The Influence Of Disc Degeneration On The Mechanical Behaviour Of Lumbar Motion Segment: A Finite Element Research

Objectives: To investigate the effect of degeneration of intervertebral disc on the mechanical behavior of the lumbar motion segment.Methods: A three-dimensional nonlinear geometrical and mechanical accurate finite element model of lumbar L4-L5 segment was developed. CAD methods were used to establish normal disc model and three degenerated disc models with different degenerative degree where disc lordosis angle, the gap of facet joint and all other geometrical parameters and finite element mesh partition were kept constant for all the four models. The effect of degeneration of intervertebral disc on the biomechanical properties of the lumbar segment was studied for two moment loads (flexion and extension) and for three different direct forces (compression, anterior and posterior shear forces).Results:The stiffness of the lightly degenerated disc model is decreased,while the figue of the further degenerated disc model is increased compated with the mornal disc model. The increase of the degree of disc degeneration result in increased maximum von mises stress in the annulus,decreased nucleus pressure, maximumannular fibar stress as well asmaximum disc radial bulge. The contact force of lightly degenerated disc model is increased while the figue of moderately and severely degenerated disc model is increased. As the degree of degeneration increases,the stress of vertevral body and intervertebral disc is distributed more peripherally. Conclusion: Lightly degenerated disc results in instability of lumbar spine, while the stability is recovered in further degenerated disc. With the degenerated degree of the disc increases the load transfer through such a disc is distributed more peripherally.