椎弓根外侧壁破坏对脊柱椎弓根钉内固定生物力学强度的影响

BIOMECHANICAL STRENGTH INFLUENCE OF LATERAL WALL VIOLATION ON SPINAL PEDICLE SCREW FIXATION

目的探讨椎弓根螺钉内固定术中椎弓根外侧壁穿破后,向内侧重新定向后打入矫正螺钉（redirectionally correctly placed pedicle screw,RS）对脊柱内固定的生物力学影响。方法 6只市售家猪,体重95-105 kg,雌雄不限。取其新鲜腰椎标本30个（L1-5椎体各6个）。每个椎体标本一侧椎弓根打入最佳位置的椎弓根螺钉（optimu m placed pedicle screw,OS）;对侧在椎弓根和椎体连接处破坏椎弓根外侧壁,然后拧入RS螺钉。分别测量每个椎弓根钉最大拧入扭矩、锁紧扭矩、螺钉松动力和轴向拔出力。结果 OS螺钉和RS螺钉的最大拧入扭矩分别为（111.4±8.2）N·cm和（78.9±6.4）N·cm,差异有统计学意义（Z=3.038,P=0.002）;OS螺钉和RS螺钉的锁紧扭矩分别为（86.3±7.7）N·cm和（59.7±5.3）N·cm,差异有统计学意义（Z=2.802,P=0.005）。OS螺钉和RS螺钉的螺钉松动力分别为（76.3±6.2）N和（53.0±5.8）N,差异有统计学意义（Z=2.861,P=0.004）;OS螺钉和RS螺钉的轴向拔出力分别为（343.0±12.6）N和（287.0±10.5）N,差异有统计学意义（Z=2.964,P=0.003）。结论与OS相比,椎弓根外侧壁破坏后RS在最大拧入扭矩、锁紧扭矩、螺钉松动力和轴向拔出力方面均显著降低,强化螺钉可能是较好的补救方法。

Objective To compare the fixation strength of optimum placed pedicle screw（OS） with redirectionally correctly placed pedicle screw（RS） following a violation of lateral pedicle. Methods Thirty fresh lumbar vertebrae（L1-5） were obtained from 6 pigs weighing 95-105 kg, male or female. Each vertebra was instrumented with a monoaxial pedicle screw into each pedicle using two different techniques. On one side, a perfect screw path was created using direct visualization and fluoroscopy. A pedicle screw of 5 mm in diameter and 35 mm in length was placed with a digital torque driver（OS）. On the other side, a lateral pedicle wall violation was created at the pedicle-vertebral body junction with a guide wire, a cannulated tap, and a pedicle probe. This path was then redirected into a correct position, developed, and instrumented with a 5-mm-diameter by 35-mm-long pedicle screw（RS）. For each pedicle screw, the maximal torque, seating torque, screw loosening force, and post-loosening axial pullout were measured. Screw loosening and axial pullout were assessed using an MTS machine. Results Maximal insertion torque was（111.4±8.2） N·cm and（78.9±6.4） N·cm for OS and RS respectively, showing significant difference（Z=3.038, P=0.002）. The seating torque was（86.3±7.7） N·cm and（59.7±5.3） N·cm for OS and RS respectively, showing significant difference（Z=2.802, P=0.005）. The screw loosening force was（76.3±6.2） N and（53.0±5.8） N for OS and RS respectively, showing significant difference（Z=2.861, P=0.004）. The post-loosening axial pullout force was（343.0±12.6） N and（287.0±10.5） N for OS and RS respectively, showing significant difference（Z=2.964, P=0.003）. Conclusion Compared with OS, RS placement after a lateral wall violation shows significantly decreased maximal insertion torque, seating torque, screw loosening force, and post-loosening axial pullout. On this occasion, RS augmentation is a probable option for remediation.