双节段颈前路椎间盘切除融合术应用零切迹系统或钢板联合融合器固定后颈椎生物力学变化的三维有限元研究

A three-dimensional finite element study of the biomechanical changes of cervical spine after 2-level anterior cervical discectomy and fusion with zero-profile system or cage-and-plate fixations

目的:通过三维有限元分析法比较双节段颈椎前路椎间盘切除融合术(anterior cervical discectomy and fusion,ACDF)应用零切迹(zero-profile,ZP)系统与钢板联合融合器(cage-and-plate,CP)固定后颈椎的生物力学变化。方法:采集1例正常成年女性志愿者颈椎C3~C7节段CT扫描数据,建立C3~C7颈椎有限元模型并通过对比前期研究验证模型有效性。ZP固定模型与CP固定模型的手术节段均设定为C4/5与C5/6节段。在C3椎体上方施加轴向压缩负荷73.6N的模拟重力,并逐步施加1.8N·m的转矩,进而模拟屈伸、侧屈及轴向旋转等颈椎运动。测定并比较手术模型融合节段活动度(range of motion,ROM)、邻近节段椎间盘内应力、C5椎体及融合器装置应力。结果:CP固定模型融合节段的ROM在屈伸、侧屈、旋转位均明显小于ZP固定模型;CP固定模型相邻节段(C3/4、C6/7)的椎间盘内应力均远远高于ZP固定模型,两种模型融合节段上方的椎间盘内应力均高于融合节段下方;各工况下,ZP固定模型的C5椎体应力均明显高于CP固定模型,在前屈位时,两模型C5椎体应力最小(ZP固定模型为7.36Mpa,CP固定模型为2.01Mpa);各工况下,ZP固定模型的C4/5、C5/6椎间融合器的应力均大于CP固定模型。结论:相较于CP固定,ACDF术中应用ZP固定对手术节段的限制更小,手术节段ROM更高、微运动更多,融合器及中间椎体应力更大,术后更易发生融合器下沉甚至中间椎体塌陷。

Objectives:To analyze and compare the biomechanical changes after 2-level anterior cervical discectomy and fusion(ACDF)with zero-profile(ZP)system and cage-and-plate(CP)fixations through 3D finite element study.Methods:The CT parameters of C3-C7 of a normal female adult volunteer were collected to develop a finite element model of the cervical spine of C3-C7,and the validity of the model was verified through comparison with previous studies.The surgical segments of both ZP fixation model and CP fixation model were set as C4/5 and C5/6.An axial compression preload of 73.6N was applied over the C3 vertebral body to simulate gravity,and a torque of 1.8N·m was gradually applied to simulate the cervical motions of flexion and extension,lateral bending,and axial rotation.The range of motion(ROM)of the fusion levels,intradiscal stresses of adjacent segments,C5 vertebral body and fusion device stresses were measured and compared between both fixation models.Results:The ROMs of the fused levels of the CP fixation model were all significantly smaller than those of ZP fixation model,respectively,in flexion-extension,lateral bending,and rotation motion states;The intradiscal stress of the adjacent segments(C3/4 and C6/7)of the CP model was much higher than that of ZP model,and the intradiscal stress of the upper vertebra of the fused segments was higher than that of the lower vertebra.In all motion states,the C5 vertebral body stress was all significantly higher in ZP model than that of CP model,which was minimum in flexion(7.36Mpa vs 2.01Mpa);The stresses in the C4/5 and C5/6 intervertebral fusion devices were all greater in ZP model than in CP model.Conclusions:Comparing with CP fixation,ZP fixation in ACDF has smaller limitations to surgical segments,bigger ROM&more micromovements of fusion segements,and greater stress in the fusion device and middle vertebra,which is prone to postoperative cage subsidence or even middle vertebra collapse.