Abstract
Introduction
Quantifying the determinants of bone strength is essential to understanding if or how the structure will fail under load. Determining failure requires knowledge of material and geometric properties. However, characterizing the relative contributions of geometric parameters of bone to overall bone strength has been difficult to date because of limitations in imaging technology. Peripheral quantitative computed tomography (pQCT) uses digital images to derive estimates of bone strength in the peripheral skeleton and is a relatively safe technique to differentiate cortical from trabecular bone and assess bone geometry and density. However, in a compromised osteoporotic bone, thin cortices and low scan resolution can limit accurate analysis.
Methods
Therefore, in this two-part investigation we scanned ten pairs (n=20) of fresh-frozen radial specimens [female, mean (SD) age 79(6) years] using pQCT (XCT 2000) at the 4 and 30% sites of the distal radius. We investigated the accuracy of four different acquisition resolutions (200, 300, 400, 500 μm) and several analysis modes and thresholds. We evaluated (1) the accuracy of the Norland/Stratec XCT 2000 pQCT in assessing low-density bones by comparing pQCT outcomes to ashing and histomorphometry and (2) the association of geometric parameters by pQCT and areal bone mineral density (aBMD) by dual-energy X-ray absorptiometry (DXA) to failure load at the distal radius.
Results
Using histomorphometry and ashing as reference standards, we found that pQCT scans varied systematically and underestimated or overestimated total area and mineral content at the radial midshaft depending on the analysis algorithm and selected threshold. Overall, most pQCT analysis modes were accurate. In the mechanical testing studies, bone mineral content and cortical bone content at the midshaft were strongly associated with failure load. The pQCT parameters that best accounted for failure load were total content at the 4% site and cortical thickness at the 30% site and they accounted for up to 81% of the variance. The best DXA predictor of failure load was total density at the distal third site and it explained 75% of the variance.
Conclusions
In summary, analysis mode, resolution and thresholding affected pQCT outputs at the radial midshaft. This study extends our understanding of pQCT analysis and provides important data regarding determinants of bone strength at the distal radius.
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Acknowledgements
We gratefully acknowledge the support of the Canadian Institutes of Health Research, Michael Smith Foundation for Health Research and the British Columbia Medical Services Foundation. We thank Dr. Neil White, Dr. Kathy Keiver, Dr. Gilles Galzi, Ms. Cecelia Tang, Ms. Jen Davis and Mr. Jesse Chen for their helpful assistance.
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Appendix
Appendix
There are several steps involved in analyzing a pQCT scan. The first step is to define the region of interest (ROI) after scan acquisition. Whatever is contained within the ROI will be included for analysis. Once the ROI is defined, the analysis parameters must be determined. This includes setting the thresholds for separating trabecular from cortical and “subcortical” bone. The XCT 2000 software version 5.50 provides the operator the choice of many combinations of analysis modes. CALCBD refers to the analysis of cancellous or trabecular bone and total bone, and CORTBD to the analysis of cortical bone. Tables 4 and 5 provide an overview of the modes available with the XCT 2000. Within CALCBD there are two parts: Contour Mode and Peel Mode. The software provides three Contour Mode and eight Peel Mode algorithms. Contour Mode (edge detection) separates bone from the surrounding soft tissue. Peel Mode separates trabecular bone from cortical/subcortical bone and CORTBD determines the cortical bone parameters.
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Ashe, M.C., Khan, K.M., Kontulainen, S.A. et al. Accuracy of pQCT for evaluating the aged human radius: an ashing, histomorphometry and failure load investigation. Osteoporos Int 17, 1241–1251 (2006). https://doi.org/10.1007/s00198-006-0110-5
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DOI: https://doi.org/10.1007/s00198-006-0110-5