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Visual augmented reality (AR) has the potential to improve the accuracy, efficiency and reproducibility of computer-assisted orthopaedic surgery (CAOS). AR Head-mounted displays (HMDs) further allow non-eye-shift target observation and egocentric view. Recently, a markerless tracking and registration (MTR) algorithm was proposed to avoid the artificial markers that are conventionally pinned into the target anatomy for tracking, as their use prolongs surgical workflow, introduces human-induced errors, and necessitates additional surgical invasion in patients. However, such an MTR-based method has neither been explored for surgical applications nor integrated into current AR HMDs, making the ergonomic HMD-based markerless AR CAOS navigation hard to achieve. To these aims, we present a versatile, device-agnostic and accurate HMD-based AR platform. Our software platform, supporting both video see-through (VST) and optical see-through (OST) modes, integrates two proposed fast calibration procedures using a specially designed calibration tool. According to the camera-based evaluation, our AR platform achieves a display error of 6.31 $\pm$ 2.55 arcmin for VST and 7.72 $\pm$ 3.73 arcmin for OST. A proof-of-concept markerless surgical navigation system to assist in femoral bone drilling was then developed based on the platform and Microsoft HoloLens 1. According to the user study, both VST and OST markerless navigation systems are reliable, with the OST system providing the best usability. The measured navigation error is 4.90 $\pm$ 1.04 mm, 5.96 $\pm$ 2.22 $^\circ$ for the VST system, and 4.36 $\pm$ 0.80 mm, 5.65 $\pm$ 1.42 $^\circ$ for the OST system. [ABSTRACT FROM AUTHOR]

Augmented reality, surgery, head mounted display. [Extracted from the article]

Aim Navigation technology has given surgeons the capacity to know precisely where their instruments are during surgery, and simulation-guided navigation is a surgical method which is based on the use of navigation technology linked to 3D virtual surgery simulation. The aim of the present study was to evaluate the absolute accuracy of simulation-guided navigation as an aid to reproduce the planned position of the distraction device vector in pediatric mandibular distraction osteogenesis. Materials and methods We retrospectively evaluated seven patients affected by unilateral (3 pts.) or bilateral (4 pts.) mandibular hypoplasia and treated with this method between 2012 and 2014 at the Maxillofacial Surgery Unit of the University of Bologna, Italy. All patients were enrolled for mandibular distraction using internal unidirectional devices (11 distraction devices implanted overall). Patients were studied through a complete three-dimensional workflow, which led to obtaining a virtual reconstruction of the facial bones and the simulation of the distraction device positioning using a specific experimental software. The surgical planning was loaded on the navigation system and the distraction device was placed following the virtual plan, which is displayed on the navigation system as a guide and tracked with the navigation instruments. Results We analyzed the outcome comparing the recorded three-dimensional coordinates of the achieved distractor position and the three-dimensional coordinates of the planned distractor position. Among the eleven placed distractors, we found a mean angular error of 3.74° ± 3.30° on the axial axis (yaw) and of 6.27° ± 5.32° on the sagittal axis (pitch), while median angular errors are 3.72° on the axial axis (yaw) and 4.08° on the sagittal axis (pitch). Conclusion Our preliminary experience seems to support that simulation-guided navigation for vector control in mandibular distraction osteogenesis could be a useful procedure for reproducing the virtually planned outcome. Nevertheless, our results cannot be considered completely satisfactory. There is a lot of room to improve accuracy and errors seem to depend mainly on the soft tissues interference during distractor placement. [ABSTRACT FROM AUTHOR]

Background: In the context of guided surgery, augmented reality (AR) represents a groundbreaking improvement. The Video and Optical See-Through Augmented Reality Surgical System (VOSTARS) is a new AR wearable head-mounted display (HMD), recently developed as an advanced navigation tool for maxillofacial and plastic surgery and other non-endoscopic surgeries. In this study, we report results of phantom tests with VOSTARS aimed to evaluate its feasibility and accuracy in performing maxillofacial surgical tasks. Methods: An early prototype of VOSTARS was used. Le Fort 1 osteotomy was selected as the experimental task to be performed under VOSTARS guidance. A dedicated set-up was prepared, including the design of a maxillofacial phantom, an ad hoc tracker anchored to the occlusal splint, and cutting templates for accuracy assessment. Both qualitative and quantitative assessments were carried out. Results: VOSTARS, used in combination with the designed maxilla tracker, showed excellent tracking robustness under operating room lighting. Accuracy tests showed that 100% of Le Fort 1 trajectories were traced with an accuracy of ±1.0 mm, and on average, 88% of the trajectory's length was within ±0.5 mm accuracy. Conclusions: Our preliminary results suggest that the VOSTARS system can be a feasible and accurate solution for guiding maxillofacial surgical tasks, paving the way to its validation in clinical trials and for a wide spectrum of maxillofacial applications. [ABSTRACT FROM AUTHOR]