Multiscale assessment of cortical bone properties with quantitative ultrasound

Abstract

Clinical bone quality assessment still relies strongly on bone mineral density (BMD). It is now well accepted that BMD predicts only around 60% of the individual fracture risk because it depends on geometrical dimensions of the bone and mechanical properties of its cortical shell. The tibia mid-shaft is a clinically relevant site for ultrasound axial transmission (AT) measurements, which allow simultaneous assessment of cortical thickness (Ct.Th) and tissue elasticity. This ex-vivo study investigated 19 representative human tibiae (native samples, mid-shaft, age range: 69–94 yrs) using AT with the aim to develop novel ultrasound biomarkers of cortical bone loss. Ct.ThAT was in good agreement with corresponding data from micro-computed tomography (R2 = 0.90). Resonant ultrasound spectroscopy was used to measure the transverse isotropic elasticity tensor of extracted bone cubes. Strong linear correlation between axial stiffness (c33) and mass density (R2 = 0.86) was found. Mechanical testing based strength was moderately correlated to c33 (R2 = 0.72) and mass density (R2 = 0.65). These findings indicate the potential of cortical elasticity to be an adequate biomarker of bone quality which combined with information about bone geometry (e.g., Ct.Th) could improve clinical fracture risk assessment.