S2-alar-iliac screw insertion without continuous fluoroscopy—cadaver study comparing conventional versus targeting jig versus robotic assistance

Abstract

Introduction: S2-alar-iliac (S2AI) screw insertion relies heavily on fluoroscopy. Here, we compare the accuracy of conventional instrumentation by experienced surgeons, a novel design S2AI screw insertion tool by inexperienced and experienced surgeons and Brainlab Cirq®, a new robotic assistive navigation device. Methodology: Cadaveric randomised trial with 54 hemi-pelvises. Specimen baseline characteristics were recorded and prepared with standardised surgical dissection. S2AI screws were inserted by either conventional free hand or with the aid of a novel instrumentation tool or by robotic arm–assisted navigation. Post insertion CT scans of all pelvises were performed. Primary outcome measures included length of screw tract, incidence of hazard zone penetration. Secondary outcomes included time of S2AI screw insertion procedure, oblique and caudal tilt angles, deviations of entry site and false tracking. Results: Screw depth was significantly longer for robotic-assisted navigation with 108.4 mm (SD 20.5) compared to instrumentation tool by experienced surgeon (101.9 mm, SD 20.8), inexperienced surgeon (77.4 mm, SD 40.8) and conventional instrumentation (83.5 mm, SD 35.2; ANOVA p=0.009). Paired sample t test comparing left and right hemipelvis with different intervention groups showed statistically significant differences (p=0.04). Robotic-assisted screw insertion took the longest time (16 minutes 30 seconds) while experienced surgeons using instrumentation tool was the fastest (3 minutes 30 seconds; ANOVA p<0.01). Inner cortical perforation was significantly higher in the inexperienced surgeon group utilising instrumentation tool (56%, with 1 partial perforation, p<0.01). Discussion: Novel instrumentation tool may help experienced surgeons reduce screw insertion time with a high degree of accuracy. Robotic-assisted screw insertion remains the most accurate.