title: In-vitro comparison of the pullout strength of 3 different thoracic screw fixation techniques.
abstract: BACKGROUND
  Dvorak et al in 1993 and Husted et al in 2003 reported 2 different screw fixation techniques at the thoracic spine as alternatives to transpedicular screws. So far, there is no investigation comparing the pullout stability of all 3 possible screw fixation techniques.
  
  
  OBJECTIVE
  To evaluate the stability of possible alternatives for transpedicular screw fixation.
  
  
  METHODS
  A biomechanical human cadaver investigation of the transpedicular and 2 different extrapedicular techniques was performed in the form of a comparative pullout test.
  
  
  METHODS
  Eighteen human vertebral bodies from Th7 to Th9 were harvested from 6 donors, dissected from surrounding tissue, and matched to 3 different fixation groups. As alternatives for transpedicular screw fixation, an extrapedicular supratransverse screw insertion from posterolateral and a tricortical screw fixation technique, penetrating the transverse process and reentering the vertebral body at the pedicle base were evaluated biomechanically. A unilateral screw fixation was performed in one of the described techniques. Axial pullout strength was measured using a Zwick Z50 servoelectric testing machine.
  
  
  RESULTS
  The average pullout strength of the pedicle screws was 400 N, whereas the supratransverse and the pertransverse screw fixation resisted 370 N pullout force on average. There was neither a statistic significant difference between the pullout forces of the 3 groups nor a significant correlation of pullout strength and bone mineral density measured by quantitative computed tomography.
  
  
  CONCLUSIONS
  In-vitro pullout resistance of thoracic screw fixation does not differ significantly in intrapedicular and extrapedicular insertion techniques.
authors.affiliation: Department for Orthopaedic and Spine Surgery, Klinikum Mutterhaus der Borromäerinnen, Trier, Germany. sebastian.fuerderer@gmx.de
authors.forename: Sebastian
authors.initials: S
authors.lastname: Fürderer
authors.forename: Niklas
authors.initials: N
authors.lastname: Scholten
authors.forename: Oliver
authors.initials: O
authors.lastname: Coenen
authors.forename: Juergen
authors.initials: J
authors.lastname: Koebke
authors.forename: Peer
authors.initials: P
authors.lastname: Eysel
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001863:Bone Screws; D006801:Humans; D016268:Internal Fixators; D008422:Materials Testing; D008875:Middle Aged; D018709:Statistics, Nonparametric; D013904:Thoracic Vertebrae / Q000601:surgery*