Finite Element Analysis of Custom Pelvic Reconstructions After Tumor Resection Surgery: Development of a Workflow to Simulate Daily Motor Tasks, and Application to a Clinical Case

Custom-made 3D printed pelvic prostheses have recently been employed in pelvis reconstruction procedures. Their use is growing since they dramatically shorten the duration of the surgical procedure compared to previous reconstructive techniques. This thesis represents the final part of a greater project, carried out by the Computational Bioengineering Laboratory of IRCCS Istituto Ortopedico Rizzoli in Bologna, where the present thesis was carried out. The project aims to investigate the mechanical behavior of Custom-made 3D printed pelvic prostheses in terms of kinematics, kinetics, and internal stress and strain during daily tasks. Preliminary results on six patients, including gait analysis and patient-reported outcome measures, indicate a very good functional recovery. On the same patients, musculoskeletal models revealed, behind quasi-normal kinematic patterns, some relevant asymmetries in joint reactions and muscles forces. These forces were the input data for the present study. Little is known about the internal mechanical behavior of the bone and of the prosthesis under physiological loading conditions and no subject-specific Finite Element Analysis has yet been published, to our knowledge. Therefore, this thesis aims to: (i) develop a procedure to build, using state of the art methods, a subject-specific Finite Element model of a pelvis reconstructed through a custom-made 3D printed prosthesis, with boundary conditions mimicking daily motor tasks, to be used in the biomechanical analysis of post-operative follow-up. (ii) estimate the strain and stress distribution of the bone and the prosthesis during daily tasks, to evaluate prosthesis and bone safety factors in the long-term follow-up. To this aim: i) I carried out a detailed literature review to - identify validated models of the pelvis. - define each single modeling step: geometry extraction, material properties, mesh characteristics, ligaments modeling, cartilage modeling, bone-prosthesis interaction. - define loads and boundary conditions to mimic physiological conditions. ii) As no consensus emerged from literature on the construction of subject-specific pelvic models for Finite Element Analysis, a replicable protocol for further analysis was proposed. Innovative modeling strategies were devised where no robust procedures could be extracted from literature (e.g. cartilage modeling). iii) The model was created from one of the six patients studied in the project and tested for the walking activity. Preliminary results were obtained in terms of prosthesis safety factors and bone fracture or resorption risk over time for the walking task. The next steps will include testing other motor tasks as well as the construction of pelvic models for the other patients.