Effects of shear force on vertebral endplate

English Keywords:Disc degeneration  Animal model  Shear force  Vertebral endplate

English Abstract:

  【Abstract】 Objectives: To investigate the effect of shear force on the endplate of rabbit lumbar vertebra and the relationship between shear force and degeneration of the IVD. Methods: A stainless external shear loading attaching to L4 and L5 vertebral bones of the rabbit in a dorsoventral direction device was made to apply a constant shear. 38 skeletally mature female Japanese white rabbits(aging 5-6 months) weighing an average of 3kg were used. The rabbits were randomly assigned into non-operated group(n=8), non-loaded group(n=10) and two experimental groups of shear loading for 1 and 2 months(n=10 for each group) respectively. In the experimental groups, the discs were subjected to shear force by using an external loading device. In non-loaded group, the external loading device was situated, but the discs remained unloaded. After loading, the loading devices were removed at 4 and 8 weeks and the animals were given X-ray and MRI examination, then radiological hallmarks and the signal intenity on T2-weighted MRI were analyzed. After X-ray and MRI examination, the rabbits were killed and lumbar vertebra samples were harvested for micro-CT and histologic studies to demonstrate the influences of shear force on the endplate and disc degeneration in animal model. Then, the porosity was calculated as the average of 1-BV/TV for analyzing the influences of shear force on endplate mobility. Results: All the animals tolerated the application of the external loading device. After 1 month of loading, radiographic findings showed narrowing of L4/5 discs, and the surfaces of endplates were flat. The narrowing of intervertebral space at 2 months was significant less and rough surface or slight lumbar spondylolisthesis was observed. MRI showed a significant decrease in nucleus pulposus area and signal intensity in T2-weighted images. Histologically, disorganization and hyperplasia of the chondrocyte occurred. The porosity of the endplate in group A ranged from 28.4% to 37.0%, which showed no significant differences with group B(ranging 26.2% to 40.0%). However, significant differences were found between the experimental and control groups. Conclusions: Shear force can relieve the injury to the vertebral body. Cartilage degeneration and the reduction of endplate mobility can be induced by long term shear force loading, which may result in disc degeneration.