Influência da distância entre parafusos bicorticais no comportamento mecânico evidenciado por uma fratura transversa de fémur imobilizada com placa de osteossíntese interna
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2017
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A utilização de placas de osteossíntese internas é um método bastante comum para a redução das fraturas no tecido ósseo. Para melhorar a estabilização das placas e reduzir as necroses ósseas têm-se desenvolvido vários estudos de natureza numérica e experimental. Nesta dissertação, pretende-se avaliar a influência da distância entre parafusos no comportamento mecânico evidenciado por uma fratura transversa imobilizada com uma placa de osteossíntese interna. Para tal, utilizaram-se três placas DCP (Dynamic Compression Plate) com comprimentos diferentes, em que a sua fixação foi conseguida através de seis parafusos com o mesmo diâmetro. A avaliação do efeito da distância entre parafusos foi concebida com o posicionamento de três parafusos em cada extremo da placa. Para cada montagem, realizaramse ensaios de flexão em quatro pontos e, para evitar a dispersão geométrica e das propriedades elásticas do tecido ósseo, utilizou-se um material substituto, a madeira de Eucalyptus globulus Labill, de forma a comparar a rigidez e a carga máxima para cada uma das ligações. Posteriormente, modelaram-se as montagens pelo método dos elementos finitos, recorrendo a modelos coesivos, com o objetivo de simular a iniciação e a propagação do dano evidenciado no ensaio mecânico e reproduzir numericamente as curvas força-deslocamento, com o intuito de validar os modelos numéricos. A partir dos modelos numéricos que conjugavam várias combinações de parafusos foi possível concluir que a distância entre parafusos influencia significativamente os valores de rigidez e carga máxima, principalmente os que se encontram nas extremidades da placa e os mais próximos da fratura. O modelo numérico da combinação de parafusos que apresenta os valores de rigidez e carga máxima mais próximos dos valores experimentais do tubo intacto foi considerado o modelo mais adequado para garantir a estabilidade de fixação da placa DCP.
The use of internal bone plates is a very common method to perform the reduction of fractures in the bone tissue. Numerical and experimental studies have already been used to improve the stabilization of the plates and also reduce bone necrosis. This MSc Thesis aims evaluating the influence of the distance between (bicortical) screws on the mechanical behaviour of a transversal fracture immobilized by an internal bone plate. To do so, three DCP (Dynamic Compression Plate) with different lengths were used in which the fixation was made through the use of six screws with the same diameter. The evaluation of the distance between screws was done with the positioning of three screws in each of the plate's edges. To each assembly, four-point bending tests were performed and, to avoid the bone tissue's geometrical dispersion, it was utilized a substitute material, Eucalyptus globulus Labill wood, in order to compare the stiffness and the ultimate flexural load for each one of the wood-plate connect points. After that the assembly was modelled by the finite element method, using cohesive models, with the purpose to simulate the mechanical test and numerically reproduce the force – displacement curve, in order to validate the numerical model number. From the numerical models that conjugated several combinations of screws, it was possible to conclude that the distance between those screws influences in a significant form the values of stiffness and ultimate flexural load, mainly of those that are at the extremities of the plate and the ones closer to the fracture line. The numerical model of the screw's combination that presents the values of stiffness and ultimate flexural load closer to the experimental values of the intact tube was considered the most suitable model to guarantee the stability of fixation of the DCP.
The use of internal bone plates is a very common method to perform the reduction of fractures in the bone tissue. Numerical and experimental studies have already been used to improve the stabilization of the plates and also reduce bone necrosis. This MSc Thesis aims evaluating the influence of the distance between (bicortical) screws on the mechanical behaviour of a transversal fracture immobilized by an internal bone plate. To do so, three DCP (Dynamic Compression Plate) with different lengths were used in which the fixation was made through the use of six screws with the same diameter. The evaluation of the distance between screws was done with the positioning of three screws in each of the plate's edges. To each assembly, four-point bending tests were performed and, to avoid the bone tissue's geometrical dispersion, it was utilized a substitute material, Eucalyptus globulus Labill wood, in order to compare the stiffness and the ultimate flexural load for each one of the wood-plate connect points. After that the assembly was modelled by the finite element method, using cohesive models, with the purpose to simulate the mechanical test and numerically reproduce the force – displacement curve, in order to validate the numerical model number. From the numerical models that conjugated several combinations of screws, it was possible to conclude that the distance between those screws influences in a significant form the values of stiffness and ultimate flexural load, mainly of those that are at the extremities of the plate and the ones closer to the fracture line. The numerical model of the screw's combination that presents the values of stiffness and ultimate flexural load closer to the experimental values of the intact tube was considered the most suitable model to guarantee the stability of fixation of the DCP.
Descrição
Dissertação de Mestrado em Engenharia Mecânica
Palavras-chave
Tecido ósseo cortical , Elementos finitos , Simulação , Redução de fraturas internas , Bloqueio parafusos/placa , Distância entre parafusos