Virtual fluoroscopy: Computer-assisted fluoroscopic navigation

Study Design: In vitro accuracy assessment of a novel virtual fluoroscopy system. Objectives: To investigate a new technology combining image-guided surgery with C-arm fluoroscopy. Summary of Background Data: Fluoroscopy is a useful and familiar technology to all musculoskeletal surgeons. its limitations include radiation exposure to the patient and operating team and the need to reposition the fluoroscope repeatedly to obtain surgical guidance in multiple planes. Methods: Fluoroscopic images of the lumbar spine of an intact, unembalmed cadaver were obtained, calibrated, and saved to an image-guided surgery system (StealthStation; Medtronic Sofamor-Danek, Memphis, TN). A virtual fluoroscopy system (FluoroNav; Medtronic Surgical Navigation Technologies, Broomfield, CO) was used for the sequential insertion of a light-emitting diode-fitted probe into the pedicles of L1-S1 bilaterally. The trajectory of a "virtual tool" corresponding to the tracked tool was overlaid onto the saved fluoroscopic views in real time. Live fluoroscopic images of the inserted pedicle probe were then obtained. Distances between the tips of the virtual and fluoroscopically displayed probes were quantified using the image-guided computer's measurement tool. Trajectory angle differences were measured using a standard goniometer and printed copies of the workstation computer display. The surgeon's radiation exposure was measured using thermolucent dosimeter rings. Results: Excellent correlation between the virtual fluoroscopic images and live fluoroscopy was observed. Mean probe tip error was 0.97 +/- 0.40 mm. Mean trajectory angle difference between the virtual and fluoroscopically displayed probes was 2.7 degrees +/- 0.6 degrees The thermolucent dosimeter rings measured no detectable radiation exposure for the surgeon. Conclusions: Virtual fluoroscopy offers several advantages over conventional fluoroscopy while providing acceptable targeting accuracy. It enables a single C-arm to provide real-time, multiplanar procedural guidance. It also dramatically reduces radiation exposure to the patient and surgical team by eliminating the need for repetitive fluoroscopic imaging for tool placement.