腰椎矢状面固定角度对相邻节段应力强度影响的实验研究

目的通过体外生物力学实验评价腰椎矢状面固定角度对相邻节段应力强度的影响。方法9具成人新鲜尸体腰椎标本L1～S2用于实验。完整脊柱测试后,在每个标本的L3、4、5用椎弓根螺钉随机顺序地进行矢状面三种角度的固定:①原位(前凸10o);②后凸位(后凸5o);③超前凸位(前凸25o)。每组分别进行加载,记录相邻节段L2/3、L5/S1椎间盘和关节突的应力强度,并加以比较。结果在前屈试验中,所有固定组的相邻节段应力强度均显著高于完整脊柱组(P<0.05),后凸位固定组的应力强度最高。在后伸试验中,后凸位固定的应力强度显著高于其他固定组(P<0.05);但原位固定和超前凸固定组间无显著差异(P>0.05)。侧屈位试验变化规律与后伸试验相似。结论脊柱固定可导致相邻节段的应力强度增加,并且矢状面异常固定角度更破坏其生物力学环境。在腰椎稳定重建同时,应该获得正常腰椎前凸角。

Effect of sagittal fixation angle in lumbar fusion on stresses of adjacent segments

Objectives To evaluate the effect of sagittal fixation angle on the stresses of adjacent segments in lumbar fusion in vitro.Methods Lumbar spine(L1-S2) specimens from nine fresh human cadavers were used.After intact tests of the original normal spines,fixations with three different sagittal angles(1) in situ(lordosis 10 degrees),(2) kyphotic(kyphosis 5 degrees) and(3) hyper-lordotic(lordosis 25 degrees) at L3,4 and 5 were randomly conducted using pedicle screws on each specimen.Subsequently,biomechanical tests were performed under flexion,extension and lateral bending modes.Stresses of the facet joints and intervertebral disks at L2/3 and L5/S1 were measured and compared.Results In flexion tests,all the three fixation strategies resulted in higher stresses within the adjacent segments than that of the intact spine,the highest being the kyphotic fixation group.In extension tests,stresses of the kyphotic group were significantly higher than that of the other two fixation groups.However,there was no statistical difference among the in situ and hyper-lordotic fixation group.The results of bilateral bending were similar to that in extension.Conclusions Spinal fixation can cause stress increase within adjacent segments.Lumbar fixations with abnormal angles may further deteriorate the associated biomechanical condition.Therefore,for lumbar reconstruction,it is crucial to keep the lumbar alignment to its normal orientation.