title: Simple mathematical model of sacroiliac screws safe-zone-Easy to implement by pelvic inlet and outlet views.
abstract: Percutaneous sacral screw fixation is the mainstay of posterior pelvic ring fixation. This study quantifies the accuracy of fluoroscopic screw placement using post-operative CT scans and redefines the fluoroscopic safe zone using a mathematical calculation obtained from Inlet and outlet images. The authors hypothesized that a mathematical calculation of screw placement within the ala will improve accuracy of screw placement. A retrospective review of consecutive patients admitted to a level 1 trauma center with pelvic fractures fixed with iliosacral screws from January 2011 to December 2014 was performed. Accuracy of screw placement was determined by comparing fluoroscopy to post-operative CT scans. A mathematical calculation of screw position within the sacral ala was applied to determine assess screw position and compared to CT findings. Ninety-four patients with 156 screws met inclusion criteria, of which 50 (32.0%) had a cortical breech on CT. The sensitivity and specificity of the inlet-outlet safe zone using mathematical calculation were 97.1% and 84.0%, respectively. The positive and negative predictive values were 92.7% and 93.3%, respectively. Overall accuracies of the radiographic inlet-outlet and lateral safe zones were 92.9% and 70.0%, respectively (p-value = 0.004). Sacral dysmorphism was not found to be associated with sacral cortical breech. A Simple mathematical calculation (screw position relative to percentage of bone width) on the inlet-outlet provides an accurate way to predict the accuracy of sacroiliac screws. The method is easy to implement, part of the surgery work-flow, and provides higher accuracy than relying on subjective interpretation of inlet, outlet, and lateral images. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1478-1484, 2017.
authors.affiliation: Chaim Sheba Medical Center, Tel-Hashomer, Israel Affiliated to the Faculty of Medicine, Tel-Aviv University, Tel-Aviv, Israel.|Talpiot Medical Leadership Program, Sheba Medical Centre, Ramat-Gan, Israel.
authors.forename: Amir
authors.initials: A
authors.lastname: Herman
authors.affiliation: Hughston Clinic, Orange Park, Florida.
authors.forename: Emily
authors.initials: E
authors.lastname: Keener
authors.affiliation: Center for Orthopaedic Research and Education, University of Arizona at Phoenix, Phoenix, Arizona.
authors.forename: Candice
authors.initials: C
authors.lastname: Dubose
authors.affiliation: Center for Orthopaedic Research and Education, University of Arizona at Phoenix, Phoenix, Arizona.
authors.forename: Jason A
authors.initials: JA
authors.lastname: Lowe
mesh_terms: D000328:Adult; D001863:Bone Screws; D005260:Female; D005471:Fluoroscopy; D005593:Fracture Fixation, Internal / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D012189:Retrospective Studies; D012446:Sacroiliac Joint / Q000601:surgery*; D012447:Sacrum / Q000000981:diagnostic imaging; D055815:Young Adult
keywords: closed reduction; internal fixation; pelvic fractures