Introduction: Technological advances have been made to improve safety and accuracy of pedicle screw fixation. We evaluated the accuracy of the virtual screw placement (Stealth projection) compared to actual screw placement (intra-operative O-Arm) and examined for differences based on the distance from the reference frame.
Methods: A retrospective evaluation of prospectively collected data was conducted from January 2013 to September 2013. We evaluated thoracic and lumbosacral pedicle screws placed using intraoperative O-arm and Stealth navigation by obtaining virtual screw projections and intraoperative O-arm images after screw placement. The screw trajectory angle to the midsagittal line and superior endplate was compared in the axial and sagittal views, respectively. Percent error and paired t-test statistics were then performed.
Results: Thirty-one patients with 240 pedicle screws (146 thoracic, 94 lumbosacral) were analyzed. The mean angular difference between the virtual and actual image in all screws was statistically significant (p=0.0016) at 2.17° ± 2.20 on axial images but was not significant (p=0.19) on sagittal images at 2.16° ± 2.24. The axial and sagittal angular differences (%error) were the same at 1.1% and 1.2%, respectively. When comparing thoracic and lumbar screws, there was a significant difference in the sagittal angulation between the two distributions, however there were no pedicle screw breaches (anterior, lateral, medial or superior). No statistical differences were found in relation to the distance from the reference frame.
Conclusions: The virtual projection view is clinically accurate compared to the actual placement on intra-operative CT in both the axial and sagittal views. There is slight imprecision (2.17°) in the axial plane and a minor difference in the sagittal thoracic and lumbar angulation, although all screws were still in optimal position within the pedicle with no breaches. Distance from the reference frame did not affect accuracy of the screw placement.
Patient Care: This will allow surgeons to better understand the accuracy of spinal navigation and apply this knowlege in their patient population.
Learning Objectives: By the conclusion of this session, participants should be able to 1) Describe the importance of navigated pedicle screw instrumentation, 2)Identify a new approach to assessing the accuracy of navigational systems