• Lerchl, Tanja
• Ribeiro, Marx
• Nicolini, Luis Fernando
• Gruber, Gabriel
• Jaramillo, Héctor Enrique
• Wilke, Hans-Joachim
• Kirschke, Jan S.
• Senner, Veit
• Nispel, Kati

Abstract

<jats:p><jats:bold>Introduction:</jats:bold> Numerical modeling of the intervertebral disc (IVD) is challenging due to its complex and heterogeneous structure, requiring careful selection of constitutive models and material properties. A critical aspect of such modeling is the representation of annulus fibers, which significantly impact IVD biomechanics. This study presents a comparative analysis of different methods for fiber reinforcement in the annulus fibrosus of a finite element (FE) model of the human IVD.</jats:p><jats:p><jats:bold>Methods:</jats:bold> We utilized a reconstructed L4-L5 IVD geometry to compare three fiber modeling approaches: the anisotropic Holzapfel-Gasser-Ogden (HGO) model (HGO fiber model) and two sets of structural rebar elements with linear-elastic (linear rebar model) and hyperelastic (nonlinear rebar model) material definitions, respectively. Prior to calibration, we conducted a sensitivity analysis to identify the most important model parameters to be calibrated and improve the efficiency of the calibration. Calibration was performed using a genetic algorithm and <jats:italic>in vitro</jats:italic> range of motion (RoM) data from a published study with eight specimens tested under four loading scenarios. For validation, intradiscal pressure (IDP) measurements from the same study were used, along with additional RoM data from a separate publication involving five specimens subjected to four different loading conditions.</jats:p><jats:p><jats:bold>Results:</jats:bold> The sensitivity analysis revealed that most parameters, except for the Poisson ratio of the annulus fibers and C<jats:sub>01</jats:sub> from the nucleus, significantly affected the RoM and IDP outcomes. Upon calibration, the HGO fiber model demonstrated the highest accuracy (R<jats:sup>2</jats:sup> = 0.95), followed by the linear (R<jats:sup>2</jats:sup> = 0.89) and nonlinear rebar models (R<jats:sup>2</jats:sup> = 0.87). During the validation phase, the HGO fiber model maintained its high accuracy (RoM R<jats:sup>2</jats:sup> = 0.85; IDP R<jats:sup>2</jats:sup> = 0.87), while the linear and nonlinear rebar models had lower validation scores (RoM R<jats:sup>2</jats:sup> = 0.71 and 0.69; IDP R<jats:sup>2</jats:sup> = 0.86 and 0.8, respectively).</jats:p><jats:p><jats:bold>Discussion:</jats:bold> The results of the study demonstrate a successful calibration process that established good agreement with experimental data. Based on our findings, the HGO fiber model appears to be a more suitable option for accurate IVD FE modeling considering its higher fidelity in simulation results and computational efficiency.</jats:p>

Topics

• impedance spectroscopy
• phase
• simulation
• anisotropic