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Master's Dissertation
DOI
https://doi.org/10.11606/D.17.2021.tde-09092021-080719
Document
Author
Full name
Mário Augusto Ferreira Cruz
Institute/School/College
Knowledge Area
Date of Defense
Published
Ribeirão Preto, 2021
Supervisor
Committee
Volpon, José Batista (President)
Louzada, Mario Jefferson Quirino
Soni, Jamil Faissal
Title in Portuguese
Hastes intramedulares flexíveis para fixação de fraturas subtrocantéricas de fêmur simuladas em modelos pediátricos: avaliação da estabilidade mecânica e método dos elementos finitos
Keywords in Portuguese
Análise de elementos finitos
Fixação intramedular de fraturas
Fraturas do fêmur
Mecânica
Abstract in Portuguese
Fundamento: A indicação convencional para o uso das hastes intramedulares flexíveis é na fixação das fraturas diafisárias do fêmur da criança na idade escolar. Entretanto, não está estabelecido o grau de segurança em que esses implantes podem ser usados nas fraturas localizadas na região mais proximal do osso. Objetivo: Avaliar a estabilidade proporcionada por duas hastes intramedulares flexíveis em osteotomias completas e oblíquas localizadas nas regiões subtrocantérica e trocantérica em modelo de fêmur infantil. Métodos: Foram utilizados 18 modelos sintéticos de fêmures infantis em que duas hastes flexíveis de titânio foram inseridas de maneira retrógrada no canal intramedular até a região cervicotrocantérica. Depois, foram simuladas fraturas por meio de cortes oblíquos, completos, localizados em três níveis e criados três grupos com seis exemplares cada: Controle - corte na região mediodiafisária; Subtrocantérico - corte 3,5 cm distais ao trocanter menor; Trocantérico - corte rasante ao trocanter menor. Cada grupo foi submetido a ensaios de flexocompressão com aplicação de força de compressão vertical na cabeça femoral, à velocidade de 0,1 mm/s, até o limite de 85 N. Foram obtidas a deformação e a rigidez relativa do conjunto modelo-implante. Os mesmos exemplares foram submetidos a testes de torção, com rotação no sentido horário do fragmento proximal à taxa de 0,5º/s, até a deformação de 20º. Foi obtido o torque médio do conjunto modelo-implante. Na análise pelo método de elementos finitos (MEF) as imagens tomográficas dos conjuntos foram importadas para reconstrução tridimensional e analisadas pelo programa SimLab®(HyperWorks, United States). Após simulação da 85,0 N, foi determinado o valor médio da deformação, as tensões máxima e mínima principais e as tensões de Von Mises nos implantes. Nos ensaios mecânicos, as variáveis deformação e torque relativos receberam análise estatística pelos testes ANOVA e Tukey. A variável rigidez relativa recebeu análise pelos testes de Kruskal-Wallis e Dunn. O nível de significância foi estabelecido em 5%. Resultados: A média da rigidez relativa foi: 54,360 x 10³ N/m nos cortes mediodiafisários; 31,415 x10³ N/m nos cortes subtrocantéricos (42,2% menor que o controle) e 30,912 x10³ N/m nos cortes trocantéricos (43,1% menor que o controle). As deformações médias do conjunto foram: 1,645 mm no grupo mediodiafisário; 2,424 mm nos cortes subtrocantéricos e 2,508 mm nos cortes trocantéricos, com significância entre os grupos (p<0,05). Nos testes de torção, os torques médios foram: 1,410 Nm no grupo mediodiafisário (controle); 1,116 Nm no grupo subtrocantérico (20,8% inferior o grupo controle) e 2,19 4 Nm no grupo trocantérico (55,6% superior ao grupo controle), com diferença estatística entre os grupos (p<0,05). Nas simulações pelo MEF, com carga de 85,0 N, o deslocamento na osteotomia no grupo controle foi 0,04 mm, enquanto as osteotomias subtrocantérica e trocantérica apresentaram deslocamento de 0,05 e 0,06 mm, respectivamente. O valor encontrado de tensão máxima principal no corte mediodiafisário foi 10,4 Pa, no corte subtrocantérico foi 7,52 Pa (27% menor que o controle), e no corte trocantérico foi 26,4 Pa (153% maior que o controle). A maior tensão de Von Mises nas hastes flexíveis ocorreu na região do corte, sendo maior no corte trocantérico. Conclusão: A estabilidade proporcionada pelas hastes elásticas nas fixações nas osteotomias no nível trocantérico e subtrocantérico sugerem que essas regiões não sejam adequadas para o uso de hastes intramedulares flexíveis.
Title in English
Flexible intramedullary nails for fixation of simulated subtrochanteric femur fractures in pediatric models: evaluation of mechanical stability and finite element method
Keywords in English
Femoral fractures
Finite element analysis
Fracture fixation
Intramedullary
Mechanics
Abstract in English
Background: The conventional indication for the use of flexible intramedullary elastic nails is for the fixation of the diaphyseal fractures of the femur of school age children. However, the degree to which elastic nails can be used safely for the fractures located in the most proximal region of the bone has not been established. Objective: To evaluate the stability provided by two flexible titanium intramedullary nails in the stabilization of osteotomies at the subtrochanteric and trochanteric regions in children's femur models. Methods: Eighteen synthetic models of infant femurs were used, in which two flexible titanium nails were inserted retrograde and divergently into the intramedullary canal until the cervicotrochanteric region. Then, fractures were simulated by causing complete oblique osteotomies in the femur models that were located at three levels and three groups were created with six specimens each: control group with osteotomy at the mid-diaphyseal region; subtrochanteric group with osteotomy 3.5 cm distal to the lesser trochanter; and trochanteric group with osteotomy at the lesser trochanter. Each group was subjected to flex compression tests with the application of a vertical compression force on the femoral head, at a speed of 0.1 mm/s, up to the limit of 85 N. The deformation and relative stiffness of the model-implant set were obtained. The same specimens were subjected to torsion tests, with clockwise rotation of the proximal fragment at a rate of 0.5º/s until a deformation of 20º was achieved. The average torque of the model-implant set was obtained. For the analysis using the finite element method (FEM), the tomographic images of the sets were imported for three-dimensional reconstruction and were analyzed by the SimLab® program (HyperWorks, United States). After the simulation of 85 N, the mean deformation value at the site of the osteotomies, maximum and minimum stress and the Von Mises stress in the implants were determined. In the mechanical tests, the relative strain and torque variables were statistically analyzed by analysis of variance and Tukey tests. The relative stiffness variable was analyzed using the Kruskal-Wallis and Dunn tests. The level of significance was set at 5%. Results: The average relative stiffness was 54.360 x 10³ N/m for the mid-diaphyseal, 31.415 x 10³ N/m for the subtrochanteric (42.2% less than the control), and 30.912 x 10³ N/m for the trochanteric osteotomies (43.1% less than the control). The average deformation of the set was 1.645 mm in the mid-diaphyseal, 2.424 mm in the subtrochanteric, and 2.508 mm in the trochanteric group. Statistically significant difference was observed between the groups (p<0.05). For torsion, the average torques were 1.410 Nm in the mid-diaphyseal (control), 1.116 Nm in the subtrochanteric (20.8% lower than the control group), and 2.194 Nm in the trochanteric group (55.6% higher than the control group), with no statistically significant difference between the groups (p<0.05). In the FEM simulations, with a load of 85 N, the displacement at the osteotomy site in the control group was 0.04 mm, while the subtrochanteric and trochanteric osteotomies showed a displacement of 0.05 and 0.06 mm, respectively. The main maximum tension in the mid-diaphyseal osteotomies was 10.4 Pa, in the subtrochanteric osteotomy, it was 7.52 Pa (27% less than the control), and in the trochanteric osteotomy, it was 26.4 Pa (153% higher than the control). The greatest Von Mises tension in the flexible nails occurred at the osteotomy site, being the highest in the trochanteric osteotomy. Conclusion: The stability provided by the elastic nails for fixation of the osteotomies at the trochanteric and subtrochanteric levels suggests that flexible intramedullary nails are not a suitable option for treating fractures at these regions.
 
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Publishing Date
2021-10-01
 
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