Introduction
Augmented Reality (AR) and Mixed Reality (MR) can be used for surgical navigation to execute the pre-operative plan. HoloMA is a novel AR/MR application which can guide the user to place surgical instruments on the planned location within the patient. In this pilot study, the AR/MR-guidance of HoloMA was used to place personalized canine acetabular roof implants on the pre-planned location on the iliac bone.

Methods
Dedicated tools to perform the AR/MR patient registration and surgical guidance were developed. An in silico patient registration test was conducted to assess if the available bony surface during the acetabular roof surgery was suitable to perform the patient registration accurately. Pilot tests to place implants using the AR/MR-guidance of HoloMA were conducted on phantoms, a cadaver and in an in vivo dog patient. The translational and angulation error between the planned and the post-operative implant positions were determined. The aim was to achieve implant placement with a maximum translational error of 4.0 mm and a maximum angulation error of 5.0° relative to the pre-operative plan.

Results
The in silico patient registration test demonstrated a mean translational error of 0.94 ± 0.23 mm and a mean angulation error of 2.49 ± 0.34°. In the phantom tests, implants (n=6) were placed with a mean translational error of 1.94 ± 0.79 mm. The mean angulation errors in this test were: 2.87 ± 1.81° (transversal plane), 1.72 ± 1.64° (dorsal plane) and 3.10 ± 2.52° (sagittal plane). Two of the implants of the phantom test and both implants of the cadaveric test (n=2) were positioned with a translational error exceeding 4.0 mm and/or angulation error exceeding 5.0° from the planned positions. No implants were placed using AR/MR-guidance in the in vivo dog patient test.

Conclusion
The results of the in silico patient registration test hold promise for the use of AR/MR-guidance in positioning personalized acetabular roof implants. However, the moderate outcomes observed in the phantom and cadaveric test suggest the need for further testing and improvements before deploying this AR/MR technology in a clinical setting.