LAUSR

OBJECTIVES To evaluate the accuracy and safety of SI screw placement for traumatic pelvic ring instability using a standardized protocol, using lateral radiographs as the primary guide for screw placement. DESIGN Prospective Cohort Diagnostic Imaging Study. SETTING Two level 1 trauma centers in Australia and NorwayPatients/Participants: Consecutive pelvic trauma patients requiring posterior fixation with sacroiliac screws. INTERVENTION A uniform intraoperative image intensifier (ii) protocol with standardized views was followed, using a lateral radiograph as the determinant for screw entry and positioning, and subsequent inlet and outlet views to verify extra-foraminal placement. MAIN OUTCOME MEASUREMENTS Screw positioning was evaluated on post operative CT in all cases. Screws were deemed safe or malpositioned. RESULTS 343 screws were placed in 196 patients with a median age of 45 years, for pelvic ring instability between January 2016 and December 2019. 237 S1 screws were placed and 106 S2 screws. On post operative CT there were 312 screws with secure placement completely in cancellous bone. 23 screws abutted the cortex but were deemed juxtacortical and safe. 8 screws were judged intraforaminal. 1 screw was revised for neurological compromise. CONCLUSIONS The use of lateral ii shots as the corner stone of screw placement to guide percutaneous SI screw insertion is accurate and safe in terms of screw placement within cortical margins of safe zone corridors. The screw revision rate of 0.3% is low, despite the high number of cases reviewed from two institutions and cases performed by multiple surgeons of differing training grades. LEVEL OF EVIDENCE Level - II - Prospective Diagnostic Imaging Study.