枢椎棘突螺钉单侧应用联合对侧椎弓根螺钉固定的有限元分析

Biomechanical stability of atlantoaxial and occipitocervical fixations with unilateral spinous process screw plus contralateral pedicle screw:a finite element analysis

目的分析枢椎棘突螺钉单侧应用联合对侧椎弓根螺钉固定在寰枢和枕颈固定中的生物力学稳定性。方法构建正常枢椎解剖、椎板薄和椎动脉变异椎弓根细小3种不同解剖状态下的完整上部颈椎有限元模型作为完整模型组,然后分别模拟齿状突骨折进行寰枢固定和寰椎骨折进行枕颈固定。在寰枢固定中,比较单侧枢椎棘突螺钉+对侧椎弓根螺钉+双侧寰椎侧块螺钉固定组(棘突螺钉组)和枢椎双侧椎弓根螺钉+双侧寰椎侧块螺钉固定组(椎弓根螺钉组);在枕颈固定中,比较单侧枢椎棘突螺钉+对侧椎弓根螺钉+枕骨螺钉固定组(棘突螺钉组)和枢椎双侧椎弓根螺钉+枕骨螺钉固定组(椎弓根螺钉组)。枢椎棘突螺钉分别测试水平、斜向、垂直置钉3种不同的固定技术。模拟颈椎运动,测量枕颈的屈伸、侧屈、旋转的关节活动范围(ROM)。结果在寰枢和枕颈固定中,棘突螺钉组和椎弓根螺钉组的C1~C2屈伸、侧屈、旋转ROM均较完整模型组均明显下降。在寰枢固定中棘突螺钉组C0~C2屈伸、侧屈、旋转的ROM大于椎弓根螺钉组;在枕颈固定中,棘突螺钉组C1~C2侧屈的ROM大于椎弓根螺钉组,棘突螺钉组的C0~C2旋转的ROM大于椎弓根螺钉组。枢椎棘突螺钉分别测试水平、斜向、垂直固定间有差异,但不明显。结论在寰枢和枕颈固定中,枢椎双侧椎弓根螺钉固定和枢椎单侧棘突螺钉联合对侧椎弓根螺钉组合式固定方法均具有良好的稳定性。在寰枢固定中,相对于枢椎棘突螺钉组合式固定,枢椎双侧椎弓根螺钉固定具有更好的寰枢稳定性。在枕颈固定中,枢椎双侧椎弓根螺钉固定在侧屈和旋转活动上较枢椎棘突螺钉组合式固定稳定性更好。枢椎三种棘突螺钉置钉技术间的稳定性差异并不明显。

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.