title: Do facet screws provide the required stability in lumbar fixation? A biomechanical comparison of the Boucher technique and pedicular fixation in primary and circumferential fusions.
abstract: BACKGROUND
  Transfacet pedicle screws are scarcely used in primary posterior fixation, and have limited use unilaterally or with existing anterior instrumentation. Nevertheless, the incomplete literature suggests equivalent or better performance of ipsilateral, bilateral, facet screws compared to bilateral pedicle screws.
  
  
  METHODS
  Two groups of seven human cadaver spines (L3-S1) were tested under pure moments of 6 Nm. Each specimen was tested in a primary and circumferential fixation (Spacer, Spacer+Plate) environment. Both transfacet and bilateral pedicle screws were used as posterior fixation, in separate groups. Motion was obtained at L4-L5 for single-level constructs in flexion-extension, lateral bending and axial rotation modes.
  
  
  RESULTS
  In primary fixation, both transfacet and bilateral pedicle screws reduced motion below intact levels. Statistically, the level of circumferential fixation (anterior, posterior, or both) proved to be more influential than the type of posterior fixation. Incorporating a spacer and plate with pedicle screws provided a greater relative gain in stability than with facet screws. The interpretation is explained through a model describing the location of fixation with respect to the center-of-rotation of the vertebral bodies. In lateral bending and axial rotation, bilateral pedicle screw constructs were stiffer than transfacet pedicle screw constructs as a trend.
  
  
  CONCLUSIONS
  Transfacet pedicle screws provided similar fixation to bilateral pedicle screws in primary and circumferential fixations during flexion-extension. In the other modes, transfacet screw rigidity is, on average, less than bilateral pedicle screws when used alone, but with the addition of other anterior instrumentation the differences are minimized. Therefore, facet screws are warranted based on the surgical effect desired, and in the presence of additional anterior fixation.
authors.affiliation: Panorama Orthopedics & Spine, Golden, CO 80401-9522, USA. aagarwala@panoramaortho.com
authors.forename: Amit
authors.initials: A
authors.lastname: Agarwala
authors.forename: Brandon
authors.initials: B
authors.lastname: Bucklen
authors.forename: Aditya
authors.initials: A
authors.lastname: Muzumdar
authors.forename: Mark
authors.initials: M
authors.lastname: Moldavsky
authors.forename: Saif
authors.initials: S
authors.lastname: Khalil
mesh_terms: D001863:Bone Screws; D002102:Cadaver; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology* / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000503:physiopathology* / Q000601:surgery*; D016059:Range of Motion, Articular; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D016896:Treatment Outcome; D021801:Zygapophyseal Joint / Q000503:physiopathology* / Q000601:surgery