Background: Pedicle screw insertions are commonly used for posterior fixation to treat various spine disorders. However, the misplacement of pedicle screws can lead to disastrous complications. Inaccurate pedicle screw placement is relatively common even when placement is performed under fluoroscopic control. In order to improve the accuracy of the screw placement, we applied a technique using guide wires and a cannulated tapping device with the assistance of a fluoroscopic pedicle axis view.
Methods: From 2006 to 2011, 854 pedicle screws were placed in 176 patients in lumbosacral spinal fusion surgeries. The accuracy of screw placement was evaluated using postoperative reconstructed computed tomography images. Screw misplacement was classified as minor (cortical perforation <3 mm), moderate (cortical perforation 3-6 mm), or severe (cortical perforation >6 mm). Using logistic regression analysis, we also investigated the potential risk factors associated with screw misplacement.
Results: Pedicle screw misplacement was observed in 37 screws (4.3 %) in 34 patients. In the sub-classification analysis, 28 screws (3.3 %) were determined to be minor perforations, 7 screws (0.8 %) were considered to be moderate perforations, and 2 screws (0.2 %) was judged to be a severe perforation (cortical perforation >6 mm). None of the 28 screws that were considered to be minor perforations were associated with any significant symptoms in the patients. However, 2 of the 9 screws that were determined to be moderate or severe perforations caused neurological symptoms (1 of which required revision). No significant differences were observed in the incidence of screw misplacement among the vertebral levels. Significant risk factors for screw misplacement were obesity and degenerative scoliosis. The odds ratios of these significant risk factors were 3.593 (95 % confidence interval (CI), 1.061-12.175) for obesity and 8.893 for degenerative scoliosis (95 % CI, 1.200-76.220).
Conclusions: A modified fluoroscopic technique using a pedicle axis view and a cannulated tapping instrument can achieve safe and accurate pedicle screw placement. In addition, obesity and degenerative scoliosis were identified as significant risk factors for screw misplacement.