NONLINEAR FINITE ELEMENT ANALYSIS OF INTERVERTEBRAL DISC: A COMPARATIVE STUDY

The aims of this study are i) to build up finite element model of the functional spinal unit without ligaments from cervical region, and ii) to compare the effects of mildly, moderately and severely level degenerated intervertebral disc on the stress during flexion, lateral bending, and rotation. For this, the three-dimensional vertebral model was build up as a three-layered structure with different material properties, from a twodimensional computed tomography image taken from a subject. The disc was defined by hyperelastic material properties. C3 vertebra is fixed from its inferior endplate at 6 axes movements. 50 N axial compression force was applied to superior endplate of the C2 vertebrae. 1 Nm of flexion, lateral bending and rotation moments were applied to superior endplate of the C2 vertebra. The von Mises stress on the annulus and nucleus for healthy and different level degenerated intervertebral disc were calculated for the different direction of movements by finite element analysis. The results showed that the effect of flexion moment increased the stress in the annulus more than the other moment directions as the degeneration progressed. While the stress in the nucleus decreased during flexion as degeneration progressed, the stress either remained the same or decreased by a small percentage (6%) under lateral bending and rotation moment except for rotation of the model with the severely degenerated intervertebral disc.

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