[Analysis of lumbar disc degeneration using three-dimensional nonlinear finite element method].

OBJECTIVE

To explore the effects of intervertebral disc degeneration on the biomechanical behavior of the lumbar motion segment.

METHODS

A three-dimensional nonlinear finite element model of L4-L5 segment was established using CAD technique based on CT images. A normal disc model and three degenerative disc models were established by changing the parameters such as disc material properties and disc height. The effects of disc degeneration on the biomechanical properties, including stiffness, nucleus pressure, maximum von Mises stress in the annulus, and force of posterior structure were studied under two moment loads (flexion and extension) and for three different direct forces (compression, and anterior and posterior shear forces), and the stress distribution of vertebral body and end- plate was also analyzed.

RESULTS

The stiffness of the lightly degenerative disc model was decreased compared with that of the normal disc, while it was increased in the moderately and severely degenerative disc models when compared with the normal disc. The force of posterior structure in the lightly degenerative disc model was increased while the values of force of posterior structure in the moderately and severely degenerative disc models were decreased gradually. The maximum von Mises stress in the annulus increased, and the nucleus pressure decreased as the disc degeneration progressed. Moreover, the stress of intervertebral disc, vertebral body, and end-plate was distributed more peripherally.

CONCLUSION

Light degeneration of intervertebral disc leads to instability of lumbar spine, while the stability restores with further degeneration of disc. There is a negative correlation between the force of posterior structure and the load on the intervertebral disc. With the disc degeneration progressing, the intervertebral disc load pattern changes, the stress of intervertebral disc, vertebral body, and end-plate is concentrated peripherally.