title: Cortical bone trajectory and traditional trajectory--a radiological evaluation of screw-bone contact.
abstract: BACKGROUND
  Cortical bone trajectory (CBT), a relatively new technique for pedicle screw insertion in the lumbar spine, is believed to have equivalent pullout and toggle characteristics compared with the traditional trajectory (TT). It has been hypothesized that the new trajectory offers higher cortical bone contact with the pedicle screws and therefore has an improved anchoring property over the traditional trajectory where the screws are inserted into the vertebral body trabecular space. The aim of this study is to evaluate the pedicle screw-cortical bone contact between the two trajectories from a radiological standpoint.
  
  
  METHODS
  Two hundred twenty-two patients with degenerative lumbar spine disease underwent computed tomography scanning. For each patient, axial slices of the L4 and L5 vertebra were cut in two planes, one horizontal to the pedicle representing the plane at which pedicle screws are inserted using the TT and another in a more caudo-cranial plane representing the plane at which pedicle screws are inserted using CBT. For each trajectory, a region of interest (ROI) was selected within the area in which the screws are inserted. A CT number (Hounsfield scale) was then calculated within each ROI to compare the bone density.
  
  
  RESULTS
  The CT numbers within the ROI for CBT were constantly almost over four times higher than that for the TT, and there was a significant difference between the values (p < 0.0001).
  
  
  CONCLUSIONS
  This study has demonstrated that, with the cortical bone trajectory, the pedicle screws penetrate a region that is richer in cortical bone compared to when using the traditional trajectory. This is in keeping with previous hypotheses that the new trajectory offers higher cortical bone contact.
authors.affiliation: Spine and Spinal Cord Center, Mita Hospital, International University of Health and Welfare, 1-4-3 Mita, Tokyo, 108-8329, Japan, dr.kota.kojima@keio.jp.
authors.forename: Kota
authors.initials: K
authors.lastname: Kojima
authors.forename: Shunji
authors.initials: S
authors.lastname: Asamoto
authors.forename: Yoshiomi
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Masayuki
authors.initials: M
authors.lastname: Ishikawa
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Fukui
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D055959:Intervertebral Disc Degeneration / Q000000981:diagnostic imaging / Q000601:surgery*; D007405:Intervertebral Disc Displacement / Q000000981:diagnostic imaging / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D065289:Pedicle Screws; D011859:Radiography; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*; D055815:Young Adult