Development and Validation of a Poroelastic Finite Element model of a human Lumbar Spine Segment

Author: Nishant Bazzad

Bazzad, Nishant, 2023 Development and Validation of a Poroelastic Finite Element model of a human Lumbar Spine Segment, Flinders University, College of Science and Engineering

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Low back pain is a significant problem that affects 580 million people around the world. Finite element (FE) models are used to analyse the biomechanics of the lumbar spine, which can be used to understand the injury mechanisms. An FE model of the L1-L2 functional spinal unit (FSU) was created in a previous study, with the geometry based on an experimental specimen that had undergone testing in 11 loading directions. This model neglected the time-dependent behaviour due to the fluid-dependent poroelasticity. Direct validation is where the FE model closely matches the experimental specimen, and the FE results are directly compared to the experimental results for the same specimen. No studies in the literature have directly validated a FE model of the lumbar FSU in 11 loading directions. The aim of this project was to implement poroelastic behaviour in the FE model of the L1-L2 FSU, verify the model against literature and directly validate the model in 11 loading directions. In the FE model of the L1-L2 FSU, the poroelastic behaviour was implemented on the intervertebral disc (IVD). To simulate the osmotic behaviour, a boundary pore pressure was prescribed on the boundary of the IVD which forced the flow of fluid to maintain this pressure. The FE model was verified against three studies that focused on different aspects of the model including the osmotic behaviour, loading behaviour and pore pressure distribution. Significant discrepancies were found between the FE model and literature, which were due to the various limitations of the FE model. The FE model was directly validated against the experimental results during the 12-hour axial compressive preload, where the axial displacement of the L1 vertebrae had a significantly different initial response, however the results were in reasonable agreement at the end of the preload. Due to the time constraints of the project and the steep learning curve for the author, the final model was not able to be directly validated in 11 loading directions. However, this project laid the foundations for directly validating the model in 11 loading directions, which has various future applications including the simulation of IVD degeneration.

Keywords: development, finite element, lumbar spine, poroelastic, spine biomechanics, validation, verification

Subject: Engineering thesis

Thesis type: Masters
Completed: 2023
School: College of Science and Engineering
Supervisor: John Costi