Three-dimensional finite element study of the effect of sagittal angle asymmetry of cervical facet joint on the stress of cervical intervertebral disc annulus fibrosus

English Keywords:Facet tropism  Cervical intervertebral disc  Annulus fibrosus  Stress  Finiteelement analysis

English Abstract:

  【Abstract】 Objectives: The effects of facet tropism on cervical intervertebral disc and facet joint were investigated by finite element analysis. Methods: The finite element model was constructed using CT scans of a 26-year-old female volunteer. Firstly, a cervical model was constructed from C3 to C7. The model was verified using data from previously published studies. Secondly, the facet orientation at C5-C6 level was altered to simulate the facet tropism with respect to the sagittal plane. Three models were reconstructed, including symmetric model(90° facet joint angle at the both side), moderate facet tropism model(100° facet joint angle at the left side and 90° facet joint angle at the right side), and severe facet tropism model(110° facet joint angle at the left side and 90° facet joint angle at the right side). In each model, the stress of annular fiberswere studied under four pure moments and combined loading. Results: Three models just had little differ on the stress of annulus fiber and the pressure of facet joint under flexion, extension, lateral bending, left rotation and flexion combined with left rotation moment. But under right rotation and flexion combined with right rotation moment, there were significant differences in the stress of annulus fiber and the pressure of facet joint among the three models. Compared with the symmetric model, the annular fiber stress of moderate facet tropism model and severe facet tropism model showed an increasing trend(increased by 16.65% and 35.16% respectively under right axial rotation; flexion combined with right axial rotation increased 19.47% and 54.39%, respectively), and severe facet tropism model was more obvious. The pressure of facet joint showed a decreasing trend(reduced by 3.31% and 5.95% respectively under right axial rotation; flexion combined with right axial rotation reduced by 7.19% and 15.52%, respectively), and the decrease was more obvious in the severe facet tropism model. Conclusions: Cervical facet tropism increases the stress of intervertebral disc annulus fiber, and the greater the degree of facet tropism, the more obvious the stress increases, it may be one of the pathological anatomic factors of cervical disc degeneration or herniation.