Effect of Fatigue Load on Internal Mechanical Properties of the Intervertebral Disc

Abstract

Lumbar disc herniation is considered to be the main pathological factor for the common clinical disease of low back pain. Biomechanical factor is an important cause of lumbar disc herniation, so it is urgent to analyze the stress/strain behavior of intervertebral disc under different loading condition. Slow repetitive loading is considered to be an important factor of spine and disc injuries, and the effect of fatigue load on internal displacement in the intervertebral disc was investigated by applying the optimized digital image correlation technique in this study. The first finding was that fatigue load had a significant effect on the displacement distribution in the intervertebral disc under compression. Superficial AF exhibited the largest axial displacements before fatigue load, while it exhibited the smallest axial displacements after fatigue load. Inner AF exhibited slightly smaller radial displacements than outer AF before fatigue load, while it exhibited significantly greater radial displacements than outer AF displacements after fatigue load. The second finding was that fatigue load had a certain effect on the internal displacement distribution in the flexed intervertebral disc under compression. Middle AF exhibited the smallest axial displacements before fatigue load, while deep AF exhibited the smallest axial displacements after fatigue load. The radial displacement distribution did not change before and after fatigue load, as the radial displacement in outer AF was the smallest, while the radial displacement in inner AF was the largest. The third finding was that with the increase in fatigue time and amplitude, the Young's modulus of the intervertebral disc increased significantly. This study can provide the basis for clinical intervertebral disc disease prevention and treatment?and is important for mechanical function evaluation of artificial intervertebral disc as well.

Study of Nonlinear Viscoelastic Mechanical Properties of Degenerated Intervertebral Discs

“…Overall, the axial displacement of superficial AF is greater than that of deep AF. This is consistent with the findings of Liu et al (2020), who studied the effect of fatigue loading on the internal displacement of the disc by applying the optimized digital image correlation technique and found that the axial displacement of the superficial AF was the greatest before fatigue loading. Meakin et al (2000) measured the displacement of the internal marker points of the nucleus pulposus discectomy with the interactive image analysis software, and concluded that when the nucleus pulposus discectomy is subjected to compressive load, the outer edge of the fibrous ring deforms outward, which is consistent with the phenomenon we observed.…”

“…The internal displacement was measured by optimized DIC technology (Liu et al, 2020), the intervertebral disc was cut along the sagittal plane, and the iron oxide nanoparticles were evenly coated on the incision surface as a marker point to record the deformation of different areas of the intervertebral disc. A pair of marked points a1 (x1, y1) and a2 (x2, y2) with similar x value were selected, and the axial displacement distribution will be reflected by comparing the y value between this pair of points before and after loading.…”