title: Biomechanical comparison of an interspinous fusion device and bilateral pedicle screw system as additional fixation for lateral lumbar interbody fusion.
abstract: BACKGROUND
  This investigation compares an interspinous fusion device with posterior pedicle screw system in a lateral lumbar interbody lumbar fusion.
  
  
  METHODS
  We biomechanically tested six cadaveric lumbar segments (L1-L2) under an axial preload of 50N and torque of 5Nm in flexion-extension, lateral bending and axial rotation directions. We quantified range of motion, neutral zone/elastic zone stiffness in the following conditions: intact, lateral discectomy, lateral cage, cage with interspinous fusion, and cage with pedicle screws.
  
  
  RESULTS
  A complete lateral discectomy and annulectomy increased motion in all directions compared to all other conditions. The lateral cage reduced motion in lateral bending and flexion/extension with respect to the intact and discectomy conditions, but had minimal effect on extension stiffness. Posterior instrumentation reduced motion, excluding interspinous augmentation in axial rotation with respect to the cage condition. Interspinous fusion significantly increased flexion and extension stiffness, while pedicle screws increased flexion/extension and lateral bending stiffness, with respect to the cage condition. Both posterior augmentations performed equivalently throughout the tests except in lateral bending stiffness where pedicle screws were stiffer in the neutral zone.
  
  
  CONCLUSIONS
  A lateral discectomy and annulectomy generates immediate instability. Stand-alone lateral cages restore a limited amount of immediate stability, but posterior supplemental fixation increases stability. Both augmentations are similar in a single level lateral fusion in-vitro model, but pedicle screws are more equipped for coronal stability. An interspinous fusion is a less invasive alternative than pedicle screws and is potentially a conservative option for various interbody cage scenarios.
authors.affiliation: H. Lee Moffitt Cancer Center & Research Institute, NeuroOncology Program and Department of Neurosurgery and Orthopedics, University of South Florida, College of Medicine, Tampa, FL 33612, USA; Dept of Mechanical Engineering, University of South Florida, Tampa, FL 33620, USA. Electronic address: James.Doulgeris@moffitt.org.
authors.forename: James J
authors.initials: JJ
authors.lastname: Doulgeris
authors.affiliation: H. Lee Moffitt Cancer Center & Research Institute, NeuroOncology Program and Department of Neurosurgery and Orthopedics, University of South Florida, College of Medicine, Tampa, FL 33612, USA.
authors.forename: Kamran
authors.initials: K
authors.lastname: Aghayev
authors.affiliation: H. Lee Moffitt Cancer Center & Research Institute, NeuroOncology Program and Department of Neurosurgery and Orthopedics, University of South Florida, College of Medicine, Tampa, FL 33612, USA.
authors.forename: Sabrina A
authors.initials: SA
authors.lastname: Gonzalez-Blohm
authors.affiliation: Dept of Chemical & Biomedical Engineering, University of South Florida, Tampa, FL 33620, USA.
authors.forename: William E
authors.initials: WE
authors.lastname: Lee
authors.affiliation: H. Lee Moffitt Cancer Center & Research Institute, NeuroOncology Program and Department of Neurosurgery and Orthopedics, University of South Florida, College of Medicine, Tampa, FL 33612, USA.
authors.forename: Frank D
authors.initials: FD
authors.lastname: Vrionis
mesh_terms: D001696:Biomechanical Phenomena; D002102:Cadaver; D017586:Diskectomy / Q000295:instrumentation; D005260:Female; D006801:Humans; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000502:physiology* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D065289:Pedicle Screws; D016059:Range of Motion, Articular; D012399:Rotation; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods*; D019415:Torque
keywords: Biomechanics; Lumbar spine; Posterior fixation; Range of motion; Stiffness