title: Comparison of revision strategies for failed C2-posterior cervical pedicle screws: a biomechanical study.
abstract: OBJECTIVE
  With increasing usage within challenging biomechanical constructs, failures of C2 posterior cervical pedicle screws (C2-pCPSs) will occur. The purpose of the study was therefore to investigate the biomechanical characteristics of two revision techniques after the failure of C2-pCPSs.
  
  
  METHODS
  Twelve human C2 vertebrae were tested in vitro in a biomechanical study to compare two strategies for revision screws after failure of C2-pCPSs. C2 pedicles were instrumented using unicortical 3.5-mm CPS bilaterally (Synapse/Synthes, Switzerland). Insertion accuracy was verified by fluoroscopy. C2 vertebrae were potted and fixed in an electromechanical testing machine with the screw axis coaxial to the pullout direction. Pullout testing was conducted with load and displacement data taken continuously. The peak load to failure was measured in newtons (N) and is reported as the pullout resistance (POR). After pullout, two revision strategies were tested in each vertebra. In Group-1, revision was performed with 4.0-mm C2-pCPSs. In Group-2, revision was performed with C2-pedicle bone-plastic combined with the use of a 4-mm C2-pCPSs. For the statistical analysis, the POR between screws was compared using absolute values (N) and the POR of the revision techniques normalized to that of the primary procedures (%).
  
  
  RESULTS
  The POR of primary 3.5-mm CPSs was 1,140.5 ± 539.6 N for Group-1 and 1,007.7 ± 362.5 N for Group-2; the difference was not significant. In the revision setting, the POR in Group-1 was 705.8 ± 449.1 N, representing a reduction of 38.1 ± 32.9 % compared with that of primary screw fixation. For Group-2, the POR was 875.3 ± 367.9 N, representing a reduction of 13.1 ± 23.4 %. A statistical analysis showed a significantly higher POR for Group-2 compared with Group-1 (p = 0.02). Although the statistics showed a significantly reduced POR for both revision strategies compared with primary fixation (p < 0.001/p = 0.001), the loss of POR (in %) in Group-1 was significantly higher compared with the loss in Group-2 (p = 0.04).
  
  
  CONCLUSIONS
  Using a larger-diameter screw combined with the application of a pedicle bone-plastic, the POR can be significantly increased compared with the use of only an increased screw diameter.
authors.affiliation: Department for Traumatology and Sports Injuries, Paracelsus Medical University, Muellner Hauptstrasse 48, 5020 Salzburg, Austria. mi.mayer@salk.at
authors.forename: Michael
authors.initials: M
authors.lastname: Mayer
authors.forename: Juliane
authors.initials: J
authors.lastname: Zenner
authors.forename: Robert
authors.initials: R
authors.lastname: Bogner
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Hitzl
authors.forename: Markus
authors.initials: M
authors.lastname: Figl
authors.forename: Arvind
authors.initials: A
authors.lastname: von Keudell
authors.forename: Daniel
authors.initials: D
authors.lastname: Stephan
authors.forename: Rainer
authors.initials: R
authors.lastname: Penzkofer
authors.forename: Peter
authors.initials: P
authors.lastname: Augat
authors.forename: Gundobert
authors.initials: G
authors.lastname: Korn
authors.forename: Herbert
authors.initials: H
authors.lastname: Resch
authors.forename: Heiko
authors.initials: H
authors.lastname: Koller
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001863:Bone Screws; D002102:Cadaver; D002574:Cervical Vertebrae / Q000601:surgery*; D006801:Humans; D008297:Male; D008422:Materials Testing; D012086:Reoperation / Q000295:instrumentation / Q000379:methods; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*