title: Biomechanical advantage of C1 pedicle screws over C1 lateral mass screws: a cadaveric study.
abstract: OBJECTIVE
  The established technique for posterior C1 screw placement is via the lateral mass. Use of C1 monocortical pedicle screws is an emerging technique which utilizes the bone of the posterior arch while avoiding the paravertebral venous plexus and the C2 nerve root. This study compared the relative biomechanical fixation strengths of C1 pedicle screws with C1 lateral mass screws.
  
  
  METHODS
  Nine human C1 vertebrae were instrumented with one lateral mass screw and one pedicle screw. The specimens were subjected to sinusoidal, cyclic (0.5 Hz) fatigue loading. Peak compressive and tensile forces started from ±25 N and constantly increased by 0.05 N every cycle. Testing was stopped at 5 mm displacement. Cycles to failure, displacement, and initial and end stiffness were measured. Finally, CT scans were taken and the removal torque measured.
  
  
  RESULTS
  The pedicle screw technique consistently and significantly outperformed the lateral mass technique in cycles to failure (1,083 ± 166 vs. 689 ± 240 cycles), initial stiffness (24.6 ± 3.9 vs. 19.9 ± 3.2 N/mm), end stiffness (16.6 ± 2.7 vs. 11.6 ± 3.6 N/mm) and removal torque (0.70 ± 0.78 vs. 0.13 ± 0.09 N m). Only 33 % of pedicle screws were loose after testing compared to 100 % of lateral mass screws.
  
  
  CONCLUSIONS
  C1 pedicle screws were able to withstand higher toggle forces than lateral mass screws while maintaining a higher stiffness throughout and after testing. From a biomechanical point of view, the clinical use of pedicle screws in C1 is a promising alternative to lateral mass screws.
authors.affiliation: Department of Trauma, Hand and Reconstructive Surgery, University Medical Center Hamburg-Eppendorf, Martinistraße 52, 20246, Hamburg, Germany, f.fensky@uke.de.
authors.forename: Florian
authors.initials: F
authors.lastname: Fensky
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Kueny
authors.forename: Kay
authors.initials: K
authors.lastname: Sellenschloh
authors.forename: Klaus
authors.initials: K
authors.lastname: Püschel
authors.forename: Michael M
authors.initials: MM
authors.lastname: Morlock
authors.forename: Johannes M
authors.initials: JM
authors.lastname: Rueger
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lehmann
authors.forename: Gerd
authors.initials: G
authors.lastname: Huber
authors.forename: Nils
authors.initials: N
authors.lastname: Hansen-Algenstaedt
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001863:Bone Screws; D001270:Cervical Atlas / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D065289:Pedicle Screws; D013718:Tensile Strength; D014057:Tomography, X-Ray Computed; D019415:Torque; D016474:Weight-Bearing