title: [Biomechanical study of the influence of stability for the pedicle screws fixation by injured vertebral screw when the pedicle cortex perforation].
abstract: 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.
authors.affiliation: Graduate School of Hebei North University,Zhangjiakou,Hebei 075000,China.
authors.forename: Shi
authors.initials: S
authors.lastname: Yan
authors.affiliation: Department of Spine Surgery, First Affiliated Hospital of Hebei North University,Zhangjiakou,Hebei 075000,China.
authors.forename: Feng
authors.initials: F
authors.lastname: Su
authors.affiliation: Department of Radiology,First Affiliated Hospital of Hebei North University,Zhangjiakou,Hebei 075000,China.
authors.forename: Zhi-min
authors.initials: ZM
authors.lastname: Zhang
mesh_terms: D000818:Animals; D065289:Pedicle Screws; D012756:Sheep; D016103:Spinal Fractures / Q000601:surgery*