Augmented reality–assisted pedicle screw insertion: a cadaveric proof-of-concept study

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OBJECTIVE

Augmented reality (AR) is a novel technology that has the potential to increase the technical feasibility, accuracy, and safety of conventional manual and robotic computer-navigated pedicle insertion methods. Visual data are directly projected to the operator’s retina and overlaid onto the surgical field, thereby removing the requirement to shift attention to a remote display. The objective of this study was to assess the comparative accuracy of AR-assisted pedicle screw insertion in comparison to conventional pedicle screw insertion methods.

METHODS

Five cadaveric male torsos were instrumented bilaterally from T6 to L5 for a total of 120 inserted pedicle screws. Postprocedural CT scans were obtained, and screw insertion accuracy was graded by 2 independent neuroradiologists using both the Gertzbein scale (GS) and a combination of that scale and the Heary classification, referred to in this paper as the Heary-Gertzbein scale (HGS). Non-inferiority analysis was performed, comparing the accuracy to freehand, manual computer-navigated, and robotics-assisted computer-navigated insertion accuracy rates reported in the literature. User experience analysis was conducted via a user experience questionnaire filled out by operators after the procedures.

RESULTS

The overall screw placement accuracy achieved with the AR system was 96.7% based on the HGS and 94.6% based on the GS. Insertion accuracy was non-inferior to accuracy reported for manual computer-navigated pedicle insertion based on both the GS and the HGS scores. When compared to accuracy reported for robotics-assisted computer-navigated insertion, accuracy achieved with the AR system was found to be non-inferior when assessed with the GS, but superior when assessed with the HGS. Last, accuracy results achieved with the AR system were found to be superior to results obtained with freehand insertion based on both the HGS and the GS scores. Accuracy results were not found to be inferior in any comparison. User experience analysis yielded “excellent” usability classification.

CONCLUSIONS

AR-assisted pedicle screw insertion is a technically feasible and accurate insertion method.

ABBREVIATIONS AR-HMD = augmented reality head-mounted display; GS = Gertzbein scale; HGS = Heary-Gertzbein scale; LCL = lower control limit; LS = least squares; LSCL = lower 1-sided 95% confidence limit; NI = non-inferiority margin; PRC = percentage of reference control; UEQ = user experience questionnaire.

Article Information

Correspondence Camilo A. Molina: Johns Hopkins University School of Medicine, Baltimore, MD. cmolina2@jhmi.edu.

INCLUDE WHEN CITING Published online March 29, 2019; DOI: 10.3171/2018.12.SPINE181142.

Disclosures Augmedics Ltd. provided support to conduct cadaveric experiments including financial support for cadaveric sample procurement and provision of augmented reality head-mounted display hardware and software. K2M Inc. provided support by lending instruments and implants employed in this study.

Dr. Molina is a consultant for Augmedics Ltd. Dr. Theodore is an inventor of a device manufactured by Globus Medical Inc., which was used in the Discussion section. He is entitled to royalty payments on future sales of the device and he is a paid consultant to Globus Medical Inc. This arrangement has been reviewed and approved by the Johns Hopkins University in accordance with its conflict of interest policies. Dr. Mirovsky is a member of the Advisory Board for Augmedics Ltd. Dr. Harel received payment for clinical work from Augmedics Ltd. Dr. Witham receives support of a non–study-related clinical research effort that he oversees in a grant from Eli Lilly and Co. and from the Gordon and Marilyn Macklin Foundation. Dr. Sciubba is a consultant for Medtronic, K2M, Misonix, DePuy-Synthes, Stryker, NuVasive, and Baxter.

© AANS, except where prohibited by US copyright law.

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Figures

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    Positioning of spinous process clamps and registration marker. Left: The registration marker (labeled B) is placed prior to CT acquisition and subsequently removed, with only 1 or 2 of the spinous process tracking clamps (labeled A and C) remaining. The number of spinous process clamps applied depends on how many segments are instrumented. Right: Image visualizing the automatic 3D segmentation of the CT scanned cadaveric specimen and a spinous process tracking clamp (A). Figure is available in color online only.

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    Listing of navigated instruments that were available to operators. Operators had the option of manual tapping and screw insertion or power tapping and power driving inserted screws. Figure is available in color online only

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    Augmented reality head-mounted display (AR-HMD). A: The HMD is composed of an infrared camera (a) that provides tracking of the registered instruments in relation to the spinous process clamps and lenses (b) on which the stereoscopic semitransparent 3D image is viewed. B: The AR-HMD unit in use. C: Example of the type of images seen by the operator’s left and right eyes. In this example, the view is of a guided instrument on the 3D segmented spine with the associated axial and sagittal planes demonstrating the instrument’s trajectory. Figure is available in color online only.

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    UEQ results displaying operators’ impression of their experience. Operators were asked 26 questions regarding clinical usability (originality, simulation). Each question is evaluated by a 7-point Likert-type scale, on which a score of −3 indicates full agreement with a negative term and a score of +3 indicates full agreement with a positive term. Figure is available in color online only.

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