The Effect of Disc Degeneration on the Biomechanical Response of the Lumbar Spine under Vibration Loading Condition

The dynamic response of the lumbar spine under vibration conditions when it is affected by intervertebral disc degeneration is a topic that remains unclear. Therefore, thirteen finite element (FE) lumbar spine models (L3-S1) with different degrees of intervertebral disc degeneration were constructed to investigate this point.

The model of the normal lumbar spine was validated under static and cyclic loading before the construction of the degenerative models. To replicate the vibration state during dynamic simulation, a compressive follower load of 500 N was first applied and a sinusoidal axial vertical load of ± 40 N at the frequency of 5 Hz with a duration of 0.6s was then imposed.

With the aggravation of degeneration, the axial displacement of each vertebra was reduced for all models and intradiscal pressure (IDP) of the degenerated segments of the lumbar spine decreased while the stress (Von Mises Stress) in the annulus fibrosus increased. The two adjacent segments’ dynamic response curves for the IDP and stress in annulus fibrosus did not change substantially as the degeneration increased, and analysis of the magnitude data revealed that they decreased with the increase of degeneration. The parameter of intervertebral disc height displayed the highest effect on the vibration characteristics of the human lumbar spine, followed by material properties and finally size of anterior osteophyte.

Vibration affects mainly the diseased segments and changes their vibration characteristics, and it does not contribute to the degeneration of the adjacent segment. The finding that intervertebral disc height is an important parameter in vibration characteristics may provide clinical guidance for patients with lumbar disc degeneration disease who often work in a vibration environment.