经伤椎置钉对椎弓根皮质劈裂合并椎体骨折的生物力学稳定性的影响

目的 探讨椎弓根皮质劈裂对椎体骨折内固定生物力学稳定性的影响,评价椎弓根皮质劈裂后不同骨折椎体置钉方式对椎体生物力学稳定性的影响。方法 取新鲜成年绵羊胸腰椎脊柱标本(T13~L3)36具,采用随机数字表法分为4组,分别为A、B、C、D组,每组9具。采用Chiba法在4组标本的L1椎体建立压缩性骨折模型。4组均采用在骨折椎体上下临近椎体置入4个椎弓根螺钉内固定；在此基础上,C组经骨折椎体置入1个椎弓根螺钉,D组经骨折椎体置入2个椎弓根螺钉。内固定后切除B、C、D组T14椎体左侧椎弓根外侧1/4,建立椎体压缩性骨折合并椎弓根皮质劈裂模型。以(300±105)N的载荷对4组模型进行10 000次循环加压,比较4组模型的轴向压缩刚度、T14椎体椎弓根劈裂侧螺钉拔出力及4个方向的活动范围。结果 A、C、D组的轴向压缩刚度和最大螺钉拔出力均显著大于B组(P均=0.000),B组模型在屈伸、侧弯4个方向的运动范围均显著高于A、C、D组(P均=0.000),C、D组的轴向压缩刚度、最大螺钉拔出力均显著大于A组(P均=0.000),C、D组在屈伸、侧弯4个方向的运动范围均显著低于A组(P=0.002,P=0.005),C组各个检测指标与D组比较,差异均无统计学意义(P均>0.05)。结论 椎弓根皮质劈裂影响椎体骨折内固定的稳定性,经骨折椎体置入螺钉内固定能提高劈裂椎弓根内固定的稳定性。

Biomechanical Study of the Influence of Stability for the Pedicle Screws Fixation by Injured Vertebral Screw when the Pedicle Cortex Perforation

Objective To explore the impact of pedicle cortex perforation on the stability of internal fixation of the vertebral body fracture,and to compare the stability of the vertebrae with pedicle cortex perforation after the injured vertebra transpedicular screw fixation by different ways. Methods A total of 36 fresh thoracic and lumbarvertebrae samples of adult sheep (T13-L1) were equally divided into four groups (A,B,C and D) by using the random number table method. The vertebral compression fracture was performed in the L1 vertebral body of the four groups using the Chiba’s method. Four pedicle screws were fixed on the upper and lower injured vertebrae of four groups. In addition,the group C was fixed into a pedicle screw through the injured vertebrae；D group was set two pedicle screws through the injured vertebrae. Then the samples of group B,C,and D were removed a quarter of either side of lateral T14 thoracic pedicle,which was considered as the pedicle cortex perforation model. Four groups were performed fatigue test of 10 000 times by(300±105)N load. The drawing force of the screw and the stability of injured thoracolumbar vertebrae were measured and the differences in every group were compared. Results The axial compressive stiffness and maximum drawing force of screws in the other three groups were significantly higher than those in group B (all P=0.000). The maximum range of motion in four directions of group B were significantly larger than those of the other three groups (all P=0.000). The stiffness and the drawing force in groups C and D were significantly larger than those in the group A (all P=0.000),and the maximum range of motion in four directions of the two groups were lower than that of group A (P=0.002,P=0.005). Every testing indicator in group C had no significant difference when compared with group D (P>0.05). Conclusions The pedicle cortex perforation seriously affects the stability of the fractured vertebral body. The injured vertebra transpedicular screw can increase the stability of internal fixation.