Hadi S. Hosseini

Institute for Surgical Technology
and Biomechanics,
University of Bern,
Stauffacherstr. 78,
Bern CH-3014, Switzerland
e-mail: hadi.seyed@istb.unibe.ch

Allison L. Clouthier, Philippe K. Zysset

Institute for Surgical Technology
and Biomechanics,
University of Bern,
Stauffacherstr. 78,
Bern CH-3014, Switzerland

Contributed by the Bioengineering Division of ASME for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING. Manuscript received July 9, 2013; final manuscript received December 29, 2013; accepted manuscript posted January 2, 2014; published online March 24, 2014. Assoc. Editor: Pasquale Vena.

J Biomech Eng 136(4), 041006 (Mar 24, 2014) (10 pages) Paper No: BIO-13-1307; doi: 10.1115/1.4026409 History: Received July 09, 2013; Revised December 29, 2013; Accepted January 02, 2014

Osteoporosis-related vertebral fractures represent a major health problem in elderly populations. Such fractures can often only be diagnosed after a substantial deformation history of the vertebral body. Therefore, it remains a challenge for clinicians to distinguish between stable and progressive potentially harmful fractures. Accordingly, novel criteria for selection of the appropriate conservative or surgical treatment are urgently needed. Computer tomography-based finite element analysis is an increasingly accepted method to predict the quasi-static vertebral strength and to follow up this small strain property longitudinally in time. A recent development in constitutive modeling allows us to simulate strain localization and densification in trabecular bone under large compressive strains without mesh dependence. The aim of this work was to validate this recently developed constitutive model of trabecular bone for the prediction of strain localization and densification in the human vertebral body subjected to large compressive deformation. A custom-made stepwise loading device mounted in a high resolution peripheral computer tomography system was used to describe the progressive collapse of 13 human vertebrae under axial compression. Continuum finite element analyses of the 13 compression tests were realized and the zones of high volumetric strain were compared with the experiments. A fair qualitative correspondence of the strain localization zone between the experiment and finite element analysis was achieved in 9 out of 13 tests and significant correlations of the volumetric strains were obtained throughout the range of applied axial compression. Interestingly, the stepwise propagating localization zones in trabecular bone converged to the buckling locations in the cortical shell. While the adopted continuum finite element approach still suffers from several limitations, these encouraging preliminary results towardsthe prediction of extended vertebral collapse may help in assessing fracture stability in future work.

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Figures

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Fig. 1

(a) A vertebral body cleaned from the soft tissues and the posterior elements, and (b) the PMMA end-cap, upon which the shape of the endplate is printed

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Fig. 2

Compression device used to apply the axial load to the vertebral body. The device is mounted on the XtremeCT machine after each loading step.

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Fig. 3

(a) The μCT reconstruction of a vertebral body, and (b) the hFE mesh showing the distribution of the homogenized BV/TV for each element

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Fig. 4

The BV/TV of the transverse slices calculated from the (a) μCT image, and (b) FE mesh in their intact state

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Fig. 5

Three-dimensional representation of a vertebral body collapse up to very large compression. Trabecular bone densification is represented by the volumetric strain ln J. The corresponding applied compressive deformation is distinguished by the red circle on the force-displacement curves.

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Fig. 6

Qualitative analysis of the vertebral body collapse in five specimens. Trabecular bone densification is represented by the volumetric strain ln J. The corresponding applied compressive deformation is distinguished by the red circle on the force-displacement curves.

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Fig. 7

Qualitative analysis of the vertebral body collapse in four specimens. Trabecular bone densification is represented by the volumetric strain ln J. The corresponding applied compressive deformation is distinguished by the red circle on the force-displacement curves.

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Fig. 8

Qualitative analysis of the vertebral body collapse in four specimens where the hFE simulations failed in the correct prediction of the localization pattern. Trabecular bone densification is represented by the volumetric strain ln J. The corresponding applied compressive deformation is distinguished by the red circle on the force-displacement curves.

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Fig. 9

Quantitative analysis of Δ(BV/TV) for 13 vertebrae up to 68% of apparent compressive strain

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