title: Comparison between single-screw and triangulated, double-screw fixation in anterior spine surgery. A biomechanical test.
abstract: METHODS
  The advantage to fixation strength of triangulated, double-screw fixation compared with that of single-screw instrumentation in anterior spine surgery was evaluated by in vitro testing.
  
  
  OBJECTIVE
  To compare the fixation strength of single-screw instrumentation with ventral derotation spondylodesis screws with the fixation strength of triangulated, double-screw instrumentation with Cotrel-Dubousset-Hopf screws. Resistance against pull-out load and against load perpendicular to the axis of the screws was evaluated. To avoid the bias caused by different screw design, the pull-out strength of single screws of both devices was compared first.
  
  
  BACKGROUND
  To the authors' knowledge, no study comparing anterior single with triangulated screws has been published.
  
  
  METHODS
  A pull-out test was performed when one vertebra in each spine specimen was instrumented with a ventral derotation spondylodesis screw, one with an isolated Cotrel-Dubousset-Hopf screws, and one with two triangulated, Cotrel-Dubousset-Hopf screws linked by a Cotrel-Dubousset-Hopf block. Load perpendicular to the axis of the screw was applied on the bone-device interface after instrumentation of further specimens with ventral derotation spondylodesis and triangulated, Cotrel-Dubousset-Hopf devices.
  
  
  RESULTS
  Use of isolated Cotrel-Dubousset-Hopf screws compared with ventral derotation spondylodesis screws showed no significant differences in pull-out strength. The use of triangulated, double-screw fixation with Cotrel-Dubousset-Hopf screws led to a significant 79% increase in resistance against pull-out and a 73% increase in resistance against load perpendicular to the screw axis compared with the resistance produced using ventral derotation spondylodesis single-screw instrumentation.
  
  
  CONCLUSIONS
  In anterior surgery, fixation of the vertebra-device interface can be improved considerably by application of two triangulated screws.
authors.affiliation: Department of Orthopaedic Surgery, University of Innsbruck, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Ogon
authors.forename: C
authors.initials: C
authors.lastname: Haid
authors.forename: M
authors.initials: M
authors.lastname: Krismer
authors.forename: W
authors.initials: W
authors.lastname: Sterzinger
authors.forename: R
authors.initials: R
authors.lastname: Bauer
mesh_terms: D000368:Aged; D001863:Bone Screws; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008422:Materials Testing; D008875:Middle Aged; D011859:Radiography; D013123:Spinal Fusion / Q000295:instrumentation*; D016474:Weight-Bearing