Improved Predictions of Human Rib Structural Properties Using Bone Mineral Content

Abstract

<div>Rib fractures are associated with high rates of morbidity and mortality. Improved methods to assess rib bone quality are needed to identify at-risk populations. Quantitative computed tomography (QCT) can be used to calculate volumetric bone mineral density (vBMD) and bone mineral content (BMC), which may be related to rib fracture risk. The objective of this study was to determine if vBMD and BMC from QCT predict human rib structural properties. 127 mid-level (5th–7th) ribs were obtained from adult female (<i>n</i> = 67) and male (<i>n</i> = 60) postmortem human subjects (PMHS). Isolated rib QCT scans were performed to calculate vBMD and BMC. Each rib was subsequently tested to failure in a dynamic simulated frontal impact and structural properties, peak force (<i>F</i><sub>Peak</sub>), percent displacement (<i>δ</i><sub>Peak</sub>), linear structural stiffness (<i>K</i>), and total energy (<i>U</i><sub>Tot</sub>) were calculated. vBMD demonstrated no significant differences between sexes (<i>p</i> > 0.05); however, males had a higher BMC than females (<i>p</i> < 0.001). Further, sex-specific differences were observed in all rib structural properties except for <i>δ</i><sub>Peak</sub> (<i>p</i> > 0.05). Age had a significant relationship with both vBMD and BMC (<i>p</i> < 0.001) but only in females when separated by sex (<i>p</i> < 0.001). vBMD predicted <i>F</i><sub>Peak</sub>, <i>δ</i><sub>Peak</sub>, <i>K</i>, and <i>U</i><sub>Tot</sub> (<i>R</i><sup>2</sup> = 9.2%–30.9%, <i>p</i> < 0.05) but was not able to predict <i>δ</i><sub>Peak</sub> in males. Similarly, BMC also predicted all rib structural properties, except for <i>δ</i><sub>Peak</sub> in males, but explained more meaningful amounts of variation (<i>R</i><sup>2</sup> = 22.2%–67.7%, <i>p</i> < 0.001). When predicting rib structural properties, BMC captures sex-specific variations in bone size that are obfuscated by vBMD and contribute to the biomechanical response of the rib during mechanical loading. Incorporating BMC into assessments of injury risk may therefore provide additional insight into the multifaceted nature of rib bone quality and differential fracture resistance.</div>