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. 2021 Feb;15(1):161-168.
doi: 10.14444/8021. Epub 2021 Feb 18.

Augmented Reality Navigated Sacral-Alar-Iliac Screw Insertion

Cyrill Dennler  1 , Nico Akhavan Safa  1 , David Ephraim Bauer  1 , Florian Wanivenhaus  1 , Florentin Liebmann  2   3 , Tobias Götschi  1 , Mazda Farshad  1
Affiliations

Augmented Reality Navigated Sacral-Alar-Iliac Screw Insertion

Cyrill Dennler et al. Int J Spine Surg. 2021 Feb.

Abstract

Background: Sacral-alar-iliac (SAI) screws are increasingly used for lumbo-pelvic fixation procedures. Insertion of SAI screws is technically challenging, and surgeons often rely on costly and time-consuming navigation systems. We investigated the accuracy and precision of an augmented reality (AR)-based and commercially available head-mounted device requiring minimal infrastructure.

Methods: A pelvic sawbone model served to drill pilot holes of 80 SAI screw trajectories by 2 surgeons, randomly either freehand (FH) without any kind of navigation or with AR navigation. The number of primary pilot hole perforations, simulated screw perforation, minimal axis/outer cortical wall distance, true sagittal cranio-caudal inclination angle (tSCCIA), true axial medio-lateral angle, and maximal screw length (MSL) were measured and compared to predefined optimal values.

Results: In total, 1/40 (2.5%) of AR-navigated screw hole trajectories showed a perforation before passing the inferior gluteal line compared to 24/40 (60%) of FH screw hole trajectories (P < .05). The differences between FH- and AR-guided holes compared to optimal values were significant for tSCCIA with -10.8° ± 11.77° and MSL -65.29 ± 15 mm vs 55.04 ± 6.76 mm (P = .001).

Conclusions: In this study, the additional anatomical information provided by the AR headset and the superimposed operative plan improved the precision of drilling pilot holes for SAI screws in a laboratory setting compared to the conventional FH technique. Further technical development and validation studies are currently being performed to investigate potential clinical benefits of the AR-based navigation approach described here.

Level of evidence: 4.

Keywords: HoloLens; augmented reality; lumbo-pelvic fixation; mixed reality; navigation; sacral-alar-iliac.

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Conflict of interest statement

Disclosures and COI: Cyrill Dennler and Nico Akhavan Safa contributed equally to this publication. The project was funded by the Balgrist University Hospital, which receives funding from different sources. The authors did not receive separate funding for this project. One of the authors (MF) declared a potential conflict of interest, as he is the founder of two spin-off companies for AR surgical navigation. However, there is no direct conflict of interest concerning this article. For the remaining authors, none were declared.

Figures

Figure 1
Figure 1
Pelvic models mounted to a wooden board with different angulations and tilts.
Figure 2
Figure 2
Pelvic models covered with a surgical drape.
Figure 3
Figure 3
3D model of a pelvis, segmented from computed tomography data, with screw trajectories.
Figure 4
Figure 4
Surgeon drilling a pilot hole with augmented reality navigation for a sacral-alar-iliac screw.
Figure 5
Figure 5
AruCo marker placed on pelvis to be drilled.
Figure 6
Figure 6
View from of the surgeon. Draped pelvises with an overlay of a virtual 3D pelvis (blue) including the screw trajectories (purple).
Figure 7
Figure 7
Pelvis and left sacral-alar-iliac drill axis (red). The anterior pelvic plane, defined by the anterior superior iliac spines and the pubic tubercles (all in green circles), was defined as the frontal plane (green). The axial plane (blue) was defined as perpendicular to both frontal and anatomical sagittal (reddish) planes. The cranio-caudal inclination angle was measured between the drill axis and the axial plane. The medio-lateral convergence angle was measured between the drill axis and the sagittal plane. The angles were measured between the axis and their orthogonal projection onto the respective plane using multiplanar reconstruction of the computed tomography data.
Figure 8
Figure 8
Real (pilot hole) and simulated numbers of bone perforations with different screw diameters.
See this image and copyright information in PMC

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