改良Brooks技术和寰枢椎椎弓根螺钉内固定系统生物力学特点

Biomechanical features of modified Brooks technique and atlantoaxial pedicle screw fixation

目的通过有限元分析比较改良Brooks技术和寰枢椎椎弓根螺钉内固定系统的生物力学性能。方法对健康青年男性进行上颈椎(枕骨底~C_(3))CT薄层扫描,建立健康上颈椎有限元模型,再构建齿突Ⅱ型骨折伴寰枢椎不稳模型,并在该模型中模拟改良Brooks技术和寰枢椎椎弓根螺钉内固定,分析前屈、后伸、侧曲及旋转工况下上颈椎各节段的活动度(ROM),绘制应力云图,分析应力分布差异。结果与正常模型相比,2种内固定模型寰枢椎ROM均明显减小,并且改良Brooks模型寰枢椎ROM减小程度略低于椎弓根螺钉模型,尤其在旋转和后伸时。在大多数情况下,2种内固定模型相邻节段(寰枕关节、C_(2)/C_(3))ROM均大于正常模型,而改良Brooks模型与正常模型更接近。椎弓根螺钉模型中C_(1)螺钉、改良Brooks模型中钛缆分别承受最大应力,在前屈和后伸时应力最大,应力主要集中在螺钉根部及钛缆与寰椎后弓、连接棒交界处。与椎弓根螺钉模型相比,改良Brooks模型C_(2)螺钉所受应力较小,且邻近椎间盘(C_(2)/C_(3))所受应力也较小,与正常模型相近。结论改良Brooks技术具有良好的生物力学稳定性,对邻近节段影响较小,在寰椎、椎动脉解剖发育异常致寰椎置钉困难时,可作为治疗寰枢椎不稳的补充方法,弥补寰枢椎椎弓根螺钉技术的不足。

Objective To compare biomechanical properties of modified Brooks technique and atlantoaxial pedicle screw fixation by finite element method.Methods The finite element model of normal upper cervical spine(bottom of occipital bone to C_(3))was developed and validated by CT thin-layer scanning of a healthy young man,and the finite element model of normal upper cervical spine and atlantoaxial instability with typeⅡodontoid process fracture was constructed.The fixation models with modified Brooks technique(modified Brooks model)and atlantoaxial pedicle screw fixation(pedicle screw model)were respectively evaluated by finite element analysis.The range of motion(ROM)under load cases of flexion,extension,bending and rotation were measured,then the stress nephogram were drawn and the difference of stress distribution was analyzed.Results Compared with the normal model,the atlantoaxial ROM of the 2 fixation models decreased significantly,and the ROM of modified Brooks model was a little larger than that of pedicle screw model,especially in rotation and extension.Most of the adjacent segments(atlantooccipital joint and C_(2)/C_(3))ROM of the fixation models were both larger than that of the normal model,while the ROM of modified Brooks model was closer to that of the normal model.In the pedicle screw model and the modified Brooks model,the C1 screw and the titanium cable bore the maximum stress respectively,especially under flexion and extension load case.The stress was concentrated mainly at the screw root and the junction of the titanium cable with posterior arch and connecting rod of the atlas.The stresses of C_(2) screw and adjacent disc(C_(2)/C_(3))in the modified Brooks model were both significantly smaller than that in the pedicle screw model.Conclusions The modified Brooks technique results in sufficient stability,which has little effect on the degeneration of adjacent segments.When the abnormal anatomy of the atlas and vertebral artery appears,it can make up for the deficiency of atlantoaxial pedicle screw fixation,as an alternative method for atlantoaxial instability.