Sensitivity Study of Ultrasonic Guided Waves to Cortical Bone Mechanical Properties with Axial and Circumferential Propagation

Bone quality assessment using ultrasonic guided waves has the potential to lead to major improvements in the diagnosis of osteporosis. This paper attempts to identify suitable ultrasonic guided modes for assessing the mechanical properties of the human cortical bone. The aim of this paper is to determine the sensitivity of potentiel guided wave modes to the degradation of mechanical properties as a first step to realize a non-invasive, economical and safe method to estimate the risk of fracture and identify osteoporosis. The circumferential and axial propagation of ultrasonic guided waves were compared and three different modes were identified as potential candidates. Experimentations were performed on bone phantoms and finite element models run to identify suitable guided wave modes. These results were compared with either the Semi-Analytical Finite Element (SAFE) method or analytical methods which provided dispersion curves for the bone models. The sensitivity of these modes (S-0, A(0) and F(1,4)) to mechanical properties were then investigated, with an evolution of the mechanical properties of cortical bone considered as a weakly orthotropic material. The S-0 mode is mainly sensitive to E-2 (-4.15%), nu(12) (-4.32%), G(12) (-7.57%) and to the density (-4.24%); the A(0) mode is mainly sensitive to E-1 (-5.01%), E-2 (-3.14%), G(12) (-7.62%) and the density (4.08%), and finally F(1, 4) is mainly sensitive to E-1 (-5.78%) and G(23) (5.38%). The most sensitive mode to density variation is So. The A(0) and F(1, 4) modes appear to be more suitable to the detection of the Young's moduli.