经后路椎弓根钉置入内固定结合硫酸钙椎体成形治疗胸腰椎压缩性骨折的生物力学特征

背景:目前硫酸钙骨水泥用于胸腰椎压缩性骨折的生物力学研究仅限于骨折椎的单个椎体,未对脊柱压缩性骨折经后路椎弓根固定以及骨折椎体硫酸钙骨水泥成形后的脊柱单元进行生物力学分析,如作为一个整体进行分析更符合临床的实际情况.目的:分析经后路椎弓根螺钉置入内固定结合硫酸钙椎体成形术治疗胸腰椎压缩性骨折的生物力学性能.设计、时间及地点:对比观察,于2009-03在上海大学生物力学研究所完成.材料:采集15具新鲜成年小牛胸腰椎标本,制成T_(11)～L_1脊柱功能单位,将标本分成3组,即正常完整标本组、后路复位椎弓根钉固定组及椎弓根钉固定结合硫酸钙椎体成形组.方法:除正常完整标本组外,将其他两组标本制成T_(12)椎体屈曲压缩性骨折模型,分别采用后路复位椎弓根钉固定及后路复位椎弓根钉固定结合硫酸钙椎体成形术.主要观察指标:3组标本在WE-10型万能材料试验机上加载不同级别载荷,在轴向压缩、屈曲、伸展、侧屈4种状态下检测脊柱功能单位的载荷-应变关系、载荷-位移关系、强度、刚度及抗扭等生物力学性能,进行组间比较.结果:胸腰椎载荷-应变及载荷-位移关系呈线性变化,椎弓根钉固定结合硫酸钙椎体成形组的椎体和椎间盘平均应变比后路复位椎弓根钉固定组低14%和12%,比正常完整标本组的低21%和13%.3组标本位移比较,椎弓根钉固定结合硫酸钙椎体成形组位移分别比后路复位椎弓根钉固定组、正常完整标本组减少25%和37%.胸腰椎脊柱功能单位的椎体和椎间盘的强度,椎弓根钉固定结合硫酸钙椎体成形组比后路复位椎弓根钉固定组高14%和24%,比正常完整标本组高13%和20%.胸腰椎刚度方面,椎弓根钉固定结合硫酸钙椎体成形组比后路复位椎弓根钉固定组、正常完整标本组分别高44%和53%.胸腰椎脊柱功能单位最大抗扭强度方面,椎弓根钉固定结合硫酸钙椎体成形组分别比后路复位椎弓根钉固定组、正常完整标本组高18%和30%;扭转刚度方面,椎弓根钉固定结合硫酸钙椎体成形组分别比后路复位椎弓根钉固定组、正常完整标本组高30%和40%.以上数据差异均具有显著性意义(P<0.05).结论:经后路椎弓根螺钉置入内固定结合硫酸钙椎体成形术治疗胸腰椎压缩性骨折的生物力学性能是优越的,不但强度、刚度大,而且术后的胸腰椎体稳定,有利于减轻内植物的应力负荷,进而降低螺钉的松动、折断发生率及术后椎体高度的丢失.

Biomechanical characteristics of posterior transpedicular screw fixation combined with calcium sulfate vertebroplasty in treatment of thoracolumbar compression fracture

BACKGROUND: The biomechanical studies about calcium sulfate cement vertebroplasty are only limited to the single fracture vertebra, not performed in spinal compression fracture unit with posterior transpedicular screw fixation. Furthermore, performing experimental study in the whole function spine unit (FSU) conforms to actual clinical situation. OBJECTIVE: To assess the biomechanical properties of calcium sulfate vertebroplasty combined with posterior transpedicular screw fixation in treatment of thoracolumbar compression fractures. DESIGN, TIME AND SETTING: A controlled experiment was performed at the Biomechanical Laboratory of Shanghai University in March 2009. MATERIALS: Fifteen fresh thoracolumbar spines were harvested from male calves and made into T_(11)-L_1 FSU, then divided into 3 groups randomly: normal control group, posterior transpedicular screw fixation group and transpedicular screw fixation plus vertebroplasty group. METHODS: T_(12) flexion-compression fracture models were made in all specimens of posterior transpedicular screw fixation group and transpedicular screw fixation plus vertebroplasty group, undergoing reduction and posterior transpedicular screw fixation, and calcium sulfate vertebroplasty combined with posterior transpedicular screw fixation respectively. MAIN OUTCOME MEASURES: All specimens were placed on the WE-10A universal testing machine for mechanical test. Load-straining, load-displacing, rigidity, strength and torsion of the FSU were performed in axial compression, flexion, extension and lateral bending states. The experimental outcomes were collected and compared by statistic analysis. RESULTS: The load-strain and loed-displacement showed a linear relationship. Straining values in vertebral body and intervertebral disc of calcium sulfate vertebroplasty plus posterior transpedicular screw fixation group were 14% and 12% less than that of posterior transpedicular screw fixation group, 21% and 13% less than that of normal control group. The thoracolumbar displacement in calcium sulfate vertebroplasty Plus posterior transpedicular screw fixation group decreased 25% and 37% as compared with other 2 groups respectively. Compared with normal control and posterior transpedicular screw fixation group, the thoracolumbar stiffness in calcium sulfate vertebroplasty plus posterior transpedicular screw fixation group increased 53% and 44% respectively. The strength in vertebral body and intervertebral disc of calcium sulfate vertebroplasty plus posterior transpedicular screw fixation group were 14% and 24% higher than that of posterior transpedicular screw fixation group, 13% and 20% higher than that of normal control group. The maximal twisting strength of FSU in calcium sulfate vertebroplasty plus posterior transpedicular screw fixation group were 18% and 30% higher than that of other 2 groups, the twisting stiffness were 30% and 40% higher than that of other 2 groups. The data above were significant differences statistically (P < 0.05). CONCLUSION: Posterior transpedicular screw fixation combined with calcium sulfate vertebroplasty show superior biomechanical properties for treatment of thoracolumbar compression fractures, which exhibits not only strong strength and stiffness, but also stable FSU, thus could decrease the stress loading of the internal fixation, the incidences of screw breakage and avoid the altitude loss of vertebral body.