[Biomechanical stability evaluation of the fixation technique for crossed rods consisting of occipital plate and C 2 bilateral lamina screws]

Abstract

Objective: To evaluate the stability of the fixation technique for the crossed rods consisting of occipital plate and C ₂ bilateral lamina screws by biomechanical test.

Methods: Six fresh cervical specimens were harvested and established an atlantoaxial instability model. The models were fixed with parallel rods and crossed rods after occipital plate and C ₂ bilateral laminae screws were implanted. The specimens were tested in the following sequence: atlantoaxial instability model (unstable model group), under parallel rods fixation (parallel fixation group), and under crossed rods fixation (cross fixation group). The range of motion (ROM) of the C _0-2 segments were measured in flexion-extension, left/right lateral bending, and left/right axial rotation. After the test, X-ray film was taken to observe the internal fixator position.

Results: The biomechanical test results showed that the ROMs in flexion-extension, left/right lateral bending, and left/right axial rotation were significantly lower in the cross fixation group and the parallel fixation group than in the unstable model group ( P<0.05). There was no significant difference between the cross fixation group and the parallel fixation group in flexion-extension and left/right lateral bending ( P>0.05). In the left/right axial rotation, the ROMs of the cross fixation group were significantly lower than those of the parallel fixation group ( P<0.05). After the test, the X-ray film showed the good internal fixator position.

Conclusion: The axial rotational stability of occipitocervical fusion can be further improved by crossed rods fixation when the occipital plate and C ₂ bilateral lamina screws are used.

Keywords: Occipitocervical fixation; atlantoaxial instability; biomechanics; crossed rods.