Publicação
Biomechanical analysis of surgical treatments of the cervical spine
| Resumo: | The main objective of this thesis was to study the biomechanical implications related to different surgical procedures for decompressing the intervertebral discs in the cervical spine. The different surgical techniques were evaluated so as to assess how load transfer to the adjacent vertebrae would be affected, thereby ascertaining the potential risks of failure of these vertebrae when compared to the vertebrae in the native (healthy) state. For this purpose an initial analysis of the cervical spine was performed, specifically on the C4-C6 segment, from an anatomical, biomechanical and pathological point of view. An analysis of surgical reconstructive processes was also carried out, with particular focus on the two procedures known as arthrodesis and arthroplasty. Finite element models were then developed from CT images obtained from a healthy male patient, with the purpose of comparing the surgical cases of arthrodesis and arthroplasty to the native case. For these tests the selected implants were the Fidji PEEK cage (Zimmer, Inc) for the arthrodesis case and the ProDisc-C (Synthes, Inc.) for the arthroplasty case. The different models generated from medical CT imaging were reconstructed with the help of 3D modelling and finite element software and submitted to loading conditions that simulated the weight of the human head in the anatomical (upright) position. The results obtained for each model enabled the evaluation, and therefore the comparison, of the alterations in load transfer from one model too another. These alterations were determined through the measurement of the variations in the principal strain values in the cortical bone of vertebrae C5 and C6, adjacent to the implant, and in vertebra C4, which was positioned directly above vertebra C5. Compressive strain values were also analysed in the trabecular bone for all three vertebrae. The principal strain values in the anterior vertebral body of vertebrae C5 and C6, obtained from the numerical models developed, were compared with the respective results obtained from the experimental models subsequently used in this study. In addition to the numerical models developed, experimental models of the C5-C6 segment in rigid polyurethane foam were created. The different surgical techniques (arthroplasty and arthrodesis) were performed in-vitro. The purpose behind the development of these models was to ascertain the extent to which the results obtained for the numerical models could be experimentally replicated. Alterations in load transfer in these models was registered by means of rosette strain gauges placed in the anterior region of the vertebrae, allowing the evaluation of the principal strain values on the model’s surface. These experimental models were submitted to the same loading conditions as the numerical models. A high correlation between the principal strain values was obtained when comparing the numerical models with the experimental models, thus revealing the ability of the numerical models to recreate the mechanical behaviour of the experimental models. The comparison made between the native numerical model (in which mechanical bone properties had not been simplified) and the model where mechanical properties were discretized, into cortical and trabecular bone properties, revealed differences that should not be overlooked. When comparing implanted models with the native model an increase in principal strain values of cortical and trabecular bone, particularly in the lateral areas of the vertebral body were revealed, relatively to the native model. On average these increases were lower in the cortical bone for the arthroplasty case than in the arthrodesis case, but higher in the trabecular bone. Thus, it is concluded that both surgical techniques contribute to the increase of mechanical strain on the vertebrae adjacent to the implants, and thus possibly increase the risk of failure of the bone structure due to fatigue. |
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| Autores principais: | Rodrigues, Diana Rebecca Esteves Cardoso Gavazzo |
| Assunto: | Engenharia mecânica Biomecânica Artroplastia Implantes ortopédicos Coluna vertebral |
| Ano: | 2011 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Aveiro |
| Idioma: | inglês |
| Origem: | RIA - Repositório Institucional da Universidade de Aveiro |
| Resumo: | The main objective of this thesis was to study the biomechanical implications related to different surgical procedures for decompressing the intervertebral discs in the cervical spine. The different surgical techniques were evaluated so as to assess how load transfer to the adjacent vertebrae would be affected, thereby ascertaining the potential risks of failure of these vertebrae when compared to the vertebrae in the native (healthy) state. For this purpose an initial analysis of the cervical spine was performed, specifically on the C4-C6 segment, from an anatomical, biomechanical and pathological point of view. An analysis of surgical reconstructive processes was also carried out, with particular focus on the two procedures known as arthrodesis and arthroplasty. Finite element models were then developed from CT images obtained from a healthy male patient, with the purpose of comparing the surgical cases of arthrodesis and arthroplasty to the native case. For these tests the selected implants were the Fidji PEEK cage (Zimmer, Inc) for the arthrodesis case and the ProDisc-C (Synthes, Inc.) for the arthroplasty case. The different models generated from medical CT imaging were reconstructed with the help of 3D modelling and finite element software and submitted to loading conditions that simulated the weight of the human head in the anatomical (upright) position. The results obtained for each model enabled the evaluation, and therefore the comparison, of the alterations in load transfer from one model too another. These alterations were determined through the measurement of the variations in the principal strain values in the cortical bone of vertebrae C5 and C6, adjacent to the implant, and in vertebra C4, which was positioned directly above vertebra C5. Compressive strain values were also analysed in the trabecular bone for all three vertebrae. The principal strain values in the anterior vertebral body of vertebrae C5 and C6, obtained from the numerical models developed, were compared with the respective results obtained from the experimental models subsequently used in this study. In addition to the numerical models developed, experimental models of the C5-C6 segment in rigid polyurethane foam were created. The different surgical techniques (arthroplasty and arthrodesis) were performed in-vitro. The purpose behind the development of these models was to ascertain the extent to which the results obtained for the numerical models could be experimentally replicated. Alterations in load transfer in these models was registered by means of rosette strain gauges placed in the anterior region of the vertebrae, allowing the evaluation of the principal strain values on the model’s surface. These experimental models were submitted to the same loading conditions as the numerical models. A high correlation between the principal strain values was obtained when comparing the numerical models with the experimental models, thus revealing the ability of the numerical models to recreate the mechanical behaviour of the experimental models. The comparison made between the native numerical model (in which mechanical bone properties had not been simplified) and the model where mechanical properties were discretized, into cortical and trabecular bone properties, revealed differences that should not be overlooked. When comparing implanted models with the native model an increase in principal strain values of cortical and trabecular bone, particularly in the lateral areas of the vertebral body were revealed, relatively to the native model. On average these increases were lower in the cortical bone for the arthroplasty case than in the arthrodesis case, but higher in the trabecular bone. Thus, it is concluded that both surgical techniques contribute to the increase of mechanical strain on the vertebrae adjacent to the implants, and thus possibly increase the risk of failure of the bone structure due to fatigue. |
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