脊柱侧凸前路去旋转椎体融合手术矫形的生物力学研究

Research on biomechanics of the adolescent idiopathic scoliosis treated by the ventral derotation spondylodesis(VDS)

目的利用三维有限元模型研究减小前路去旋转椎体融合手术(VDS)中螺钉拔出风险的手术策略。方法CT扫描MS患者的脊柱,用图像处理软件读取CT数据文件,转入有限元软件,建成侧凸脊柱三维有限元分析模型,继而将矫形内植入物加入模型中。利用模型模拟7种不同矫形力分布的VDS的矫形方案对矫形效果和螺钉受力的影响。结果在所有矫形方案中,头端椎体和中间椎体上固定的螺钉受到轴向拉伸力(140～480 N),其余螺钉上产生轴向压力(20～140 N);头端和尾端的螺钉受较大的剪力(200～1480 N)。在头端运动节段的强力矫形方案导致轴向拉伸的和横向剪切的力堕最大(440 N和1480 N),从而增加了头端螺钉拔出的风险。结论宜采用中间运动节段强力矫形,而头端运动节段适度矫形的矫形策略,来取得理想的矫形效果,同时降低螺钉拔出的风险。

Objective To study the different surgical strategies to reduce the risk of screw pullout using the 3D finite element model of the scolitic spine and internal fix implant. Methods Geometry Data from T1 to sacrococcyx of a scoliotic spine was obtained using spiral computed tomography. Contour line of the bone tissure was gained by image software called Medgraphics and stored in IGES format and transferred to ANSYS software. Solid model was defined with the material property and meshed to construct a 3D finite element model of the scoliotic spine. Implant was directly added into the model of the spine. The finite element model was used to simulate the 7 different surgical strategies. The correction effect and the screw force were observed. Results An axial tensile force which ranged from 140 to 480 N was calculated for the farthest cranial screw and for screw fixed on the middle vertebrae respectively. An compressive forces ranged from 20 to 140 N were predicted for the rest screws. The transverse force ranged from 200 to 1480 N was highest at the screws of the end vertebrae. A strategy in which surgical correction was strong in the outer segment cranially led to higher axial force 440 N and transverse force 1480 N of the outermost screw. Conclusion A strategy in which correction is strong in the middle segments and moderate in the outer ones is ideal to lead to a good reduction of the cobb angle, a wide derotation angle, and relatively low risk of screw pullout.