腰髂固定钉道的优化及有限元分析

目的建立腰椎髂骨联合内固定的有限元模型并进行生物力学分析。方法选择1位健康成年男性志愿者,行腰椎及骨盆64排螺旋CT扫描,将原始数据以.dicom格式导入Mimics 16.0软件,进行骨盆三维重建,同时确定L4、L5椎弓根和髂骨安全区螺钉置入几何钉道、自由钉道;通过Solidwoks 2012软件建立髂骨腰椎联合内固定钉棒系统模型,导入Ansys 12.0软件中进行装配。应用500 N轴向压缩载荷,测量两种钉道模型在前伸、后屈、左右侧屈及左右旋转等工况下的位移、von Misses应力分布结果。结果两种钉道模型在前屈、侧屈、后伸工况下整体位移、应力及在前屈、侧屈工况下螺钉的最大应力值表现的较为接近,但在旋转工况下几何钉道模型的整体位移、应力以及在后伸、旋转工况下螺钉的应力均明显小于自由钉道模型。骨盆最大应力均在固定螺钉表面,数值在190~260 MPa,连接骶骨与椎体的2枚螺钉的折弯处为应力集中区域,最大von Misses应力出现在纵向杆的L4~L5椎弓根螺钉。在旋转载荷情况下,连接L4~L5椎弓根螺钉和髂骨螺钉的纵杆上部承受最大应力。结论通过数字化分析确定的腰髂固定几何钉道有更高的抗疲劳、抗旋转以及整体稳定性,腰髂内固定系统可有效分担椎体所受应力。

Optimization and finite element analysis of a safe screw pathway in bilateral lumbo-iliac fixation

Objective To analyze the biomechanical characteristics of bilateral lumbo-iliac fixation by finite element analysis after digital optimization of a safe screw pathway.Methods Firstly,a healthy adult male volunteer was recruited for this study who underwent CT scanning of the lumbus and pelvis,with a slice thickness of 0.625 mm.The original data were imported into Mimics 16.0 software for 3D lumbar and pelvic reconstruction.At the same time,a geometric screw pathway and a free screw pathway were generated in the pedicles of L4 and L5 and ilium.Secondly,all 3D models were imported into Ansys 12 software to assemble a finite element model.The displacements and von Misses stress distribution were measured in the conditions of forward bending,backward extending,lateral bending to the left and right,and left and right rotations in the models of 2 kinds of pathway after gravity axial load of 500 N was applied.Results The models of 2 different pathways were similar in comprehensive displacement and stress in the conditions of forward bending,lateral bending and backward extending,and in the maximum stress of the screw in the conditions of forward bending and lateral bending.However,the comprehensive displacement and stress in the condition of rotation and the stress of the screw in the conditions of backward extending and rotating in the model of geometric screw pathway were obviously smaller than those in the model of free screw pathway.The maximum pelvic stress was on the screw surface between 190 and 260 MPa,concentrated on the bending area of the 2 screws connecting the sacrum and vertebral body.The lumbar-iliac fixation model showed high com-pressive stiffness.The maximum von Misses stress appeared in the L4-L5 pedicle screw on the longitudinal rod.Under rotational loading,the upper longitudinal rod connecting the L4-L5 pedicle screw and the iliac bone screw bore the maximum stress.Conclusions Our finite element analysis shows that double verte-bral bodies and long screw fixation are effective ways of iliolumbar fixation.The geometric screw path optimized by digital analysis exhibits better fatigue resistance,rotation resistance and overall stability.Internal lum-bo-iliac fixation can effectively share the stress of vertebral bodies.