title: On the Use of Biaxial Properties in Modeling Annulus as a Holzapfel-Gasser-Ogden Material.
abstract: Besides the biology, stresses and strains within the tissue greatly influence the location of damage initiation and mode of failure in an intervertebral disk. Finite element models of a functional spinal unit (FSU) that incorporate reasonably accurate geometry and appropriate material properties are suitable to investigate such issues. Different material models and techniques have been used to model the anisotropic annulus fibrosus, but the abilities of these models to predict damage initiation in the annulus and to explain clinically observed phenomena are unclear. In this study, a hyperelastic anisotropic material model for the annulus with two different sets of material constants, experimentally determined using uniaxial and biaxial loading conditions, were incorporated in a 3D finite element model of a ligamentous FSU. The purpose of the study was to highlight the biomechanical differences (e.g., intradiscal pressure, motion, forces, stresses, strains, etc.) due to the dissimilarity between the two sets of material properties (uniaxial and biaxial). Based on the analyses, the biaxial constants simulations resulted in better agreements with the in vitro and in vivo data, and thus are more suitable for future damage analysis and failure prediction of the annulus under complex multiaxial loading conditions.
authors.affiliation: Mechanical, Industrial and Manufacturing Engineering Department, University of Toledo , Toledo, OH , USA ; Engineering Center for Orthopaedic Research Excellence, University of Toledo , Toledo, OH , USA.
authors.forename: Narjes
authors.initials: N
authors.lastname: Momeni Shahraki
authors.affiliation: Mechanical, Industrial and Manufacturing Engineering Department, University of Toledo , Toledo, OH , USA.
authors.forename: Ali
authors.initials: A
authors.lastname: Fatemi
authors.affiliation: Engineering Center for Orthopaedic Research Excellence, University of Toledo , Toledo, OH , USA ; Bioengineering Department, University of Toledo , Toledo, OH , USA.
authors.forename: Vijay K
authors.initials: VK
authors.lastname: Goel
authors.affiliation: Engineering Center for Orthopaedic Research Excellence, University of Toledo , Toledo, OH , USA ; Bioengineering Department, University of Toledo , Toledo, OH , USA.
authors.forename: Anand
authors.initials: A
authors.lastname: Agarwal
keywords: annulus material modeling; finite element modeling of intervertebral disk; functional spinal unit; hyperelastic and anisotropic behavior; uniaxial vs. biaxial stress state