title: Biomechanical comparison of single- and dual-lead pedicle screws in cadaveric spine.
abstract: OBJECTIVE
  The pedicle screw (PS) is the cornerstone of spinal instrumentation, and its failure often entails additional surgery. Screw pullout is one of the most common reasons for screw failure, particularly in the elderly population. In this study the authors undertook a biomechanical comparison of the maximum pullout force (MPF) required for single- and dual-lead PSs in cadaver vertebrae.
  
  
  METHODS
  Radiographs of 40 cadaveric vertebrae (T11-L5) were obtained, and bone mineral density (BMD) was measured in the lateral plane using dual-x-ray absorptiometry with a bone densitometer. One screw of each design was implanted for side-by-side comparison. Vertebrae were potted and mounted on an MTS test frame for accurate measurement of MPF. A total of 80 PSs were tested, 40 each of single- and dual-lead design types.
  
  
  RESULTS
  The average MPF for dual-lead screws (533.89 +/- 285.7 N) was comparable to that of single-lead screws (524.90 +/- 311.6 N) (p = 0.3733). The BMD had a significant correlation with MPF for both dual-lead (r = 0.56413, p < 0.0001) and single-lead screws (r = 0.56327, p < 0.0001).
  
  
  CONCLUSIONS
  Barring the effect of BMD, this in vitro biomechanical test showed no significant difference in MPF between single- and dual-lead PSs. Dual-lead PSs can be used to achieve a faster insertion time, without compromising pullout force.
authors.affiliation: Department of Neurosurgery, University of Iowa, Iowa, USA.
authors.forename: Arun T
authors.initials: AT
authors.lastname: Jacob
authors.forename: Aditya V
authors.initials: AV
authors.lastname: Ingalhalikar
authors.forename: John H
authors.initials: JH
authors.lastname: Morgan
authors.forename: Scott
authors.initials: S
authors.lastname: Channon
authors.forename: Tae-Hong
authors.initials: TH
authors.lastname: Lim
authors.forename: James C
authors.initials: JC
authors.lastname: Torner
authors.forename: Patrick W
authors.initials: PW
authors.lastname: Hitchon
mesh_terms: D015502:Absorptiometry, Photon; D000497:Alloys / Q000737:chemistry; D001696:Biomechanical Phenomena; D015519:Bone Density / Q000502:physiology; D001863:Bone Screws; D002102:Cadaver; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008422:Materials Testing; D013123:Spinal Fusion / Q000295:instrumentation*; D013314:Stress, Mechanical; D013499:Surface Properties; D013904:Thoracic Vertebrae / Q000601:surgery*; D014025:Titanium / Q000737:chemistry
chemical_list: D000497:Alloys; C031462:titanium alloy (TiAl6V4); D014025:Titanium