title: A simple approach for the preoperative assessment of sacral morphology for percutaneous SI screw fixation.
abstract: BACKGROUND
  Percutaneous sacroiliac screw fixation under fluoroscopic control is an effective method for posterior pelvic ring stabilization. However, sacral dysmorphism has a high risk of L5 nerve injury. This study describes a simple method for the preoperative assessment of the sacral morphology using CT scans with widely available tools.
  
  
  METHODS
  CT scans of 1000 patients were analyzed. True inlet, outlet, and lateral views of the sacrum were obtained using a two-dimensional reconstruction tool to align the sacrum in a reproducible manner. Corridor morphology in the inlet view was measured to calculate different morphological types: (1) Ascending type, (2) Horizontal type, and (3) Descending type. In a second step, the corridor was analyzed for the presence of an anterior indentation of the sacrum between the SI joint and the midsagittal plane with proximity to the nerve root L5, which, therefore, may be harmed during screw misplacement.
  
  
  RESULTS
  A notch was found in the majority of cases with relative frequencies ranging from 69 % (upper quartile of S1) to 95 % (upper quartile of S2). Descending types were, by far, the most frequent corridor type with one exception: In the upper quartile of S1, the ascending type was the most frequent corridor (71 %). Horizontal types were less frequent with a relative incidence between 2 and 14 %.
  
  
  CONCLUSIONS
  This study should increase the awareness for sacral dysmorphism, emphasize the importance of a preoperative assessment of the osseous corridor, and provide a simple method for the preoperative assessment with widely available tools.
authors: Department of Trauma Surgery, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria.
authors: Michael
authors: M
authors: Goetzen
authors: Department of Trauma Surgery, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria.
authors: Kevin
authors: K
authors: Ortner
authors: Department of Trauma Surgery, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria.
authors: Richard A
authors: RA
authors: Lindtner
authors: Department of Trauma Surgery, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria.
authors: Rene
authors: R
authors: Schmid
authors: Department of Trauma Surgery, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria.
authors: Michael
authors: M
authors: Blauth
authors: Department of Trauma Surgery, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria. dietmar.krappinger@i-med.ac.at.
authors: Dietmar
authors: D
authors: Krappinger
mesh_terms: D000368:Aged; D001863:Bone Screws; D005260:Female; D005593:Fracture Fixation, Internal / Q000379:methods*; D050723:Fractures, Bone / Q000000981:diagnostic imaging / Q000601:surgery*; D006801:Humans; D007431:Intraoperative Complications / Q000517:prevention & control; D008297:Male; D061330:Multidetector Computed Tomography; D059348:Peripheral Nerve Injuries / Q000517:prevention & control; D011300:Preoperative Care; D012446:Sacroiliac Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D012447:Sacrum / Q000000981:diagnostic imaging* / Q000601:surgery
keywords: Pelvic ring; Pelvic ring fracture; SI screw fixation; Sacral corridor; Sacral morphology