title: Primary stiffness of a modified transforaminal lumbar interbody fusion cage with integrated screw fixation: cadaveric biomechanical study.
abstract: METHODS
  In vitro biomechanical study using human fresh-frozen vertebrae.
  
  
  OBJECTIVE
  To investigate the influence of the additional screw fixation on the stability of a noncommercially available prototype transforaminal lumbar interbody fusion (TLIF) cage, when used as a stand-alone fusion device and in combination with pedicle screws (PSs).
  
  
  BACKGROUND
  Generally interbody fusion cages are supplemented by additional fixation devices such as PS. However, such posterior instrumented techniques are associated with additional soft-tissue trauma and potentially increased complication rate. To limit such drawbacks, a conventional posterior TLIF cage was modified to allow supplemental screw fixation to the adjacent vertebral bodies, to increase initial stiffness and possibly allow as a stand-alone posterior interbody cage.
  
  
  METHODS
  Six monosegmental lumbar spine segments were loaded in a spine simulator with pure bending moments of 7.5 Nm in lateral bending, flexion/extension, and axial rotation. The following paradigms were tested: intact spines; a destabilized spine (i.e., after discectomy and unilateral facetectomy); and the modified TLIF cage with (i.e., fixed TLIF cage) and without (i.e., TLIF cage) integrated screw fixation as a stand-alone model and with and without additional posterior fixation with bilateral PS. The range of motion (RoM) was recorded by a 3-dimensional motion analysis system.
  
  
  RESULTS
  The TLIF cage with integrated screw fixation had minimal additional stabilizing effect in all motion planes with or without supplemental PS fixation. Moreover, compared with the intact spines, the stand-alone TLIF cage with and without integrated screw fixation did not reduce the RoM in any of the 3 motion planes. Comparison of the TLIF cage with integrated screw fixation to the TLIF cage supplemented with PS showed a significantly greater RoM in all testing conditions (P < 0.05).
  
  
  CONCLUSIONS
  In several testing paradigms, the prototype TLIF cage with the integrated screw fixation had limited effect in reducing RoM and providing stability. The PS was the main contributor in reducing RoM in the destabilized spine and remains the current "gold standard" in posterolateral spinal fixation.
  
  
  METHODS
  N/A.
authors.affiliation: *Department of Trauma Surgery, Medical University Innsbruck, Austria †Department of Neurosurgery, Greater Manchester Neurosciences Centre, Salford Royal Foundation Trust, Manchester, United Kingdom; and ‡Institute of Inflammation and Repair, Manchester Academic Health Sciences Centre, University of Manchester, Manchester, United Kingdom.
authors.forename: Alexander
authors.initials: A
authors.lastname: Keiler
authors.forename: Werner
authors.initials: W
authors.lastname: Schmoelz
authors.forename: Stefanie
authors.initials: S
authors.lastname: Erhart
authors.forename: Kanna
authors.initials: K
authors.lastname: Gnanalingham
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws; D002102:Cadaver; D017586:Diskectomy / Q000379:methods; D006801:Humans; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000601:surgery*; D008161:Lumbosacral Region / Q000601:surgery*; D016059:Range of Motion, Articular / Q000502:physiology; D013123:Spinal Fusion / Q000379:methods