Using Quantitative Ultrasound to Evaluate Postmortem Adult Bone Quality

Abstract

Postmortem investigations into material and structural properties of bone have great potential for use in medicolegal investigations when assessing whether skeletal trauma might be the result of metabolically compromised bone. Current imaging technologies used to evaluate bone quality, including dual-energy X-ray absorptiometry (DXA) and computed tomography (CT), are expensive, large, and produce ionizing radiation (IR). Quantitative ultrasound (QUS) is a portable, less expensive alternative to these technologies that does not produce IR. However, the specific physical properties of bone quantified by QUS remains unresolved and few studies have explored its practical capacity for assessing the skeleton after death. This study sought to explore the utility of QUS for postmortem assessment of the human skeleton by quantifying the effects of: (1) embalming, (2) skeletal site, (3) biological sex, and (4) relative bone mineral density (BMD), on speed of sound (SOS), the chief output of QUS. We also compared SOS to traditional measures of bone quality (DXA and micro-CT), and evaluated SOS for its ability to discriminate individuals based on BMD status. Our sample comprised 9 male and 9 female cadavers aged 57 – 84 years. Our sample sites included the distal radius (DR) and midshaft tibia (MT), sites commonly used in QUS with different weight bearing demands. Results indicated that SOS does not vary significantly between unembalmed tissue and tissue embalmed with an ethylene glycol-based fixative at both the DR (Z = -1.428; p = 0.153) and MT (Z = 0.459; p = 0.646). Males exhibited significantly higher SOS values than females at the MT (U = 66.00; p = 0.002) but not the DR (U = 138.00; p = 0.462). Individuals with normal BMD exhibited significantly higher SOS values than individuals with low BMD at both sites (DR: U = 69.00; p = 0.005; MT: U = 47.00; p < 0.000). While limb side was not shown to have a significant effect on SOS values (DR: U = 151.00; p = 0.743; MT: U = 153.00; p = 0.791), the DR was found to exhibit significantly higher SOS values than the MT in the same individual (U = 50.00; p < 0.000). When using receiver operating characteristic (ROC) analysis, SOS values from both locations were found to correctly discriminate individuals with normal BMD from individuals with low BMD better than random chance (DR: AUC = 0.766; p = 0.032; MT: AUC = 0.844; p < 0.000). Finally, results from the ROC analyses demonstrated that a SOS value of 4022.17 m/s at the MT was the optimal cutoff point within the sample for distinguishing normal BMD from low BMD individuals. The discriminatory capability of SOS at both skeletal sites supports the idea that QUS could be applied in clinical or postmortem settings for the assessment of relative BMD status, representing a potentially useful tool for researchers, clinicians, and forensic scientists. Future studies should attempt to replicate this research with a larger and more diverse sample size in order to confirm these findings and create more robust reference threshold values and classification models that allow for practical application within the population.