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. 2016 Oct 24:10:38.
doi: 10.14444/3038. eCollection 2016.

Reliability of the Planned Pedicle Screw Trajectory versus the Actual Pedicle Screw Trajectory using Intra-operative 3D CT and Image Guidance

Catherine A Miller  1 , Charles G Ledonio  1 , Matthew A Hunt  1 , Farhan Siddiq  2 , David W Polly Jr  3
Affiliations

Reliability of the Planned Pedicle Screw Trajectory versus the Actual Pedicle Screw Trajectory using Intra-operative 3D CT and Image Guidance

Catherine A Miller et al. Int J Spine Surg. .

Abstract

Background: Technological advances, including navigation, 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 were analyzed. The mean angular difference between the virtual and actual image in all screws was 2.17° ± 2.20° on axial images and 2.16° ± 2.24° on sagittal images. There was excellent agreement between actual and virtual pedicle screw trajectories in the axial and sagittal plane with ICC = 0.99 (95%CI: 0.992-0.995) (p<0.001) and ICC= 0.81 (95%CI: 0.759-0.855) (p<0.001) respectively. When comparing thoracic and lumbar screws, there was a significant difference in the sagittal angulation between the two distributions. No statistical differences were found distance from the reference frame.

Conclusion: 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°) in the axial and sagittal planes and a minor difference in the sagittal thoracic and lumbar angulation, although these did not affect clinical outcomes. In general, we find that pedicle screw placement using intraoperative cone beam CT and navigation to be accurate and reliable, and as such have made it a routine part of our spine practice. This study was approved by the University of Minnesota IRB (#1303E30544).

Keywords: accuracy; navigation; pedicle screws.

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Figures

Fig. 1
Fig. 1
Axial and sagittal images of the virtual screw and actual screw angles relative to the mid sagittal line and superior endplate, respectively. (A) Example of most accurate screw placement (B) Example of least accurate screw placement.
Fig. 2
Fig. 2
(A) The patient is in a prone position, and a reference frame is attached to a spinous process. (B) The O-arm is brought into the field and a CT scan obtained. (C) The position of the navigated instruments is projected onto the CT images on a monitor visible to the surgeon.
Fig. 3
Fig. 3
Image of the Stealth Station navigation screen showing the axial, sagittal, and coronal virtual screw projection.
Fig. 4
Fig. 4
Using a navigated screwdriver, the surgeon is able visualize the real-time trajectory of the screw on the Stealth Station screen during placement.
Fig. 5
Fig. 5
AP and lateral spinal preoperative (A, B) and postoperative (C, D) x-rays after a Stealth guided posterior spinal instrumentation.
Fig. 6
Fig. 6
Axial intraoperative CT scan of the three pedicle screws which were removed or revised. Two screws breached medially and one screw was too long.
Fig. 7
Fig. 7
Varying degrees of accuracy from an ideal screw trajectory in the lumbar spine.
See this image and copyright information in PMC

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