title: Biomechanical Analysis of a Pedicle Screw-Rod System with a Novel Cross-Link Configuration.
abstract: METHODS
  The strength effects of a pedicle screw-rod system supplemented with a novel cross-link configuration were biomechanically evaluated in porcine spines.
  
  
  OBJECTIVE
  To assess the biomechanical differences between a conventional cross-link pedicle screw-rod system versus a novel cross-link instrumentation, and to determine the effect of the cross-links.
  
  
  BACKGROUND
  Transverse cross-link systems affect torsional rigidity, but are thought to have little impact on the sagittal motion of spinal constructs. We tested the strength effects in pullout and flexion-compression tests of novel cross-link pedicle screw constructs using porcine thoracic and lumbar vertebrae.
  
  
  METHODS
  Five matched thoracic and lumbar vertebral segments from 15 porcine spines were instrumented with 5.0-mm pedicle screws, which were then connected with 6.0-mm rods after partial corpectomy in the middle vertebral body. The forces required for construct failure in pullout and flexion-compression tests were examined in a randomized manner for three different cross-link configurations: un-cross-link control, conventional cross-link, and cross-link passing through the base of the spinous process. Statistical comparisons of strength data were analyzed using Student'st-tests.
  
  
  RESULTS
  The spinous process group required a significantly greater pullout force for construct failure than the control group (p=0.036). No difference was found between the control and cross-link groups, or the cross-link and spinous process groups in pullout testing. In flexion-compression testing, the spinous processes group required significantly greater forces for construct failure than the control and cross-link groups (p<0.001 andp=0.003, respectively). However, there was no difference between the control and cross-link groups.
  
  
  CONCLUSIONS
  A novel cross-link configuration that features cross-link devices passing through the base of the spinous processes increased the mechanical resistance in pullout and flexion-compression testing compared to un-cross-link constructs. This configuration provided more resistance to middle-column damage under flexion-compression testing than conventional cross-link configuration.
authors.affiliation: Department of Neurosurgery, Inazawa Municipal Hospital, Inazawa, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Nakajima
authors.affiliation: Department of Neurosurgery, Inazawa Municipal Hospital, Inazawa, Japan.
authors.forename: Masahito
authors.initials: M
authors.lastname: Hara
authors.affiliation: Department of Neurosurgery, Inazawa Municipal Hospital, Inazawa, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Umebayashi
authors.affiliation: Department of Neurosurgery, Nagoya University Graduate School of Medicine, Nagoya, Japan.
authors.forename: Shoichi
authors.initials: S
authors.lastname: Haimoto
authors.affiliation: Department of Neurosurgery, Inazawa Municipal Hospital, Inazawa, Japan.
authors.forename: Yu
authors.initials: Y
authors.lastname: Yamamoto
authors.affiliation: Department of Neurosurgery, Nagoya University Graduate School of Medicine, Nagoya, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Nishimura
authors.affiliation: Department of Neurosurgery, Nagoya University Graduate School of Medicine, Nagoya, Japan.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Wakabayashi
keywords: Biomechanics; Cross-link; Pedicle screw-rod; Spinal fusion; Spinous process