Comparative FEM study on intervertebral disc modeling: Holzapfel-Gasser-Ogden vs. structural rebars

• Published in: Frontiers in bioengineering and biotechnology 2024-06, Vol.12, p.1391957
• Main Authors: Gruber, Gabriel, Nicolini, Luis Fernando, Ribeiro, Marx, Lerchl, Tanja, Wilke, Hans-Joachim, Jaramillo, Héctor Enrique, Senner, Veit, Kirschke, Jan S, Nispel, Kati
• Format: Article
• Language: English
• Subjects: Bioengineering and Biotechnology; calibration; fiber reinforcement; finite element method; intervertebral disc; sensitivity analysis; spine
• ISSN: 2296-4185; 2296-4185
• DOI: 10.3389/fbioe.2024.1391957

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. 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 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. The sensitivity analysis revealed that most parameters, except for the Poisson ratio of the annulus fibers and C from the nucleus, significantly affected the RoM and IDP outcomes. Upon calibration, the HGO fiber model demonstrated the highest accuracy (R = 0.95), followed by the linear (R = 0.89) and nonlinear rebar models (R = 0.87). During the validation phase, the HGO fiber model maintained its high accuracy (RoM R = 0.85; IDP R = 0.87), while the linear and nonlinear rebar models had lower validation scores (RoM R = 0.71 and 0.69; IDP R = 0.86 and 0.8, respectively). 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.