People with osteoarthritis (OA) suffer from joint degeneration and pain as well as difficulty performing daily activities. Joint contact forces (JCF) are important for understanding individual joint loading, however, these contact force cannot be directly measured without instrumented implants. Musculoskeletal modeling is a tool for estimating JCF without the need for surgery. The results from these models can be very different due to different approaches used in the development of a model that was used for simulation. Therefore, the first purpose of this study was to develop and validate a musculoskeletal model in which lower extremity JCF were calculated at the hip, knee, and ankle in 10 participants with hip OA (H-OA) and 10 healthy control participants using OpenSim 4.0 [simtk.org, 23]. The generic gait2392 model was scaled to participant demographics, then the inverse kinematics (IK) solution and kinetic data were input into the Residual Reduction Algorithm (RRA) to reduce modeling errors. Kinematic solutions from RRA were used in the Computed Muscle Control (CMC) tool to compute muscle forces, then JCF were estimated using the Joint Reaction Analysis tool. Validation included JCF comparisons to published data of similar participant samples during level walking, and movement simulation quality was assessed with residual forces and moments applied at the pelvis, joint reserve actuators, and kinematic tracking errors. The computed JCFs were similar to the overall trends of published JCF results from similar participant samples, however the values of the computed JCFs were anywhere from 0.5 times body weight (BW) to 3BW larger than those in published studies. Simulation quality assessment resulted in low residual forces and moments, and low tracking errors. Most of the reserve actuators were small as well, besides pelvis rotation and hip rotation. The computed JCF were then used in the second portion of this study to determine the effect of group and side on JCF during both the weight acceptance and push-off phases of level walking. It was determined that there was a significant difference in the knee and ankle JCF during the weight acceptance portion of stance phase and at all joints during the push-off phase when comparing the H-OA and control groups on the affected limb. A significant interaction between group and limb was found for the peak hip JCF timing (% stance) during the push-off portion of the stance phase (p=0.009). These results demonstrate that H-OA participants experience an earlier peak hip JCF during propulsion on their affected limb. Based on previous research in OA that has examined spatiotemporal measures, this finding suggests that H-OA participants may use step or stride length changes as a strategy to decrease or limit pain and loading on the affected limb. Knowledge of potential JCF differences in H-OA participants, such as timing of the peaks in either portion of the stance phase, could provide useful insight to clinicians and therapists to make decisions on how to proceed with treatment or rehabilitation programs. / Master of Science / People with osteoarthritis suffer from joint degeneration and pain as well as difficulty performing daily activities, like walking. It is important to understand the forces and loading within individual joints. Musculoskeletal modeling is one way that researchers can estimate these joint contact forces (JCF) without needing a joint replacement implant that can measure these forces. When it comes to modeling simulations, there is a wide variety of results. Therefore, the first purpose of this study was to develop and validate a musculoskeletal model in which JCFs were calculated at the hip, knee, and ankle in 10 participants with hip osteoarthritis and 10 healthy adults. Validation of the model was completed through a comparison between computed results and published data of similar participant samples during level walking. The computed results were similar to the overall trends of published JCF results, however the numerical values themselves were larger than those in published studies. The computed JCFs were then used in the second portion of this study to determine how the two groups and limbs differ during level walking. There was a significant difference in the knee and ankle JCF during the first half of the stance phase and in all joints during the second half of stance when comparing the two groups. The hip osteoarthritis participants also experience an earlier peak hip JCF during the second half of stance phase on their affected limb. This finding suggests that hip osteoarthritis participants may change the way they take a step as a strategy to decrease or limit pain and loading on the affected limb. Knowledge of potential JCF differences, such as timing of the peaks in either portion of the stance phase, could provide useful insight to clinicians and therapists to make decisions on how to proceed with treatment or rehabilitation programs.

Total knee arthroplasty has been effective in reducing pain, but less so in restoring function, especially for activities requiring deep knee flexion. The philosophy of this dissertation was that more functionally effective and optimally designed artificial knees could be created for high flexion activities, if the knee joint kinematics and joint contact forces applied during finite element testing, knee simulator testing, and fatigue testing were more physiologically accurate. The objective of this work was to determine knee joint kinematics and contact forces that could be used in high flexion total knee replacement design and pre-clinical testing. Knee kinematics were determined during high flexion activities for total knee replacement patients and asymptomatic subjects by tracking the motion of skin-mounted sensors. In addition, a protocol was developed to determine the effect of soft tissue artefact on the accuracy of the skin-mounted sensor system in high flexion. The ranges of motion determined for the studied activities can be used as a benchmark to measure the functional success of high flexion total knee replacements. Tibiofemoral joint contact forces were estimated during high flexion activities of daily living using a simple, non-invasive, inverse dynamics based model. The accuracy of the joint contact force estimates was investigated by comparing the estimated forces to in vivo forces measured directly using implanted instrumented tibial components. The comparison showed that the model underestimates the measured axial joint contact force, most likely because the model neglects antagonistic muscle co-contraction. The measured and modeled joint contact forces and the measured knee kinematics could be used to form industry standards for knee simulator and fatigue testing to ensure that the implants are being tested physiologically. Healthy target populations can be studied using the methods outlined in this thesis to define testing standards for target populations: Kinematics can be determined as they were in this work for a group of Middle Eastern subjects, and the non-invasive inverse dynamics based model (with some consideration for the underestimation of forces) could be used to determine the tibiofemoral joint contact forces that the implant might be subjected to during activities of daily living. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2010-10-25 11:33:06.162

Joints are the main features encountered in rock and sliding of rock blocks on joints is classified as the principal source of instability in underground excavations. In this regard, joints’ peak shear strength is the controlling parameter. However, given the difficulty in estimating it, shear tests are often performed. These are often quite expensive and also time consuming and, therefore, it would be valuable if shear tests could be artificially performed using numerical models. The objective of this study is to prove the possibility to perform virtual numerical shear tests in a PCF2D environment that resemble the laboratory ones. A numerical model of a granite rock joint has been created by means of a calibration process. Both the intact rock microparameters and the smooth joint scale have been calibrated against macroparameters derived from shear tests performed in laboratory. A new parameter, the length ratio, is introduced which takes into account the effective length of the smooth joint compared to the theoretical one. The normal and shear stiffnesses, the cohesion and the tensile force ought to be scaled against the length ratio. Four simple regular joint profiles have been tested in the PFC2D environment. The analysis shows good results both from a qualitative and from a quantitative point of view. The difference in peak shear strength with respect to the one computed with Patton´s formula is in the order of 1% which indicates a good accuracy of the model. In addition, four profiles of one real rough mated joint have been tested. From the scanned surface data, a two-dimensional profile has been extracted with four different resolutions. In this case, however, interlocking of particles along the smooth joint occurs, giving rise to an unrealistic distribution of normal and shear forces. A possible explanation to the problem is discussed based on recent developments in the study of numerical shear tests with PFC2D.

Knee osteoarthritis (OA) is a debilitating disease affecting the entire knee joint by inducing pathological changes to the cartilage and menisci. Currently, the etiology of OA is not completely understood. However, altered gait mechanics, specifically increased joint loading, of OA patients have a clear association with both symptomatic and structural OA progression. Non-surgical intervention tools, such as variable stiffness shoes (VSS), have been developed as a way to decrease loading within the knee joint. However, with external moments being surrogate measures for knee loading, it is unclear if changes in knee moments with the footwear are sufficient to result in a clinical benefit. Therefore, this project’s purpose was to investigate whether a VSS intervention can alter knee joint loading and menisci function in a knee OA population. We used gait analysis, musculoskeletal modeling, and finite element (FE) analysis to determine the effect of VSS on gait mechanics, knee joint contact force, and menisci stress and strain, compared to a control shoe. We found knee moments did not decrease with the VSS intervention. Furthermore, participants who did experience a decrease in knee adduction moment did not always experience a decrease in medial compartment contact force. However, results from our FE modeling of the tibiofemoral joint indicate significant changes in knee joint contact force can influence stress placed on the menisci. Results from this study suggest knee contact forces and tissue stress, not only external moments, should be considered when investigating if VSS can positively impact an OA population.

[pt] Em uma mina a céu aberto, a estabilidade dos taludes rochosos é um dos maiores desafios na engenharia das rochas devido aos processos geodinâmicos que formaram o depósito de minério, fazendo de cada depósito complexo e único. Algumas das complexidades encontradas comumente são: a geologia nos arredores do depósito, a alta variabilidade das propriedades, os complexos defeitos estruturais, o grau de alteração das rochas, a informação geomecânica limitada, etc. Antes de avaliar a estabilidade de taludes devemos caracterizar o maciço rochoso. Para caracterizá-lo se têm construído os modelos geológico, estrutural e do maciço rochoso para formar o modelo geotécnico como recomenda o projeto Large Open Pit (LOP), um projeto de pesquisa internacional relacionado à estabilidade de taludes de rocha nas minas a céu aberto. Uma vez construídos os domínios geotécnicos, a estabilidade de taludes rochosos pode ser avaliada para cada domínio pelos métodos de equilíbrio limite ou numéricos como o método dos elementos finitos ou o método dos elementos discretos. O uso do método depende de diversos fatores, como a influência dos elementos estruturais, a importância da análise, a informação disponível, etc. Os métodos de equilíbrio limite como os tradicionais de Bishop e Janbu podem ser usados na avaliação de estabilidade de grandes taludes de rocha que são susceptíveis a falhas rotacionais do maciço rochoso. Já o método de elementos finitos se tem desenvolvido rapidamente e tem ganhado popularidade para a análise de estabilidade de taludes no caso em que o mecanismo de falha não esteja controlado por estruturas discretas geológicas. Os métodos de elementos finitos estão baseados em modelos constitutivos de tensão – deformação para rochas intactas e têm dificuldades em simular famílias com um número grande de descontinuidades dentro do maciço rochoso. O método dos elementos discretos permite simular um número grande de descontinuidades assim como também permite a simulação de grandes deformações. A presente dissertação usa o modelo SRM (Synthetic Rock Mass) para avaliar a estabilidade de taludes de uma mina a céu aberto no Peru. O SRM é uma nova técnica para simular o comportamento mecânico de maciços rochosos fraturados e permite simular a propagação de fraturas e os efeitos da anisotropia. Está técnica usa o modelo BPM (Bonded Particle Model) para representar a rocha intacta e o SJM (Smooth - Joint Contact Model) para representar as estruturas do maciço rochoso dentro do programa PFC. Para a modelagem estrutural se utilizou o método DFN (Discrete Fracture Network). Para a determinação dos modelos geológicos e estrutural se utilizou o programa Petrel e para a análise de estabilidade de taludes usando o modelo SRM se utilizou o programa PFC 4.0 na versão 2D. / [en] In an open pit mine, stability of rock slope is one of the most challenges in rock mechanics due to geodynamic processes that formed the ore deposit, making each deposit complex and unique. Some of the complexities commonly encountered are: the geology in the vicinity of the deposit, the high variability of properties, the complex structural defects, the rock alteration degree, limited geomechanical data, etc. Before evaluating the slope stability we should characterize the rock mass. To characterize it we have built the geological model, structural model and rock mass model to form the geotechnical model as it recommends the Large Open Pit project (LOP), an international research project related to stability of rock slope in open pit mines. Once constructed geotechnical domains, the stability of rock mass slope can be evaluated for each domain by using some known methods like limit equilibrium, the finite elements and discrete element methods. The use of the method depends of different factors like influence of structural elements (defects), importance of analysis, available information, etc. Limit equilibrium traditional methods like Bishop and Janbu can be used to evaluate the stability of large rock slopes that are susceptible to rotational failure of rock mass. Since the finite element method has developed rapidly and has gained popularity for the slope stability analysis in the case where failure mechanism is not controlled by discrete geological structure. Finite element method is based on constitutive models of stress-strain for intact rocks and has difficulties in simulating sets with a large number of discontinuities within the rock mass. The discrete element method allows to simulate a large number of discontinuities and also allows the simulation of large deformations. This dissertation uses the SRM (Synthetic Rock Mass) model to evaluate the stability of slopes in an open pit mine in Peru. The SRM model is a new technique that allows the simulation of the mechanical behavior of fractured rock mass taking into account propagation of fractures and anisotropic effects. This technique uses two well established techniques like BPM (Bonded Particle Model) for representation of intact rock and the SJM (Smooth-Joint Contact Model) to represent the structural fabric within the PFC program. For structural modeling it was used DFN method (Discrete-Fracture Network). To determine the geological and structural model it was used the Petrel program (Version 2010.1) and for slope stability analysis with the SRM model it was used the version 2D of the PFC 4.0 program.

Jointed rock masses are formed of intact rock and joints. There-fore, proper characterization of rock mass behavior has to consid-er the combined behavior of the intact rock blocks and that of the joints. This thesis presents the theoretical background of the Synthetic Rock Mass (SRM) modeling technique along with example applica-tions. The SRM technique is a new approach for simulating the mechanical behavior of jointed rock masses. The technique uses the Bonded Particle Model (BPM) for rock to represent intact ma-terial and the Smooth-Joint Contact Model (SJM) to represent the in situ joint network. In this manner, the macroscopic behaviour of an SRM sample depends on both the creation of new fractures through intact material, and slip/opening of pre-existing joints. SRM samples containing thousands of non-persistent joints can be submitted to standard laboratory tests (UCS, triaxial loading, and direct tension tests) or tested under a non-trivial stress path repre-sentative of the stresses induced during the engineering activity under study. Output from the SRM methodology includes pre-peak properties (modulus, damage threshold, peak strength) and post-peak proper-ties (brittleness, dilation angle, residual strength, fragmentation). Of particular interest is the ability to obtain predictions of rock mass scale effects, anisotropy and brittleness; properties that can-not be obtained using empirical methods of property estimation. Additionally, the nature of yielding and fracturing can be studied as the rock mass fails. This information can improve our understand-ing of rock mass failure mechanisms. / QC20100720

Advancements in computational capabilities have allowed researchers to turn towards modeling as an efficient tool to replicate and predict outcomes of complex systems. Computational models of the musculoskeletal system have gone through various iterations with early versions employing dramatic simplifications. In this work, a three-dimensional computational model of the wrist joint was developed. It accurately recreated the skeletal structures of the hand and wrist and represented the constraints imposed by soft tissue structures like ligaments, tendons, and other surrounding tissues. It was developed to function as a tool to investigate the biomechanical contributions of structures and the kinematic response of the wrist joint. The model was created with the use of a commercially available computer-aided design software employing the rigid body modeling methodology. It was validated against three different cadaveric experimental studies which investigated changes in biomechanical response following radioscapholunate fusion and proximal row carpectomy procedures. The kinematic simulations performed by the model demonstrated quantitatively accurate responses for the range of motions for both surgical procedures. It also provided some understanding to the trends in carpal bone contact force changes observed in surgically altered specimens. The model provided additional insight into the importance of structures like the triangular fibrocartilage and the capsular retinacular structures, both of which are currently not very well understood. As better understanding of components of the wrist joint is achieved, this model could function as an important tool in preoperative planning and generating individualized treatment regiments.

Einleitung: Die Ellbogengelenkdysplasie (ED) stellt eine der häufigsten Lahmheitsursachen bei jungen Hunden mittelgroßer und großer Rassen dar. Dabei wird der radioulnaren Inkongruenz eine maßgebliche Rolle in der Pathogenese zugesprochen. GUILLOU und Mitarbeiter (2011) konnten zeigen, dass eine axiale radioulnare Translation von bis zu 1 mm in gesunden kaninen Ellbogengelenken in vivo auftritt. Auf dieser Basis entstand die Hypothese einer vermehrten radioulnaren Beweglichkeit in dysplastischen Gelenken, die zu einer dynamischen Inkongruenz führen könnte, da ca. 40 % der Patienten keine messbare Stufe aufweisen. Ziele der Untersuchungen: Ziel der Studie war der Vergleich der dynamischen radioulnaren Inkongruenz bei orthopädisch gesunden und dysplastischen Hunden in vivo. Material und Methoden: Sieben dysplastische Ellbogengelenke von sechs Hunden und sechs orthopädisch gesunde Ellbogengelenke von fünf Hunden sind in die Studie eingegangen. Alle Probanden der ED Gruppe zeigten einen fragmentierten Processus coronoideus medialis ulnae. Nach Implantation von jeweils mindestens drei Markern in Humerus, Radius und Ulna erfolgte die biplanare, fluoroskopische Untersuchung der Gelenke, während die Hunde im Schritt auf einem Laufband geführt wurden. Die gewonnenen Röntgenvideoaufnahmen wurden aufgearbeitet und die gemessene Bewegung der Marker auf rekonstruierte dreidimensionale Knochenmodelle jedes Probanden übertragen. Alle Animationen wurden visuell beurteilt und anschließend die relative radioulnare und humeroulnare Bewegung an den animierten Knochenmodellen gemessen und als Translation in Millimeter und Rotation in Grad angegeben. Weiterhin wurden die Kontaktflächenmuster für die ulnare Gelenkfläche in dysplastischen und gesunden Gelenken bestimmt und gegeneinander visuell verglichen. Ergebnisse: Für die relative radioulnare Translation konnten in der Kontrollgruppe 0,7 mm und in der ED Gruppe 0,5 mm gemessen werden. Beide Werte unterschieden sich nicht signifikant voneinander (P= 0,2092; Konfidenzintervall -0,6 – 0,2). Die relative humeroulnare Rotation lag in der Kontrollgruppe bei 2,9 Grad und in der ED Gruppe bei 5,3 Grad. Damit lag ein signifikanter Unterschied zwischen beiden Gruppen vor (P= 0,0229; Konfidenzintervall 0,4 – 4,4). Die Kontaktflächenmuster zeigten in der Kontrollgruppe, während der dargestellten Fußungsphase, eine homogene Verteilung des Kontaktes über das gesamte mediale Koronoid. Hingegen konnte in dysplastischen Gelenken eine Reduktion des Kontaktes im kraniolateralen Anteil des Koronoids beobachtet werden. Schlussfolgerung: Die radioulnare Bewegung zeigt zwischen gesunden und dysplastischen Gelenken keinen signifikanten Unterschied auf. Die Hypothese einer ausgeprägten Translation zwischen Radius und Ulna in Gelenken erkrankter Hunde, die während der Bewegung zu einer dynamischen RUI führt kann damit widerlegt werden. Allerdings zeigt der Humerus in dysplastischen Gelenken eine vermehrte Rotationsbewegung, die zu einer Verlagerung der Trochlea humeri gegen den medialen Kronfortsatz führt. Dieser visuell und quantitativ erfasste Effekt spiegelt sich auch in den Kontaktflächenmustern wieder. Da Pathologien im Sinne des FPC typischerweise im Bereich des dargestellten, konzentrierten Kontaktes auftreten, ist davon auszugehen, dass es durch die humerale Rotation zu einer vermehrten Belastung des Koronoids kommt, welche zur Fragmentation des Kronfortsatzes führen kann. Die Ursache dieser vermehrten Bewegung ist derzeit nicht bekannt. Möglicherweise spielen Weichteilpathologien eine Rolle, ähnlich der Pathogenese der Hüftgelenksdysplasie. Neben der bereits bekannten und beschriebenen statischen RUI scheint die Rotationsinstabilität des Humerus eine entscheidende Rolle in der Pathogenese der ED zu spielen, insbesondere in kongruent erscheinenden Gelenken. / Introduction: Elbow dysplasia (ED) is one of the most frequent reasons for forelimb lameness especially in young large breed dogs. Radio-ulnar incongruence is discussed to be one of the main factors in the pathogenesis of ED. GUILLOU et al. (2011) described an axial translation between the radius and the ulna up to 1 mm in sound canine elbow joints in vivo. Based on this study we developed the hypothesis that pronounced radio-ulnar movement in dysplastic joints leads to a dynamic radio-ulnar incongruence. This dynamic incongruence might explain why 40 % of dysplastic dogs show no measurable step formation. Objective: The aim of the study was to compare the dynamic radio-ulnar incongruence in sound and dysplastic dogs in vivo. Material and Methods: Seven dysplastic joints in six dogs and six sound joints in five dogs were evaluated. All dysplastic joints showed a fragmented coronoid process and a radio-ulnar incongruence and cartilage lesions on the ulnar and humeral joint surface in a varying degree. A minimum of three Tantalum markers were implanted into the Humerus, Radius and Ulna each. Afterwards biplanar fluoroscopic gait analysis was performed while the dogs were walking on a treadmill. Gained marker movement was transferred onto reconstructed three dimensional CT bone models of each dog. The 3D animations were visually assessed and relative movement between the radius and ulna as well as between the humerus and ulna was measured and expressed as translation (millimeter) and rotation (degree). Further the joint contact patterns of the ulnar joint surface were determined for all dysplastic and sound joints and visually compared to each other. Results: Relative radio-ulnar translation was 0.7 mm in sound joints and 0.5 mm in dysplastic joints. There was no significant difference between these two groups (P= 0.2092; convidence interval -0.6 to 0.2). A significant difference between the dysplastic and the sound group was present in the relative humeral rotation (P= 0.0229; convidence interval 0.4 to 4.4). Humeral rotation relative to the ulna was 2.9 degree in sound and 5.3 degree in dysplastic joints. Humero-ulnar contact at the medial coronoid process was evenly distributed over the medial coronoid process in control elbows, while contact area in dysplastic elbows was reduced and shifted to the lateral aspect of the medial coronoid process Conclusion: Radio-ulnar movement is not significantly different between dysplastic and sound elbow joints. So the hypothesis of a pronounced axial translation between the radius and the ulna in dysplastic joints, leading to dynamic RUI can be neglected. However the humerus shows a significantly pronounced rotational movement in dysplastic joints compared to sound elbows. The trochlea humeri moves towards cranio-lateral and hits the medial coronoid process at its cranio-lateral aspect. The effect of this rotational movement can be shown in the joint contact patterns of the ulnar joint surface. Contact is shifted towards the tip and the lateral aspect of the coronoid process. In that area fragmentation of the medial coronoid process is typically observed. It seems that rotation of the humerus relative to the ulna leads to reduced contact and mechanical overload of the coronoid process. The cause of this increased rotational movement remains unknown. Maybe the documented movement could be interpreted as joint instability similar to the pathogenesis of hip dysplasia in which soft tissue laxity results in joint instability and degenerative joint disease. Besides the already described static radio-ulnar incongruence humeral rotational instability seems to play a role in the pathogenesis of elbow dysplasia, especially in congruent joints.

It has been noticed that the need for total knee replacement surgery is increasing for Asian region. A total knee replacement is a permanent surgical solution for a patient having debilitating pain in knee joint suffering from arthritis. In this surgery, knee joint is replaced with components made up of bio-compatible materials after which the patient can resume the normal day to day activities. Western population has bigger build compared to Asian population. Most of the total knee replacement prosthesis are designed for western population. When these total knee prosthesis are used for Asian population, they cause a mismatch leading to various clinical complications such as reduced range of motion and pain. The studies have been limited to clinical complications caused by the mismatch. To address this limitation, current study is aimed to find the mechanical implications such as stress distribution, maximum stresses, maximum displacements etc., caused by mismatch of total knee replacement components with knee. A surgeon selects total knee components for a patient based on some critical dimensions of femur and tibia bone of knee. In addition, a method to accurately calculate these dimensions of the femur and tibia bone of a real knee was developed in the current study. This method calculated the points of curvature greater than a threshold (decided based on the radius of the curvature) found out using the formula of curvature. Further, the highest point was calculated based on maximum height from a line drawn between initial and final point within the captured points, also the extreme points were calculated based on the sign change in slope of points within the captured points, giving multiple points on the boundary of bones extracted in an MRI image of a patient. The distance between two selected farthest points, out of these points, in specific direction was the basis for selection of the TKR components. Total knee replacement components were modeled in Geomatics Studio 12 software, bones were modeled in Rhinoceros 5 software, assembly of bones and total knee replacements components was done in Solid works 2013 software, the finite element model of the assembly was developed in Hyper mesh 11 software and, the stress analysis and post processing was done in ABAQUS 6.13 software. A static, implicit non linear analysis was performed. Simulations were performed for two conditions: at standing (0o of flexion) and at hyper-flexed (120o of flexion). In order to figure out if there were any mechanical implications of mismatch, the full model of assembly consisting of femur, tibia and fibula bones assembled with total knee replacement components, and the reduced model consisting of only total knee replacement components were simulated separately, results of which have been discussed in the current thesis. In this work, the effect of change of length of ligaments at 120o of flexion in detail was also studied. This study brought out various outcomes of contact mechanics and kinematics between the components of total knee replacement prosthesis.

Einleitung: Die Ellbogengelenkdysplasie (ED) stellt eine der häufigsten Lahmheitsursachen bei jungen Hunden mittelgroßer und großer Rassen dar. Dabei wird der radioulnaren Inkongruenz eine maßgebliche Rolle in der Pathogenese zugesprochen. GUILLOU und Mitarbeiter (2011) konnten zeigen, dass eine axiale radioulnare Translation von bis zu 1 mm in gesunden kaninen Ellbogengelenken in vivo auftritt. Auf dieser Basis entstand die Hypothese einer vermehrten radioulnaren Beweglichkeit in dysplastischen Gelenken, die zu einer dynamischen Inkongruenz führen könnte, da ca. 40 % der Patienten keine messbare Stufe aufweisen. Ziele der Untersuchungen: Ziel der Studie war der Vergleich der dynamischen radioulnaren Inkongruenz bei orthopädisch gesunden und dysplastischen Hunden in vivo. Material und Methoden: Sieben dysplastische Ellbogengelenke von sechs Hunden und sechs orthopädisch gesunde Ellbogengelenke von fünf Hunden sind in die Studie eingegangen. Alle Probanden der ED Gruppe zeigten einen fragmentierten Processus coronoideus medialis ulnae. Nach Implantation von jeweils mindestens drei Markern in Humerus, Radius und Ulna erfolgte die biplanare, fluoroskopische Untersuchung der Gelenke, während die Hunde im Schritt auf einem Laufband geführt wurden. Die gewonnenen Röntgenvideoaufnahmen wurden aufgearbeitet und die gemessene Bewegung der Marker auf rekonstruierte dreidimensionale Knochenmodelle jedes Probanden übertragen. Alle Animationen wurden visuell beurteilt und anschließend die relative radioulnare und humeroulnare Bewegung an den animierten Knochenmodellen gemessen und als Translation in Millimeter und Rotation in Grad angegeben. Weiterhin wurden die Kontaktflächenmuster für die ulnare Gelenkfläche in dysplastischen und gesunden Gelenken bestimmt und gegeneinander visuell verglichen. Ergebnisse: Für die relative radioulnare Translation konnten in der Kontrollgruppe 0,7 mm und in der ED Gruppe 0,5 mm gemessen werden. Beide Werte unterschieden sich nicht signifikant voneinander (P= 0,2092; Konfidenzintervall -0,6 – 0,2). Die relative humeroulnare Rotation lag in der Kontrollgruppe bei 2,9 Grad und in der ED Gruppe bei 5,3 Grad. Damit lag ein signifikanter Unterschied zwischen beiden Gruppen vor (P= 0,0229; Konfidenzintervall 0,4 – 4,4). Die Kontaktflächenmuster zeigten in der Kontrollgruppe, während der dargestellten Fußungsphase, eine homogene Verteilung des Kontaktes über das gesamte mediale Koronoid. Hingegen konnte in dysplastischen Gelenken eine Reduktion des Kontaktes im kraniolateralen Anteil des Koronoids beobachtet werden. Schlussfolgerung: Die radioulnare Bewegung zeigt zwischen gesunden und dysplastischen Gelenken keinen signifikanten Unterschied auf. Die Hypothese einer ausgeprägten Translation zwischen Radius und Ulna in Gelenken erkrankter Hunde, die während der Bewegung zu einer dynamischen RUI führt kann damit widerlegt werden. Allerdings zeigt der Humerus in dysplastischen Gelenken eine vermehrte Rotationsbewegung, die zu einer Verlagerung der Trochlea humeri gegen den medialen Kronfortsatz führt. Dieser visuell und quantitativ erfasste Effekt spiegelt sich auch in den Kontaktflächenmustern wieder. Da Pathologien im Sinne des FPC typischerweise im Bereich des dargestellten, konzentrierten Kontaktes auftreten, ist davon auszugehen, dass es durch die humerale Rotation zu einer vermehrten Belastung des Koronoids kommt, welche zur Fragmentation des Kronfortsatzes führen kann. Die Ursache dieser vermehrten Bewegung ist derzeit nicht bekannt. Möglicherweise spielen Weichteilpathologien eine Rolle, ähnlich der Pathogenese der Hüftgelenksdysplasie. Neben der bereits bekannten und beschriebenen statischen RUI scheint die Rotationsinstabilität des Humerus eine entscheidende Rolle in der Pathogenese der ED zu spielen, insbesondere in kongruent erscheinenden Gelenken. / Introduction: Elbow dysplasia (ED) is one of the most frequent reasons for forelimb lameness especially in young large breed dogs. Radio-ulnar incongruence is discussed to be one of the main factors in the pathogenesis of ED. GUILLOU et al. (2011) described an axial translation between the radius and the ulna up to 1 mm in sound canine elbow joints in vivo. Based on this study we developed the hypothesis that pronounced radio-ulnar movement in dysplastic joints leads to a dynamic radio-ulnar incongruence. This dynamic incongruence might explain why 40 % of dysplastic dogs show no measurable step formation. Objective: The aim of the study was to compare the dynamic radio-ulnar incongruence in sound and dysplastic dogs in vivo. Material and Methods: Seven dysplastic joints in six dogs and six sound joints in five dogs were evaluated. All dysplastic joints showed a fragmented coronoid process and a radio-ulnar incongruence and cartilage lesions on the ulnar and humeral joint surface in a varying degree. A minimum of three Tantalum markers were implanted into the Humerus, Radius and Ulna each. Afterwards biplanar fluoroscopic gait analysis was performed while the dogs were walking on a treadmill. Gained marker movement was transferred onto reconstructed three dimensional CT bone models of each dog. The 3D animations were visually assessed and relative movement between the radius and ulna as well as between the humerus and ulna was measured and expressed as translation (millimeter) and rotation (degree). Further the joint contact patterns of the ulnar joint surface were determined for all dysplastic and sound joints and visually compared to each other. Results: Relative radio-ulnar translation was 0.7 mm in sound joints and 0.5 mm in dysplastic joints. There was no significant difference between these two groups (P= 0.2092; convidence interval -0.6 to 0.2). A significant difference between the dysplastic and the sound group was present in the relative humeral rotation (P= 0.0229; convidence interval 0.4 to 4.4). Humeral rotation relative to the ulna was 2.9 degree in sound and 5.3 degree in dysplastic joints. Humero-ulnar contact at the medial coronoid process was evenly distributed over the medial coronoid process in control elbows, while contact area in dysplastic elbows was reduced and shifted to the lateral aspect of the medial coronoid process Conclusion: Radio-ulnar movement is not significantly different between dysplastic and sound elbow joints. So the hypothesis of a pronounced axial translation between the radius and the ulna in dysplastic joints, leading to dynamic RUI can be neglected. However the humerus shows a significantly pronounced rotational movement in dysplastic joints compared to sound elbows. The trochlea humeri moves towards cranio-lateral and hits the medial coronoid process at its cranio-lateral aspect. The effect of this rotational movement can be shown in the joint contact patterns of the ulnar joint surface. Contact is shifted towards the tip and the lateral aspect of the coronoid process. In that area fragmentation of the medial coronoid process is typically observed. It seems that rotation of the humerus relative to the ulna leads to reduced contact and mechanical overload of the coronoid process. The cause of this increased rotational movement remains unknown. Maybe the documented movement could be interpreted as joint instability similar to the pathogenesis of hip dysplasia in which soft tissue laxity results in joint instability and degenerative joint disease. Besides the already described static radio-ulnar incongruence humeral rotational instability seems to play a role in the pathogenesis of elbow dysplasia, especially in congruent joints.