title: In vitro biomechanical comparison of transpedicular versus translaminar C-2 screw fixation in C2-3 instrumentation.
abstract: OBJECTIVE
  In instrumentation of the upper cervical spine, placement of pedicle screws into C-2 is generally safe, although there is the potential for injury to the vertebral arteries. Owing to this risk, translaminar screws into C-2 have been used. The aim of this study was to compare the stability of the in vitro cadaveric spine using C-2 laminar compared with C-2 pedicle screws in C2-3 instrumentation.
  
  
  METHODS
  Eight fresh frozen human cadaveric cervical spines (C1-6) were potted at C1-2 and C5-6. Pure moments in increments of 0.3 Nm to a maximum of 1.5 Nm were applied in flexion, extension, right and left lateral bending, and right and left axial rotation. Each specimen was tested sequentially in three modes: 1) intact; 2) C2 pedicle screw-C3 lateral mass fixation; and 3) C2 laminar screw-C3 lateral mass fixation. The sequence of fixation testing was randomized. Motion was tracked with reflective markers attached to C-2 and C-3.
  
  
  RESULTS
  Spinal levels with instrumentation showed significantly less motion than the intact spine in all directions and with all loads greater than 0.3 Nm (p < 0.05). Although there was no significant difference between C2 pedicle screw-C3 lateral mass fixation and C2 laminar screw-C3 lateral mass fixation, generally the former type of fixation was associated with less motion than the latter.
  
  
  CONCLUSIONS
  When pedicle screws in C-2 are contraindicated or inappropriate, laminar screws in C-2 offer a safe and acceptable option for posterior instrumentation.
authors.affiliation: Department of Neurosurgery, University of Iowa, Iowa City, Iowa, USA.
authors.forename: Chandan
authors.initials: C
authors.lastname: Reddy
authors.forename: Aditya V
authors.initials: AV
authors.lastname: Ingalhalikar
authors.forename: Scott
authors.initials: S
authors.lastname: Channon
authors.forename: Tae-Hong
authors.initials: TH
authors.lastname: Lim
authors.forename: James
authors.initials: J
authors.lastname: Torner
authors.forename: Patrick W
authors.initials: PW
authors.lastname: Hitchon
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001268:Atlanto-Axial Joint / Q000503:physiopathology* / Q000601:surgery*; D001863:Bone Screws; D002102:Cadaver; D002574:Cervical Vertebrae / Q000601:surgery*; D004867:Equipment Design; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology*; D013123:Spinal Fusion / Q000295:instrumentation*; D016474:Weight-Bearing / Q000502:physiology