Virtual fluoroscopy: Safe zones for pelvic screw fixations

Abstract

Hypothesis: Percutaneous pelvic screw fixations are technically demanding. Purpose of this prospective study: To define appropriate fluoroscopy projections for the safe placement of SI screws, anterior column screw, posterior column screw and iliac screw using fluoroscopy based navigation. Material & Methods: A conventional C-arm (Ziehm®) and two different navigation systems were used (Medivision SurgiGate® and Sofamore Danek Stealth Station®). In 6 pelvic models and 4 cadaver pelves three to four projections per screw position were defined and a total of 84 screws were inserted. Evaluation of accuracy was performed with X-ray, CT and dissection. Results: The following fluoroscopy projections proved to be appropriate: SI srews: Lateral, lateral 20° a.p., inlet, outlet Ant. Column: Inlet30° ipsilateral, obturator outlet ipsilateral, obturator outlet contralateral, obturator Post. Column: Obturator outlet ipsilateral, obturator outlet contralateral, outlet 20° contralateral Iliac screw: Inlet 30° ipsilateral, obturator ipsilateral, obturator contralateral The average fluoroscopy time was 6 seconds/ screw in pelvic models and 86 seconds/ screw in cadaver pelves. In the first series with 60 screws in the pelvic models, 51 screws were inserted correctly. In five cases there was minor displacement without perforating the cortex, in four cases the cortex was perforated. In the cadaver study 19 of 24 screws were placed correctly, two were satisfactory and three were not satisfactory (one SI, ant. Column, post. Column each). Conclusion: With a remarkable low fluoroscopy time of 6 seconds/ screw in pelvic models and 86 seconds/ procedure in cadaver pelves 83% of all pelvic screws were inserted perfectly. With further improvements in fluoroscopic image quality the method of fluoroscopy based navigation will be very helpful not only for pelvic screw fixations but for many applications in Traumatology.