Biomechanical stability of atlantoaxial and occipitocervical fixations with unilateral spinous process screw plus contralateral pedicle screw: a finite element analysis / 中华创伤骨科杂志

ABSTRACT

Objective:To determine the biomechanical stability of atlantoaxial and occipitocervical fixations with unilateral spinous process screw plus contralateral pedicle screw.Methods:After nonlinear finite element models of the intact upper cervical spine (C0-3) were constructed and validated, they were processed into 3 kinds with normal axis anatomy, a high-riding vertebral artery and a thin axis lamina, re-spectively.In the models, the odontoid fracture stabilized by atlantoaxial fixation and the atlas fracture sta-bilized by occipitocervical fixation were simulated.In the atlantoaxial fixation, the group of unilateral spinous process screw+contralateral pedicle screw+bilateral atlas lateral mass screws (spinous process screw group) was compared with that of bilateral axis pedicle screws+bilateral atlas lateral mass screws (pedicle screw group); in the occipitocervical fixation, the group of unilateral spinous process screw+contralateral pedicle screw+occipital screws (spinous process screw group) was compared with that of bilateral axis pedicle screws+occipital screws (pedicle screw group).Three different techniques in insertion of spinous process screws (horizontal, oblique and vertical) were applied.The range of motion (ROM) was measured in extension-flexion, lateral flexion and rotation of occipitocervical bodies (C0-C3) after internal fixation.Results:Compared with the intact models, the ROMs of extension-flexion, lateral flexion and rotation of C1-C2 were obviously reduced in the spinous process screw group and the pedicle screw group in the models with atlantoaxial and occipitocervical fixations.In the atlantoaxial fixation, the ROMs of extension-flexion, lateral flexion and rotation of C1-C2 were greater in the spinous process screw group than in the pedicle screw group; in the occipitocervical fixation, the spinous process screw group had greater ROM of lateral flexion of C1-C2 and greater ROM of rotation of C0-C2 than the pedicle screw group.There were unobvious differences in insertion of spinous process screws between the horizontal, oblique and vertical techniques.Conclusions:In the atlantoaxial and occipitocervical fixations, the unilateral spinous process screw plus contralateral pedicle screw can provide as fine stability as the bilateral axis pedicle screws.In the atlantoaxial fixation, the bilateral axis pedicle screws may lead to better stability of C1-C2 than the unilateral spinous process screw plus contralateral pedicle screw.In the occipitocervical fixation, the bilateral axis pedicle screws may lead to better stability of C1-C2 in lateral flexion and rotation than the unilateral spinous process screw plus contralateral pedicle screw. The 3 different techniques in insertion of spinous process screws lead to an unobvious difference in the stability of C1-C2.