Background: Extended Reality (XR) has demonstrated significant improvements in multiple surgical specialties by reducing operative times and enhancing surgical outcomes. Nevertheless, its usability for perforator visualization in deep inferior epigastric perforator (DIEP) breast reconstruction remains largely unexplored.

Objective: The primary aim of this study was to assess the usability and potential added value of XR in DIEP flap breast reconstruction to enhance the three-dimensional understanding of the deep inferior epigastric artery and its perforators. The secondary objective of this study was to determine if the weight of DIEP flaps can be accurately estimated through the virtual model required for XR visualization.

Methods: This multicenter pilot study involved plastic surgeons and patients undergoing DIEP flap breast reconstruction at three Dutch medical centers. Abdominal computed tomography angiography (CTA) images were used to create virtual 3D models. Surgeons utilized the HoloLens 2 (Microsoft Corporation) to compare intraoperative findings regarding perforator caliber, location within the flap, and the intramuscular course of perforators against CTA. Usability was assessed via the System Usability Scale (SUS). The SUS, perforator characteristics, and the added value of XR in addition to CTA for preoperative planning of DIEP flap breast reconstruction were scored using a 5-point Likert scale with a minimum score of 1 and a maximum score of 5. Furthermore, DIEP flap weight estimations were derived from the segmentations of the DIEP flap required for the virtual model and compared with a two-dimensional method for DIEP flap weight predictions extracted from literature.

Results: This study presents the preliminary results. Up until now, five patients and surgeons have been included. SUS scores were 66 for CTA and 70 for XR, meaning both visualization methods have ‘Good’ usability. XR scored slightly higher compared to CTA regarding perforator caliber with median scores of 3 for CTA and 4 for XR. Location within the flap yielded median scores of 4 for CTA and 5 for XR. The median score for the intramuscular course was 4 for both CTA and XR. The median scores for utilizing XR in addition to CTA for preoperative planning of DIEP flap breast reconstruction and recommending it to a colleague were both 4. DIEP flap weight prediction derived from the virtual model compared to true flap weight showed a mean difference of 333 grams and a mean percentage difference of 18.9%, whereas the two-dimensional method showed a mean difference of 937 grams and a mean percentage difference of 44.5%.

Conclusion: The preliminary results from this study indicate that XR technology, using the HoloLens 2, is a feasible and potentially advantageous tool for preoperative planning in DIEP flap breast reconstruction. The usability of XR was found to be comparable to CTA, with slightly better performance in visualizing perforator characteristics. The positive feedback from participating surgeons suggests that XR could enhance the understanding of the DIEA and its perforators, potentially improving surgical outcomes. Accurate prediction of DIEP flap weight based on the virtual model using the methodology employed in this study is currently not feasible.

Introduction
An innovative, patient-specific, hip implant was developed for canine patients suffering from developmental hip dysplasia. In a first cohort study, the post-operative positions of the implants deviated with an average of 5 mm when compared to the pre-operatively planned positions. A novel augmented reality (AR) based intra-operative navigation method (Holoma) was proposed to decrease implant positioning errors to a maximum of 3 mm. Holoma provides ArUco marker-based, mixed reality surgical navigation on the Hololens 2. The goal of this study was to quantify the error associated with each technical component in Holoma, to determine its navigational accuracies.

Methods
Holoma’s technical errors were quantified in a laboratory setting within a surgical operation room. The accuracy of ArUco marker localization and the amount of jittering (falsely detected marker movement) were tested by performing stationary and dynamic experiments. The precision of three image-to-patient registration methods (marker pose, point-to-point, point cloud) was determined by calculating the euclidean distance between multiple registration attempts. Lastly, implant navigation accuracy was quantified by positioning an implant on a precisely predetermined position and recording Holoma’s navigation instructions.

Results
Holoma’s ArUco marker localization accuracy had a median error of -0.97 mm (min; max: -2.04; -0.27) with a marker-to-camera distance of 60 cm, and median jittering was 0.65 mm (min; max: 0; 2.07). Median image-to-patient registration precision was 2.20 mm (min; max: 0.39; 6.00), 3.52 mm (0.21; 6.92), and 3.79 mm (0.55; 8.83), for marker pose, point-to-point, and point cloud registration, respectively. Lastly, implant navigation instructions showed median errors of 2 mm (min; max: 0; 7), 3 mm (0; 7), and 4 mm (0; 9) after marker pose, point-to-point, and point cloud registration, respectively.

Discussion and conclusion
The experiments suggest an accumulation of technical errors in Holoma’s navigation application. The accuracy and precision of the navigation software were determined to be inadequate to decrease patient specific hip implant placement errors, at the time of investigating. Future improvements within Holoma will determine its feasibility for accurate implant navigation. Other navigation techniques should be considered in the search for optimal implant positioning guidance.

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.

Introduction
Osteoarthritis (OA) is a prevalent joint disease affecting 7% of the global population in 2020. Lower limb malalignment emerges as a significant contributor to OA, presenting as varus or valgus misalignment. This deviation induces unicompartmental pathology, leading to the wear and tear of the protective cartilage. Surgical interventions, including osteotomies, are essential in managing unicompartmental knee OA. During osteotomies, hinge fractures are a common complication. This paper focuses on optimizing open wedge osteotomies, specifically exploring complications in medial open wedge distal femoral osteotomy (DFO) using finite element models. And investigates the viability of the medial open wedge DFO compared to the lateral open wedge DFO.
Method
The research employed a systematic approach to investigate ways to avoid hinge fractures in Distal Femoral Osteotomy (DFO). Finite Element Modelling (FEM) served as the cornerstone of our methodology, providing a numerical solution. The process involved the creation of finite element models from CT scans through the subdivision of femoral geometry. The automated generation of these models was facilitated by a combination of 3-matic, Mimics, and Abaqus. Using Python scripting in these different programs, a workflow for model creation and parameter variation was created. The lateral open wedge DFO model, serving as the baseline, underwent systematic alterations to explorethe impact of hinge size, osteotomy gap angle, and other variables. The creation of finite element models involved several key steps, including geometry creation, mesh generation, addition of material properties, and the application of boundary and loading conditions. Material properties were assigned based on a simplified isotropic model derived from Hounsfield units. Extra attention was given to automate the process of model generation to ensure efficiency and reproducibility.
Results
Six distinct models were created with a comprehensive analysis of their attributes and shortcomings. The study finds that the medial open wedge DFO does not induce hinge tension. Comparative analyses in both opening and loading stages reveal nuanced stress and strain differences with the lateral open wedge DFO. No clear conclusion can be given as to the viability of the medial open wedge DFO compared to the lateral open wedge DFO. In-depth exploration indicates that smaller hinges are favourable for osteotomy gap opening, while larger hinges (10mm and above) contribute to stability during loading. Minimal impact on stress concentration is observed for osteotomy gap angle variations. The study explores the effectiveness of drill holes in stress relief, highlighting precision challenges.
Discussion
Acknowledging inherent limitations such as partial volume effects and assumptions about material properties. The study suggests promising avenues for future research. Recommendations for future research include in vivo experiments, exploration of XFEM and fracture mechanics, and further refinement of modelling techniques. This study provides nuanced insights into hinge fractures during open wedge DFO, guiding future research and bridging the gap between finite element modelling and
clinical realities.