title: Triangular osteosynthesis and iliosacral screw fixation for unstable sacral fractures: a cadaveric and biomechanical evaluation under cyclic loads.
abstract: OBJECTIVE
  To conduct a biomechanical comparison of a new triangular osteosynthesis and the standard iliosacral screw osteosynthesis for unstable transforaminal sacral fractures in the immediate postoperative situation as well as in the early postoperative weight-bearing period.
  
  
  METHODS
  Twelve preserved human cadaveric lumbopelvic specimens were cyclicly tested in a single-limb-stance model. A transforaminal sacral fracture combined with ipsilateral superior and inferior pubic rami fractures were created and stabilized. Loads simulating muscle forces and body weight were applied. Fracture site displacement in three dimensions was evaluated using an electromagnetic motion sensor system.
  
  
  METHODS
  Specimens were randomly assigned to either an iliosacral and superior pubic ramus screw fixation or to a triangular osteosynthesis consisting of lumbopelvic stabilization (between L5 pedicle and posterior ilium) combined with iliosacral and superior pubic ramus screw fixation.
  
  
  METHODS
  Peak loaded displacement at the fracture site was measured for assessment of initial stability. Macroscopic fracture behavior through 10,000 cycles of loading, simulating the early postoperative weight-bearing period, was classified into type 1 with minimal motion at the fracture site, type 2 with complete displacement of the inferior pubic ramus, or type 3 with catastrophic failure.
  
  
  RESULTS
  The triangular osteosynthesis had a statistically significantly smaller displacement under initial peak loads (mean +/- standard deviation [SD], 0.163 +/- 0.073 cm) and therefore greater initial stability than specimens with the standard iliosacral screw fixation (mean +/- SD, 0.611 +/- 0.453 cm) ( = 0.0104), independent of specimen age or sex. All specimens with the triangular osteosynthesis demonstrated type 1 fracture behavior, whereas iliosacral screw fixation resulted in one type 1, two type 2, and three type 3 fracture behaviors before or at 10,000 cycles of loading.
  
  
  CONCLUSIONS
  Triangular osteosynthesis for unstable transforaminal sacral fractures provides significantly greater stability than iliosacral screw fixation under in vitro cyclic loading conditions. In vitro cyclic loading, as a limited simulation of early stages of patient mobilization in the postoperative period, allows for a time-dependent evaluation of any fracture fixation system.
authors.affiliation: Department of Orthopaedics & Sports Medicine, Harborview Medical Center, University of Washington, 325 Ninth Avenue, Seattle, WA 98104, USA. thomas.a.schildhauer@ruhr-uni-bochum.de
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Schildhauer
authors.forename: William R
authors.initials: WR
authors.lastname: Ledoux
authors.forename: Jens R
authors.initials: JR
authors.lastname: Chapman
authors.forename: M Bradford
authors.initials: MB
authors.lastname: Henley
authors.forename: Allan F
authors.initials: AF
authors.lastname: Tencer
authors.forename: M L Chip
authors.initials: ML
authors.lastname: Routt
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws; D005593:Fracture Fixation, Internal / Q000379:methods*; D006801:Humans; D012447:Sacrum / Q000293:injuries*