Impact of vertebrae shape variation on lumbar spine loading: an image-based computational modeling study

Many computational spine studies rely on simplified vertebrae geometries and evaluate only a limited number of models, which restricts insight into how anatomical variation affects spinal loading and may overlook important biomechanical differences across individuals. This study aims to assess how natural variation in vertebral shape influences facet joint forces and intervertebral disc loads using a large population of image-based computational models. A total of 360 detailed lumbar spine motion segment models were generated from high-resolution CT scans of 60 asymptomatic subjects. Each model included anatomically accurate representations of vertebral bodies and facet joints, with simplified intervertebral discs and loading conditions to isolate the effects of vertebral shape. Over 2,500 simulations were conducted under various loading scenarios—including flexion, extension, axial twisting, lateral bending, and combined compression with anterior-posterior shear—to evaluate biomechanical responses across subjects and spinal levels. Significant inter-subject variability was observed in both facet forces and intervertebral disc loading. Loading patterns varied significantly by vertebral level and exertion type and exhibited left-right asymmetry. A single representative “average” subject did not adequately reflect the range of loading patterns seen in the population, underscoring the limitations of using a single model to generalize spinal biomechanics. Natural variation in vertebral shape, especially facet geometry, has a substantial impact on facet forces and disc loading. These findings highlight the importance of subject-specific modeling and diverse anatomical representation to enhance the accuracy and relevance of spine simulations.