The most frequent reasons for revision of total knee arthroplasty are loosening and abnormal axial alignment leading to an unphysiological kinematic of the knee implant. To get an idea about the postoperative kinematic of the implant, it is essential to determine the position and orientation of the tibial and femoral prosthesis. Therefore we developed a registration method for fitting 3D CAD-models of knee joint prostheses into an 3D MR image. This rigid registration is the basis for a quantitative analysis of the kinematics of knee implants. Firstly the surface data of the prostheses models are converted into a voxel representation; a recursive algorithm determines all boundary voxels of the original triangular surface data. Secondly an initial preconfiguration of the implants by the user is still necessary for the following step: The user has to perform a rough preconfiguration of both remaining prostheses models, so that the fine matching process gets a reasonable starting point. After that an automated gradient-based fine matching process determines the best absolute position and orientation: This iterative process changes all 6 parameters (3 rotational- and 3 translational parameters) of a model by a minimal amount until a maximum value of the matching function is reached. To examine the spread of the final solutions of the registration, the interobserver variability was measured in a group of testers. This variability, calculated by the relative standard deviation, improved from about 50% (pure manual registration) to 0.5% (rough manual preconfiguration and subsequent fine registration with the automatic fine matching process).

Das Ziel der vorliegenden Arbeit ist die Entwicklung von dreidimensionalen Bildverarbeitungsmethoden zur in-vivo-Analyse der Biomechanik des Kniegelenks auf der Basis magnetresonanztomographischer Bilddaten. Die Verwendung eines offenen Magnetresonanztomographen ermoglicht die Generierung von Bilddatensatzen des Kniegelenks sowohl in unterschiedlichen Flexionsstellungen als auch bei gleichzeitiger Aktivierung der Beinmuskulatur. Nach Segmentierung und dreidimensionaler Rekonstruktion von Femur, Tibia und Patella konnen durch Einfuhrung eines Tibiaplateau-basierten Koordinatensystems und die Berechnung einer epikondylaren Achse fur das Femur femoro-tibiale Translation und Rotation analysiert werden. Ein Patella-basiertes Koordinatensystem und femorale Referenzpunkte ermoglichen eine Analyse der Patellakinematik. Zudem konnen mittels Triangulierung segmentierter Kontaktstrecken die Grosen der femoro-tibialen und femoro-patellaren Knorpelkontaktflachen bestimmt werden. Nach einer Studie zur Intra-Untersucher-Reproduzierbarkeit wird die Biomechanik im Kniegelenk in einer klinischen Studie untersucht. Verglichen werden die femoro-tibialen Translations- und Rotationsmuster, die Patellakinematik und die Grosen der femoro-tibialen und femoro-patellaren Knorpelkontaktflachen einer gesunden Probanden-Gruppe, mit den Ergebnissen einer Gruppe von Patienten mit schwerer Gonarthrose. Die entwickelten Methoden erwiesen sich als sehr reproduzierbar und genau. Es konnte gezeigt werden, dass Dorsaltranslation und Ausenrotation des Femur bei Knieflexion von 0° auf 90° bei schwerer Gonarthrose deutlich verringert sind. Zusatzlich kommt es bei den Arthrose-Patienten wahrend der Knieflexion zu einer Zunahme des Patella-Tilt und des Patella-Shift nach lateral. Die Analyse der Kontaktflachen zeigte, dass es bei schwerer Gonarthrose zu einer ausgepragten Vergroserung der femoro-tibialen und femoro-patellaren Knorpelkontaktflachen kommt. Die entwickelten Methoden konnen damit zum Verstandnis von Entwicklung und Verlauf von Kniegelenkserkrankungen wie der Gonarthrose beitragen.

FEMORO-TIBIAL 3D KINEMATICS IN PATIENTS WITH POSTERIOR CRUCIATE LIGAMENT DEFICIENCY Stefan Hinterwimmer1,2, Anke Schützeberg2, Rüdiger von Eisenhart-Rothe2,3, Thomas Vogl4, Heiko Graichen2,3 1Orthopedic Sports Medicine, Technical University, Munich, München, Germany; 2Forschungsgruppe Kinematik und Biomechanik, Goethe Universitiy, Frankfurt, Frankfurt, Germany; 3Asklepios Orthopädische Klinik Lindenlohe, Schwandorf, Germany; 4Institut für Diagnostische und Interventionelle Radiologie, Goethe University, Frankfurt, Frankfurt, Germany stefan.hinterwimmer@lrz.tum.de

Objective: Ex vivo studies have suggested that cartilage contact areas and pressure are of high clinical relevance in the ethiology of osteoarthritis in patients with patellar subluxation. The aims of this study were therefore to validate in vivo measurements of contact areas with 3D open magnetic resonance imaging (MRI), and to study knee joint contact areas in patients with patellar subluxation at different angles of knee flexion in comparison with healthy subjects. Methods: 3D-MR image data sets of 12 healthy volunteers and 8 patients with patellar subluxation were acquired using a standard clinical (1.5T) and an open (0.2T) MRI scanner. We compared femoro-patellar and femoro-tibial contact areas obtained with two different sequences from open MRI [dual-echo-steady-state (DESS) and fast-low-angle-shot (FLASH) sequences] with those derived from standard clinical 1.5 T MRI. We then analyzed differences in joint contact areas between healthy subjects and patients with patellar subluxation at 0, 30 and 90 of knee flexion using open MRI. Results: The correlation of the size of contact areas from open MRI with standard clinical MRI data ranged from r = 0.52 to 0.92. Open-MRI DESS displayed a smaller overestimation of joint contact areas (+21 % in the femoro-patellar, +12% in the medial femoro-tibial, and +19% in the lateral femoro-tibial compartment) than FLASH (+40%, +37%, +30%, respectively). The femoro-patellar contact areas in patients were significantly reduced in comparison with healthy subjects (− 47% at 0, − 56% at 30, and − 42% at 90 of flexion; all p Conclusions: Open MRI allows one to quantify joint contact areas of the knee with reasonable accuracy, if an adequate pulse sequences is applied. The technique permits one to clearly identify differences between patients with patellar subluxation and healthy subjects at different flexion angles, demonstrating a significant reduction and lateralization of contact areas in patients. In the future application of this in vivo technique is of particular interest for monitoring the efficacy of different types of surgical and conservative treatment options for patellar subluxation.

Objective: Current drug treatment for atrial. fibrillation is suboptimal and percutaneous catheter-based ablation techniques may be associated with complications. The aim of this study is to assess the cost-effectiveness of (1) high-intensity focused ultrasound (HIFU)-assisted surgical ablation, (2) the classic 'cut and sew' maze procedure and (3) percutaneous ablation, all concomitant to cardiac surgery (e. g. CABG, valve repair) in comparison with non-interventional (drug) treatment. Methods: A Markov model was developed to predict the cost-effectiveness of the interventional approaches. The model consisted of four disease states (sinus rhythm without complications, atrial. fibrillation without complications, stroke and death), allowing for 3-monthly transitions between these states and using direct UK costs from the National Health Service perspective. Clinical input data are obtained from literature and cost input data from National Health Service sources and literature. Five-year total and incremental costs are calculated. Incremental effects are expressed in quality-adjusted-life-years-gained (QALYG). Results: All interventional treatments show good incremental cost-effectiveness ratios in all atrial. fibrillation types, compared to drug treatment. For classic maze the incremental cost-effectiveness ratio compared to non-interventional atrial fibrillation treatment varies from 1343 to 3471 GBP/ QALYG, for HIFU-assisted surgical ablation from 4005 to 7448 GBP/QALYG and for percutaneous ablation from 7041 to 17,372 GBP/QALYG depending on the atrial fibrillation type. Sensitivity analyses showed the robustness of the data. Conclusions: Performing a classic maze procedure or HIFU-assisted surgical ablation concomitant to a scheduled CABG or valve procedure is highly cost-effective. Performing a percutaneous ablation in a subsequent procedure is also cost-effective, but to a tower extent. Both the maze procedure and the HIFU-assisted surgical ablation are cheaper and more effective than percutaneous ablation in a subsequent procedure. (C) 2007 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.

Objective: To study the effect of new interactive computer input devices on cartilage segmentation in terms of time, consistency between input devices, and precision in quantitative magnetic resonance imaging (qMRI). Design: We compared two new input devices, an interactive digitizing tablet and an interactive touch-sensitive screen, to a traditional mouse. Medial tibial and patellar cartilage of six healthy and six osteoarthritic knees were segmented using each input device. Cartilage volume, surface area and mean thickness were assessed using a validated algorithm and used to determine consistency and precision. Segmentation time was also measured. Results: Segmenting with an interactive touch-sensitive screen reduced segmentation time by 15% when compared to the traditional mouse but we found no significant difference in segmentation time between the interactive digitizing tablet and the traditional mouse. We found no difference in consistency or precision of cartilage volume, mean thickness or surface area between the three input devices tested. Conclusions: We conclude that measurements of cartilage made using articular cartilage segmentation from MR images are independent of the input device chosen for user interaction. (C) 2004 OsteoArthritis Research Society International. Published by Elsevier Ltd. All rights reserved.

Background. Patients with genu varum of the knee and moderate to severe osteoarthritis often suffer from additional symptoms of the patello-femoral joint. These patients have a poor prognosis following high tibial osteotomy. It is unclear whether varus knees with only mild femoro-tibial osteoarthritis are also associated with alterations of patella biomechanics, and affect the prognosis of intended high tibial osteotomy.Methods. Fifteen patients with germ varum and mild osteoarthritis and 15 healthy volunteers were assessed in an open MRI-scanner. 3D-GRE sequences of the knee were obtained in 0degrees, 30degrees and 90degrees with and without activity of the extensor muscles. After segmentation of patella, femur, tibia and the adjacent cartilage, a patella.-based local coordinate system was established. Femoral and tibial reference points allowed definition of the spatial position of the patella. Contact areas were defined by intersection of opposing cartilage volumes.Findings. No significant differences in patella kinematics and patello-femoral contact areas could be found (P > 0.05) between varus knees with mild osteoarthritis and healthy knees either at different flexion angles or under extending muscle activity.Interpretation. In knees with genu varum and mild medial osteoarthritis we could detect no alterations in patello-femoral kinematics. Since the alterations of patients with genu varum and mild osteoarthritis are restricted to the medial femoro-tibial joint high tibial osteotomy might be successful. (C) 2004 Elsevier Ltd. All rights reserved.

Vorgestellt wird ein Verfahren zur 3D/3D Registrierung der wesentlichen Teile eines künstlichen Kniegelenks in postoperativen MRT Bildern. Ausgehend von einem Algorithmus zur Konvertierung der einzelnen Prothesenteile von einem CAD-Format in eine zum MRT Bild passende Voxeldarstellung, werden die einzelnen Prothesen-Modelle dann mit Hilfe eines Programmes im MRT Bild halbautomatisch registriert. Dabei wird der Anwender von einer Matching-Funktion und einem automatischen Optimierungsverfahren unterstützt. Das Ziel der Registrierung ist ein Verfahren, mit dem die Kniegelenkskinematik bei Patienten bestimmt werden kann.

Objective: To validate quantitative magnetic resonance imaging (qMRI) for the assessment of cartilage volume and thickness in thin and curved cartilage layers, such as the shoulder.Methods: Eight shoulder specimens from healthy individuals (aged 31–69 years) were investigated using a 3D gradient echo sequence with selective water excitation. After segmentation with a B-spline Snake algorithm, the cartilage volume and thickness were determined three dimensionally. The cartilage volume data were compared with water displacement of surgically removed tissue, and the thickness with A-mode ultrasound.Results: The glenoid and humeral head cartilage volume from qMRI agreed highly with that from water displacement (systematic difference, ±1 to ±3%; absolute difference, 4 to 7%). For the cartilage thickness, the mean systematic difference ranged from −17% (mean cartilage thickness of the glenoid) to +7% (maximal cartilage thickness of the glenoid); the standard error of the estimate was 3.7% for the humeral head, and 6.4% for the glenoid.Conclusions: The applied technique can be used for accurate determination of cartilage volume and thickness in human joints with highly curved and thin cartilage layers, such as the shoulder. In vivo application of this method will depend on the development of efficient surface coils that allow high resolution imaging under in situ conditions.

Die Magnetresonanztomographie (MRT) stellt für Diagnostik und Verlaufsbeurteilung der Osteoarthrose (OA) ein geeignetes Verfahren dar. Zusammen mit dreidimensionalen Bildverarbeitungsmethoden eignet sie sich für eine genaue Quantifizierung struktureller Veränderungen des Gelenkknorpels. Bei fortgeschrittener OA muss der geschädigte Knorpel nicht immer zusammenhängend sein. Eine quantitative Beschreibung auch einzelner Knorpelfragmente erscheint in diesem Zusammenhang sinnvoll. Unser System erlaubt — neben der Segmentierung —eine automatische Rekonstruktion, Analyse und Darstellung auch stark fragmentierter Gelenkknorpel.

Patello-femoral disorders Lire often caused by changes of patello-femoral and/or tibio-femoral kinematics. However, until now there has been no quantitative in vivo technique, that is able to obtain 3D kinematics and contact areas of all knee compartments simultaneously on a non-invasive basis. The aim Of this Study was therefore to develop and apply a technique which allows for determination of 3D kinematics and contact areas of the patello-femoral and tibio-femoral joint during different knee flexion angles and under neuromuscular activation patterns.One knee of each of the 10 healthy Volunteers was examined in an open MR system under flexing isometric Muscle activity at 30degrees and 90degrees. Three-dimensional kinematics and contact areas of the patello-femoral and tibio-femoral joints were analyzed by 3D image postprocessing.The reproducibility of the imaging technique yielded a coefficient of variation of 4.6% for patello-femoral, 4.7% for femoro-tibial displacement and 8.6%, for contact areas. During knee flexion (30-90degrees), patella tilt (opened to medial) decreased (8.8+/-3.4degrees vs. 4.6+/-3.1degrees, p < 0.05), while lateral patellar shift increased significantly (1.6+/-2.3 mm vs. 3.4+/-3.0 mm, p < 0.05).Furthermore, I significant posterior translation and external rotation of the femur relative to the tibia was observed. Patello-femoral contact areas increased significantly in size (134+/-60 vs. 205+/-96 mm(2)) during knee flexion.This technique shows a high reproducibility and provides physiologic in vivo data of 3D kinematics and contact areas of the patello-femoral and the tibio-femoral joint during knee flexion. This allows for advanced in vivo diagnostics, and may help to improve therapy of patello-femoral disorders in the future. (C) 2003 Elsevier Ltd. All rights reserved.

In view of an increasing use of breast MRI supplementing X-ray mammography, the purpose of this study was the development of a method for fast and efficient analysis of dynamic MR image series of the female breast. The image data sets were acquired with a saturation-recovery-turbo-FLASH sequence facilitating the detection of the kinetics of the contrast agent concentration in the whole breast with a high temporal and spatial resolution. In addition, a morphological 3D-FLASH data set was acquired. The dynamic image data sets were analyzed by tracer kinetic modeling in order to describe the physiological processes underlying the contrast enhancement in mathematical terms and thus enable the estimation of functional tissue specific parameters, reflecting the status of microcirculation. To display morphological and functional tissue information simultaneously, a multidimensional real-time visualization system (using 3D-texture mapping) was developed, which enables a practical and intuitive human-computer interface in virtual reality. The spatially differentiated representation of the computed functional tissue parameters superimposed on the anatomical information offers several possibilities: improved discernibility of contrast enhancement, inspection of the data volume in 3D-space and localization of lesions in space and thus fast and more natural recognition of topological coherencies. In a feasibility study, it could be demonstrated that multidimensional visualization of contrast enhancement in virtual reality is practical. Especially, detection and localization of multiple breast lesions may be an important application

PURPOSEStrengthening of the shoulder depressors is an important component in the treatment of impingement syndrome. However, the quantitative effect of various muscle forces on the width of the subacromial space has never been demonstrated in vivo. Therefore, the purpose of this study was to analyze the influence of adducting and abducting muscle forces on the subacromial space width in healthy volunteers in various arm positions.METHODSThe shoulders of 12 healthy volunteers were imaged with an open MR system at 30 degrees, 60 degrees, 90 degrees, 120 degrees, and 150 degrees of arm elevation under both isometric adducting and abducting muscle activity (15 N). After segmentation and three-dimensional reconstruction of anatomically relevant structures, the minimal spatial acromiohumeral and claviculohumeral distances were quantified.RESULTSAdducting muscle forces led to a significant increase of the acromiohumeral distance in all arm positions (P < 0.01), varying from 32% (30 degrees ) to 138% (90 degrees ) relative to abducting muscle forces. The claviculohumeral distance showed an increase of 9% (30 degrees ) to 24% (90 degrees ), this increase being also statistically significant at all positions (P < 0.05). During elevation of the arm (30-120 degrees ), the absolute subacromial space width was reduced significantly (P = 0.001) by 30% under isometric contraction of the adductors compared with 53% (P = 0.001) under activation of the abductors.CONCLUSIONThis in vivo study shows for the first time that adducting muscle forces lead to a significant increase of the subacromial space width compared with abducting muscle activity. In the future, this technique and data can be used to objectively quantify the effect of physical therapy protocols focused on increasing the depressor effect of adducting muscles in the postoperative and conservative treatment of impingement syndrome of the shoulder.

Despite their wide clinical application and success, our understanding of the biomechanical effects of foot orthoses is relatively limited. The aim of this study was to assess the effect of medially wedged and laterally wedged foot orthoses on the kinematics and joint moments of the rearfoot complex, knee, hip and pelvis and the ground reaction forces. The principal effect of the foot orthoses was on the rearfoot complex, where significant changes in joint rotations and moments were observed. Medially wedged orthoses decreased rearfoot pronation and increased the laterally directed ground reaction force during the contact phase, suggesting reduced shock attenuation. The laterally wedged orthoses increased rearfoot pronation and decreased the laterally directed ground reaction force during the contact phase, suggesting increased shock attenuation. The effects of the orthoses on knee, hip and pelvis kinematics were generally minimal. In view of the minimal effect the orthoses had on joints proximal to the foot, it is suggested that the orthoses may have additional effects on the passive and active soft tissues of the lower limb and it is these changes that result in the documented clinical success.

In view of an increasing use of breast MRI supplementing X-ray mammography, the purpose of this study was the development of a method for fast and efficient analysis of dynamic MR image series of the female breast. The image data sets were acquired with a saturation-recovery-turbo-FLASH sequence facilitating the detection of the kinetics of the contrast agent concentration in the whole breast with. In addition, a morphological 3D-FLASH data set was acquired. The dynamic image data sets were analyzed by tracer kinetic modeling in order to describe the physiological processes underlying the contrast enhancement in mathematical terms and thus to enable the estimation of functional tissue specific parameters, reflecting the status of microcirculation. To display morphological and functional tissue information simultaneously, a multidimensional real-time visualization system (using 3D-texture mapping) was developed, which enables a practical and intuitive human-computer interface in virtual reality. The spatially differentiated representation of the computed functional tissue parameters superimposed on the anatomical information offers several possibilities: improved discernibility of contrast enhancement; inspection of the data volume in 3D-space using the features of rotation and transparency variation; localization of lesions in space and thus fast and more natural recognition of topological coherencies. In a feasibility study, it could be demonstrated that multidimensional visualization of contrast enhancement in virtual reality is a practicable idea. Especially, detection and localization of multiple breast lesions may be an important application.

Objective: To analyze menisco-tibial and femoro-tibial translation patterns in healthy and ACL-deficient knees in different knee flexion angles under muscle activity.Methods: The ACL-deficient and contralateral healthy knees of 10 patients were examined with an open MR system at 30degrees and 90degrees of knee flexion. under isometric contraction of the extensors or flexor muscle groups. Translations between the tibia, the femoral condyles and the menisci were analyzed by three-dimensional image postprocessing.Results: Posterior translation of the femur and menisci relative to the tibia occurred during knee flexion (30-90degrees) in all knees. In ACL-deficient knees, posterior translation of the medial femoral condyle (+1.3 +/- 3.8 mm) was significantly larger than in healthy knee (-0.9 +/- 2.9 mm; p < 0.05), while the translation pattern of the menisci was similar (med. meniscus 0.6 +/- 2.3 mm vs. 0.6 +/- 2.7 mm). Under isometric contraction of the extensors (relative to the flexor muscle group), an increased posterior position of the femur and menisci was observed at 30degrees knee flexion, but not at 90degrees. This applied to ACL-deficient and healthy knees.Conclusions: This study shows a significant increase of translation of the medial femoral condyle in ACL-deficient knees, whereas menisco-tibial translation remains almost unchanged. This difference in translation patterns indicates that the posterior horn of the medial meniscus might encounter shear, potentially explaining the high rate of secondary medial meniscal tears in patients with ACL-deficiency. (C) 2003 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.

Mit der folgenden Arbeit soll gezeigt werden, dass es, durch den simultanen Einsatz der offenen MRT in Verbindung mit dreidimensionalen Bildverarbeitungsmethoden, möglich ist, am Lebenden den Einfluss der Gelenkstellung und der Muskelaktivität auf das Translationsverhalten der Femurkondylen im Kniegelenk zu quantifizieren. Nach Bilddatenakquirierung, Segmentierung, Interpolation und dreidimensionaler Rekonstruktion von Femur, Tibia, Fibula, Patella, Innen- und Außenmeniskus wurde ein auf das Tibiaplateau bezogenes Koordinatensystem eingeführt. Für die Analyse der femoralen Bewegung wurde eine reproduzierbare Epikondularachse bestimmt. Bei der Flexion des Kniegelenks zeigte sich eine posteriore Translation der Femurkondylen.

The objective of this work is to develop image processing methods for analysing the morphology of the joint cartilage with magnetic resonance imaging. Quantitative data on the morphological distribution of the joint cartilage are of great interest for both research as well as for diagnosis. The cartilage thickness provides information on the local cartilage occurance and may therefore be helpful in early and objective diagnosing degenerative cartilage changes, monitoring the pathogenesis of osteoarthritis, and controlling the success of chondroprotective treatment. In biomechanics, the thickness distribution serves to analyse the functional adaptation or the compression of the cartilage under loading and may be used for numerical simulation of load transmission in the joint.

We developed 3D MR based image processing methods for biomechanical analysis of joints. These methods provide quantitative data on the morphological distribution of the joint cartilage as well as biomechanical analysis of relative translation and rotation of joints. After image data acquisition in an open MR system, the segmentation of the different joint structures was performed by a semi automatic technique based on a gray value oriented region growing algorithm. After segmentation 3D reconstructions of cartilage and bone surfaces were performed. Principal axis decomposition is used to calculate a reproducible tibia plateau based coordinate system that allows the determination of relative rotation and translation of the condyles and menisci in relation to the tibia plateau. The analysis of the femoral movement is based on a reproducible, semi automatic calculated epicondylar axis. The analysis showed a posterior translation of the meniscus and even more of the femur condyles in healthy knees and in knees with an insufficiency of the anterior cruciate ligament (ACL).