滑动椎弓根钉棒系统的研制和生物力学测试

背景:现今临床上常用的椎弓根钉内固定系统为钉棒锁定结构系统,妨碍了处于生长发育期青少年脊柱的纵向生长,所以迫切需要一种能够滑动的椎弓根钉内固定系统.以减少或避免对脊柱生长的影响.目的:对比观察自行研制的滑动椎弓根钉棒系统与传统锁定椎弓根钉棒系统固定脊椎的力学性能.设计:对比观察. 单位:解放军第三军医大学新桥医院骨科,解放军第二一一医院骨科.材料:实验于2007-06-29在哈尔滨工业大学材料科学院完成.自行设计的滑动椎弓根钉棒系统,材质是钛合金,由江苏省常州市武进第三医疗器械厂生产,包括滑动椎弓根钉、矫形棒和横向连接装置三部分.新鲜猪脊椎标本12具,仔细剔除T1～L5椎体所附肌肉,保留主要韧带及后关节突结构的完整性.方法:将标本随机分成滑动组和锁定组,每组6具标本.切除T12椎骨的部分椎板、周围韧带及T11-12、T12～L1椎间双侧小关节造成脊柱失稳,再将滑动椎弓根钉系统和锁定椎弓根钉系统固定于各组的T10, T12,L2椎体上.将标本稳妥安装在夹具内,置于INSTAON-4505轴 向压缩机上.将应变片连接于YJ-31静电电阻应变仪上,模拟人体脊柱载荷并加载于重心点.以便造成前屈、后伸、侧屈、轴向压缩等运动状态.载荷在100,200,300,400,500 N实施分级加载,在不同情况下测量T12椎体的位移.主要观察指标:①在前屈、后伸、侧屈、轴向压缩情况下,主应变及位移变化.②脊柱固定强度和刚度.结果:滑动组和锁定组在屈伸、侧屈、轴向压缩情况下,其主应变、位移变化及固定强度差异均无显著性性意义(P>0.05).结论;滑动椎弓根钉棒系统可以获得与锁定椎弓根钉棒系统相同的生物力学稳定性.滑动椎弓根钉系统将椎弓根钉与矫形棒之间的连接设计为滑动式,使之可随脊柱生长而延长.用于生长发育期脊柱侧凸的的治疗具有可行性.

Design and biomechanical test of sliding Instrumentation of a pedicle screw system

BACKGROUND: Locking pedicle screw system is commonly used in clinic, but it often suppresses spinal longitudinal growth of adolescent at growth phase. Thus, a pedicle screw system that can reduce even avoid the inhibition to spinal growth is needed. OBJECTIVE: To compare the biomechanical performance of sliding instrumentation of pedicle screw system and traditional locking pedicle screw system. DESIGN: Comparative observation. SETTING: Department of Orthopedics, Xinqiao Hospital of Third Military Medical University of Chinese PLA, and Department of Orthopedics, the 211 Hospital of Chinese PLA. MATERIALS: The experiment was performed at Department of Material Science, Harbin Institute of Technology on June 29th, 2007. Self-designed sliding pedicle screw system was made of Ti alloy by Wujin No. 3 Medical Instrument Factory Co., Ltd., Jiangsu Province. It consisted of sliding pedicle screw, orthopaedic rod and transversal coupling device. Twelve samples of fresh porcine spine were selected, and muscles attached on vertebral bodies of TrL5 were removed carefully but integrity of main ligament and precessus articularis posterior was retained. METHODS: The samples were randomly divided into sliding system group and locking system group with 6 samples in each group. Partial vertebral plate and surrounding ligaments of T12as well as bilateral facet joints between T11-12 and T12-L1 were removed to induce spinal destabilization, then sliding pedicle screw system and locking pedicle screw system were respectively fixed onto T10, T12, and L2 vertebral bodies of two groups. The samples then were fixed into fixture, and put onto INSTAON-4505 axial compressor. The strain gauge was connected with YJ-31 static electricity resistance strain gauge instrument human to simulate human spinal load, and the center of gravity was loaded to induce forward flexion, backward extension, lateral flexion and axial construction. Load of 100, 200, 300, 400 and 500 N was given gradually, and displacement of T12 was measured under different loads. MAIN OUTCOME MEASURES: ①Changns in principal stress and displacement under forward flexion, backward extension, lateral flexion and axial construction; ②Spinal fixation intensity and rigidity. RESULTS: No statistical difference was detected in main straining, displacement of apical vertebrae and intensity of fixation between sliding system group and locking system group under forward flexion, backward extension, lateral flexion and axial construction (P > 0.05). CONCLUSION: Sliding pedicle screw system has identical biomechanical stability as locking system. Furthermore, in sliding pedicle screw system, the screw and rod are coupled by sliding pattern, which extend along with spinal growth. It can be used to treat scoliosis at growth phase.