title: Safe placement of S1 and S2 iliosacral screws: the "vestibule" concept.
abstract: OBJECTIVE
  To determine the optimal starting points for placement of S1 and S2 iliosacral screws as well as the pertinent anatomy surrounding the S1 and S2 vertebral bodies.
  
  
  METHODS
  Normal subject study evaluating helical CT scans of thirty normal posterior pelvic rings.
  
  
  METHODS
  Methodist Hospital, Indianapolis, Indiana, Level I trauma center.
  
  
  METHODS
  Consenting adults for limited pelvis CT.
  
  
  METHODS
  The three-dimensional anatomy of the posterior pelvic ring pertinent to S1 and S2 iliosacral screw placement. Safety of simulated S1 iliosacral screw placement using different lateral ilium starting points.
  
  
  RESULTS
  The transversely placed (horizontal) iliosacral screw was the least safe of the screws tested. The safest lateral ilium starting point for our entire population was at the posterior sacral body sagittally and at the inferior S1 foramen coronally. S2 iliosacral screws had less cross-sectional area for placement than S1 screws. Placement of the S2 screw slightly to the S1 foraminal side of the S2 vertebral body increased the safety of placement.
  
  
  CONCLUSIONS
  The iliosacral screw starting point at the posterior sacral body and inferior S1 foramen was the safest when considering the entire population. Careful attention to the size and orientation of the S2 vertebral body should be taken if S2 iliosacral screws are placed.
authors.affiliation: Orthopaedics Indianapolis, Indiana 46278, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Carlson
authors.forename: D K
authors.initials: DK
authors.lastname: Scheid
authors.forename: D C
authors.initials: DC
authors.lastname: Maar
authors.forename: J R
authors.initials: JR
authors.lastname: Baele
authors.forename: D M
authors.initials: DM
authors.lastname: Kaehr
mesh_terms: D000328:Adult; D001863:Bone Screws; D006801:Humans; D007085:Ilium / Q000033:anatomy & histology*; D012447:Sacrum / Q000033:anatomy & histology*