title: Biomechanical impact of C2 pedicle screw length in an atlantoaxial fusion construct.
abstract: BACKGROUND
  Posterior, atlantoaxial (AA) fusions of the cervical spine may include either standard (26 mm) or short (16 mm) C2 pedicle screws. This manuscript focused on an in vitro biomechanical comparison of standard versus short C2 pedicle screws to perform posterior C1-C2 AA fusions.
  
  
  METHODS
  Twelve human cadaveric spines underwent C1 lateral mass screw and standard C2 pedicle screw (n = 6) versus short C2 pedicle screw (n = 6) fixation. Six additional controls were not instrumented. The peak torque, peak rotational interval, and peak stiffness of the constructs were analyzed to failure levels.
  
  
  RESULTS
  The peak torque to construct failure was not statistically significantly different among the control spine (12.2 Nm), short pedicle fixation (15.5 Nm), or the standard pedicle fixation (11.6 Nm), P = 0.79. While the angle at the peak rotation statistically significantly differed between the control specimens (47.7° of relative motion) and the overall instrumented specimens (P < 0.001), the 20.7° of relative rotation in the short C2 pedicle screw specimens was not statistically significantly higher than the 13.7° of relative rotation in the standard C2 pedicle screw specimens (P = 0.39). Similarly, although the average stiffness was statistically significantly lower in control group (0.026 Nm/degree) versus the overall instrumented specimens (P = 0.001), the standard C2 pedicle screws (2.54 Nm/degree) did not differ from the short C2 pedicle screws.
  
  
  CONCLUSIONS
  Both standard and short C2 pedicle screws allow for equally rigid fixation of C1 lateral mass-C2 AA fusions. Usage of a short C2 pedicle screw may be an acceptable method of stabilization in carefully selected patient populations.
authors.affiliation: Johns Hopkins University School of Medicine, Medical Scientist Training Program, Baltimore, Maryland, USA ; Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA ; Johns Hopkins Spinal Column Biomechanics and Surgical Outcomes Laboratory, Baltimore, Maryland, USA.
authors.forename: Risheng
authors.initials: R
authors.lastname: Xu
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA ; Johns Hopkins Spinal Column Biomechanics and Surgical Outcomes Laboratory, Baltimore, Maryland, USA.
authors.forename: Mohamad
authors.initials: M
authors.lastname: Bydon
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA ; Johns Hopkins Spinal Column Biomechanics and Surgical Outcomes Laboratory, Baltimore, Maryland, USA.
authors.forename: Mohamad
authors.initials: M
authors.lastname: Macki
authors.affiliation: Department of Orthopedic Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Belkoff
authors.affiliation: Department of Orthopedic Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Evan R
authors.initials: ER
authors.lastname: Langdale
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA ; Johns Hopkins Spinal Column Biomechanics and Surgical Outcomes Laboratory, Baltimore, Maryland, USA.
authors.forename: Kelly
authors.initials: K
authors.lastname: McGovern
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA ; Johns Hopkins Spinal Column Biomechanics and Surgical Outcomes Laboratory, Baltimore, Maryland, USA.
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Wolinsky
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA ; Johns Hopkins Spinal Column Biomechanics and Surgical Outcomes Laboratory, Baltimore, Maryland, USA.
authors.forename: Ziya L
authors.initials: ZL
authors.lastname: Gokalsan
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA ; Johns Hopkins Spinal Column Biomechanics and Surgical Outcomes Laboratory, Baltimore, Maryland, USA.
authors.forename: Ali
authors.initials: A
authors.lastname: Bydon
keywords: Atlantoaxial; C1; C2; biomechanics; pars; pedicle