title: Biomechanical effect of the C2 laminar decortication on the stability of C2 intralaminar screw construct and biomechanical comparison of C2 intralaminar screw and C2 pars screw.
abstract: BACKGROUND
  There have been no reports of biomechanical stability of C1-2 constructs after decortication of the C2 lamina. In addition, few studies have compared the stability of C2 laminar screw and pars screw constructs.
  
  
  OBJECTIVE
  To compare the biomechanical stability of 3 different C1-2 construct conditions (C2 pars screw, C2 intralaminar screw, C2 intralaminar construct with C2 laminar decortication).
  
  
  METHODS
  Fourteen fresh-frozen cadaveric cervical specimens (C1-3) were used. In 7 specimens, pure moments of 1.5 Nm were applied in flexion/extension, lateral bending, and axial rotation. Each specimen was tested in the normal state, in the destabilized state (after odontoidectomy and resection of transverse atlantal ligament), and after application of constructs. After kinematic study, these 7 specimens underwent axial pullout strength testing of pars screw and 50% decorticated C2 intralaminar screws. In another 7 specimens, insertion torque and pullout strength were measured to compare the pars screw and intact C2 intralaminar screw.
  
  
  RESULTS
  : There were no statistically significant differences between the intact C2 intralaminar and 50% decorticated C2 intralaminar screw constructs in terms of range-of-motion limitations. The C2 pars screw construct was significantly superior to the C2 laminar screw construct in lateral bending (P < .01) and axial rotation (P < .01) and equivalent to the C2 laminar screw construct in flexion/extension (P = .42). There was no significant pullout strength difference between the 3 kinds of C2 screw.
  
  
  CONCLUSIONS
  The C1 lateral mass-C2 pars screws construct was stronger than the C1 lateral mass-C2 intralaminar screw construct. Decortication of C2 laminar (up to 50%) did not affect the immediate stability of the C1-2 construct.
authors.affiliation: Department of Neurosurgery, Catholic University of Korea, St Vincent's Hospital, Suwon, South Korea.
authors.forename: Jae Taek
authors.initials: JT
authors.lastname: Hong
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Takigawa
authors.forename: Ranjith
authors.initials: R
authors.lastname: Udayakunmar
authors.forename: Hun Kyu
authors.initials: HK
authors.lastname: Shin
authors.forename: Peter
authors.initials: P
authors.lastname: Simon
authors.forename: Alejandro A
authors.initials: AA
authors.lastname: Espinoza Orías
authors.forename: Nozomu
authors.initials: N
authors.lastname: Inoue
authors.forename: Howard S
authors.initials: HS
authors.lastname: An
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws; D002102:Cadaver; D002574:Cervical Vertebrae / Q000601:surgery*; D006801:Humans; D016059:Range of Motion, Articular; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods*