Analysis of the effect of disc degeneration on dynamic characteristics of the lumbar spine using a whole-human body finite element model.

This study aimed to investigate the effects of L4-L5 disc degeneration and different loading frequencies on the dynamic response of the lumbar spine under whole-body vibration. A healthy and a degenerative whole-human body finite element model were developed, with the degenerative model constructed by changing disc height and nucleus pulposus material properties. Both models, coupled with the same seat, underwent 9.8 m/s2 gravitational acceleration and vertical sinusoidal displacement loads (±5 mm) at 3, 5, and 7 Hz. With disc degeneration, the maximum value and vibration amplitude of nucleus pressure and disc bulge all decreased, while those of annulus stress all increased. Specifically, the maximum value and vibration amplitude of annulus stress under a 5 Hz load were 0.737 and 0.596 MPa respectively, which were 19.3% and 19.0% higher than those of the corresponding healthy model. The dynamic responses under 5 Hz loading were several times higher than those under 3 and 7 Hz loading. Under the same loading condition, the distributions of nucleus pressure and annulus stress in both models remained largely unchanged, and the extreme values were all located in the posterior region of the disc. The results showed that disc degeneration significantly altered the vibration characteristics of the degenerative disc segment. Vibration near the resonance frequency of the human body was more likely to cause spinal injury than that at other frequencies, and the posterior regions of the nucleus and annulus were more susceptible to fatigue damage.