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Technical Briefs

Spatial Correlations of Trabecular Bone Microdamage with Local Stresses and Strains Using Rigid Image Registration

[+] Author and Article Information
Srinidhi Nagaraja, Oskar Skrinjar

 Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332,  Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, GA 30332 Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA 30332

Robert E. Guldberg1

 Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332;  Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, GA 30332;  Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA 30332 e-mail: robert.guldberg@me.gatech.edu

1

Corresponding author.

J Biomech Eng 133(6), 064502 (Jun 14, 2011) (5 pages) doi:10.1115/1.4004164 History: Received December 26, 2008; Revised July 01, 2009; Posted May 05, 2011; Published June 14, 2011; Online June 14, 2011

Although microdamage is known to accumulate in trabecular bone with overloading and aging, the tissue-level stresses and strains associated with local bone failure are not well known. Local correlation of microdamage with microstructural stresses and strains requires methods to accurately register histological sections with micro-computed tomography (micro-CT) based finite element models. In addition, the resolution of correlation (i.e., grid size) selected for analysis may affect the observed results. Therefore, an automated, repeatable, and accurate image registration algorithm was developed to determine the range of local stresses and strains associated with microdamage initiation. Using a two-dimensional rigid registration algorithm, bone structures from histology and micro-CT imaging were aligned. Once aligned, microdamaged regions were spatially correlated with local stresses and strains obtained from micro-CT based finite element analysis. Using this more sophisticated registration technique, we were able to analyze the effects of varying spatial grid resolution on local stresses and strains initiating microdamage. The results indicated that grid refinement to the individual pixel level (pixel-by-pixel method) more precisely defined the range of microdamage initiation compared to manually selected individual damaged and undamaged trabeculae. Using the pixel-by-pixel method, we confirmed that trabecular bone from younger cows sustained higher local strains prior to microdamage initiation compared to older bone.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Flow chart for automated two-dimensional spatial correlations of microdamage (histology) to local stress/strain (micro-CT/finite element analysis)

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Figure 2

Representation section displaying centerlines (“skeletons”) of trabecular bone structure in both micro-CT (left) and histology (middle) sections. Aligned centerlines are displayed in white (right).

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Figure 3

Example of grid arrangements for correlations between microdamage and local stresses. Images were divided into various grid sizes ranging from 0.42 mm2 to 0.03 mm2 for each grid. A 6 × 6 arrangement is displayed on the left and a 24 × 24 arrangement on the right.

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Figure 4

Example of two-dimensional automated image registration (top). Histology section is iteratively rotated and translated to optimally align with the micro-CT section. Once registered, the pixel-by-pixel method was used to analyze the stresses/strains in microdamaged and undamaged pixels (bottom).

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Figure 5

Using automated image registration, only overlapping regions were used to calculate the range of microdamage initiation. Registered trabecular bone structures in both micro-CT (left) and histology (middle) sections. Overlapped images (right) showing registered regions are in white. Only regions in white were utilized for analysis.

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Figure 6

Average local compressive principal stresses and strains for damaged and undamaged grids ranging from 0.42 mm2 (6 × 6 grid) to 0.0004 mm2 (PP) within young (2 year old) bovine trabecular bone. Individual trabeculae analysis obtained in a previous study is displayed for comparison purposes. Pairwise comparisons: An asterisk indicates significant difference (p < 0.01).

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Figure 7

Average local compressive principal stresses and strains for damaged and undamaged grids ranging from 0.42 mm2 (6 × 6 grid) to 0.0004 mm2 (PP) within older (10 year old) bovine trabecular bone. Individual trabeculae analysis obtained in a previous study is displayed for comparison purposes. Pairwise comparisons: An asterisk indicates significant difference (p < 0.01).

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Figure 8

Comparison of microdamage initiation ranges between IT and PP approaches for both young (2 year old) and older (10 year old) bovine trabecular bone. Compared to the IT method, the PP analysis more precisely defined the range of microdamage initiation.

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