This research has investigated the influence of gait cycle, malalignment and overweight on total knee replacements using a finite element method. Dynamic and finite element models of fixed- and mobile-bearing implants have been created and solved; the fixed- and mobile-bearing implants demonstrated different performance on movement and contact pressure distribution in the tibio-femoral contact surfaces. More contact areas were found in the mobilebearing implant than in the fixed-bearing implant, but the maximum contact pressures were almost the same in both. The thickness of the tibial bearing component influenced the fixed- and mobile-bearing implants differently. A dynamic model of an implanted knee joint has been developed using MSC/ADAMS and MSC/MARC software. Stress shielding was found in the distal femur in the implanted knee joint. The stresses and strains in the distal femur were found to increase with body weight, especially during the stance phase. Serious stress shielding and more bone loss appear in condition of overweight. The increase of bone loss rate and stress in the distal femur with increase of body weight will result in a higher risk of migration of femoral component after total knee replacement. The peg size effect has been studied using this dynamic model; a longer peg with smaller diameter was found to be the best. Varus/valgus malalignment redistributed the tibio-femoral contact force and stress/strain distribution in the distal femur. The difference between contact forces on the medial and lateral condyle decreased in the valgus malalignment condition. Contact pressure increased in the varus/valgus malalignment condition in the dynamic models of both the fixed- and mobile-bearing implant. However, the mobile-bearing implant performed better in conditions of malalignment, especially malrotation. Body weight had less influence on the maximum contact pressure in the mobile-bearing implant.

Osteoarthritis (OA) is a debilitating joint disease that leads to significant pain, loss of mobility and quality of life. Knee malalignment results in increased joint pressure, which is a primary cause for OA progression. High Tibial Osteotomy (HTO) is a surgical procedure to correct malalignment and redistribute load in the knee joint, reduce peak pressure and delay OA progression. However, clinical outcomes have been unpredictable. Therefore, the aim of this study was to determine the relationship between malalignment and knee contact mechanics. A 3D computational model was created from magnetic resonance images of a cadaveric knee joint. A ligament tuning process was conducted to determine material properties. Finite element analyses were conducted, simulating end of weight acceptance during walking. Different wedge geometries were virtually removed to simulate malalignments from 14° valgus to 16° varus. Contact mechanics were sensitive to soft tissue material properties. In-vitro experiments were compared with computational modelling of the same specimen. Percent full-scale errors for contact force and pressure were less than 8%, demonstrating a unique subject-specific model validation. The native alignment of the cadaveric knee (1° varus) had medial and lateral compartment peak pressures of 4.28 MPa and 2.42 MPa, respectively. The medial:lateral force ratio was 70%:30%. Minimum contact stress did not occur at a Mechanical Axis Deviation (MAD) of zero millimetres nor at the Fujisawa Point, which are common targets for HTO correction. Results showed very strong correlations (r >0.94) between MAD and joint contact loading. This study is the first to demonstrate the relationship between stress (normal, shear, contact pressure) and MAD in a subject-specific model. This is a prerequisite for the development of a tool that could help surgeons make informed decisions on the degree of realignment required to minimise peak joint loading, thereby delaying OA progression.

Orientador: João Batista de Miranda / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas / Made available in DSpace on 2018-08-18T13:37:30Z (GMT). No. of bitstreams: 1 Ferreira_DanielBecharaJacob_M.pdf: 1620645 bytes, checksum: 6452df17927d464b10dd8a697e2a2126 (MD5) Previous issue date: 2011 / Resumo: Introdução: A osteotomia valgizante no terço proximal da tíbia é considerada um método confiável para o tratamento de pacientes jovens com osteoartrite medial do joelho, associado a alinhamento em varo. Entretanto, procedimentos realizados para a correção de desalinhamentos no plano frontal podem alterar o alinhamento do plano sagital. Vários fatores estão relacionados ao aumento da inclinação posterior do planalto tibial pós-osteotomia valgizante no terço proximal da tíbia. Hipótese: O posicionamento posterior da placa-calço está relacionado com menor alteração da inclinação posterior do planalto tibial. Modelo do estudo: Estudo clínico retrospectivo. Métodos: Foram realizadas 42 osteotomias entre abril de 2007 e agosto de 2008. Imagens radiográficas em perfil do joelho foram obtidas no pré-operatório e no pós-operatório recente. Determinou-se o ângulo formado entre a tangente do planalto tibial medial e uma linha perpendicular ao eixo da cortical posterior da tíbia por medidas goniométricas manuais, antes e após cirurgia. Determinou-se também a posição relativa da placa-calço em relação à cortical posterior da tíbia. Resultados: Houve aumento de aproximadamente 34% no valor da inclinação posterior do planalto tibial após a cirurgia, com a média subindo de 7,6° para 10,2° (p = 0,0006). Existe correlação entre o ângulo de inclinação do planalto tibial pré-operatório e o seu valor pós-cirúrgico (r = 0,4131 e p = 0,0065). A posição relativa e o tamanho do implante não influenciaram as alterações do alinhamento sagital. Conclusão: Nesta população amostral houve aumento estatisticamente significativo da angulação da superfície articular tibial proximal, no plano sagital, após osteotomia valgizante no terço proximal da tíbia. O posicionamento posterior da placa-calço não foi relacionado a um menor aumento desta angulação / Abstract: Background: The high tibial osteotomy is considered a reliable method for the treatment of young patients with medial knee osteoarthritis associated with varus alignment. However, procedures performed to correct misalignments in the frontal plane can change the alignment of the sagittal plane. Several factors are related to the increase in the posterior inclination of the tibial plateau after high tibial osteotomy. Hypothesis: The posterior positioning of the Puddu plate causes less alteration of the posterior inclination of the tibial plateau. Study design: Retrospective clinical trial. Methods: Forty-two opening-wedge high tibial osteotomies were carried out. Lateral radiographic images of the knee were obtained preoperatively and right after surgery. The angle between the tangent of the medial tibial plateau and a line perpendicular to the axis of the posterior tibial cortex was determined by manual goniometric measurements before and after surgery. We also determined the relative position of the Puddu plate in relation to the posterior tibial cortex. Results: There was an increase of approximately 34% in the tibial slope after surgery, with the mean value rising from 7.6° to 10.2°. This difference was statistically significant (p = 0.0006). There is a correlation between the preoperative and postoperative inclination angles of the tibial plateau (r = 0.4131, p = 0.0065). The relative position and the size of the implant did not influence the changes in sagittal alignment. Conclusion: There was a statistically significant increase in the angulation of the proximal tibial articular surface in the sagittal plane after high tibial osteotomy. The posterior positioning of the Puddu plate was not related to a smaller increase of this angle / Mestrado / Fisiopatologia Cirúrgica / Mestre em Ciências

Prosthetic alignment is the principle of the position and orientation and of the components in a lower limb prosthesis to achieve desirable biomechanical characteristics. Poor alignment of lower limb prostheses is related to decreased balance, knee and hip arthritis, and higher energy expenditure for the user. Clinicians, the prosthetists, have declared they need better tools and increased knowledge in how to perform lower limb prosthetic alignments. Therefore, the aim was to develop a tool concept for clinicians to use in the prosthetic alignment process. This thesis mapped out most of the variables a clinician must consider in the alignment process, identified the clinicians needs of an alignment tool, and screened the market for existing solutions. A systematic approach was applied to develop a conceptual tool from the gathered information. The needs of the customer were based on interviews with clinicians and competing products were benchmarked. Two different conceptual tools were developed, tested with clinicians with promising results, and presented in this thesis. Due to confidentiality agreements with the cooperating company, the designs and functions of the final concepts cannot be shown in the report and are therefore covered in the publication. / Protesuppställning är principen av att orientera och positionera komponenterna i en benprotes för att uppnå önskvärda biomekaniska egenskaper. Undermålig protesuppställning är relaterat till försämrad balans, knä- och höftartros, samt högre energiförbrukning hos användaren. Ortopedingenjörer har uttalat att de behöver bättre verktyg och ökad kunskap kring hur man bäst utför uppställning för benproteser. Uppsatsen ämnade därför att utveckla ett verktygskoncept för ortopedingenjören att använda i protesuppställningen. Den här uppsatsen har kartlagt de flesta variabler som en ortopedingenjör behöver överväga i uppställningsprocessen, identifierat ortopedingenjörers behov i ett uppställningsverktyg, samt undersökt marknaden för existerande lösningar. Ett systematiskt tillvägagångsätt användes för att utveckla ett konceptuellt verktyg baserat på den insamlade informationen. Kundens behov identifierades genom intervjuer med ortopedingenjörer och konkurrerande lösningar sammanställdes i en konkurrensanalys. Två olika konceptuella verktyg utvecklades, testades tillsammans med ortopedingenjörer med lovande resultat, samt har presenterats i denna uppsats. På grund av sekretessavtal med företaget som ingått i samarbetet kunde designen och funktioner, som ingår i de slutliga koncepten och resultatet, inte visas i denna rapport och är därmed övertäckta vid publicering.

Le cubitus proximal détient une courbe sagittale unique pour chaque individu, nommée « Proximal Ulna Dorsal Angulation (PUDA) ». Une reconstruction non-anatomique du cubitus proximal, suite à une fracture complexe peut engendrer une malunion, de l’arthrose et de l’instabilité. L’objectif de cette étude était d’évaluer la magnitude de malalignement au niveau de l’angulation proximale dorsale du cubitus qui causerait un malalignement radio-capitellaire, avec et sans un ligament annulaire intact. Afin d’atteindre cet objectif, une étude biomécanique fut conduite sur six spécimens frais congelés avec un simulateur de mouvement du coude. Des fractures simulées au niveau du PUDA, furent stabilisées avec une fixation interne dans cinq configurations différentes. Des images fluoroscopiques furent prises dans différentes positions du coude et de l’avant-bras, avec le ligament annulaire intact, puis relâché. Le déplacement de la tête radiale fut quantifié avec le ratio radio-capitellaire. Une interaction significative fut découverte entre les positions du coude, les angles de malalignement et l’intégrité du ligament annulaire. La subluxation de la tête radiale fut accentuée lors de la déchirure du ligament annulaire. Une augmentation de la subluxation antérieure de la tête radiale fut observée lorsque le malalignement était fixé en extension et lors de mouvements de flexion progressive du coude. D’autre part, un malalignement en flexion et une extension graduelle du coude occasionnait une subluxation postérieure. En conclusion, les résultats ont démontré l’importance d’une reconstruction anatomique du cubitus proximal, car un malalignement de 5 degrés engendre une subluxation de la tête radiale, surtout lors d’une déchirure du ligament annulaire. / It has been shown that the proximal ulna has a sagittal bow, named the Proximal Ulna Dorsal Angulation (PUDA), unique for each individual. Non-anatomic reconstruction of the proximal ulna following a complex injury may lead to malunion, arthrosis and instability, hence the importance of understanding its initial anatomy. The purpose of this study was to evaluate the magnitude of angular malalignement at the proximal ulna dorsal angulation that would lead to radiocapitellar malalignement, with and without an intact annular ligament. In order to achieve our goal, a biomechanical study was conducted on six fresh frozen specimens, with an elbow movement simulator. Simulated fractures at the PUDA were stabilized with internal fixation at five different angles. Then, fluoroscopic images were taken in different elbow and forearm positions, first with the annular ligament intact and then released. Radial head displacement was quantified with the Radio-Capitellar-Ratio (RCR). Overall, a significant interaction was found between elbow positions, angles of malalignement and annular ligament integrity. Radial head subluxation was emphasized when the annular ligament was ruptured. Moreover, anterior subluxation of the radial head increased as malalignement was fixed into extension and with progressive elbow flexion. Furthermore, posterior subluxation increased with malalignement into flexion and with elbow extension. In conclusion, our results demonstrate the importance of obtaining an anatomic reconstruction, specific for each individual’s unique proximal ulna dorsal angulation, following a proximal ulna fracture. Indeed, malalignment of 5 degrees can lead to abnormal tracking of the radial head, especially when associated with annular ligament tear.