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Purpose: Three-dimensional (3D) preoperative planning has become the gold standard for orthopedic surgeries, primarily relying on CT-reconstructed 3D models. However, in contrast to standing radiographs, a CT scan is not part of the standard protocol but is usually acquired for preoperative planning purposes only. Additionally, it is costly, exposes the patients to high doses of radiation and is acquired in a non-weight-bearing position. Methods: In this study, we develop a deep-learning based pipeline to facilitate 3D preoperative planning for high tibial osteotomies, based on 3D models reconstructed from low-dose biplanar standing EOS radiographs. Using digitally reconstructed radiographs, we train networks to localize the clinically required landmarks, separate the two legs in the sagittal radiograph and finally reconstruct the 3D bone model. Finally, we evaluate the accuracy of the reconstructed 3D models for the particular application case of preoperative planning, with the aim of eliminating the need for a CT scan in specific cases, such as high tibial osteotomies. Results: The mean Dice coefficients for the tibial reconstructions were 0.92 and 0.89 for the right and left tibia, respectively. The reconstructed models were successfully used for clinical-grade preoperative planning in a real patient series of 52 cases. The mean differences to ground truth values for mechanical axis and tibial slope were 0.52° and 4.33°, respectively. Conclusions: We contribute a novel framework for the 2D–3D reconstruction of bone models from biplanar standing EOS radiographs and successfully use them in automated clinical-grade preoperative planning of high tibial osteotomies. However, achieving precise reconstruction and automated measurement of tibial slope remains a significant challenge. [ABSTRACT FROM AUTHOR]

Corrective osteotomy allows to improve joint loading, pain and function. In complex deformities, the biggest challenge is to define the optimal surgical solution, while considering anatomical, technical and biomechanical factors. While the single-cut osteotomy (SCOT) and focal dome osteotomy (FDO) are well-established treatment options, their mathematical relationship remain largely unclear. The aim of the study was (1) to describe the close mathematical relationship between the SCOT and FDO and (2) to analyze and introduce a novel technique—the stepped FDO—as a modification of the classic FDO. The mathematical background and relationship of SCOT and FDO are described for the example of a femoral deformity correction and visualized using a 3D surface model taking into account the benefits for the clinical application. The novel modifications of the stepped FDO are introduced and its technical and clinical feasibility demonstrated. Both, SCOT and FDO, rely on the same deformity axis that defines the rotation axis k for a 3D deformity correction. To achieve the desired correction using a SCOT, the resulting cutting plane is perpendicular to k, while using a FDO will result in a cylindrical cut with a central axis parallel to k. The SCOT and FDO demonstrate a strong mathematical relation, as both methods rely on the same deformity axis, however, resulting in different cutting planes. These characteristics enable a complementary use when defining the optimal type of osteotomy. This understanding enables a more versatile planning approach when considering factors as the surgical approach, biomechanical characteristics of fixation or soft tissue conditions. The newly introduced stepped FDO facilitates an exact reduction of the bone fragments and potentially expands the clinical applicability of the FDO. [ABSTRACT FROM AUTHOR]

Background: The use of 3D planning to guide corrective osteotomies of the lower extremity is increasing in clinical practice. The use of computer-tomography (CT) data acquired in supine position neglects the weight-bearing (WB) state and the gold standard in 3D planning involves the manual adaption of the surgical plan after considering the WB state in long-leg radiographs (LLR). However, this process is subjective and dependent on the surgeons experience. A more standardized and automated method could reduce variability and decrease costs. Purpose: The aim of the study was (1) to compare three different three-dimensional (3D) planning modalities for medial open-wedge high tibial osteotomy (MOWHTO) and (2) to describe the current practice of adapting NWB CT data after considering the WB state in LLR. The purpose of this study is to validate a new, standardized approach to include the WB state into the 3D planning and to compare this method against the current gold standard of 3D planning. Our hypothesis is that the correction is comparable to the gold standard, but shows less variability due compared to the more subjective hybrid approach. Methods: Three surgical planning modalities were retrospectively analyzed in 43 legs scheduled for MOWHTO between 2015 and 2019. The planning modalities included: (1) 3D hybrid (3D non-weight-bearing (NWB) CT models after manual adaption of the opening angle considering the WB state in LLR, (2) 3D NWB (3D NWB CT models) and (3) 3D WB (2D/3D registration of 3D NWB CT models onto LLR to simulate the WB state). The pre- and postoperative hip-knee-ankle angle (HKA) and the planned opening angle (°) were assessed and differences among modalities reported. The relationship between the reported differences and BMI, preoperative HKA (LLR), medial meniscus extrusion, Outerbridge osteoarthritis grade and joint line convergence angle (JLCA) was analyzed. Results: The mean (std) planned opening angle of 3D hybrid did not differ between 3D hybrid and 3D WB (0.4 ± 2.1°) (n.s.) but was higher in 3D hybrid compared to 3D NWB (1.1° ± 1.1°) (p = 0.039). 3D WB demonstrated increased preoperative varus deformity compared to 3D NWB: 6.7 ± 3.8° vs. 5.6 ± 2.7° (p = 0.029). Patients with an increased varus deformity in 3D WB compared to 3D NWB (> 2 °) demonstrated more extensive varus alignment in LLR (p = 0.009) and a higher JLCA (p = 0.013). Conclusion: Small intermodal differences between the current practice of the reported 3D hybrid planning modality and a 3D WB approach using a 2D/3D registration algorithm were reported. In contrast, neglecting the WB state underestimates preoperative varus deformity and results in a smaller planned opening angle. This leads to potential under correction in MOWHTO, especially in patients with extensive varus deformities or JLCA. Clinical Relevance: Incorporating the WB state in 3D planning modalities has the potential to increase accuracy and lead to a more consistent and reliable planning in MOWHTO. The inclusion of the WB state in automatized surgical planning algorithms has the potential to reduce costs and time in the future. [ABSTRACT FROM AUTHOR]

Introduction: The periacetabular osteotomy is a technically demanding procedure with the goal to improve the osseous containment of the femoral head. The options for controlled execution of the osteotomies and verification of the acetabular reorientation are limited. With the assistance of augmented reality, new possibilities are emerging to guide this intervention. However, the scientific knowledge regarding AR navigation for PAO is sparse. Methods: In this cadaveric study, we wanted to find out, if the execution of this complex procedure is feasible with AR guidance, quantify the accuracy of the execution of the three-dimensional plan, and find out what has to be done to proceed to real surgery. Therefore, an AR guidance for the PAO was developed and applied on 14 human hip cadavers. The guidance included performance of the four osteotomies and reorientation of the acetabular fragment. The osteotomy starting points, the orientation of the osteotomy planes, as well as the reorientation of the acetabular fragment were compared to the 3D planning. Results: The mean 3D distance between planned and performed starting points was between 9 and 17 mm. The mean angle between planned and performed osteotomies was between 6° and 7°. The mean reorientation error between the planned and performed rotation of the acetabular fragment was between 2° and 11°. Conclusion: The planned correction can be achieved with promising accuracy and without serious errors. Further steps for a translation from the cadaver to the patient have been identified and must be addressed in future work. [ABSTRACT FROM AUTHOR]

Purpose: Over the last years, interest and efforts to implement augmented reality (AR) in orthopedic surgery through head-mounted devices (HMD) have increased. However, the majority of experiments were preclinical and within a controlled laboratory environment. The operating room (OR) is a more challenging environment with various confounding factors potentially affecting the performance of an AR-HMD. The aim of this study was to assess the performance of an AR-HMD in a real-life OR setting. Methods: An established AR application using the HoloLens 2 HMD was tested in an OR and in a laboratory by two users. The accuracy of the hologram overlay, the time to complete the trial, the number of rejected registration attempts, the delay in live overlay of the hologram, and the number of completely failed runs were recorded. Further, different OR setting parameters (light condition, setting up partitions, movement of personnel, and anchor placement) were modified and compared. Results: Time for full registration was higher with 48 s (IQR 24 s) in the OR versus 33 s (IQR 10 s) in the laboratory setting (p < 0.001). The other investigated parameters didn't differ significantly if an optimal OR setting was used. Within the OR, the strongest influence on performance of the AR-HMD was different light conditions with direct light illumination on the situs being the least favorable. Conclusion: AR-HMDs are affected by different OR setups. Standardization measures for better AR-HMD performance include avoiding direct light illumination on the situs, setting up partitions, and minimizing the movement of personnel. [ABSTRACT FROM AUTHOR]

Purpose: Robot-assisted ultrasound (rUS) systems have already been used to provide non-radiative three-dimensional (3D) reconstructions that form the basis for guiding spine surgical procedures. Despite promising studies on this technology, there are few studies that offer insight into the robustness and generality of the approach by verifying performance in various testing scenarios. Therefore, this study aims at providing an assessment of a rUS system, with technical details from experiments starting at the bench-top to the pre-clinical study. Methods: A semi-automatic control strategy was proposed to ensure continuous and smooth robotic scanning. Next, a U-Net-based segmentation approach was developed to automatically process the anatomic features and derive a high-quality 3D US reconstruction. Experiments were conducted on synthetic phantoms and human cadavers to validate the proposed approach. Results: Average deviations of scanning force were found to be 2.84±0.45 N on synthetic phantoms and to be 5.64±1.10 N on human cadavers. The anatomic features could be reliably reconstructed at mean accuracy of 1.28±0.87 mm for the synthetic phantoms and of 1.74±0.89 mm for the human cadavers. Conclusion: The results and experiments demonstrate the feasibility of the proposed system in a pre-clinical setting. This work is complementary to previous work, encouraging further exploration of the potential of this technology in in vivo studies. [ABSTRACT FROM AUTHOR]

Purpose: Previous work has demonstrated the high accuracy of augmented reality (AR) head-mounted displays for pedicle screw placement in spinal fusion surgery. An important question that remains unanswered is how pedicle screw trajectories should be visualized in AR to best assist the surgeon. Methodology: We compared five AR visualizations displaying the drill trajectory via Microsoft HoloLens 2 with different configurations of abstraction level (abstract or anatomical), position (overlay or small offset), and dimensionality (2D or 3D) against standard navigation on an external screen. We tested these visualizations in a study with 4 expert surgeons and 10 novices (residents in orthopedic surgery) on lumbar spine models covered by Plasticine. We assessed trajectory deviations ( ∘ ) from the preoperative plan, dwell times (%) on areas of interest, and the user experience. Results: Two AR visualizations resulted in significantly lower trajectory deviations (mixed-effects ANOVA, p<0.0001 and p<0.05) compared to standard navigation, whereas no significant differences were found between participant groups. The best ratings for ease of use and cognitive load were obtained with an abstract visualization displayed peripherally around the entry point and with a 3D anatomical visualization displayed with some offset. For visualizations displayed with some offset, participants spent on average only 20% of their time examining the entry point area. Conclusion: Our results show that real-time feedback provided by navigation can level task performance between experts and novices, and that the design of a visualization has a significant impact on task performance, visual attention, and user experience. Both abstract and anatomical visualizations can be suitable for navigation when not directly occluding the execution area. Our results shed light on how AR visualizations guide visual attention and the benefits of anchoring information in the peripheral field around the entry point. [ABSTRACT FROM AUTHOR]

Despite the undeniable advantages of image-guided surgical assistance systems in terms of accuracy, such systems have not yet fully met surgeons' needs or expectations regarding usability, time efficiency, and their integration into the surgical workflow. On the other hand, perceptual studies have shown that presenting independent but causally correlated information via multimodal feedback involving different sensory modalities can improve task performance. This article investigates an alternative method for computer-assisted surgical navigation, introduces a novel four-DOF sonification methodology for navigated pedicle screw placement, and discusses advanced solutions based on multisensory feedback. The proposed method comprises a novel four-DOF sonification solution for alignment tasks in four degrees of freedom based on frequency modulation synthesis. We compared the resulting accuracy and execution time of the proposed sonification method with visual navigation, which is currently considered the state of the art. We conducted a phantom study in which 17 surgeons executed the pedicle screw placement task in the lumbar spine, guided by either the proposed sonification-based or the traditional visual navigation method. The results demonstrated that the proposed method is as accurate as the state of the art while decreasing the surgeon's need to focus on visual navigation displays instead of the natural focus on surgical tools and targeted anatomy during task execution. [ABSTRACT FROM AUTHOR]

Purpose: Medial open wedge high tibial osteotomy (MOWHTO) is an effective treatment option for realignment of a varus knee. However, a simple supra-tuberositary osteotomy can lead to patella baja and potentially increases the tibial tuberosity–trochlear groove distance (TTTG). The purpose of this study was to quantify the influence of MOWHTO on TTTG. Methods: Three-dimensional (3D) surface models of five lower extremities with a varus hip–knee–ankle angle (HKA) and a borderline TTTG (≥ 15 mm), five lower extremities with a varus HKA and a normal TTTG (< 15 mm) and a 3D statistical shape model (SSM) of a neutrally aligned healthy knee were analysed by simulating MOWHTO with a stepwise increment of one degree of valgisation from the preoperative coronal deformity (0°–15°) for each patient, resulting in a total of 165 simulations. Postoperative 3D TTTG and tibial torsion (TT) were measured for each simulation. A mathematical formula was developed to calculate the increase of TTTG after MOWHTO. Mean differences between simulated and calculated TTTG were analysed. Results: Mean preoperative HKA was 6.5 ± 3.0° varus (range 0.8°–11.5°). Mean TTTG increased from 14.2 ± 3.2 mm (range 9.6–19.1) preoperatively to 18.8 ± 3.8 mm (range 14.5–25.0) postoperatively (p = 0.001). TTTG increased approximately linear by + 0.5 ± 0.2° (range 0.3–0.8) per 1° of valgisation with a high positive correlation (0.99, p = 0.001) from 0° to 15°. Mean difference between simulated and calculated TTTG was 0.03 ± 0.02 mm (range 0.01–0.07) per 1° of valgisation (p < 0.001). Conclusion: MOWHTO results in an approximately linear increase in TTTG of + 0.5 mm per 1° of valgisation in the range from 0° to 15° and the lateralisation of the tibial tuberosity can be calculated reliably using the described formula. Preoperative analysis of TTTG in patients undergoing MOWHTO may prevent unintentional patellofemoral malalignment. Level of evidence: III. [ABSTRACT FROM AUTHOR]

Purpose: High-grade patellofemoral dysplasia is often associated with concomitant axial and frontal leg malalignment. However, curvature of the femur and sagittal flexion of the trochlea has not yet been studied in patellofemoral dysplastic knees. The aim of the study was to quantify the femoral curvature and sagittal flexion of the trochlea in both high-grade patellofemoral dysplastic and healthy knees. Methods: A retrospective case–control study matched 19 high-grade patellofemoral dysplastic knees (Dejour types C and D) with 19 healthy knees according to sex and body mass index. Three-dimensional (3D) femoral curvature and sagittal trochlea flexion were analysed. To analyse femoral curvature, the specific 3D radius of curvature (ROC) was calculated. Trochlear flexion was quantified through the development of the trochlea flexion angle (TFA), which is a novel 3D measurement in relation to the anatomical and mechanical femur axis and is referred to as 3D TFAanatomic and 3D TFAmech. The influence of age, gender, height, weight and frontal and axial alignment on ROC and TFA was analysed in a multiple regression model. Results: Overall ROC was significantly smaller in dysplastic knees, compared with the control group [898.4 ± 210.8 mm (range 452.9–1275.1 mm) vs 1308.4 ± 380.5 mm (range 878.3–2315.8 mm), p < 0.001]. TFA was significantly higher in dysplastic knees, compared with the control group, for 3D TFAmech [13.8 ± 7.2° (range 4.4–33.4°) vs 6.5 ± 2.3° (range 0.8–10.2°), p < 0.001] and 3D TFAanatomic [12.5 ± 7.2° (range 3.1–32.2°) vs 6.4 ± 1.9° (range 2.1–9.1°), p = 0.001]. A smaller ROC was associated with smaller height, female gender and higher femoral ante torsion. An increased TFA was associated with valgus malalignment. Conclusion: High-grade patellofemoral dysplastic knees demonstrated increased femoral curvature and sagittal flexion of the trochlea, compared with healthy knees. The ROC and newly described TFA allowed the quantification of the sagittal femoral deformity. TFA and ROC should be incorporated in future deformity analysis to investigate their potential as a target for surgical correction. Level of Evidence: Level III. [ABSTRACT FROM AUTHOR]

Background: To achieve an optimal clinical outcome in reverse total shoulder arthroplasty (RSA), accurate placement of the components is essential. The recently introduced navigation technology of augmented reality (AR) through head-mounted displays (HMD) offers a promising new approach to visualize the anatomy and navigate component positioning in various orthopedic surgeries. We hypothesized that AR through HMD is feasible, reliable, and accurate for guidewire placement in RSA baseplate positioning. Methods: Twelve human cadaver shoulders were scanned with computed tomography (CT) and RSA baseplate positioning was 3-D planned using dedicated software. The shoulders were prepared through a deltopectoral approach and an augmented reality hologram was superimposed using the HMD Microsoft HoloLense. The central guidewire was then navigated through the HMD to achieve the planned entry point and trajectory. Postoperatively, the shoulders were CT-scanned a second time and the deviation from the planning was calculated. Results: The mean deviation of the entry point was 3.5 mm ± 1.7 mm (95% CI 2.4 mm; 4.6 mm). The mean deviation of the planned trajectory was 3.8° ± 1.7° (95% CI 2.6°; 4.9°). Conclusion: Augmented reality seems feasible and reliable for baseplate guidewire positioning in reverse total shoulder arthroplasty. The achieved values were accurate. [ABSTRACT FROM AUTHOR]

Purpose: Augmented reality (AR) is an emerging technology with great potential for surgical navigation through its ability to provide 3D holographic projection of otherwise hidden anatomical information. This pilot cadaver study investigated the feasibility and accuracy of one of the first holographic navigation techniques for lumbar pedicle screw placement. Methods: Lumbar computer tomography scans (CT) of two cadaver specimens and their reconstructed 3D models were used for pedicle screw trajectory planning. Planned trajectories and 3D models were subsequently uploaded to an AR head-mounted device. Randomly, k-wires were placed either into the left or the right pedicle of a vertebra (L1-5) with or without AR-navigation (by holographic projection of the planned trajectory). CT-scans were subsequently performed to assess accuracy of both techniques. Results: A total of 18 k-wires could be placed (8 navigated, 10 free hand) by two experienced spine surgeons. In two vertebrae, the AR-navigation was aborted because the registration of the preoperative plan with the intraoperative anatomy was imprecise due to a technical failure. The average differences of the screw entry points between planning and execution were 4.74 ± 2.37 mm in the freehand technique and 5.99 ± 3.60 mm in the AR-navigated technique (p = 0.39). The average deviation from the planned trajectories was 11.21° ± 7.64° in the freehand technique and 5.88° ± 3.69° in the AR-navigated technique (p = 0.09). Conclusion: This pilot study demonstrates improved angular precision in one of the first AR-navigated pedicle screw placement studies worldwide. Technical shortcomings need to be eliminated before potential clinical applications. [ABSTRACT FROM AUTHOR]

Background: Accurate glenoid positioning in reverse total shoulder arthroplasty (RSA) is important to achieve satisfying functional outcome and prosthesis longevity. Optimal component placement can be challenging, especially in severe glenoid deformities. The use of patient-specific instruments (PSI) and 3D computer-assisted optical tracking navigation (NAV) are already established methods to improve surgical precision. Augmented reality technology (AR) promises similar results at low cost and ease of use. With AR, the planned component placement can be superimposed to the surgical situs and shown directly in the operating field using a head mounted display. We introduce a new navigation technique using AR via head mounted display for surgical navigation in this feasibility study, aiming to improve and enhance the surgical planning. Methods: 3D surface models of ten human scapulae were printed from computed tomography (CT) data of cadaver scapulae. Guidewire positioning of the central back of the glenoid baseplate was planned with a dedicated computer software. A hologram of the planned guidewire with dynamic navigation was then projected onto the 3D-created models of the cadaver shoulders. The registration of the plan to the anatomy was realized by digitizing the glenoid surface and the base of the coracoid with optical tracking using a fiducial marker. After navigated placement of the central guidewires, another CT imaging was recorded, and the 3D model was superimposed with the preoperative planning to analyze the deviation from the planned and executed central guides trajectory and entry point. Results: The mean deviation of the ten placed guidewires from the planned trajectory was 2.7° ± 1.3° (95% CI 1.9°; 3.6°). The mean deviation to the planned entry point of the ten placed guidewires measured 2.3 mm ± 1.1 mm (95% CI 1.5 mm; 3.1 mm). Conclusion: AR may be a promising new technology for highly precise surgical execution of 3D preoperative planning in RSA. [ABSTRACT FROM AUTHOR]

Introduction: Idiopathic scoliosis, defined as a > 10° curvature of the spine in the frontal plane, is one of the most common spinal deformities. Age, initial curve magnitude and other parameters define whether a scoliotic deformity will progress or not. Still, their interactions and amounts of individual contribution are not fully elaborated and were the aim of this systematic review. Methods: A systematic literature search was conducted in the common databases using MESH terms, searching for predictive factors of curve progression in adolescent idiopathic scoliosis ("adolescent idiopathic scoliosis" OR "ais" OR "idiopathic scoliosis") AND ("predictive factors" OR "progression" OR "curve progression" OR "prediction" OR "prognosis"). The identified and analysed factors of each study were rated to design a top five scale of the most relevant factors. Results: Twenty-eight investigations with 8255 patients were identified by literature search. Patient-specific risk factors for curve progression from initial curve were age (at diagnosis < 13 years), family history, bone mineral status (< 110 mg/cm3 in quantitative CT) and height velocity (7–8 cm/year, peak 11.6 ± 1.4 years). Relevant radiological criteria indicating curve progression included skeletal maturity, marked by Risser stages (Risser < 1) or Sanders Maturity Scale (SMS < 5), the initial extent of the Cobb angle (> 25° progression) and curve location (thoracic single or double curve). Discussion: This systematic review summarised the current state of knowledge as the basis for creation of patient-specific algorithms regarding a risk calculation for a progressive scoliotic deformity. Curve magnitude is the most relevant predictive factor, followed by status of skeletal maturity and curve location. [ABSTRACT FROM AUTHOR]

Purpose: Tracking of tools and surgical activity is becoming more and more important in the context of computer assisted surgery. In this work, we present a data generation framework, dataset and baseline methods to facilitate further research in the direction of markerless hand and instrument pose estimation in realistic surgical scenarios. Methods: We developed a rendering pipeline to create inexpensive and realistic synthetic data for model pretraining. Subsequently, we propose a pipeline to capture and label real data with hand and object pose ground truth in an experimental setup to gather high-quality real data. We furthermore present three state-of-the-art RGB-based pose estimation baselines. Results: We evaluate three baseline models on the proposed datasets. The best performing baseline achieves an average tool 3D vertex error of 16.7 mm on synthetic data as well as 13.8 mm on real data which is comparable to the state-of-the art in RGB-based hand/object pose estimation. Conclusion: To the best of our knowledge, we propose the first synthetic and real data generation pipelines to generate hand and object pose labels for open surgery. We present three baseline models for RGB based object and object/hand pose estimation based on RGB frames. Our realistic synthetic data generation pipeline may contribute to overcome the data bottleneck in the surgical domain and can easily be transferred to other medical applications. [ABSTRACT FROM AUTHOR]

In this work, we developed and validated a computer method capable of robustly detecting drill breakthrough events and show the potential of deep learning-based acoustic sensing for surgical error prevention. Bone drilling is an essential part of orthopedic surgery and has a high risk of injuring vital structures when over-drilling into adjacent soft tissue. We acquired a dataset consisting of structure-borne audio recordings of drill breakthrough sequences with custom piezo contact microphones in an experimental setup using six human cadaveric hip specimens. In the following step, we developed a deep learning-based method for the automated detection of drill breakthrough events in a fast and accurate fashion. We evaluated the proposed network regarding breakthrough detection sensitivity and latency. The best performing variant yields a sensitivity of 93.64 ± 2.42 % for drill breakthrough detection in a total execution time of 139.29 ms . The validation and performance evaluation of our solution demonstrates promising results for surgical error prevention by automated acoustic-based drill breakthrough detection in a realistic experiment while being multiple times faster than a surgeon's reaction time. Furthermore, our proposed method represents an important step for the translation of acoustic-based breakthrough detection towards surgical use. [ABSTRACT FROM AUTHOR]

Objectives: 3D preoperative planning of lower limb osteotomies has become increasingly important in light of modern surgical technologies. However, 3D models are usually reconstructed from Computed Tomography data acquired in a non-weight-bearing posture and thus neglecting the positional variations introduced by weight-bearing. We developed a registration and planning pipeline that allows for 3D preoperative planning and subsequent 3D assessment of anatomical deformities in weight-bearing conditions. Methods: An intensity-based algorithm was used to register CT scans with long-leg standing radiographs and subsequently transform patient-specific 3D models into a weight-bearing state. 3D measurement methods for the mechanical axis as well as the joint line convergence angle were developed. The pipeline was validated using a leg phantom. Furthermore, we evaluated our methods clinically by applying it to the radiological data from 59 patients. Results: The registration accuracy was evaluated in 3D and showed a maximum translational and rotational error of 1.1 mm (mediolateral direction) and 1.2° (superior-inferior axis). Clinical evaluation proved feasibility on real patient data and resulted in significant differences for 3D measurements when the effects of weight-bearing were considered. Mean differences were 2.1 ± 1.7° and 2.0 ± 1.6° for the mechanical axis and the joint line convergence angle, respectively. 37.3 and 40.7% of the patients had differences of 2° or more in the mechanical axis or joint line convergence angle between weight-bearing and non-weight-bearing states. Conclusions: Our presented approach provides a clinically feasible approach to preoperatively fuse 2D weight-bearing and 3D non-weight-bearing data in order to optimize the surgical correction. [ABSTRACT FROM AUTHOR]

Purpose of Review: Augmented reality (AR) is becoming increasingly popular in modern-day medicine. Computer-driven tools are progressively integrated into clinical and surgical procedures. The purpose of this review was to provide a comprehensive overview of the current technology and its challenges based on recent literature mainly focusing on clinical, cadaver, and innovative sawbone studies in the field of orthopedic surgery. The most relevant literature was selected according to clinical and innovational relevance and is summarized. Recent Findings: Augmented reality applications in orthopedic surgery are increasingly reported. In this review, we summarize basic principles of AR including data preparation, visualization, and registration/tracking and present recently published clinical applications in the area of spine, osteotomies, arthroplasty, trauma, and orthopedic oncology. Higher accuracy in surgical execution, reduction of radiation exposure, and decreased surgery time are major findings presented in the literature. Summary: In light of the tremendous progress of technological developments in modern-day medicine and emerging numbers of research groups working on the implementation of AR in routine clinical procedures, we expect the AR technology soon to be implemented as standard devices in orthopedic surgery. [ABSTRACT FROM AUTHOR]

Purpose: Pathological tibial torsion is known to negatively influence the functionality of the lower extremity, and therefore, its assessment might play an important role. While 3D imaging is used for many examinations of the musculoskeletal system, for the determination of tibial torsion no 3D measurement technique has been available so far. We developed a 3D measurement method and assess its interobserver reliability as well as its correlation with standard 2D measurement methods. Methods: CT scans of 82 tibiae in 79 patients with a mean age of 41 years were included. A novel 3D measurement technique was developed and applied. Measurements were compared with two frequently used 2D measurement methods. ICC (intraclass correlation coefficient) for the new technique was determined and compared to the 2D measurement method. Furthermore, differences between left and right legs as well as between males and females were assessed. Results: The ICC for the 2D methods was 0.917 and 0.938, respectively. For the 3D measurements, ICCs were calculated to be 0.954 and 0.950. Agreement between 2 and 3D methods was moderate to good with ICCs between 0.715 and 0.795. Torsion values for left and right legs did not differ significantly in 2D and in 3D (26.2 vs 28.5° and 27.2 vs. 25.9°). The same is true for the differences between male and female in 2D and 3D (26.2 vs. 29.6° and 25.0 vs. 31.2°). Conclusion: The newly developed 3D measurement technique shows a high intraclass agreement and offers an applicable opportunity to assess the tibial torsion three-dimensionally. [ABSTRACT FROM AUTHOR]

Purpose: Flexion and rotation of the knee joint are supposed to alter the measurement of the mechanical leg axis on long leg radiographs. However, in patients with varus or valgus alignment it has not been systematically analyzed so far. The hypothesis is that measurement of the mechanical leg axis is more influenced by flexion and rotation in presence of varus or valgus alignment compared to patients with a straight coronal alignment.Methods: 3D surface models of the lower extremities of seven individuals with varying degrees of coronal alignment were created based on CT data. The coronal alignment of the seven individuals captured the range between 9° varus and 9° valgus with equal steps of 3°. Combinations of internal and external rotations of 10°, 20°, and 30° with flexion of 5°, 10°, 15°, 20°, and 30° were simulated. The mechanical leg axis was measured for each combination as the antero-posterior (ap)-projected hip-knee-ankle (HKA-) angle.Results: 294 simulations with all combinations of rotation and flexion were performed. Ranges of deviation of HKA never showed a critical deviation of more than 3° from median values. Deviations from baseline appeared normally distributed for all flexion and rotation combinations (p < 0.05) and the probability for a deviation from the mean mechanical leg axis of more than 3° was less than 0.03 for all combinations. Comparability of the models, therefore, could be assumed.Conclusion: Deviations in HKA-angle measurements, caused by rotation or flexion, does not vary relevantly through the range of coronal alignment of 9° varus to 9° valgus. As a clinical relevance, deviations in HKA-angle measurements can be considered as comparable in patients with different coronal alignment.Level Of Evidence: III. [ABSTRACT FROM AUTHOR]

Purpose: Patellofemoral instability can be caused by tibial or femoral torsional deformity. Established surgical treatment options are rotational osteotomies, but the transfer from pre-operative planning to surgical execution can be challenging. Patient-specific instruments (PSI) are proofed to be helpful tools in realignment surgery. However, accuracy of PSI in femoral and tibial rotational osteotomies remains still unknown. Goal of the present study was to evaluate the accuracy of PSI in femoral and tibial rotational osteotomies in a patient population suffering from patellofemoral instability. Methods: All patients that underwent femoral or tibial rotational osteotomy using PSI in case of patellofemoral instability from October 2015 until April 2019 in our clinic were included. Twelve knees with twelve supracondylar femoral and seven supratuberositary tibial rotational osteotomies could be included. Accuracy of the correction was assessed using pre- and post-operative CT scans based on conventional measurements and, in 3D, based on 3D bone models of the respective patients. Results: CT measurements revealed an absolute difference between planned and achieved rotation of 4.8° ± 3.1° for femoral and 7.9° ± 3.7° for tibial rotational osteotomies without significant difference (p = 0.069). Regarding 3D assessment, a significant difference could be observed for the residual error between femoral and tibial rotational osteotomies in the 3D angle (p = 0.014) with a higher accuracy for the femoral side. Conclusion: The application of PSI for femoral and tibial rotational osteotomy is a safe surgical treatment option. Accuracy for femoral rotational osteotomies is higher compared with tibial rotational osteotomies using PSI. [ABSTRACT FROM AUTHOR]

Purpose: Patient-specific instruments (PSIs) are helpful tools in high tibial osteotomy (HTO) in patients with symptomatic varus malalignment of the mechanical leg axis. However, the precision of HTO can decrease with malpositioned PSI. This study investigates the influence of malpositioned PSI on axis correction, osteotomy, and implant placement.Methods: With a mean three-dimensional (3D) model (0.8° varus), PSI-navigated HTOs were computer simulated. Two different guide designs, one with stabilising hooks and one without, were used. By adding rotational and translational offsets of different degrees, wrong placements of PSI were simulated. After 5° valgisation of the postoperative mechanical axis, the distance between joint-plane and osteotomy screws, respectively, were measured. The same simulations were performed in a patient with varus deformity (7.4° varus).Results: In the mean 3D model, the postoperative mechanical axis was within 3.9°-4.5° valgus with mean value of 4.1° ± 0.1° (correct axis 4.2° valgus). Surgical failure concerning osteotomy occurred in 17 of 76 HTOs. Significantly safer screw placement was observed using PSI with stabilising hooks (p = 0.012). In the case of the 3D model with 7.4° varus deformity, the postoperative mechanical axis was within 3.2°-3.9° valgus with mean value of 3.8° ± 0.2° (correct axis 3.9° valgus). Surgical failure concerning osteotomy occurred in 3 of 38 HTOs. Screws were always within the safety distance.Conclusion: The clinical relevance of the presented study is that malpositioning of a PSI within the possible degrees of freedom does not have a relevant influence on the axis correction. The most vulnerable plane for surgical failure is the sagittal plane, wherefore the treating surgeon should verify correct guide placement to prevent surgical failure, particularly in this plane.Level Of Evidence: III. [ABSTRACT FROM AUTHOR]

State-of-the-art of preoperative planning for forearm orthopaedic surgeries is currently limited to simple bone procedures. The increasing interest of clinicians for more comprehensive analysis of complex pathologies often requires dynamic models, able to include the soft tissue influence into the preoperative process. Previous studies have shown that the interosseous membrane (IOM) influences forearm motion and stability, but due to the lack of morphological and biomechanical data, existing simulation models of the IOM are either too simple or clinically unreliable. This work aims to address this problematic by generating 3D morphological and tensile properties of the individual IOM structures. First, micro- and standard-CT acquisitions were performed on five fresh-frozen annotated cadaveric forearms for the generation of 3D models of the radius, ulna and each of the individual ligaments of the IOM. Afterwards, novel 3D methods were developed for the measurement of common morphological features, which were validated against established optical ex-vivo measurements. Finally, we investigated the individual tensile properties of each IOM ligament. The generated 3D morphological features can provide the basis for the future development of functional planning simulation of the forearm. [ABSTRACT FROM AUTHOR]

Purpose: In spinal fusion surgery, imprecise placement of pedicle screws can result in poor surgical outcome or may seriously harm a patient. Patient-specific instruments and optical systems have been proposed for improving precision through surgical navigation compared to freehand insertion. However, existing solutions are expensive and cannot provide in situ visualizations. Recent technological advancement enabled the production of more powerful and precise optical see-through head-mounted displays for the mass market. The purpose of this laboratory study was to evaluate whether such a device is sufficiently precise for the navigation of lumbar pedicle screw placement. Methods: A novel navigation method, tailored to run on the Microsoft HoloLens, was developed. It comprises capturing of the intraoperatively reachable surface of vertebrae to achieve registration and tool tracking with real-time visualizations without the need of intraoperative imaging. For both surface sampling and navigation, 3D printable parts, equipped with fiducial markers, were employed. Accuracy was evaluated within a self-built setup based on two phantoms of the lumbar spine. Computed tomography (CT) scans of the phantoms were acquired to carry out preoperative planning of screw trajectories in 3D. A surgeon placed the guiding wire for the pedicle screw bilaterally on ten vertebrae guided by the navigation method. Postoperative CT scans were acquired to compare trajectory orientation (3D angle) and screw insertion points (3D distance) with respect to the planning. Results: The mean errors between planned and executed screw insertion were 3. 38 ∘ ± 1.73 ∘ for the screw trajectory orientation and 2.77±1.46 mm for the insertion points. The mean time required for surface digitization was 125±27 s. Conclusions: First promising results under laboratory conditions indicate that precise lumbar pedicle screw insertion can be achieved by combining HoloLens with our proposed navigation method. As a next step, cadaver experiments need to be performed to confirm the precision on real patient anatomy. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate whether 3D-printed vertebrae offer realistic haptic simulation of posterior pedicle screw placement and decompression surgery with normal to osteoporotic-like properties.Methods: A parameterizable vertebra model was developed, adjustable in cortical and cancellous bone thicknesses. Based on this model, five different L3 vertebra types (α, β, γ1, γ2, and γ3) were designed and fourfold 3D-printed. Four spine surgeons assessed each vertebra type and a purchasable L3 Sawbones vertebra. Haptic behavior of six common steps in posterior spine surgery was rated from 1 to 10: 1-2: too soft, 3-4: osteoporotic, 5-6: normal, 7-8: hard, and 9-10: too hard. Torques were measured during pedicle screw insertion.Results: In total, 24 vertebrae (six vertebra types times four examiners) were evaluated. Mean surgical assessment scores were: α 3.2 ± 0.9 (osteoporotic), β 1.9 ± 0.7 (too soft), γ1 4.7 ± 0.9 (osteoporotic-normal), γ2 6.3 ± 1.1 (normal), and γ3 7.5 ± 1.1 (hard). All surgeons considered the 3D-printed vertebrae α, γ1, and γ2 as more realistic than Sawbones vertebrae, which were rated with a mean score of 4.1 ± 1.7 (osteoporotic-normal). Mean pedicle screw insertion torques (Ncm) were: α 32 ± 4, β 12 ± 3, γ1 74 ± 4, γ2 129 ± 13, γ3 196 ± 34 and Sawbones 90 ± 11.Conclusions: In this pilot study, 3D-printed vertebrae displayed haptically and biomechanically realistic simulation of posterior spinal procedures and outperformed Sawbones. This approach enables surgical training on bone density-specific vertebrae and provides an outlook toward future preoperative simulation on patient-specific spine replicas. These slides can be retrieved under Electronic Supplementary Material. [ABSTRACT FROM AUTHOR]

Purpose: The contralateral anatomy is regularly used as a reconstruction template for corrective osteotomies of several deformities and pathological conditions. However, there is lack of evidence that the intra-individual differences between both tibiae are sufficiently small to use the contralateral tibia as a 3D reconstruction template for complex osteotomies. The aim of this study was to evaluate the intra-individual side differences of the tibia in length, torsion, angulation, and translation using 3D measurement techniques.Methods: 3D surface models of both tibiae were created from computed tomography data of 51 cadavers. The (mirrored) models of the right tibiae were divided into two halves at the centre of the shaft. Thereafter, the proximal and distal segments were aligned to the left (contralateral) tibia in an automated fashion. The relative 3D transformation between both aligned segments was measured to quantify the side difference in 6° of freedom (3D translation vector, 3 angles of rotation).Results: The mean side difference in tibia length was 2.1 mm (SD 1.3 mm; range 0.2-5.9 mm). The mean side difference in torsion was 4.9° (SD 4.1°; range 0.2°-17.6°). The mean side difference in the coronal and sagittal planes was 1.1° (SD 0.9°; range 0.0°-4.6°) and 1.0° (SD 0.8°; range 0.1°-2.9°), respectively.Conclusion: The present study confirms small side differences in torsion between the left and right tibia, while the side differences in the coronal and sagittal plane are probably negligible. The contralateral tibia seems to be a reliable reconstruction template for the 3D preoperative planning of complex corrective osteotomies of the tibia. However, torsional differences should be interpreted with caution, as a single cut-off value of a clinically relevant torsional side difference cannot be defined. The presented results are relevant to surgeons considering the contralateral tibia as a 3D reconstruction template for corrective osteotomies of the tibia.Level Of Evidence: Basic science. [ABSTRACT FROM AUTHOR]

Purpose: Planning orthopedic surgeries is commonly performed in computed tomography (CT) images due to the higher contrast of bony structure. However, soft tissues such as muscles and ligaments that may determine the functional outcome of a procedure are not easy to identify in CT, for which fast and accurate segmentation in MRI would be desirable. To be usable in daily practice, such method should provide convenient means of interaction for modifications and corrections, e.g., during perusal by the surgeon or the planning physician for quality control. Methods: We propose an interactive segmentation framework for MR images and evaluate the outcome for segmentation of bones. We use a random forest classification and a random walker-based spatial regularization. The latter enables the incorporation of user input as well as enforcing a single connected anatomical structures, thanks to which a selective sampling strategy is proposed to substantially improve the supervised learning performance. Results: We evaluated our segmentation framework on 10 patient humerus MRI as well as 4 high-resolution MRI from volunteers. Interactive humerus segmentations for patients took on average 150 s with over 3.5 times time-gain compared to manual segmentations, with accuracies comparable (converging) to that of much longer interactions. For high-resolution data, a novel multi-resolution random walker strategy further reduced the run time over 20 times of the manual segmentation, allowing for a feasible interactive segmentation framework. Conclusions: We present a segmentation framework that allows iterative corrections leading to substantial speed gains in bone annotation in MRI. This will allow us to pursue semi-automatic segmentations of other musculoskeletal anatomy first in a user-in-the-loop manner, where later less user interactions or perhaps only few for quality control will be necessary as our annotation suggestions improve. [ABSTRACT FROM AUTHOR]

Modeling ligaments as three-dimensional strings is a popular method for in vivo estimation of ligament length. The purpose of this study was to develop an algorithm for automated generation of non-penetrating strings between insertion points and to evaluate its feasibility for estimating length changes of the medial patellofemoral ligament during normal knee flexion. Three-dimensional knee models were generated from computed tomography (CT) scans of 10 healthy subjects. The knee joint under weight-bearing was acquired in four flexion positions (0°-120°). The path between insertion points was computed in each position to quantify string length and isometry. The average string length was maximal in 0° of flexion (64.5 ± 3.9 mm between femoral and proximal patellar point; 62.8 ± 4.0 mm between femoral and distal patellar point). It was minimal in 30° (60.0 ± 2.6 mm) for the proximal patellar string and in 120° (58.7 ± 4.3 mm) for the distal patellar string. The insertion points were considered to be isometric in 4 of the 10 subjects. The proposed algorithm appears to be feasible for estimating string lengths between insertion points in an automatic fashion. The length measurements based on CT images acquired under physiological loading conditions may give further insights into knee kinematics. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

The current clinical gold standard to assess the condition and detect loosening of pedicle screw implants is radiation-emitting medical imaging. However, solely based on medical imaging, clinicians are not able to reliably identify loose implants in a substantial amount of cases. To complement medical imaging for pedicle screw loosening detection, we propose a new methodology and paradigm for the radiation-free, non-destructive, and easy-to-integrate loosening detection based on vibroacoustic sensing. For the detection of a loose implant, we excite the vertebra of interest with a sine sweep vibration at the spinous process and use a custom highly sensitive piezo vibration sensor attached directly at the screw head to capture the propagated vibration characteristics which are analyzed using a detection pipeline based on spectrogram features and a SE-ResNet-18. To validate the proposed approach, we propose a novel, biomechanically validated simulation technique for pedicle screw loosening, conduct experiments using four human cadaveric lumbar spine specimens, and evaluate our algorithm in a cross-validation experiment. The proposed method reaches a sensitivity of 91.50±6.58%\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$91.50 \pm 6.58 \%$$\end{document} and a specificity of 91.10±2.27%\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$91.10 \pm 2.27 \%$$\end{document} for pedicle screw loosening detection.Graphical abstract: The current clinical gold standard to assess the condition and detect loosening of pedicle screw implants is radiation-emitting medical imaging. However, solely based on medical imaging, clinicians are not able to reliably identify loose implants in a substantial amount of cases. To complement medical imaging for pedicle screw loosening detection, we propose a new methodology and paradigm for the radiation-free, non-destructive, and easy-to-integrate loosening detection based on vibroacoustic sensing. For the detection of a loose implant, we excite the vertebra of interest with a sine sweep vibration at the spinous process and use a custom highly sensitive piezo vibration sensor attached directly at the screw head to capture the propagated vibration characteristics which are analyzed using a detection pipeline based on spectrogram features and a SE-ResNet-18. To validate the proposed approach, we propose a novel, biomechanically validated simulation technique for pedicle screw loosening, conduct experiments using four human cadaveric lumbar spine specimens, and evaluate our algorithm in a cross-validation experiment. The proposed method reaches a sensitivity of 91.50±6.58%\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$91.50 \pm 6.58 \%$$\end{document} and a specificity of 91.10±2.27%\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$91.10 \pm 2.27 \%$$\end{document} for pedicle screw loosening detection. [ABSTRACT FROM AUTHOR]