Virtual fluoroscopy vs. conventional C-arm guided sacroiliac screw placement - An evaluation of surgical time, fluoroscopy time, and radiation dose receive in cadaver pelves

摘要

Objectives/Background: Iliosacral screw fixation is technically demanding, and all authors emphasize the importance of optimizing visualization of the posterior pelvis with ideal fluoroscopic projections to ensure accurate screw placement [1, 4, 5]. Traditionally, this has required the acquisition of large numbers of fluoroscopic images during the surgical procedure, often with the surgeon's dominant hand near the radiating beam of the fluoroscopy unit. Furthermore, the patient's GU system may be exposed to high levels of radiation as protective shielding obscures visualization of the SI joints [2, 3]. Virtual fluoroscopy uses stored fluoroscopic images to provide multi-planar intra-operative navigational guidance, eliminating the need to repeatedly reposition the C-arm and obtain multiple images during the surgical procedure. The purpose of this study was to determine if the virtual fluoroscopy technology decreases the radiation dose received by the both the surgeon and the patient as well as the total fluoroscopy time when compared to the traditional C-arm guided technique. Design/Methods: 12 fresh frozen cadaveric pelves were instrumented with 48 cannulated 6.5mm titanium screws. Screws were placed at the S1 and S2 levels on one side under conventional fluoroscopic guidance; the contralateral side was instrumented with the use of the FluoroNavTM virtual fluoroscopy system. TLD radiation-sensitive badges were placed on the cadavers' umbilicus as well as on the operating surgeon's dominant hand to monitor the radiation dose equivalent received during each procedure. The total duration of fluoroscopy was recorded as was the duration of fluoroscopy for the set-up, the S1 and the S2 screw insertions for both methods. The total surgical time was monitored with digital stop watches as were the set-up and screw insertion times. After both SI joints had been instrumented, anatomic dissection was performed to identify any misdirected screws violating the anterior sacral cortex or the sacral foramen. Results: The virtual fluoroscopy (VF) navigational technique decreased the average duration of fluoroscopy per procedure by more than 50% (93.83 +- 37.40 seconds for C-arm vs. 40.67 +- 16.06 seconds for VF, p value 0.0039). While the set up time was longer for the virtual fluoroscopy system (7:27 +-1:14 min. vs. 2:42 +- 1:24 min. for C-arm), the total surgical time was not found to be significantly prolonged. The superficial/skin level dose equivalent received by the cadaveric pelves was decreased 40% under virtual fluoroscopy guidance (24.5 +-16.40 millirems for VF vs. 39.17 +- 28.51 millirems for C-arm), while the deep dose/organ dose equivalent was decreased 30% (21.50 +- 13.34 millirems for VF vs. 31.67 +- 18.90 millirems for C-arm.) The radiation dose received by the operating surgeon's hand was decreased four fold (0.83 millirems for VF vs. 3.75 millirems for C-arm.) The accuracy was comparable with both techniques, and no screws were found to violate neither the anterior sacral cortex nor the foramen in either group. Conclusions: The virtual fluoroscopy system enables the surgeon to accurately navigate optically sensed surgical instruments throughout the anatomy using pre-acquired coupled images, eliminating the need to repeatedly reposition the C-arm in order to update instrument position. The computer assisted navigational system was found to significantly decrease the duration of fluoroscopy utilization for iliosacral screw fixation as well as the radiation dose received by the patient and the operating surgeon. The system allows excellent visualization of the posterior pelvic ring, and there were no aberrantly placed screws based on anatomic dissection. Finally, while anecdotal experience and previous reports indicate that computer assisted navigational systems increase total surgical time; our finding was that the total surgical time was equal with virtual fluoroscopy when compared to conventional C-arm guided SI screw placeme