A finite element analysis of aspinous process screw as a third anchor point in C2 for occipitocervical fixation

English Keywords:Finite element analysis  Cervical spine  Spinous process screw

English Abstract:

  【Abstract】 Objectives: This study aimed to determine the biomechanical feasibility of aspinous process screw as a third anchor point in C2 for occipitocervical fixation through a finite element analysis. Methods: A models of the upper cervical spine (C0-C3) supplied by an adult were reconstructed using computed tomography images. The images were processed using commercially-available software, such as Mimics, Hypermesh and Abaqus software. A nonlinear finite element model of C0-C3 had been developed and validated. Then the C1 fracture models were simulated and occipitocervical fixation was completed. Two different fixation techniques of occipitocervical fixation were applied. The inferior surface of the C3 vertebra was constrained completely. Vertical load of 50N was applied on the C0 to simulate head weight, and 1.5N·m torque was applied to the C0 to simulate flexion, extension, lateral bending, and axial rotation. The range of motion(ROM) of the C0/1, C1/2 and C2/3 segments of the models was measured for intact and fixation models respectively. Results: A nonlinear finite element model of C0-C3 had been developed and validated with the normal upper cervical spine. Since the boundary and loading conditions in these studies were comparable, we compared the ROM of the C0-C3 segments of the intact finite element models with the results of the in vitro test to validate our model. Compared with the intact model, both the bilateral C2 pedicle screw group and the spinous process screw as a third anchor point group reduced the ROM of C0-C2 in the occipitocervical fixation. Compared with the bilateral C2 pedicle screw group, the spinous process screw as a third anchor point group further reduced the ROM of C0-C2 in the occipitocervical fixation except lateral bending of C0/1. Conclusions: In the occipitocervical fixation, the spinous process screw as a third anchor point group combined with the bilateral C2 pedicle screw fixation may enhance the stability of the occipitocervical joint.