Abstract:
This thesis investigates the biomechanical effects of fusion mass density and location on the structural strength of a lumbar interbody fusion (LIF). Using a detailed three-dimensional finite element model (FEM) of the L3-L4 motion segment, created from cross-sectional CT images, a compressive load was applied to the superior vertebral body. The model was used to simulate various clinical scenarios by changing the density and location of the fusion mass. A key metric, the maximum sustainable load before failure, was calculated using the maximum principal strain and the compressive failure strain for vertebral cancellous bone. The study consistently found that as the density of the fusion mass increased, the maximum sustainable load also increased. When the fusion density was equal to or greater than that of the vertebral bodies, failure occurred in the vertebral body, while with lesser densities, failure was seen within the fusion mass itself. The research also explored the impact of fusion location, revealing that a lateral displacement of the fusion mass decreased the failure load, whereas a posterior displacement increased it. A more uniform strain distribution was observed in the fusion mass placed in a central-posterior location, allowing it to carry a higher load. The model was further enhanced to include posterior elements and facet joint contact, which demonstrated that contact increases the sustainable load, especially for anterior and lateral fusion placements. The findings validate the importance of clinically assessing both fusion density and precise fusion location to optimize the success and mechanical integrity of spinal fusion procedures.
