title: Biomechanical rigidity of cadaveric cervical spine with posterior versus combined posterior and anterior instrumentation.
abstract: OBJECTIVE
  In patients with cervical stenosis with myelopathy, posterior instrumentation following cervical laminectomy has been shown to reduce the incidence of postoperative instability and kyphosis. However, the indications for posterior plus anterior instrumentation are not always obvious, and using both posterior and anterior instrumentation routinely is unnecessary and excessive. This study examines the rigidity of the intact isolated cadaveric cervical spine, after C4-6 laminectomy, with posterior lateral mass instrumentation, and following posterior plus anterior instrumentation.
  
  
  METHODS
  Ten fresh-frozen human cadaveric cervical spines from C-1 to T-2 were potted in the neutral position, and retroreflective markers were placed on C-3 and C-7. Specimens were mounted on a biomechanical testing frame, and angular rotations of C-3 relative to C-7 were measured. Pure moments of 0, 0.3, 0.6, 0.9, and 1.2 Nm were applied at C-2 in all 3 planes. Each specimen was load tested as follows: 1) in the intact state; 2) after C4-6 laminectomy; 3) with C3-7 lateral mass instrumentation; and 4) with C3-7 posterior plus anterior instrumentation.
  
  
  RESULTS
  Laminectomy was not associated with a significant increase in motion compared with the intact state with any load or in any direction. Instrumentation was associated with reduction in motion in all directions, and there was no significant difference in posterior versus combined posterior and anterior instrumentation.
  
  
  CONCLUSIONS
  Rigidity imparted to the cervical spine by a 5-level posterior lateral mass fixation is not augmented by anterior instrumentation.
authors.affiliation: Department of Neurosurgery, University of Iowa College of Medicine, Iowa City, Iowa, USA.
authors.forename: Nader S
authors.initials: NS
authors.lastname: Dahdaleh
authors.forename: Satoshi
authors.initials: S
authors.lastname: Nakamura
authors.forename: James C
authors.initials: JC
authors.lastname: Torner
authors.forename: Tae-Hong
authors.initials: TH
authors.lastname: Lim
authors.forename: Patrick W
authors.initials: PW
authors.lastname: Hitchon
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001863:Bone Screws; D002102:Cadaver; D002574:Cervical Vertebrae / Q000503:physiopathology* / Q000601:surgery*; D005260:Female; D006801:Humans; D016268:Internal Fixators; D007796:Laminectomy; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*; D016474:Weight-Bearing / Q000502:physiology