title: Fixation strength of unicortical versus bicortical C1-C2 transarticular screws.
abstract: BACKGROUND
  The internal carotid artery and hypoglossal nerve lie over the anterior aspect of the lateral mass of the atlas and are at risk from bicortical C1-C2 transarticular screws. This has led to the recommendation for unicortical screws if the neurovascular structures are in close proximity to the proposed exit point. No data are available on strength of unicortical versus bicortical C1-C2 transarticular screws.
  
  
  OBJECTIVE
  To compare the biomechanical pullout strength of unicortical versus bicortical C1-C2 transarticular screws in a cadaveric model.
  
  
  METHODS
  Biomechanical study.
  
  
  METHODS
  Fifteen cervical spine specimens underwent axial pullout testing. A unicortical C1-C2 transarticular screw was placed on one side with a contralateral bicortical screw. Data were analyzed to reveal any significant differences in strength.
  
  
  RESULTS
  Mean pullout strength for the bicortical C1-C2 transarticular screws was 1,048.8 (+/-360.1) N versus 939.2 (+/-360.6) for unicortical screws (p=.22). There was no significant difference in the pullout strength of unicortical and bicortical screws.
  
  
  CONCLUSIONS
  In cases with satisfactory bone quality, it appears reasonable to use unicortical screws to avoid the risk of neurovascular injury from penetrating the anterior cortex of C1.
authors.affiliation: Department of Orthopedic Surgery, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905, USA.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Cyr
authors.forename: Bradford L
authors.initials: BL
authors.lastname: Currier
authors.forename: Jason C
authors.initials: JC
authors.lastname: Eck
authors.forename: Andrew
authors.initials: A
authors.lastname: Foy
authors.forename: Qingshan
authors.initials: Q
authors.lastname: Chen
authors.forename: Dirk R
authors.initials: DR
authors.lastname: Larson
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Yaszemski
authors.forename: Kai-Nan
authors.initials: KN
authors.lastname: An
mesh_terms: D001863:Bone Screws; D002102:Cadaver; D002574:Cervical Vertebrae / Q000601:surgery*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D008422:Materials Testing; D033081:Shear Strength; D013123:Spinal Fusion / Q000295:instrumentation*; D013314:Stress, Mechanical