Anisotropic tissue elasticity in human lumbar vertebra, by means of a coupled ultrasound-micromechanics approach

Abstract

The extremely fi ne structure of vertebral cortex challenges reliable determination of the tissue's anisotropic elasticity, which is important for the spine's load carrying patterns often causing pain in patients. As a potential remedy, we here propose a combined experimental (ultrasonic) and modeling (micromechanics) approach. Longitudinalacousticwavesaresentinlongitudinal(superior -inferior,axial)aswellastransverse(circumferential) direction through millimeter-sized samples containing thi s vertebral cortex, and corr esponding wave velocities agree very well with recently identi fi ed ‘ universal ’ compositional and acoustic characteristics (J Theor Biol 287:115,2011),whicharevalidforalargedatabasecomprisingdifferent bonesfromdifferent speciesanddifferent organs. This provides evidence that the ‘ universal ’ organization patterns inherent to all the bone tissues of the aforementioned data base also hold for vertebral bone. Con sequently, an experimentally validated model covering the mechanical effects of this organization patterns (J Theor Biol 244:597, 2007, J Theor Biol 260:230, 2009) gives access to the complete elasticity tensor of human lumbar ve rtebral bone tissue, as a valuable input for structural analyses aiming at patient-speci fi cfractureriskassessm ent, e.g. based on the Finite Element Method.