The micro-mechanics of cortical shell removal in the human vertebral body

Eswaran, Senthil Kumar; Bayraktar, Harun H.; Adams, Mark F.; Gupta, Atul; Hoffmann, Paul; Lee, Dong Hoon; Papadopoulos, Panayiotis; Keaveny, Tony M.

doi:10.1016/j.cma.2006.06.017

Cited by 44 publications

(54 citation statements)

References 28 publications

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“…A voxel size of 60 μm was chosen based on a detailed convergence study (Appendix A) which showed that the error associated with the 60-μm model was minimal for the outcome variable of interest in this study. An averaging technique [11,12] was used within an image processing software (IDL, Research Systems Inc., Boulder, CO) to identify the cortical shell and cortical endplates. Since it was difficult to clearly identify the transition from the endplate to the cortical shell, the bone tissue at the corner regions were also tagged with a unique identifier (Figure 1).…”

Section: Methodsmentioning

confidence: 99%

“…While experiments [9] have shown that disc degeneration alters the loading conditions on the cortical endplates of the vertebral body, results from computational studies [10] suggest that the average effect of the altered loading conditions on vertebral strength may not be appreciable. High-resolution micro-CT based finite element modeling of whole vertebrae (40-60 micron voxel size) has enabled accurate characterization of the thin, porous shell and trabecular microarchitecture, and has helped resolve long-standing issues such as the substantial load-bearing role of the cortical shell [11,12]. Homminga et al [6] compared a single normal vertebra to an osteoporotic vertebra and found that the osteoporotic vertebra was less resistant to "error" loads developed due to forward flexion or lifting.…”

Section: Introductionmentioning

confidence: 99%

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Locations of bone tissue at high risk of initial failure during compressive loading of the human vertebral body

Eswaran

Gupta

Keaveny

2007

Bone

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Knowledge of the location of initial regions of failure within the vertebra -cortical shell, cortical endplates vs. trabecular bone, as well as anatomic location -may lead to improved understanding of the mechanisms of aging, disease and treatment. The overall objective of this study was to identify the location of the bone tissue at highest risk of initial failure within the vertebral body when subjected to compressive loading. Toward this end, micro-CT based 60-micron voxel-sized, linearly elastic, finite element models of a cohort of thirteen elderly (age range: 54-87 years, 75 ± 9 years) female whole vertebrae without posterior elements were virtually loaded in compression through a simulated disc. All bone tissue within each vertebra having either the maximum or minimum principal strain beyond its 90 th percentile was defined as the tissue at highest risk of initial failure within that particular vertebral body. Our results showed that such high-risk tissue first occurred in the trabecular bone and that the largest proportion of the high-risk tissue also occurred in the trabecular bone. The amount of high-risk tissue was significantly greater in and adjacent to the cortical endplates than in the mid-transverse region. The amount of high-risk tissue in the cortical endplates was comparable to or greater than that in the cortical shell regardless of the assumed Poisson's ratio of the simulated disc. Our results provide new insight into the micromechanics of failure of trabecular and cortical bone within the human vertebra, and taken together, suggest that during strenuous compressive loading of the vertebra, the tissue near and including the endplates is at the highest risk of initial failure.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Locations of bone tissue at high risk of initial failure during compressive loading of the human vertebral body

Eswaran

Gupta

Keaveny

2007

Bone

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“…Nonetheless, numerous attempts have been made to distinguish their relative contributions to vertebral strength. Such attempts have included physical separation of the cortical shell [4][5][6], and use of computational modeling to predict the contribution of the cortex to strength of the vertebral body [6][7][8][9]. In addition, there is a small, but growing, body of evidence describing the structure of the cortex per se, or in relation to osteoporotic fracture.…”

Section: The Cortical Shell In Vertebral Fragilitymentioning

confidence: 99%

“…The thickness of the cortex ranges from about 280 to 800 μm, the variation of which depends on the vertebral level [10][11][12][13], the anatomical location within the vertebra [10][11][12], and the method of determination, including histomorphometry [10][11][12][13], CT [6,14,15], and micro-CT [8,9]. By histomorphometry, the thickness of the anterior cortex of lumbar vertebrae is about 450 μm.…”

Section: The Cortical Shell In Vertebral Fragilitymentioning

confidence: 99%

“…These methods give rise to estimates that range between 10 and 60% for the contribution of the cortex to vertebral body strength. The lowest of these estimates arises from the manual removal of the cortex prior to mechanical testing of the remaining centrum [4], while the higher estimates are produced from the virtual removal of the cortex using finite element analysis (FEA) [7][8][9]. Among the FEA methods, the shellforce fraction has also been estimated to be as low as 10%, where the McBroom data were modeled using standard FEA meshes [6].…”

Section: The Cortical Shell In Vertebral Fragilitymentioning

confidence: 99%

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Translational aspects of bone quality—vertebral fractures, cortical shell, microdamage and glycation: a tribute to Pierre D. Delmas

Forwood

Vashishth

2009

Osteoporos Int

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Among vertebral deformities, the prevalence of wedge fractures is about twice that of endplate (biconcave) deformities, both of which are greater than that of crush deformities. The anterior cortex is, therefore, a site of interest for understanding mechanisms of vertebral fracture. Despite its importance to vertebral mechanics, there are limited data describing the role of cortical shell, microdamage, and bone matrix parameters in vertebral fragility. This review of literature emphasizes the translational aspects of bone quality and demonstrates that a greater understanding of bone fractures will be gained through bone quality parameters related to both cortical and cancellous compartments as well as from microdamage and bone matrix parameters. In the context of vertebral fractures, measures of cortical shell and bone matrix parameters related to the organic matrix (advanced glycation products and alpha/beta CTX ratio) are independent of BMD measurements and can therefore provide an additional estimate of fracture risk in older patients.

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Microstructural Failure Mechanisms in the Human Proximal Femur for Sideways Fall Loading

Nawathe

Akhlaghpour

Bouxsein

et al. 2013

Journal of Bone and Mineral Research

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The etiology of hip fractures remains unclear but might be elucidated by an improved understanding of the microstructural failure mechanisms of the human proximal femur during a sideways fall impact. In this context, we biomechanically tested 12 cadaver proximal femurs (aged 76 AE 10 years; 8 female, 4 male) to directly measure strength for a sideways fall and also performed microcomputed tomography (CT)-based, nonlinear finite element analysis of the same bones (82-micron-sized elements, $120 million elements per model) to estimate the amount and location of internal tissue-level failure (by ductile yielding) at initial structural failure of the femur. We found that the correlation between the directly measured yield strength of the femur and the finite element prediction was high (R 2 ¼ 0.94, p < 0.0001), supporting the validity of the finite element simulations of failure. In these simulations, the failure of just a tiny proportion of the bone tissue (1.5% to 6.4% across all bones) led to initial structural failure of the femur. The proportion of failed tissue, estimated by the finite element models, decreased with decreasing measured femoral strength (R 2 ¼ 0.88, p < 0.0001) and was more highly correlated with measured strength than any measure of bone volume, mass, or density. Volumewise, trabecular failure occurred earlier and was more prominent than cortical failure in all femurs and dominated in the very weakest femurs. Femurs with low measured strength relative to their areal bone mineral density (BMD) (by dual-energy X-ray absorptiometry [DXA]) had a low proportion of trabecular bone compared with cortical bone in the femoral neck (p < 0.001), less failed tissue (p < 0.05), and low structural redundancy (p < 0.005). We conclude that initial failure of the femur during a sideways fall is associated with failure of just a tiny proportion of the bone tissue, failure of the trabecular tissue dominating in the very weakest femurs owing in part to a lack of structural redundancy.

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The micro-mechanics of cortical shell removal in the human vertebral body

Cited by 44 publications

References 28 publications

Locations of bone tissue at high risk of initial failure during compressive loading of the human vertebral body

Locations of bone tissue at high risk of initial failure during compressive loading of the human vertebral body

Translational aspects of bone quality—vertebral fractures, cortical shell, microdamage and glycation: a tribute to Pierre D. Delmas

Microstructural Failure Mechanisms in the Human Proximal Femur for Sideways Fall Loading

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