脊柱外固定器治疗相邻双节段腰椎骨折的生物力学测试

Biomechanical testing of adjacent double segment lumbar fractures treated with the spinal external fixator

背景:胸腰椎骨折固定后相邻节段退变发生的一个重要因素是相邻运动节段出现过度活动,导致该节段应力集中,并且相邻节段的头侧较尾侧更容易发生退变,固定节段数量越多,相邻节段的应力越集中,退变概率越大。目的:通过对相邻双节段腰椎爆裂性骨折经皮椎弓根螺钉外固定进行生物力学测试,评价脊柱外固定器的即刻生物力学稳定性以及上位相邻椎体的运动范围退变情况。方法:选取6具新鲜成年猪脊柱标本(T14-S1,猪胸椎共有14个椎体)。每具标本均按以下顺序进行生物力学测试:正常组、骨折组(L3,L4椎体制作成爆裂性骨折模型)、外固定组(L2,L5椎体行脊柱外固定器固定)、内固定组(取出脊柱外固定器后行L2,L5椎体传统开放后路内固定)。测试标本的固定节段(L2-L5)和上位相邻节段(L1)应用跨相邻2伤椎4钉外固定与内固定后的前屈、后伸、侧屈、轴向旋转角位移运动变化。结果与结论:骨折组各方位角位移运动范围均大于正常组,差异有显著性意义(P<0.05);两种固定状态下固定节段(L2-L5)各方位角位移运动范围均显著小于正常状态和骨折状态,差异有显著性意义(P<0.01),且两种固定状态下各方位的即刻稳定指数比较,差异均无显著性意义(P>0.05);与正常组比较,两种固定状态上位椎体(L1)的各方位角位移运动范围均增加;外固定组与正常组上位椎体(L1)三维运动范围比较:前屈、后伸时差异无显著性意义(P>0.05),侧屈、旋转时差异均有显著性意义(P<0.01);内固定组与正常组比较:前屈、后伸、侧屈、旋转时差异均有显著性意义(P<0.01)。结果可见应用脊柱外固定器治疗相邻双节段腰椎爆裂性骨折,其即刻生物力学稳定性与传统开放后路内固定系统相当;两种固定方式均能引起上位正常相邻椎体侧屈、旋转的角位移增加,但脊柱外固定器较传统内固定在前屈、后伸时不会引起上位相邻椎体的运动范围显著增加。

BACKGROUND： Overactive adjacent motion segment is an important factor for adjacent segment degeneration after thoracolumbar fracture fixation, which can cause stress concentration on this segment, and the cephalad adjacent segment is more prone to degeneration than caudal adjacent segment. The more the fixed segments are, the higher the stress concentration of the adjacent segment, and the larger the degeneration rate. OBJECTIVE： To assess the biomechanical stability and range of motion degeneration of the upper adjacent vertebrae by the biomechanics testing of the pedicle screw external fixation for adjacent double segment lumbar burst fractures. METHODS： There were 14 vertebra samples （T14-S1） from six fresh adult pig spinal specimens. Each of them underwent a biomechanical test in the following order to minimize the inter-group interference, including normal group, fracture group （L3 and L4 vertebral specimens were made into the burst fracture models）, external fixation group （L2 and L5 vertebral specimens were fixed with spine external fixtor） and internal fixation group （the I-2 and L5 vertebral specimens received the traditional open posterior fixation after the spine external fixtor removed）. The range of motion of L2-5 and the upper adjacent segment LI were measured under flexion, extension, lateral bending and axial rotation angles before and after internal fixation and external fixation. RESULTS AND CONCLUSION： Range of motion in the fracture group, internal fixation group and external fixation group was significantly larger than that of the normal group （P 〈 0.05）. Range of motion of L2-5 in the internal fixation group and external fixation group was significantly less than that of normal and fracture groups （P 〈 0.01 ）. There was no significant difference in immediate stability index between the internal fixation group and external fixation group （P 〉 0.05）. Compared with normal group, the range of motion of the upper vertebra L1 after internal and external fixation was increased; there was no significant difference in range of motion of upper vertebrae L1 under flexion and extension between external fixation group and normal group （P 〉 0.05）, but there was significant difference under lateral bending and axial rotation （P 〈 0.01 ）. There was significant difference in range of motion of the upper vertebra L1 under flexion, extension, lateral bending and axial rotation between interna fixation group and the normaL group （P 〈 0.01）. Compared with traditiona internal fixation, the immediate stability index of the spinal external fixation in treating adjacent double segment burst fractures was equal. Both two fixation methods could increase the range of motion of the adjacent upper vertebra under lateral bending and rotation. But the spinal external fixation could not increase the range of motion of adjacent upper vertebrae under flexion and extension.