Lumbar intervertebral disc biomechanics: Geometry and collagen fiber orientation configurations effects

Abstract

This study proposes a probabilistic biphasic-swelling parameterized finite element framework, with the aim of which is to systematically evaluate the impact of lumbar intervertebral disc (L-IVD) geometry and annulus fibrosus collagen fiber configuration on multi-axial biomechanical behavior. Thirty anatomical L-IVD geometric sets were sampled via Latin hypercube sampling of clinical anatomical variations. Three annulus fibrosus layer-wise fiber configurations were implemented: Constant ${30}^{\circ }$, Circumferential variation (${25}^{\circ }--{45}^{\circ }$), and Circumferential-radial variation (${23}^{\circ }--{50}^{\circ }$). Consequently, the construction of three groups, comprising a total of ninety biphasic L-IVD finite element models, was undertaken. Five loading protocols were then simulated to reveal the critical dependencies of L-IVD biomechanical behavior. A statistical comparative analysis was performed to evaluate the influence of disc geometries and orientation strategies. The findings demonstrated that fiber orientation configuration exerts a substantial influence on swelling responses, compression stiffness, and flexion stiffness ($p<.050$). Disc height exhibited strong inverse correlations with intradiscal pressure ($r<-0.80$, $p<.001$) and compression stiffness ($r<-0.85$, $p<.001$). Anterior-posterior length emerged as the primary predictor of sagittal stiffness (flexion: $r>0.70$; extension: $r>0.75$) and torsional resistance ($r>0.50$), linked to altered moment arm mechanics. The nucleus pulposus volume ratio moderately affected intradiscal pressure ($r>0.30$, $p<.05$) but showed negligible impact on segmental stiffness. This parametric modelling framework facilitates systematic investigation of L-IVD biomechanics across anatomical variations. Additionally, these findings advocate for microstructure-informed computational models to optimize personalized implant designs and biomechanical assessments.