Minamide Akihito, Akamaru Tomoyuki, Yoon S Tim, Tamaki Tetsuya, Rhee John M, Hutton William C
Department of Orthopaedic Surgery, Emory University School of Medicine, Atlanta, Georgia, USA.
J Spinal Disord Tech. 2003 Apr;16(2):144-9. doi: 10.1097/00024720-200304000-00005.
The current study is a biomechanical study using a cadaveric model of L5-S1 spondylolisthesis. The purpose of the current study was to compare, in a cadaveric model of simulated L5-S1 spondylolisthesis, the biomechanical stiffness of transdiscal fixation with traditional pedicle screw fixation, and transdiscal fixation with combined interbody/pedicle screw fixation. The surgical management of L5-S1 spondylolisthesis is a challenge because of the difficulties in achieving a reliable arthrodesis in the face of high mechanical forces. A method of lumbosacral fixation that has been used successfully in moderate grades of spondylolisthesis at our institution involves the use of transdiscal S1 pedicle screws. With this technique, S1 pedicle screws are placed through the S1 pedicle, through the superior endplate of S1, through the inferior endplate of L5, to terminate in the L5 body. Eighteen fresh human cadaveric (age 59-88 years) L5-S1 motion segments were obtained. The end of each intact motion segment was potted up to its midbody in a 10-cm-diameter polyvinylchloride end-cap using dental cement. The intact specimen was then biomechanically tested as follows: 1) axial compression (500 N), 2) flexion (10 Nm), 3) extension (10 Nm), 4) right lateral bending (10 Nm), and 5) left lateral bending (10 Nm). Stiffness values were calculated from the load-deflection curves obtained. Spondylolisthesis was then simulated by displacing L5 on S1 (% slip average = 41.3%) after performing a radical L5-S1 discectomy, L5 laminectomy, and bilateral L5-S1 facetectomies. The 18 motion segments were divided into two groups. Group I (n = 10) was biomechanically tested (as above) after pedicle screw fixation and again after replacing the S1 pedicle screws with transdiscal screws. Group II (n = 8) was biomechanically tested (as above) after combined interbody/pedicle screw fixation and again after fixation with transdiscal screws. Load-deflection curves were obtained each time, and stiffness values were calculated from the curves. Transdiscal fixation was 1.6-1.8 times stiffer than pedicle screw fixation (p < 0.05) in all loading modes tested. There were no differences in stiffness between transdiscal fixation and combined interbody/pedicle screw fixation. In a cadaveric model of simulated L5-S1 spondylolisthesis, transdiscal L5-S1 fixation produced a 1.6-1.8 times stiffer construct than traditional pedicle screw fixation. Further, the stiffness of the transdiscal fixation was equal to that of a combined interbody/pedicle screw fixation.
本研究是一项使用L5-S1椎体滑脱尸体模型的生物力学研究。本研究的目的是在模拟L5-S1椎体滑脱的尸体模型中，比较经椎间盘固定与传统椎弓根螺钉固定以及经椎间盘固定与椎间融合/椎弓根螺钉联合固定的生物力学刚度。L5-S1椎体滑脱的手术治疗是一项挑战，因为在面对高机械力时难以实现可靠的椎间融合。在我们机构，一种已成功用于中度椎体滑脱的腰骶部固定方法是使用经椎间盘S1椎弓根螺钉。采用这种技术，将S1椎弓根螺钉经S1椎弓根、S1上终板、L5下终板置入，终止于L5椎体。获取了18个新鲜的人类尸体（年龄59-88岁）L5-S1运动节段。将每个完整运动节段的末端用牙科水泥封装在直径10厘米的聚氯乙烯端帽中，直至其椎体中部。然后对完整标本进行如下生物力学测试：1）轴向压缩（500 N），2）前屈（10 Nm），3）后伸（10 Nm），4）右侧弯（10 Nm），5）左侧弯（10 Nm）。根据获得的载荷-位移曲线计算刚度值。在进行L5-S1全椎板切除、L5椎板切除术和双侧L5-S1关节突切除术后，通过将L5相对于S1移位来模拟椎体滑脱（平均滑移率=41.3%）。将18个运动节段分为两组。第一组（n = 10）在进行椎弓根螺钉固定后以及用经椎间盘螺钉替换S1椎弓根螺钉后再次进行生物力学测试（如上所述）。第二组（n = 8）在进行椎间融合/椎弓根螺钉联合固定后以及用经椎间盘螺钉固定后再次进行生物力学测试（如上所述）。每次均获取载荷-位移曲线，并根据曲线计算刚度值。在所有测试的加载模式下，经椎间盘固定的刚度比椎弓根螺钉固定高1.6-1.8倍（p < 0.05）。经椎间盘固定与椎间融合/椎弓根螺钉联合固定之间的刚度没有差异。在模拟L5-S1椎体滑脱的尸体模型中，经椎间盘L5-S1固定产生的结构刚度比传统椎弓根螺钉固定高1.6-1.8倍。此外，经椎间盘固定的刚度与椎间融合/椎弓根螺钉联合固定的刚度相等。
