Biomechanics of the Total Ankle Arthroplasty: Stress Analysis and Bone Remodeling Daniela Sofia de Oliveira Salgado Rodrigues Thesis to obtain the Master of Science Degree in Biomedical Engineering Examination Committee Chairperson: Professor João Pedro Estrela Rodrigues Conde Supervisors: Professor Paulo Rui Alves Fernandes Professor João Orlando Marques Gameiro Folgado Members of the Committee: Professor Jacinto Manuel de Melo Oliveira Monteiro Professor Luís Alberto Gonçalves de Sousa June 2013 Acknowledgements First of all, I would like to thank my supervisors, Prof. Paulo Fernandes and Prof. João Folgado. Prof. Paulo Fernandes has helped me since the beginning of my journey in IST. I have already asked him millions of questions and he has always had an answer to give me. He is an enthusiastic Professor and after attended his courses I thought that I could not have chosen a field of study other than Biomechanics. Prof. João Folgado is the most patient Professor in the world. I want to thank him for the countless hours he spent teaching me, for the suggestions and support during this work. He showed me how Biomechanics can be fascinating. I want to thank Prof. Dr. Jacinto Monteiro and Dr. Nuno Ramiro for the clinical guidance during this work. I want to express my sincere gratitude to Prof. Alberto Leardini from Bologna, Italy. Since the first e-mail, he always answered me with the same kindness and sometimes almost as fast as light. I want to thank him for the availability in the clarifications of doubts. I am eternally grateful to the entire IDMEC research group, Miguel Machado, Lina Espinha, Diogo Almeida, Ângela Chan, Paula Fernandes, Marta Dias, Nelson Ribeiro, and specially Carlos Quental, who was like my third supervisor, for sharing their time and knowledge with me. I am especially grateful to my parents, for their unconditional support, patience and encouragement in all the moments of my life. I also want to thank my grandparents, my aunts, uncles and cousins for all their support and happy moments. I am thankful to all my friends, especially Nina, with whom I lived the last 5 amazing years, Joana, Dé, Mariana and “the boys”, for all the unforgettable adventures that every day gave me motivation to continue. And now I would like to give a special thanks to Zé, for his help, encouragement and humour that gave me enthusiasm to overcome the obstacles throughout this work. Finally, I also want to thank FCT for the financial support through the funding of the Software Development for Arthroplasty Preparation project (PTDC/SAU-BEB/103408/2008), in which this thesis is integrated. I II Abstract The total ankle arthroplasty (TAA) is an alternative procedure to the arthrodesis in the treatment of advanced arthritis in the ankle joint. However, the total ankle prostheses are not yet widely accepted and do not have the same success rate of the hip, knee or even shoulder prostheses. Thus, the aim of this work is the development of a finite element (FE) model of the ankle joint complex (AJC) in order to study the influence of two different prostheses, Agility™ (considering two different designs) and S.T.A.R.™, on the stress distribution and bone remodeling. This work involved the geometric and FE modeling of the AJC and the prostheses, Agility™ and S.T.A.R.™. Subsequently, the models simulating the TAA were created. Then, stress analysis was performed, and the bone remodeling model developed in IDMEC/IST was used to determine the bone density distribution in the talus and tibia. The results indicated that the new design of Agility™ prosthesis has better performance than the old design. However, both prostheses (especially Agility™) exceeded the contact stress recommended for the intermediate/polyethylene component (10 MPa). Moreover, after the insertion of both prostheses, the stresses increased near the resected surface in the talus, which may contribute to early loosening and subsidence of the talar component. Regarding the bone remodeling analysis, both prostheses showed evidences that may lead to stress shielding effect. In conclusion, these prostheses still have some untested features and the optimal configuration is currently not known. Keywords: Biomechanics, Ankle joint complex, Total ankle arthroplasty, Finite element method, Bone remodeling III IV Resumo A artroplastia total do tornozelo (ATT) surge como alternativa à artrodese no tratamento da artrite em estadio avançado no tornozelo. No entanto, as próteses do tornozelo ainda não são amplamente aceites e não apresentam o mesmo sucesso registado nas próteses da anca, do joelho ou até do ombro. Desta forma, o objectivo deste trabalho é a criação de um modelo de elementos finitos do tornozelo, de forma a estudar a influência de duas próteses, Agility™ (considerando dois modelos diferentes) e S.T.A.R.™, na distribuição de tensões e na remodelação óssea. O trabalho envolveu a modelação geométrica e de elementos finitos do tornozelo e das próteses, Agility™ e S.T.A.R.™. De seguida, os modelos que simulam a ATT foram criados. Posteriormente foi feita a análise de tensões e o modelo de remodelação óssea desenvolvido no IDMEC/IST foi usado para determinar a distribuição de densidade óssea no tálus e na tibia. Os resultados indicaram que o novo modelo da prótese Agility™ apresenta um melhor desempenho que o antigo modelo. No entanto, ambas as próteses (especialmente a Agility™) excederam a tensão de contacto recomendada para o componente intermédio/polietileno (10 MPa). Além disso, após a inserção das próteses, as tensões aumentaram perto da superfície ressecada no tálus, contribuindo para o loosening e subsidência do componente talar. Relativamente à análise de remodelação óssea, ambas as próteses mostraram evidências de que podem originar o efeito de stress shielding. Concluindo, estas próteses apresentam algumas características que ainda não foram analisadas, sendo que a configuração óptima não é actualmente conhecida. Palavras-Chave: Biomecânica, Tornozelo, Artroplastia total do tornozelo, Método dos elementos finitos, Remodelação óssea V VI Contents Acknowledgements .................................................................................................................................. I Abstract................................................................................................................................................... III Resumo ................................................................................................................................................... V Contents ................................................................................................................................................ VII List of Figures ......................................................................................................................................... XI List of Tables .......................................................................................................................................XVII List of Symbols .....................................................................................................................................XIX Abbreviations ........................................................................................................................................XXI Chapter 1 – Introduction .......................................................................................................................... 1 1.1 Motivation ...................................................................................................................................... 1 1.2 Proposed Approach and Objectives .............................................................................................. 4 1.3 Contributions ................................................................................................................................. 6 1.4 Organization .................................................................................................................................. 6 Chapter 2 – Background .......................................................................................................................... 7 2.1 Anatomy ........................................................................................................................................ 7 2.1.1 Joints of the Human Foot ....................................................................................................... 7 2.1.2 Human AJC ............................................................................................................................ 8 2.1.2.1 Bony Configuration .......................................................................................................... 8 2.1.2.2 Ligamentous Configuration ............................................................................................. 9 2.2 Biomechanics .............................................................................................................................. 10 2.2.1 Standard Reference Terminology ........................................................................................ 10 2.2.1.1 Anatomical Reference Position ..................................................................................... 10 2.2.1.2 Anatomical Reference Planes and Axes ....................................................................... 10 2.2.1.3 Joint Motion Terminology .............................................................................................. 11