title: The effect of sacral fracture malreduction on the safe placement of iliosacral screws.
abstract: OBJECTIVE
  To determine the effects of cranial displacement on the safe placement of iliosacral screws for zone II sacral fractures.
  
  
  METHODS
  Computer imaging and dimensional analysis of a human cadaveric sacral fracture model.
  
  
  METHODS
  Cadaveric dissection, Orthopaedic Research Laboratories, Newark, New Jersey.
  
  
  METHODS
  Six cadaveric pelves with simulated zone II sacral fractures were imaged with computed tomography at controlled cranial displacements of 5, 10, 15, and 20 mm. The area of contact at the fracture site and volume of bone available for iliosacral screw placement was graphically measured using both two- and three-dimensional computer modeling. Areas of contact were also represented in terms of the maximal number of 7.0-mm screws that could be simultaneously implanted.
  
  
  RESULTS
  Cross-sectional contact area was decreased by 30%, 56%, 81%, and 90% at 5, 10, 15 and 20 mm of displacement, respectively. Volume of bone was decreased by 21%, 25%, 26%, and 34% for 5, 10, 15 and 20 mm of displacement, respectively. In 50% of the specimens at 15 mm and 66% of the specimens with 20 mm displacement, two iliosacral screws could not be contained simultaneously within bone. In 17% of the specimens displaced 15 mm and 50% of the specimens displaced 20 mm, the cross-sectional area was insufficient to contain a single iliosacral screw.
  
  
  CONCLUSIONS
  Although previous authors have accepted up to 15 mm of cranial displacement, the data demonstrate substantial compromise of available screw space with displacements greater than 1 cm. Fracture reduction is mandatory, as screw placement with residual displacement of 10 mm or more can endanger adjacent neural and vascular structures.
authors.affiliation: Department of Orthopaedic Surgery, Orthopaedic Trauma Service, New Jersey Medical School, 90 Bergen Street, Newark, NJ 07103, USA.
authors.forename: Mark C
authors.initials: MC
authors.lastname: Reilly
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Bono
authors.forename: Behrang
authors.initials: B
authors.lastname: Litkouhi
authors.forename: Michael
authors.initials: M
authors.lastname: Sirkin
authors.forename: Fred F
authors.initials: FF
authors.lastname: Behrens
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001863:Bone Screws / Q000009:adverse effects*; D003198:Computer Simulation; D005593:Fracture Fixation, Internal / Q000009:adverse effects*; D050723:Fractures, Bone / Q000000981:diagnostic imaging / Q000601:surgery*; D006801:Humans; D007085:Ilium / Q000000981:diagnostic imaging / Q000601:surgery*; D021621:Imaging, Three-Dimensional; D008875:Middle Aged; D011183:Postoperative Complications; D012447:Sacrum / Q000000981:diagnostic imaging / Q000293:injuries* / Q000601:surgery*; D014057:Tomography, X-Ray Computed