title: Evaluation of the Fixation Strength of Pedicle Screws Using Cortical Bone Trajectory: What Is the Ideal Trajectory for Optimal Fixation?
abstract: METHODS
  In vivo analysis of insertional torque of pedicle screws using cortical bone trajectory (CBT) technique.
  
  
  OBJECTIVE
  To investigate factors contributing to the fixation strength of CBT screws and to clarify the ideal cortical trajectory for lumbar fusion.
  
  
  BACKGROUND
  CBT has developed as a new minimally invasive technique of lumbar instrumentation. Despite biomechanical studies demonstrating the superior characteristics of CBT, no study has elucidated the most suitable path for optimal fixation or compared the fixation within variations of trajectory.
  
  
  METHODS
  The insertional torque of pedicle screws using CBT was measured intraoperatively in 72 consecutive patients. The detailed positions of a total of 268 screws were confirmed using postoperative reconstruction computed tomographic scans and were analyzed to identify factors contributing to the level of insertional torque. Investigated factors were as follows: (1) age, (2) bone mineral density of the femoral neck and lumbar vertebrae by dual-energy x-ray absorptiometry; (3) the pedicle width and height, (4) the length of the implant, (5) total screw length within the vertebra, (6) the screw length within the vertebral body, (7) the screw length within the lamina, (8) the cephalad and lateral angle of the trajectory, and (9) the distance from the long axis of the screw to the inferior and medial borders of the pedicle.
  
  
  RESULTS
  Multiple regression analysis showed that bone mineral density of the femoral neck, screw length within the lamina, and cephalad angle were significant independent factors affecting torque.
  
  
  CONCLUSIONS
  The fixation of CBT screws varied depending on technical factors (cephalad angle and screw length within the lamina) as well as the individual patient factor of bone mineral density. The ideal trajectory was directed 25° to 30° cranially along the inferior border of the pedicle so as to obtain maximum contact with the lamina and sufficient length within the vertebral body.
  
  
  METHODS
  2.
authors.affiliation: *Department of Orthopaedic Surgery, National Defense Medical College, Tokorozawa, Saitama, Japan; and †Department of Orthopaedic Surgery, National Hospital Organization, Murayama Medical Center, Musashimurayama, Tokyo, Japan.
authors.forename: Keitaro
authors.initials: K
authors.lastname: Matsukawa
authors.forename: Eiko
authors.initials: E
authors.lastname: Taguchi
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Yato
authors.forename: Hideaki
authors.initials: H
authors.lastname: Imabayashi
authors.forename: Naobumi
authors.initials: N
authors.lastname: Hosogane
authors.forename: Takashi
authors.initials: T
authors.lastname: Asazuma
authors.forename: Koichi
authors.initials: K
authors.lastname: Nemoto
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density; D001863:Bone Screws; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D019919:Prosthesis Implantation / Q000379:methods*; D013122:Spinal Diseases / Q000601:surgery; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*; D014057:Tomography, X-Ray Computed; D019415:Torque; D055815:Young Adult