Comparison of Three-Dimensional Fluoroscopy versus Postoperative Computed Tomography for the Assessment of Accurate Screw Placement after Instrumented Spine Surgery

While intraoperative three-dimensional fluoroscopy does not possess the resolution and image quality of computed tomography (CT), it may provide adequate information about screw placement to guide intra- and postoperative decision making. We compared the accuracy of intraoperative three-dimensional fluoroscopy visualization of proper screw placement with that of postoperative CT. We retrospectively reviewed spinal instrumentation procedures done using the O-arm (Medtronic, Minneapolis, MN, USA) that also had postoperative CT. All screws were assessed for placement accuracy on O-arm and CT images on a 4-point scale. In this study, 20 cases met the inclusion criteria. Thirteen breaches (11 grade 1 and 2 grade 2) were identified on O-arm images, and 14 breaches (10 grade 1, 3 grade 2, and 1 grade 3) were identified on CT. Sensitivity, specificity, and positive and negative predictive values were 93, 99, 99, and 98%, respectively. The Kappa value (0.96) suggested a very high degree of agreement between three-dimensional fluoroscopy and CT in determining accuracy of screw placement. These findings may allow less frequent use of postoperative CT scans, improving cost effectiveness in patients who require spinal instrumentation procedures and potentially decreasing the number of patients who require replacement of an inappropriately positioned screw.