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Objective: To analyze a novel navigation system utilizing augmented reality (AR) as a supporting method for fibula free flap (FFF) harvest and fabrication.Methods: A total of 126 simulated osteotomies supported with a cutting guide or one of two AR-based intraoperative navigation modules-simple AR (sAR) or navigated AR (nAR)-were carried out on 18 identical models of the fibula (42 osteotomies per method). After fusing postoperative computed tomography scans of the operated fibulas with the virtual surgical plan based on preoperative images, the objective outcomes-angular deviations from the planned osteotomy trajectory ( o ) and deviations of control points marked on the trajectory (mm)-were determined.Results: All analyzed methods provided similar accuracy of assisted osteotomies. The only significant difference referred to angular deviation in the sagittal plane, which was smaller after the cutting guide-assisted procedures than after the application of sAR and nAR (4.1 AE 2.29 vs. 5.08 AE 3.64 degrees, P = 0.031 and 4.1 AE 2.29 vs. 4.97 AE 2.91, P = 0.002, respectively). Mean deviation of control points after the cutting guide-assisted procedures was 2.76 AE 1.06 mm, as compared with 2.67 AE 1.09 mm for sAR and 2.95 AE 1.11 mm for nAR.Conclusion: Our study demonstrated that both novel AR-based methods provided similar accuracy of assisted harvesting and contouring of the FFF as the cutting guides. This fact, as well as the acceptability of the concept by clinicians, justify their further development and evaluation in preclinical settings.

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Objective. The purpose of the present work was to assess the validity of a six-degrees-of-freedom gait analysis model based on the ISB recommendation on definitions of joint coordinate systems (ISB 6DOF) through a quantitative comparison with the Helen Hays model (HH) and repeatability assessment. Methods. Four healthy subjects were analysed with both marker sets: an HH marker set and four marker clusters in ISB 6DOF. A navigated pointer was used to indicate the anatomical landmark position in the cluster reference system according to the ISB recommendation. Three gait cycles were selected from the data collected simultaneously for the two marker sets. Results. Two protocols showed good intertrial repeatability, which apart from pelvic rotation did not exceed 2°. The greatest differences between protocols were observed in the transverse plane as well as for knee angles. Knee internal/external rotation revealed the lowest subject-to-subject and interprotocol repeatability and inconsistent patterns for both protocols. Knee range of movement in transverse plane was overestimated for the HH set (the mean is 34°), which could indicate the cross-talk effect. Conclusions. The ISB 6DOF anatomically based protocol enabled full 3D kinematic description of joints according to the current standard with clinically acceptable intertrial repeatability and minimal equipment requirements.

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The purpose of the current study was to investigate the robustness of dynamic simulation results in the presence of uncertainties resulting from application of a scaled-generic musculoskeletal model instead of a subject-specific model as well as the effect of the choice of simulation method on the obtained muscle forces. The performed sensitivity analysis consisted of the following multibody parameter modifications: maximum isometric muscle forces, number of muscles, the hip joint centre location, segment masses as well as different dynamic simulation methods, namely static optimization with three different criteria and a computed muscle control algorithm (hybrid approach combining forward and inverse dynamics). Twenty-four different models and fifty-five resultant dynamic simulation data sets were analysed. The effects of model perturbation on the magnitude and profile of muscle forces were compared. It has been shown that estimated muscle forces are very sensitive to model parameters. The greatest impact was observed in the case of the force magnitude of the muscles generating high forces during gait (regardless of the modification introduced). However, the force profiles of those muscles were preserved. Relatively large differences in muscle forces were observed for different simulation techniques, which included both magnitude and profile of muscle forces. Personalization of model parameters would affect the resultant muscle forces and seems to be necessary to improve general accuracy of the estimated parameters. However, personalization alone will not ensure high accuracy due to the still unresolved muscle force sharing problem.

Purpose: The purpose of this study was to develop and verify an intraoperative module for supporting navigated biopsy procedures using optical see-through head-mounted display (HMD). Methods: Biopsy procedure including entry and endpoints of needle insertion was planned preoperatively having regard to the resection region segmentation and safety margin definition. Biopsy procedures were performed by two users using an intraoperative optical navigation module on a specially prepared brain phantom. Two visualization techniques were compared: an accurate augmented reality one, where a virtual plan is superimposed onto surgical field by using optical see-through HMD together with personalized calibration method and visualization on the external display. Results: Averaged errors from 24 trials using external display were 2.04 ± 0.83 mm for the first user and 2.69 ± 1.11 mm for the second one, while applying HMD 2.50 ± 0.93 mm (the first user) and 2.17 ± 0.82 mm (the second user), respectively. Conclusions: Proper usage of HMD visualization preceded by the personalized calibration allows the user to perform navigated biopsy procedure with comparable accuracy to its equivalent with the external display. Additionally, augmented reality visualization improves ergonomics and enables focusing on the surgical field without losing a direct line of sight with the field of view as it happens for external displays. However, ensuring high accuracy of augmented reality visualization still requires proper calibration and some user experience, which is challenging.