Mechanical Influence of the Intervertebral Disc on the Vertebrae

A Finite Element Analysis

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Background: To find treatment options for lower back pain, one must gain insight in the spinal anatomy and biomechanics such as joint reaction forces and movement strategies. These can be acquired with use of the Finite Element Method. Previously investigated finite element models of the lumbar intervertebral disc have been designed with the main purpose of understanding the biomechanics of the disc itself, and not necessarily its influence on other spinal elements. A change in disc biomechanics is hypothesised to cause a disruption in the surrounding structures such as the vertebrae which, in turn,
could result in lower back pain. Goal: To create a finite element model of a spinal unit for investigating mechanical influences of the disc onto its adjacent vertebrae. Assessment was performed by examining bone adaptation as a result from simulated disc generation. Methods: A MATLAB script was written to assemble an input file of a parametric model to be used for finite element analyses in Abaqus/CAE. The model was validated with experimental data from literature. A bone adaptation algorithm was used to assess a change in bone material properties before and after simulating disc degeneration by adjusting disc material properties. Results: Finite element analyses showed how a load was transferred by the disc and how bone consequently adapted in response to simulated disc degeneration. The overall trabecular structure was observed to become softer, especially in the vertebral core, while the structure inferior to the anulus became relatively stiffer. Conclusions: Visualisation of bone adaptation after simulating disc degeneration supports the hypothesis that disrupted disc biomechanics indeed affect bone configuration in the adjacent vertebrae.