Development of an in silico trial for the risk analysis of new hip replacement designs: predicting the risk of intraoperative fracture

Total Hip Arthroplasty is one of the most successful procedures, but, in the last years, the increase in the use of cementless stems has led to an increment of intraoperative femur fractures (3-5%), dependent on stem design. While numerous studies have investigated the mechanical behaviour of the femur during stem implantation through in vitro experiments, there is a notable lack of computational models specifically addressing IFF. This thesis aims to introduce a new approach for the numerical evaluation of IFF risk by using a simpler quasi-static and fully automated FE model capable of simulating crack propagation during stem insertion. In the first part of the PhD project, eleven subject-specific FE models were built starting from CT data, and the implant pose and size of a non-commercial cementless stem were identified. A compressive load was applied along the stem axis to simulate the surgeon's hammering, while the femur was distally constrained. The element deactivation technique was used to simulate the crack propagation. Three additional damage quantification criteria were investigated to automatically establish when considered the femur fractured. In the second part, the same workflow was repeated with a commercial stem design, but due to its geometry complexity, some modifications were introduced to the procedure. Additionally, a +/- one stem size uncertainty was introduced to investigate crack propagation under different canal-filling conditions. In the last part, conducted at Zimmer Biomet, the work aimed to re-implement the developed algorithm in Abaqus. The crack propagation was modelled through a material properties degradation technique for assessing the risk of tibial bone fractures in two partial knee arthroplasty FE models. The crack path and final failure load obtained with FE analysis were compared with experimental results. In conclusion, the project highlighted the algorithm's ability to simulate crack propagation with different implant designs.