title: Anatomical conditions of the posterior pelvic ring regarding bisegmental transverse sacroiliac screw fixation: a 3D morphometric study of 125 pelvic CT datasets.
abstract: BACKGROUND
  Sacroiliac (SI) screws are used for osteosynthesis in unstable posterior pelvic ring injuries. In the cases of "sacral dysplasia", in which the elevated upper sacrum does not allow a secure SI screw insertion into the S1 level, the S2 segment must be used to achieve stable fixation. The bone quality of the S2 segment is thinner compared to that of the S1 vertebra and may cause biomechanical weakness. An additional SI screw insertion into the S3 level may improve stability. With respect to the anatomical conditions of the posterior pelvic ring, there have been no anatomical investigations to date regarding SI screw placement into the third sacral segment.
  
  
  METHODS
  CT raw datasets from 125 patients (ø59 years, ø172 cm, ø76 kg) were post-processed using Amira 5.2 software to generate 3D pelvic models. A program code implemented in C++ computed a transverse bone corridor for the first, second and third sacral segments for a typical SI screw diameter of 7.3 mm. Volume, sagittal cross-section, iliac entrance area and length of the determined screw corridors were measured. A confidence interval of 95 % was assumed (p < 0.05).
  
  
  RESULTS
  The fully automatic computation revealed a possible transverse insertion for one 7.3-mm screw in the third sacral segment in 30 cases (24 %). The rate (60 %) of feasible S3 screw placements in the cases of sacral dysplasia (n = 25) is significantly higher compared to that (15 %) of "normal" sacra (n = 100). With regard to the existence of transverse iliosacroiliac corridors as a function of sacral position in between the adjacent iliac bone bilaterally, a new classification of three different shape conditions can be made: caudad, intermediate minor, intermediate major, and cephalad sacrum. Gender, age, body height and body weight had no statistically significant influence on either possible screw insertion or on the calculated data of the corridors (p > 0.05).
  
  
  CONCLUSIONS
  SI screw insertion into the third sacral level deserves discussion in the cases of sacral dysplasia. Biomechanical and practical utility must be verified.
authors.affiliation: Department of Orthopedic Surgery, Martin Luther University Halle-Wittenberg, Magdeburger Strasse 22, 06112, Halle (Saale), Germany, florian.radetzki@gmx.de.
authors.forename: Florian
authors.initials: F
authors.lastname: Radetzki
authors.forename: D
authors.initials: D
authors.lastname: Wohlrab
authors.forename: F
authors.initials: F
authors.lastname: Goehre
authors.forename: H
authors.initials: H
authors.lastname: Noser
authors.forename: K S
authors.initials: KS
authors.lastname: Delank
authors.forename: T
authors.initials: T
authors.lastname: Mendel
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001863:Bone Screws; D005260:Female; D005593:Fracture Fixation, Internal / Q000379:methods*; D006801:Humans; D007085:Ilium / Q000293:injuries / Q000601:surgery; D008297:Male; D008875:Middle Aged; D010384:Pelvic Bones / Q000000981:diagnostic imaging / Q000293:injuries*; D012447:Sacrum / Q000601:surgery; D014057:Tomography, X-Ray Computed; D055815:Young Adult