scholarly journals Effect of Specimen-Specific Anisotropic Material Properties in Quantitative Computed Tomography-Based Finite Element Analysis of the Vertebra

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Ginu U. Unnikrishnan ◽  
Glenn D. Barest ◽  
David B. Berry ◽  
Amira I. Hussein ◽  
Elise F. Morgan
Keyword(s):  
Computed Tomography ◽  
Finite Element ◽  
Mechanical Behavior ◽  
Vertebral Body ◽  
Material Properties ◽  
Anisotropic Material ◽  
Quantitative Computed Tomography ◽  
Large Contribution ◽  
Mineral Density ◽  
Peripheral Regions

Intra- and inter-specimen variations in trabecular anisotropy are often ignored in quantitative computed tomography (QCT)-based finite element (FE) models of the vertebra. The material properties are typically estimated solely from local variations in bone mineral density (BMD), and a fixed representation of elastic anisotropy (“generic anisotropy”) is assumed. This study evaluated the effect of incorporating specimen-specific, trabecular anisotropy on QCT-based FE predictions of vertebral stiffness and deformation patterns. Orthotropic material properties estimated from microcomputed tomography data (“specimen-specific anisotropy”), were assigned to a large, columnar region of the L1 centrum (n = 12), and generic-anisotropic material properties were assigned to the remainder of the vertebral body. Results were compared to FE analyses in which generic-anisotropic properties were used throughout. FE analyses were also performed on only the columnar regions. For the columnar regions, the axial stiffnesses obtained from the two categories of material properties were uncorrelated with each other (p = 0.604), and the distributions of minimum principal strain were distinctly different (p ≤ 0.022). In contrast, for the whole vertebral bodies in both axial and flexural loading, the stiffnesses obtained using the two categories of material properties were highly correlated (R2 > 0.82, p < 0.001) with, and were no different (p > 0.359) from, each other. Only moderate variations in strain distributions were observed between the two categories of material properties. The contrasting results for the columns versus vertebrae indicate a large contribution of the peripheral regions of the vertebral body to the mechanical behavior of this bone. In companion analyses on the effect of the degree of anisotropy (DA), the axial stiffnesses of the trabecular column (p < 0.001) and vertebra (p = 0.007) increased with increasing DA. These findings demonstrate the need for accurate modeling of the peripheral regions of the vertebral body in analyses of the mechanical behavior of the vertebra.

scholarly journals A New Material Mapping Procedure for Quantitative Computed Tomography-Based, Continuum Finite Element Analyses of the Vertebra

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
Ginu U. Unnikrishnan ◽  
Elise F. Morgan
Keyword(s):  
Computed Tomography ◽  
Bone Mineral Density ◽  
Finite Element ◽  
Material Properties ◽  
Quantitative Computed Tomography ◽  
Block Size ◽  
Finite Element Models ◽  
Finite Element Analyses ◽  
Mineral Density ◽  
Mapping Procedure

Inaccuracies in the estimation of material properties and errors in the assignment of these properties into finite element models limit the reliability, accuracy, and precision of quantitative computed tomography (QCT)-based finite element analyses of the vertebra. In this work, a new mesh-independent, material mapping procedure was developed to improve the quality of predictions of vertebral mechanical behavior from QCT-based finite element models. In this procedure, an intermediate step, called the material block model, was introduced to determine the distribution of material properties based on bone mineral density, and these properties were then mapped onto the finite element mesh. A sensitivity study was first conducted on a calibration phantom to understand the influence of the size of the material blocks on the computed bone mineral density. It was observed that varying the material block size produced only marginal changes in the predictions of mineral density. Finite element (FE) analyses were then conducted on a square column-shaped region of the vertebra and also on the entire vertebra in order to study the effect of material block size on the FE-derived outcomes. The predicted values of stiffness for the column and the vertebra decreased with decreasing block size. When these results were compared to those of a mesh convergence analysis, it was found that the influence of element size on vertebral stiffness was less than that of the material block size. This mapping procedure allows the material properties in a finite element study to be determined based on the block size required for an accurate representation of the material field, while the size of the finite elements can be selected independently and based on the required numerical accuracy of the finite element solution. The mesh-independent, material mapping procedure developed in this study could be particularly helpful in improving the accuracy of finite element analyses of vertebroplasty and spine metastases, as these analyses typically require mesh refinement at the interfaces between distinct materials. Moreover, the mapping procedure is not specific to the vertebra and could thus be applied to many other anatomic sites.

scholarly journals The bone bridge significantly affects the decrease in bone mineral density measured with quantitative computed tomography in ankylosing spondylitis

PLoS ONE ◽  
2021 ◽  
Vol 16 (4) ◽  
pp. e0249578
Author(s):  
So Yun Lee ◽  
Ran Song ◽  
Hyung In Yang ◽  
Sang Wan Chung ◽  
Yeon-Ah Lee ◽  
...  
Keyword(s):  
Computed Tomography ◽  
New York ◽  
Ankylosing Spondylitis ◽  
Vertebral Body ◽  
Quantitative Computed Tomography ◽  
Mineral Density ◽  
Bone Bridge ◽  
Bridge Formation ◽  
Male Patients ◽  
The Mean

Introduction and objective Ankylosing spondylitis (AS) has characteristics of spinal bone bridge and fusion. Although BMD reduction in AS may be presumed to be due to spinal inflammation, this study was designed to confirm whether immobilization of the spine due to syndesmophytes is related to BMD reduction, as immobilization itself is a risk factor for BMD reduction. Methods Among male patients diagnosed with AS according to the modified New York criteria, those who underwent bone density tests with quantitative computed tomography (QCT) were retrospectively analyzed through a chart review. The correlation between the presence or absence of bone bridges for each vertebral body level of the L spine confirmed with radiography and BMD confirmed with QCT was analyzed. Results A total of 47 male patients with AS were enrolled. The mean patient age was 46.8 ± 8.2 years, and the mean disease duration was 7.9 ± 6.4 years. The trabecular BMD of the lumbar spine (L1-L4) ranged from 23.1 to 158.45 mg/cm3 (mean 102.2 ± 37 mg/cm3), as measured with QCT. The lumbar BMD measurements showed that 30 patients (63.8%) had osteopenia or osteoporosis. Bone bridge formation showed a negative correlation with BMD. Low BMD was significantly correlated with bone bridge in the vertebral body (p < 0.05). Positive correlations were observed between bone bridge score and BASMI flexion score, whereas significant negative correlations were found between BMD and BASMI flexion score (p < 0.05). Conclusion Decreased mobility of the vertebrae due to bone bridge formation affects the decrease in BMD in patients with AS.

scholarly journals Assessment of Regional Bone Density in Fractured Vertebrae Using Quantitative Computed Tomography

2017 ◽  
Vol 11 (1) ◽  
pp. 57-62 ◽  
Author(s):  
Hany A.G. Soliman ◽  
Jean-Marc Mac-Thiong ◽  
Annie Levasseur ◽  
Stefan Parent ◽  
Yvan Petit
Keyword(s):  
Computed Tomography ◽  
Bone Mineral Density ◽  
Bone Mineral ◽  
Vertebral Body ◽  
Quantitative Computed Tomography ◽  
Significant Negative Correlation ◽  
Linear Interpolation ◽  
Fracture Site ◽  
Mineral Density ◽  
The Difference

<sec><title>Study Design</title><p>Cohort study.</p></sec><sec><title>Purpose</title><p>The aim of this study is to propose and evaluate a new technique to assess bone mineral density of fractured vertebrae using quantitative computed tomography (QCT).</p></sec><sec><title>Overview of Literature</title><p>There is no available technique to estimate bone mineral density (BMD) at the fractured vertebra because of the alterations in bony structures at the fracture site.</p></sec><sec><title>Methods</title><p>Forty patients with isolated fracture from T10 to L2 were analyzed from the vertebrae above and below the fracture level. Apparent density (AD) was measured based on the relationship between QCT images attenuation coefficients and the density of calibration objects. AD of 8 independent regions of interest (ROI) within the vertebral body and 2 ROI within the pedicles of vertebrae above and below the fractured vertebra were measured. At the level of the fractured vertebra, AD was measured at the pedicles, which are typically intact. AD of the fractured vertebral body was linearly interpolated, based on the assumption that AD at the fractured vertebra is equivalent to the average AD measured in vertebrae adjacent to the fracture. Estimated and measured AD of the pedicles at the fractured level were compared to verify our assumption of linear interpolation from adjacent vertebrae.</p></sec><sec><title>Results</title><p>The difference between the measured and the interpolated density of the pedicles at the fractured vertebra was 0.006 and 0.003 g/cm<sup>3</sup> for right and left pedicle respectively. The highest mean AD located at the pedicles and the lowest mean AD was found at the anterior ROI of the vertebral body. Significant negative correlation exist between age and AD of ROI in the vertebral body.</p></sec><sec><title>Conclusions</title><p>This study suggests that the proposed technique is adequate to estimate the AD of a fractured vertebra from the density of adjacent vertebrae.</p></sec>

scholarly journals Material properties of human vertebral trabecular bone under compression can be predicted based on quantitative computed tomography

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
Dominic Gehweiler ◽  
Marius Schultz ◽  
Martin Schulze ◽  
Oliver Riesenbeck ◽  
Dirk Wähnert ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Bone Density ◽  
Trabecular Bone ◽  
Vertebral Body ◽  
Cancellous Bone ◽  
Material Properties ◽  
Quantitative Computed Tomography ◽  
Fracture Site ◽  
Regression Analyses ◽  
Physiological Conditions

Abstract Background The prediction of the stability of bones is becoming increasingly important. Especially osteoporotic vertebral body fractures are a growing problem and an increasing burden on the health system. Therefore, the aim of this study was to provide the best possible description of the relationship between the material properties of human vertebral trabecular bone measured under the most physiological conditions possible and the bone mineral density (BMD) determined by clinical quantitative computed tomography (QCT). Methods Forty eight cylindric cancellous bone samples with a diameter of 7.2 mm obtained from 13 human fresh-frozen lumbar vertebrae from 5 donors (3 men, 2 women) have been used for this study. After the specimens were temporarily reinserted into the vertebral body, the QCT was performed. For mechanical testing, the samples were embedded in a load-free manner using polymethylmetacrylate (PMMA). The surrounding test chamber was filled with phosphate buffered saline (PBS) and heated to 37 °C during the test. After 10 preconditioning load cycles, destructive testing was performed under axial compression. After determining the fracture site, BMD has been evaluated in this region only. Regression analyses have been performed. Results Fracture site had an average length of 2.4 (±1.4) mm and a position of 43.9 (±10.9) percent of the measurement length from the cranial end. No fracture reached the embedding. The average BMD at the fracture site was 80.2 (±28.7 | min. 14.5 | max. 137.8) mgCaHA/ml. In summary the results of the regression analyses showed for all three parameters a very good quality of fit by a power regression. Conclusion The results of this study show that QCT-based bone density measurements have a good predictive power for the material properties of the vertebral cancellous bone measured under near to physiological conditions. The mechanical bone properties of vertebral cancellous bone could be modelled with high accuracy in the investigated bone density range.

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