Robot-assisted screw fixation in a cadaver utilizing magnetic resonance imaging–based synthetic computed tomography: toward radiation-free spine surgery. Illustrative case

BACKGROUND Synthetic computed tomography (sCT) can be created from magnetic resonance imaging (MRI) utilizing newer software. sCT is yet to be explored as a possible alternative to routine CT (rCT). In this study, rCT scans and MRI-derived sCT scans were obtained on a cadaver. Morphometric analysis was performed comparing the 2 scans. The ExcelsiusGPS robot was used to place lumbosacral screws with both rCT and sCT images. OBSERVATIONS In total, 14 screws were placed. All screws were grade A on the Gertzbein-Robbins scale. The mean surface distance difference between rCT and sCT on a reconstructed software model was –0.02 ± 0.05 mm, the mean absolute surface distance was 0.24 ± 0.05 mm, and the mean absolute error of radiodensity was 92.88 ± 10.53 HU. The overall mean tip distance for the sCT versus rCT was 1.74 ± 1.1 versus 2.36 ± 1.6 mm (p = 0.24); mean tail distance for the sCT versus rCT was 1.93 ± 0.88 versus 2.81 ± 1.03 mm (p = 0.07); and mean angular deviation for the sCT versus rCT was 3.2° ± 2.05° versus 4.04°± 2.71° (p = 0.53). LESSONS MRI-based sCT yielded results comparable to those of rCT in both morphometric analysis and robot-assisted lumbosacral screw placement in a cadaver study.