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It remains unclear to what extent the interosseous membrane (IOM) is affected through the whole range of motion (ROM) in posttraumatic deformities of the forearm. The purpose of this study is to describe the ligament- and bone-related factors involved in rotational deficit of the forearm. Through three-dimensional (3D) kinematic simulations on one cadaveric forearm, angular deformities of 5° in four directions (flexion, extension, valgus, varus) were produced at two locations of the radius and the ulna (proximal and distal third). The occurrence of bone collision in pronation and the linear length variation of six parts of the IOM through the whole ROM were compared between the 32 types of forearm deformities. Similar patterns could be observed among four groups: 12 types of deformity presented increased bone collision in pronation, 8 presented an improvement of bone collision with an increase of the mean linear lengthening of the IOM in neutral rotation, 6 had an increased linear lengthening of the IOM in supination with nearly unchanged bone collision in pronation and 6 types presented nearly unchanged bone collision in pronation with a shortening of the mean linear length of IOM in supination or neutral rotation. This kinematic analysis provides a better understanding of the ligament- and bone-related factors expected to cause rotational deficit in forearm deformity and may help to refine the surgical indications of patient-specific corrective osteotomy.

Purpose: Robot-assisted ultrasound (US) systems could be used to provide a non-radiative three-dimensional (3D) reconstruction that can 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 e.g. verifying performance in various testing scenarios. Therefore, this study provides an assessment of the robot-assisted US system, with technical details from experiments starting at the bench-top up to the pre-clinical study. Methods: A semi-automatic control strategy is proposed to ensure continuous and smooth scanning. Next, a method based on U-Net was developed to automatically process the anatomic features and derive a high quality 3D US reconstruction. Experiments on phantoms and human cadavers validate the proposed approach. Results: Average deviations of scanning force were found of 2.84 ± 0.45 N on synthetic phantoms and of 5.64 ± 1.10 N on human cadavers. The reconstruction yielded a mean 3D representation error of 1.28 ± 0.87 mm for the synthetic phantoms and of 1.74 ± 0.89 mm for the human cadavers. Conclusion: These results show the proposed system has high safety performance and could keep the probe force stable within the range of 1 N to obtain a good reconstruction. The experiments indicate that the proposed robotassisted US approach works in quite different experimental settings. The results encourage to also explore the potential of this technology in in-vivo studies.

Computerized surgical planning for forearm procedures that considers both soft and bony tissue, requires alignment of preoperatively acquired computed tomography (CT) and magnetic resonance (MR) images by image registration. Normalized mutual information (NMI) registration techniques have been researched to improve efficiency and to eliminate the user dependency associated with manual alignment. While successfully applied in various medical fields, the application of NMI registration to images of the forearm, for which the relative pose of the radius and ulna likely differs between CT and MR acquisitions, is yet to be described. To enable the alignment of CT and MR forearm data, we propose an NMI-based registration pipeline, which allows manual steering of the registration algorithm to the desired image subregion and is, thus, applicable to the forearm. Successive automated registration is proposed to enable planning incorporating multiple target anatomical structures such as the radius and ulna. With respect to gold-standard manual registration, the proposed registration methodology achieved mean accuracies of 0.08 ± 0.09 mm (0.01-0.41 mm range) in comparison with 0.28 ± 0.23 mm (0.03-0.99 mm range) associated with a landmark-based registration when tested on 40 patient data sets. Application of the proposed registration pipeline required less than 10 minutes on average compared with 20 minutes required by the landmark-based registration. The clinical feasibility and relevance of the method were tested on two different clinical applications, a forearm tumor resection and radioulnar joint instability analysis, obtaining accurate and robust CT-MR image alignment for both cases.

Background There is evidence that specific variants of scapular morphology are associated with dynamic and static posterior shoulder instability. To this date, observations regarding glenoid and/or acromial variants were analyzed independently, with two-dimensional imaging or without comparison with a healthy control group. Therefore, the purpose of this study was to analyze and describe the three-dimensional (3D) shape of the scapula in healthy and in shoulders with static or dynamic posterior instability using 3D surface models and 3D measurement methods. Methods In this study, 30 patients with unidirectional posterior instability and 20 patients with static posterior humeral head subluxation (static posterior instability, Walch B1) were analyzed. Both cohorts were compared with a control group of 40 patients with stable, centered shoulders and without any clinical symptoms. 3D surface models were obtained through segmentation of computed tomography images and 3D measurements were performed for glenoid (version and inclination) and acromion (tilt, coverage, height). Results Overall, the scapulae of patients with dynamic and static instability differed only marginally among themselves. Compared with the control group, the glenoid was 2.5° (P = .032), respectively, 5.7° (P = .001) more retroverted and 2.9° (P = .025), respectively, 3.7° (P = .014) more downward tilted in dynamic, respectively, static instability. The acromial roof of dynamic instability was significantly higher and on average 6.2° (P = .007) less posterior covering with an increased posterior acromial height of +4.8mm (P = .001). The acromial roof of static instability was on average 4.8° (P = .041) more externally rotated (axial tilt), 7.3° (P = .004) flatter (sagittal tilt), 8.3° (P = .001) less posterior covered with an increased posterior acromial height of +5.8 mm (0.001). Conclusion The scapula of shoulders with dynamic and static posterior instability is characterized by an increased glenoid retroversion and an acromion that is shorter posterolaterally, higher, and more horizontal in the sagittal plane. All these deviations from the normal scapula values were more pronounced in static posterior instability.

Introduction: The periacetabular osteotomy of Ganz is one of the most demanding procedures in orthopaedic surgery and requires a profound three-dimensional understanding of the human anatomy. The use of augmented reality offers new possibilities for computer-assisted interventions. The aim of our study was to investigate if the navigation of the periacetabular osteotomy of Ganz by the Microsoft HoloLens is feasible in a pilot cadaveric study.

Purpose To investigate the residual articular incongruity on computed tomography image data and the early clinical outcome of 3-dimensional planned and navigated intra-articular osteotomies of the distal radius. Methods We conducted a retrospective analysis of intra-articular osteotomies executed between 2008 and 2016. We identified 37 patients (aged 26–73 years) and performed a combined intra-articular and extra-articular osteotomy on 20 patients. A preoperative 3-dimensional plan with the superimposed bone of the contralateral healthy side was performed in each case to analyze and execute the osteotomy by intraoperative navigation. The residual articular incongruity was assessed by quantification of the maximal stepoff in the coronal or sagittal computed tomography scans. Clinical outcome, including range of motion, grip strength, and return to work, was assessed after a minimum follow-up of 12 months and compared with preoperative measurements. Results On average, the preoperative intra-articular stepoff was 2.5 mm (±0.6 mm; range, 1.4–4.2 mm) and was significantly reduced to 0.8 mm (±0.2 mm) after surgery. After surgery, 30 patients had a stepoff less than 1 mm; in 7, a stepoff of 1.1 to 1.4 mm was measured. After 1 year, 22 had no pain, 9 had slight pain during heavy work, and 5 had moderate pain with no improvement compared with their preoperative status, although wrist strength and range of motion improved in all 37 patients. One patient underwent a secondary radioscapholunate arthrodeses owing to persistent pain despite a congruent joint with a small residual intra-articular stepoff (0.6 mm). Conclusions Intra-articular osteotomies of the distal radius treated by 3-dimensional preoperative planning and patient-specific guides are an accurate technique to reduce articular incongruity to an average stepoff of 0.8 mm (range, 0.3–1.4 mm). The early clinical outcomes demonstrated overall reduction in pain and improvement of range of motion and grip strength in 36 of 37 patients. Type of study/level of evidence Therapeutic IV.

Accurate segmentation of connective soft tissues is still a challenging task, which hinders the generation of corresponding geometric models for biomechanical computations. Alternatively, one could predict ligament insertion sites and then approximate the shapes, based on anatomical knowledge and morphological studies. Here, we describe a corresponding integrated framework for the automatic modelling of human musculoskeletal ligaments. We combine statistical shape modelling with geometric algorithms to automatically identify insertion sites, based on which geometric surface and volume meshes are created. For demonstrating a clinical use case, the framework has been applied to generate models of the interosseous membrane in the forearm. For the adoption to the forearm anatomy, ligament insertion sites in the statistical model were defined according to anatomical predictions following an approach proposed in prior work. For evaluation we compared the generated sites, as well as the ligament shapes, to data obtained from a cadaveric study, involving five forearms with a total of 15 ligaments. Our framework permitted the creation of 3D models approximating ligaments' shapes with good fidelity. However, we found that the statistical model trained with the state-of-the-art prediction of the insertion sites was not always reliable. Using that model, average mean square errors as well as Hausdorff distances of the meshes increased by more than one order of magnitude, as compared to employing the known insertion locations of the cadaveric study. Using the latter an average mean square error of 0.59 mm and an average Hausdorff distance of less than 7 mm resulted, for the complete set of ligaments. In conclusion, the presented approach for generating ligament shapes from insertion points appears to be feasible but the detection of the insertion sites with a SSM is too inaccurate., Comment: 16 pages, 8 figures

3D computer-assisted corrective osteotomy has become the state-of-the-art for surgical treatment of complex bone deformities. Despite available technologies, the automatic generation of clinically acceptable, ready-to-use preoperative planning solutions is currently not possible for such pathologies. Multiple contradicting and mutually dependent objectives have to be considered, as well as clinical and technical constraints, generally requiring iterative manual adjustments. This leads to unnecessary efforts and unbearable clinical costs, hindering also the quality of patient treatment. In this paper, we propose an optimization framework for the generation of ready-to-use preoperative planning solutions in a fully automatic fashion. An automatic diagnostic assessment using patient-specific 3D models is performed for 3D malunion quantification and definition of the optimization parameters. Afterward, clinical objectives are translated into the optimization module, and controlled through tailored fitness functions based on a weighted and multi-staged optimization approach. The optimization is based on a genetic algorithm capable of solving multi-objective optimization problems with non-linear constraints. The framework outputs a complete preoperative planning solution including position and orientation of the osteotomy plane, transformation to achieve the bone reduction, and position and orientation of the fixation plate and screws. A qualitative validation was performed on 36 consecutive cases of radius osteotomy where solutions generated by the optimization algorithm (OA) were compared against the gold standard (GS) solutions generated by experienced surgeons. Solutions were blinded and presented to 6 readers, who voted OA solutions to be better in 55% of the time. The quantitative evaluation was based on different error measurements, showing average improvements with respect to the GS., Comment: 37 pages, 15 figures, submitted to Medical Image Analysis Journal

El texto Estructura Matemática para la Evaluación de Proyectos, utiliza la estructura básica de las matemáticas para desarrollar las fórmulas de las Matemáticas Financieras y establecer sus principios fundamentales. Se definen sus variables y deducen fórmulas para establecer las relaciones existentes entre ellas. Se estudian los cuatro métodos de evaluación, a saber Valor Presente Neto, Costo Anual Equivalente, Tasa Interna de Retorno y Relación Beneficio a Costo. Se introduce el concepto de tasas de interés y sus clasificaciones y propiedades. Se enseña a convertir tasas. Se hace un buen resumen de la normatividad existente en Colombia sobre tasas de interés. Se hacen ejercicios que muestran las diferentes maneras de pagar un crédito. Se estudian los métodos de pagar créditos de vivienda y ejercicios que muestran diversas maneras de constituir fondos de ahorro. Se aclara alguna aparente divergencia que algunos autores afirman como falta de convergencia de los métodos de evaluación. Se introducen los conceptos de inflación y devaluación y se muestran ejemplos de evaluación de alternativas bajo circunstancia inflacionaria y también bajo efectos de devaluación. Se estudian sistemas de medir costos de promesas futuras. Se analizan métodos de evaluar proyectos de inversión, por los métodos de Tasa Interna de Retorno, Relación Beneficio a Costo o Valor presente neto; para proyectos individuales o para proyectos de inversión mutuamente excluyentes.

Purpose To develop reproducible 3-dimensional measurements for quantification of the distal radioulnar joint (DRUJ) morphology. We hypothesized that automated 3-dimensional measurement of the ulnar variance (UV) and the sigmoid notch (SN) angle would be comparable to those of the reference standard while overcoming some drawbacks of conventional 2-dimensional measurements. Methods Radiological data of healthy forearm bones (radiographs and computed tomography) of 53 adult subjects were included in the study. Automated measurements were developed for assessment of the SN morphology based on 3-dimensional landmarks, incorporating subject-specific estimation of cartilage surface orientation. A common anatomical reference was defined among the different imaging modalities and a comparison of the SN angle and UV measurements was performed in radiographs, computed tomography scans, and 3-dimensional models. Finally, the 3-dimensional UV measurements were evaluated in an experimental setup using 3-dimensional printed bone models. Results The automated 3-dimensional measurements of SN subtypes showed a notably larger notch radius (18.9 mm) for negative SN angles compared with positive SN angles in subjects (16.9 mm). Similar UV measurements were obtained in healthy DRUJ morphologies, with a high correlation between radiographs and 3-dimensional measurements for the SN angle (0.77) and UV (0.85). In the experimental setup with pathological radial inclinations, UV was on average 1.13 mm larger in the radiographs compared with the 3-dimensional measurements, and 1.30 mm larger in the cases with pathological palmar tilts. Furthermore, UV radiograph measurements on the modified palmar tilt deviated from the 3-dimensional measurements. Conclusions The developed 3-dimensional automated measurements were able to quantify morphological differences among sigmoid notch subtypes and were comparable to those of the reference standard. Clinical relevance The developed methods do not depend on the forearm position or orientation of the distal radius and can be used for 3-dimensional quantification of DRUJ pathologies in 3-dimensional surgical planning.

Background Opening-wedge osteotomies of the distal radius, performed with three-dimensional printed patient-specific instruments, are a promising technique for accurate correction of malunions. Nevertheless, reports of residual malalignments and discrepancies in the plate and screw position from the planned fixation exist. Consequently, we developed a patient-specific ramp-guide technique, combining navigation of plate positioning, osteotomy cutting, and reduction. The aim of this study is to compare the accuracy of navigation of three-dimensional planned opening-wedge osteotomies, using a ramp-guide, over state-of-the-art guide techniques relying solely on pre-drilled holes. Methods A retrospective analysis was carried out on opening-wedge osteotomies of the distal radius, performed between May 2016 and April 2017, with patient-specific instruments. Eight patients were identified in which a ramp-guide for the distal plate fixation was used. We compared the reduction accuracy with a control group of seven patients, where the reduction was performed with pre-drilled screw holes placed with the patient-specific instruments. The navigation accuracy was assessed by comparing the preoperative plans with the postoperative segmented, computed tomography scans. The accuracy was expressed using a 3D angle and in measurements of all six degrees of freedom (3 translations, 3 rotations), with respect to an anatomical coordinate system. Results The duration of the surgery of the ramp-guide group was significantly shorter compared to the control group. Significantly less rotational and translational residual malalignment error was observed in the open-wedged osteotomies, where patient-specific instruments with ramp-guides were used. On average, a residual rotational malalignment error of 2.0° (± 2.2°) and a translational malalignment error of 0.6 mm (± 0.2 mm) was observed in the ramp-guide group, as compared to the 4.2° (± 15.0°) and 1.0 mm (± 0.4 mm) error in the control group. The used plate was not significantly positioned more accurately, but significantly fewer screws (15.6%) were misaligned in the distal fragment compared to the control group (51.9%). Conclusion The use of the presented ramp-guide technique in opening-wedge osteotomies is improving reduction accuracy, screw position, and surgical duration, compared to the existing patient-specific instrument based navigation methods.

The accurate restoration of premorbid anatomy is key for the success of reconstructive surgeries of the proximal part of the humerus. The bicipital groove has been proposed as a landmark for the prediction of humeral head retrotorsion. We hypothesized that a novel method based on bilateral registration of the bicipital groove yields an accurate approximation of the premorbid anatomy of the proximal part of the humerus.Three-dimensional (3D) triangular surface models were created from computed tomographic data of 100 paired humeri (50 cadavers). Segments of the distal part of the humerus and the humeral shaft of prespecified lengths were defined. A surface registration algorithm was applied to superimpose the models onto the mirrored contralateral humeral model based on the defined segments. We evaluated the 3D proximal humeral contralateral registration (p-HCR) errors, defined as the difference in 3D rotation of the humeral head between the models when superimposed. For comparison, we quantified the landmark-based retrotorsion (LBR) error, defined as the intra-individual difference in retrotorsion, measured with a landmark-based 3D method.The mean 3D p-HCR error using the most proximal humeral shaft (bicipital groove) segment for the registration was 2.8° (standard deviation [SD], 1.5°; range, 0.6° to 7.4°). The mean LBR error of the reference method was 6.4° (SD, 5.9°; range, 0.5° to 24.0°).Bilateral 3D registration of the bicipital groove is a reliable method for approximating the premorbid anatomy of the proximal part of the humerus.The accurate approximation of the premorbid anatomy is a key for the successful restoration of the premorbid anatomy of the proximal part of the humerus.

BACKGROUND In computer-assisted reconstructive surgeries, the contralateral anatomy is established as the best available reconstruction template. However, existing intra-individual bilateral differences or a pathological, contralateral humerus may limit the applicability of the method. The aim of the study was to evaluate whether a statistical shape model (SSM) has the potential to predict accurately the pretraumatic anatomy of the humerus from the posttraumatic condition. METHODS Three-dimensional (3D) triangular surface models were extracted from the computed tomographic data of 100 paired cadaveric humeri without a pathological condition. An SSM was constructed, encoding the characteristic shape variations among the individuals. To predict the patient-specific anatomy of the proximal (or distal) part of the humerus with the SSM, we generated segments of the humerus of predefined length excluding the part to predict. The proximal and distal humeral prediction (p-HP and d-HP) errors, defined as the deviation of the predicted (bone) model from the original (bone) model, were evaluated. For comparison with the state-of-the-art technique, i.e., the contralateral registration method, we used the same segments of the humerus to evaluate whether the SSM or the contralateral anatomy yields a more accurate reconstruction template. RESULTS The p-HP error (mean and standard deviation, 3.8° ± 1.9°) using 85% of the distal end of the humerus to predict the proximal humeral anatomy was significantly smaller (p = 0.001) compared with the contralateral registration method. The difference between the d-HP error (mean, 5.5° ± 2.9°), using 85% of the proximal part of the humerus to predict the distal humeral anatomy, and the contralateral registration method was not significant (p = 0.61). The restoration of the humeral length was not significantly different between the SSM and the contralateral registration method. CONCLUSIONS SSMs accurately predict the patient-specific anatomy of the proximal and distal aspects of the humerus. The prediction errors of the SSM depend on the size of the healthy part of the humerus. CLINICAL RELEVANCE The prediction of the patient-specific anatomy of the humerus is of fundamental importance for computer-assisted reconstructive surgeries.

The Interosseous Membrane (IOM) is a fibrous ligament bundle connecting the ulna and the radius. It is well known that the IOM allows transferring partial load from the radius to the ulna (Pfaeffle 2005). It also influences the kinematics of the radioulnar joint (Yasutomi 2002, Tarr 1984).Three-Dimensional (3D) computer-assisted methods for preoperative planning of osteotomy have been applied successfully on forearm pathologies (Fürnstahl 2010, Murase 2008, Vlachopoulos 2015). However, to the best of our knowledge, models and studies of the influence of the IOM during pro-supination are limited to a kinematics analysis of the system, either with actual bone geometry (Fürnstahl 2009) or without it (Kasten 2002). In this work, we present a physical simulation of the forearm pro-supination involving the IOM biomechanical properties, for providing insights on the influence of the IOM on the radioulnar motion. We demonstrate a preliminary validation using a sample simulation performed on a healthy forearm by comparing its outcome with literature, and analyze the kinetic data that our method allows.

BACKGROUND: With current 3-dimensional (3D) computer-based methods for the assessment of deformities, a surface registration method is applied to superimpose a computer model of the pathological bone onto a mirrored computer model of the contralateral side. However, because of bilateral differences, especially in humeral torsion, such template-based approaches may introduce bias in the assessment of a distal humeral deformity. We hypothesized that a novel registration approach might prove superior to the current approach in reducing such bias, thus yielding improved accuracy of 3D assessment of distal humeral deformities. METHODS: Three-dimensional triangular surface models were generated from computed tomographic (CT) data of 100 paired humeri without a pathological condition. Humeral segments of varying, predetermined lengths, excluding the distal part of the humerus, were defined. A surface registration algorithm was applied to superimpose the humeral models of both sides based on each selected segment. Humeral contralateral registration (HCR) errors, defined as the residual differences in apparent 3D orientation between the distal parts, were evaluated. RESULTS: The mean HCR error (and standard deviation) using the distal-most humeral shaft segment to assess the angular orientation was 2.3° ± 1.1 (range, 0.5° to 5.8°). Including the humeral head in the surface registration algorithm, however, as is done currently, resulted in a higher HCR error (p 10° in 20% of the cases and between 5° and 10° in an additional 50% of the cases. By comparison, using the proposed distal-most humeral shaft segment, the HCR error was between 5° and 10° in only 2% of cases, and was never >10°. The proximal segments are nevertheless used in the proposed method for registering humeral length. CONCLUSIONS: The proposed new approach yields a deformity assessment that is less prone to bias arising from inherent bilateral differences and therefore is more accurate than current surface registration approaches. CLINICAL RELEVANCE: Accurate 3D assessment is of fundamental importance if computer-based methods are applied in the correction of posttraumatic deformities.

Purpose To simulate the most isometric insertion points of the anterolateral ligament (ALL) in a weight-bearing 3-dimensional computed tomography (CT) model using previously published anatomic landmarks and to define radiographic landmarks, which make for an easier identification of the optimal insertion points. Methods The most isometric femoral insertion points were analyzed for 10 individuals, using data of weight-bearing CT scans in increasing knee flexion positions. An automatic string generation algorithm helped identify isometrically optimal points using an isometric score (0 indicating optimal isometry). Subsequently, a general femoral insertion point was determined, which preserved the isometry in all tested individuals. Based on the femoral insertion point, we assessed the influence of varying tibial insertion points on the isometric behavior of the ALL. Results The defined femoral insertion point, which preserved the isometry in all analyzed individuals, had a median isometric score between 0.167 × 10 −3 and 0.559 × 10 −3 . The average distance from the most prominent point of the lateral epicondyle was 9.7 mm (standard deviation [SD], 1.6) in a straight superior direction. In a straight lateral radiographic view, this point is located exactly at the intersection of a tangent set between the posterior cortex of the femur and a second perpendicular line intersecting at the level of the most (superior-) posterior point of the Blumensaat line. The best isometric behavior was found on the anatomically defined mean tibial insertion point, located at 37% of the width of the tibial plateau, which worsened gradually if corrected to anterior or posterior. Conclusions We determined femoral and tibial insertion points as well as radiographic landmarks for the reconstruction of the ALL that are based on published anatomic descriptions and preserve isometry in all analyzed individuals in this study. Clinical Relevance This study provides new information, which might be helpful to define isometrically optimal insertion points for ALL reconstruction.

Opening-wedge osteotomies of the distal radius, performed with three-dimensional printed patient-specific instruments, are a promising technique for accurate correction of malunions. Nevertheless, reports of residual malalignments and discrepancies in the plate and screw position from the planned fixation exist. Consequently, we developed a patient-specific ramp-guide technique, combining navigation of plate positioning, osteotomy cutting, and reduction. The aim of this study is to compare the accuracy of navigation of three-dimensional planned opening-wedge osteotomies, using a ramp-guide, over state-of-the-art guide techniques relying solely on pre-drilled holes.A retrospective analysis was carried out on opening-wedge osteotomies of the distal radius, performed between May 2016 and April 2017, with patient-specific instruments. Eight patients were identified in which a ramp-guide for the distal plate fixation was used. We compared the reduction accuracy with a control group of seven patients, where the reduction was performed with pre-drilled screw holes placed with the patient-specific instruments. The navigation accuracy was assessed by comparing the preoperative plans with the postoperative segmented, computed tomography scans. The accuracy was expressed using a 3D angle and in measurements of all six degrees of freedom (3 translations, 3 rotations), with respect to an anatomical coordinate system.The duration of the surgery of the ramp-guide group was significantly shorter compared to the control group. Significantly less rotational and translational residual malalignment error was observed in the open-wedged osteotomies, where patient-specific instruments with ramp-guides were used. On average, a residual rotational malalignment error of 2.0° (± 2.2°) and a translational malalignment error of 0.6 mm (± 0.2 mm) was observed in the ramp-guide group, as compared to the 4.2° (± 15.0°) and 1.0 mm (± 0.4 mm) error in the control group. The used plate was not significantly positioned more accurately, but significantly fewer screws (15.6%) were misaligned in the distal fragment compared to the control group (51.9%).The use of the presented ramp-guide technique in opening-wedge osteotomies is improving reduction accuracy, screw position, and surgical duration, compared to the existing patient-specific instrument based navigation methods.