Synchrotron tomography-based inversion pipeline for estimating elastic properties for rat vertebral endplate finite...

Lower back pain is linked to vertebral biomechanics, with vertebral endplates (VEPs) playing a key role. Finite element modelling (FEM) is a powerful tool for studying VEP biomechanics but relies on accurate material property inputs, which remain difficult to obtain. Synchrotron computed tomography (sCT) enables detailed visualisation of intact VEP microstructure under near-physiological loads in situ, with three-dimensional strain fields obtained by digital volume correlation (DVC) providing experimental reference data for FEM validation. We applied inverse finite element methodologies to estimate the elastic properties of rat VEPs by integrating DVC data into an image-based FE model. Our pipeline estimated an elastic modulus of 129 MPa and a Poisson's ratio of 0.24 in a rat lumbar segment. The first-order Wasserstein distance between FEM and DVC strain distributions ranged from 0.08% to 0.28%, with Bland-Altman analysis revealing <95% spatial agreement between FEM-predicted and DVC-derived strains across multiple loading steps. Pipeline measurement consistency was evaluated across multiple rat lumbar FE models (n = 3), yielding an estimated VEP elastic modulus = 153 ± 21 MPa and a Poisson's ratio = 0.28 ± 0.03. Regional variations of strain distribution in VEP bodies and protrusions were also identified (strain Wasserstein distance of 0.10%-0.48%). Our work demonstrates the efficacy of the established pipeline in estimating the isotropic elastic modulus and Poisson's ratio of VEPs using FEMs in a physiologically relevant, complex load transfer system. As sCT data becomes available, our pipeline lays the foundations for estimating VEP properties in larger animals and humans. STATEMENT OF SIGNIFICANCE: Back pain is the leading cause of disability worldwide. However, the mechanical role of spinal structures such as the vertebral endplate remains poorly understood due to limited knowledge of their material properties. Using synchrotron tomography and digital volume correlation, we developed an inversion pipeline that optimises finite element models against experimental strain data with micron-scale precision. This inversion pipeline enables accurate estimation of vertebral endplate elastic properties in intact spines. The method is robust across rat samples with anatomical variations and scalable to larger animals and humans. Its potential applications include exploration of healthy and diseased spinal mechanics. Our pipeline offers a powerful tool for understanding musculoskeletal diseases and informing future therapeutic strategies and bioengineering designs.