经第二骶椎髂骨翼螺钉和骶髂关节螺钉治疗C型骶髂关节脱位的有限元对比研究

Finite element comparative study of S2 alar-iliac screw and sacroiliac joint screw in treatment of type C sacroiliac joint dislocation

目的比较经第二骶椎髂骨翼（S2AI）螺钉和骶髂关节螺钉治疗单侧C型骶髂关节脱位的生物力学效果。方法选取1名成年健康男性，行骨盆CT扫描，层厚1mm，影像学资料以DCOM格式保存。应用Mimics、Geomagic、Solid Works、Abaqus等软件建立完整骨盆的三维有限元模型。建立C型单侧骶髂关节脱位的有限元模型，分别置人直径为6．5mm的1枚S1椎体骶髂关节螺钉（S1组）、1枚S2AI螺钉（S2AI组）和1枚S1椎体骶髂关节螺钉＋1枚S2椎体骶髂关节螺钉（S1＋S2组）。模拟对骶骨上表面施加500N垂直负荷，记录并分析骶髂关节的移位值、骶骨的移位值、螺钉内固定和周围骨的应力值及应力云图分布。结果位移数据显示，三组的位移分布有一致的趋势，但位移的绝对值为S1组〉S2AI组〉S1＋S2组，其中S1组的骶髂关节最大位移为0．87mm，骶骨最大位移为1．6mm；S2AI组骶髂关节最大位移为0．22mm，骶骨最大位移为0．24mm；S1＋S2组骶髂关节最大位移为0．06mm，骶骨最大位移为0．16mm。应力数据显示，内固定的应力主要分布在骶髂关节处，应力的大小为S2AI组〉S1组〉S1＋S2组，其中S1组的最大应力值为52．8MPa，S2AI组的最大应力值为62．1MPa，S1＋S2组S1螺钉最大应力为38．2MPa，S1螺钉最大应力为23．6MPa。螺钉周围骨的应力也集中于骶髂关节处，应力的大小为S。组〉S2AI组〉S1＋S2组，其中S1组最大应力值为56．8MPa，S2AI组最大应力值为11．2MPa，S1＋S2组应力最大值为5．8MPa。结论单枚S1螺钉、单枚S2AI螺钉和S1螺钉＋S2螺钉均可用于单侧C型骶髂关节脱位的治疗。单枚S1螺钉早期负重会有骶髂关节位移增大、内固定失效的风险，而S2AI螺钉固定与S1＋S2螺钉联合固定有相似的生物力学强度，可以允许患者早期负重，有助于术后康复。

Objective To compare the biomechanical characteristics between S2 alar-iliac （S2AI） screw and sacroiliac joint screw in treating unilateral type C sacroiliac joint dislocation. Methods A 25 year-old healthy male adult agreed to take computed tomography scan of the pelvis. The pelvic floor thickness was 1 mm and the image data were saved in DCOM format. A three dimensional finite element model of intact pelvis was reconstructed by Mimics, Geomagic, SolidWorks, and Abaqus softwares. A finite element model of type C unilateral sacroiliac dislocation was established. One S1 vertebral sacroiliac screw of 6.5 mm in diameter （S1 group）, one S2AI screw （S2AI group） and one S1 vertebra sacroiliac screw ＋ one S2 vertebra sacroiliac screw （S1 ＋ S2 group） were placed in the model, respectively. The 500 N vertical load on the upper surface of the sacrum was simulated. The displacement value of sacroiliac joint, the displacement of sacrum, the stress value of the internal fixation and surrounding bone, and the stress distribution cloud map were recorded and analyzed. Results The displacement data showed that displacement distribution in the three groups had a consistent trend. In terms of the absolute value of displacement the result was S1 group 〉 S 2AI group 〉 S1 ＋ S2 group, of which the maximum displacement of sacroiliac joint in S1 groups was 0. 87 mm and that of sacrum was 1.6 mm; the maximum displacement of sacroiliac joint in S2AI group was 0.22 mm, and that of sacrum was 0.24 mm; the maximum displacement of the sacroiliac joint in S1 ＋ S2 group was 0.06 mm, and that of sacrum was 0.16 mm. Stress data showed that the stress in the internal fixation was mainly distributed at the sacroiliac joint, and the stress result was S2AI group 〉 S1 group 〉 S1 ＋ S2 group, of which the maximum stress value was 52.8 MPa in S1 group, 62.1 MPa in S2AI group, and 38.2 MPa in S1 ＋ S2 group. The stress around the screws was also concentrated at the sacroiliac joint, and the stress result was S1 group 〉 S2AI group 〉 Si ＋ S2 group, of which the maximum stress value was 56.8 MPa in S1 group, 11.2 MPa in S2AI group, and 5.8 MPa in S1 ＋ S2 group. Conclusions Single S1 screw, single S2AI screw and SI screws combined S2 screws can be used for the treatment of unilateral C type sacroiliac joint dislocation. Early weight bearing of single S1 screw might lead to the risks of increased sacroiliac joint displacement and internal fixation failure. S2AI screw fixation and S1＋ S2 screw fixation have similar biomechanical strength, allowing early weight-bearing and contributing to better postoperative rehabilitation.