Quantifying Variation in Cortical Thickness (Ct.Th) and Volumetric Bone Mineral Density (vBMD) in the Human Radius
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Date
2019-05
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The Ohio State University
Abstract
Computed tomography (CT) is a prevalent clinical instrument providing three-dimensional images to assess bone quality. Quantifying bone quality is important for improving fracture predictive techniques. Cortical thickness (Ct.Th) and volumetric bone mineral density (vBMD) have both been proposed as possible predictors of bone strength across the skeleton; however, data are lacking characterizing the variation within the radius which may impact fracture initiation and propagation patterns. The purpose of this study was twofold: to investigate variation in Ct.Th and vBMD as it related to sex, and to quantify the variation in Ct.Th and vBMD present both along the radial diaphysis and within a cross-section of the radius. Fifty-six ex-vivo radii were obtained from 28 male and 28 female age-matched post-mortem human subjects (PMHS) ranging from 60 to 97 years of age (74.9 ± 10.3). A dual x-ray absorptiometry (DXA) scan was performed prior to excision to obtain 33% radius areal bone mineral density (aBMD) values. Radii were scanned using a Philips Ingenuity 64-slice CT resulting in a 0.167mm in-plane resolution. Images were segmented into 30 and 50% volumes of interest (VOI) using SkyScan (Bruker) software. vBMD and Ct.Th measurements were calculated for the total VOI as well as at four independent anatomical regions of interest (ROIs) within each cross-section: anterior, posterior, medial, and lateral. Two-sample t-tests revealed significant sex differences in Ct.Th at both VOI sites, but only for 30% vBMD (p<0.05), justifying sex-specific statistical analyses. Linear regression analyses revealed no significant declines in Ct.Th or vBMD with age (p>0.05) for males or females in this elderly sample. Paired samples t-tests showed significant differences between total 30% and 50% Ct.Th and vBMD for each sex (p<0.01), with Ct.Th being larger at the 50% VOI and vBMD being larger at the 30% VOI for both males and females. No significant differences were found in vBMD between anatomical ROIs (ANOVA, p>0.05); however, significant differences in Ct.Th between ROIs display sex-specific patterns within each VOI (p<0.05). Significant differences in vBMD between VOIs were only identified at the medial ROI (paired t-test, p<0.01), but significant differences in Ct.Th were found at all ROIs for females, and at all but the lateral ROI for males (p<0.01). Lastly, statistically significant positive linear relationships were found for both Ct.Th and vBMD compared to radial aBMD in females (Pearson correlations, p<0.05), but only between Ct.Th and radial aBMD in males (p<0.05). Overall, significant variation in Ct.Th and smaller amounts of variation in vBMD were found both within the radial cross-section at each ROI and along the radial diaphysis at different VOI sites. Considering the commonality of forearm fractures in elderly individuals, these data can ultimately be utilized to improve the accuracy of injury prediction.