title: Significance of the Pars Interarticularis in the Cortical Bone Trajectory Screw Technique: AnIn VivoInsertional Torque Study.
abstract: METHODS
  Retrospective study.
  
  
  OBJECTIVE
  Cortical bone trajectory (CBT), a more medial-to-lateral and shorter path than the traditional one for spinal fusion, is thought to be effective for severely degenerated vertebrae because screws are primarily stabilized at the posterior elements. We evaluated the efficacy of this approach throughin vivoinsertional torque measurement.
  
  
  BACKGROUND
  There has been only one priorin vivostudy on CBT insertional torque.
  
  
  METHODS
  Between January 2013 and April 2014, a total of 22 patients underwent posterior lumbar fusion using the CBT technique. The maximum insertional torque, which covers the radial strength needed for insertion, was measured for 113 screws, 8 of which were inserted for L5 spondylolysis. The insertional torque for cases with (n=8) and without (n=31) spondylolysis of L5 were compared using one-way analysis of variance (ANOVA). To evaluate vertebral degeneration, we classified 53 vertebrae without spondylolysis by lumbar radiography using semiquantitative methods; the insertional torque for the 105 screws used was compared on the basis of this classification. Additionally, differences in insertional torque among cases grouped by age, sex, and lumbar level were evaluated for these 105 screws using ANOVA and the Tukey test.
  
  
  RESULTS
  The mean insertional torque was significantly lower for patients with spondylolysis than for those without spondylolysis (4.25 vs. 8.24 in-lb). There were no statistical differences in insertional torque according to vertebral grading or level. The only significant difference in insertional torque between age and sex groups was in men <75 years and women ≥75 years (10 vs. 5.5 in-lb).
  
  
  CONCLUSIONS
  Although CBT should be used with great caution in patient with lysis who are ≥75 years, it is well suited for dealing with severely degenerated vertebrae because the pars interarticularis plays a very important role in the implementation of this technique.
authors: Department of Neurosurgery, Osaka University Graduate School of Medicine, Suita, Japan.
authors: Koshi
authors: K
authors: Ninomiya
authors: Department of Neurosurgery, Osaka University Graduate School of Medicine, Suita, Japan.
authors: Koichi
authors: K
authors: Iwatsuki
authors: Department of Neurosurgery, Osaka University Graduate School of Medicine, Suita, Japan.
authors: Yu-Ichiro
authors: YI
authors: Ohnishi
authors: Department of Neurosurgery, Osaka University Graduate School of Medicine, Suita, Japan.
authors: Toshika
authors: T
authors: Ohkawa
authors: Department of Neurosurgery, Osaka University Graduate School of Medicine, Suita, Japan.
authors: Toshiki
authors: T
authors: Yoshimine
keywords: Cortical bone trajectory; Insertional torque; Pars interarticularis; Spondylolysis; Vertebral degeneration