Sensitivity Analysis of a Morphological Finite Element L4-L5 Functional Spine Unit for Biomechanical Responses

Morphological models offer significant improvements over static vertebral models by providing predictive capabilities for personalized medicine and injury prevention. These models are invaluable for evaluating biomechanical implications of surgical outcomes and designing personalized rehabilitation plans. Traditional in vitro experiments are limited by the minimal shape variation in available populations. This study aims to assess the sensitivity of anthropometric features on the biomechanical responses of the L4-L5 lumbar functional spine unit (FSU) under moment loading conditions. A population of L4-L5 FSUs was generated using a Design of Experiment (DoE) framework. One Factor at a Time (OFAT) analysis at five levels and Constrained Lattice Hyper Cube Sampling (CLHS) with 200 samples were employed. Anthropometric variations in disc wedging angle, anteroposterior diameter, transverse diameter (TD), vertebral height, and facet sagittal angle were applied using ANSA BETA CAETM. Morphing operations ensured anatomical adaptability without compromising mesh quality. Sensitivity analysis was performed using Pearson's Correlation Coefficient to evaluate the relationship between anthropometric parameters and biomechanical responses, including range of motion, disc pressures, and facet contact forces (CF). Model responses were validated against in vitro experimental data to confirm biomechanical fidelity. Sensitivity analysis using linear regression coefficients identified transverse diameter (-0.99 against range of motion (ROM)), anteroposterior diameter (-0.97 against ROM), and disc wedging angle (0.90 against facet contact force) as the most influential input parameters across different loading scenarios. The Pearson correlation analysis further substantiated these findings, revealing strong linear associations between morphological variations and biomechanical responses. These trends exhibited good agreement with existing in vitro experimental data. This study highlights the importance of geometric variations in determining biomechanical responses of the L4-L5 FSU. The findings provide a framework for treatment planning, critical response prediction, and patient-specific surgical outcome evaluation, paving the way for advancements in personalized medicine and rehabilitation.