腰椎新型动态固定系统腰椎后路固定融合的生物力学性能

背景：脊柱融合固定过程中，用于后路固定的钉棒系统由于造成相邻椎体、椎间盘及椎间关节的应力改变以及反常活动，会导致固定融合后相邻节段的退行性变加速。目的：在腰椎后路固定融合过程中采用新型动态固定系统，验证动态固定系统在固定术后的即刻生物力学性能，并与传统固定系统相比较。设计、时间及地点：对照实验，于2007-11/12在上海大学生物力学研究所完成。材料：10具新鲜小牛T12~S5脊柱标本。方法：模拟人体生理运动情况，即轴向压缩、前屈、后伸、侧屈状态，并加上扭转状态测试。实验属稳定性实验，最大加载不超过125 N的生理载荷，无破坏性影响，故标本可重复使用。依实验进程标本分为4组，每组10具标本。先对每具标本进行生理状态测试，然后制成L5~S1滑脱腰椎失稳实验模型进行测试，之后行后路椎间融合椎弓根钉棒固定，分别采用传统钉棒和动态固定系统建立腰椎后路固定融合模型进行测试。实验过程中未出现标本破坏及内固定器械断裂失效等情况。主要观察指标：生理载荷125 N时，生理状态、滑脱状态、传统钉棒固定及动态钉棒固定状态下腰椎的水平剪切刚度、轴向刚度及扭转强度。结果：采用两种固定系统行后路固定椎间融合后，系统的稳定性均明显超过滑脱状态，达到或超过生理状态。对于临近（上位）节段的应变、位移等影响，传统钉棒系统明显超过生理状态（P < 0.05），而动态固定系统接近生理状态（P > 0.05）。结论：采用腰椎动态固定系统行后路椎间固定融合后，其稳定性达到或超过正常生理状态，能够满足对临床固定手术后即刻稳定性的要求。与传统静态钉棒固定系统相比较，动态固定系统相邻椎体、椎间盘、椎间关节所承受的应力应变均明显降低，各项生物力学性能上均接近正常腰椎生理状态，不易产生邻近节段的退行性变，具有较大的优势。

Biomechanics of a dynamic fixation for posterior lumber interbody fusion

BACKGROUND: During spinal fusion and fixation, the screw-rod system for posterior fixation may accelerate degeneration of the adjacent segments due to stress changes and abnormal activities of adjacent vertebral body, intervertebral disk, and intervertebral joint.OBJECTIVE: To evaluate initial biomechanic of the lumber intervertebral segmental stiffness after posterior lumber interbody fusion (PLIF) with dynamic fixation and compare with conventional rigid fixation. DESIGN, TIME AND SETTING: Control experiment was performed at the Institute of Biomechanics, Shanghai University from November to December 2007.MATERIALS: Ten spinal specimens of fresh calf (T12-S5).METHODS: The specimens were used to simulate human physiological movements including axial compression, flexion, extension and lateral bending as well as torsion. Because the maximum load was less than 125 N, the specimens could be used repeatedly. The specimens were divided into four groups (n=10). Firstly, the specimens were exposed to physiological test, followed by spondylolisthesis, and fixation with PLIF plus monosegmental rigid fixation or plus monosegmental dynamic fixation. No specimen damage or instrument breakage occurred during the entire process.MAIN OUTCOME MEASURES: Under physiological load (125 N), the horizontal shearing rigidity, axial rigidity and torsional strength under physiological condition, spondylolisthesis, conventional rigid fixation and PLIF dynamic fixation were determined. RESULTS: Following PLIF by two systems, the stability was significantly better than spondylolisthesis, reached or exceeded physiological condition. The influence of conventional rigid fixation such as stress and displacement on adjacent segments was more significant than physiological condition (P < 0.05), but the influence of PLIF dynamic fixation was similar to physiological condition (P > 0.05).CONCLUSION: After PLIF with the dynamic fixation, the stability is extremely approach to the intact group, which could meet the clinical requirements. Compared with the conventional rigid fixation system, the dynamic fixation system reduces strain and stress exposed to adjacent vertebral body, intervertebral disk, and intervertebral joint, and its biomechanical indexes are similar to intact condition, which may prevent or delay adjacent segment degeneration.