Finite Element Analysis of Custom Tri-Flange Acetabular Cups

Author: Ella Fairweather

Fairweather, Ella, 2022 Finite Element Analysis of Custom Tri-Flange Acetabular Cups, Flinders University, College of Science and Engineering

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Custom tri-flange acetabular components (CTAC) are frequently utilised to treat a revision total hip arthroplasty (THA) where significant acetabular bone defects are present. Approximately 10% to 15% of THA cases will undergo a revision, with the most common failure mechanism being aseptic loosening due to poor bone quality of the pelvis (Sculco et al., 2022). Poor bone quality of the host bone can result in inadequate primary stability of an implant as it is difficult for the fixation methods utilised to gain fixation. Fixation methods of a CTAC to the pelvis generally consists of a number of screws supported by three flanges. From the literature, it can be suggested that there is over-compensation of the number screws to obtain primary stability of the implant. Over-compensation can lead to further deterioration of the pelvis, especially if multiple revisions are required. The challenge that surgeons face is gaining fixation of multiple screws into the host bone intraoperatively to gain primary stability of the implant. Finite element analysis (FEA) was utilised in this study to present evidence of the force transmission into the screws under two mechanical loading conditions. A total of seven screws were modelled, where screw number 1 was fixated into the pubis, screws number 2 and 3 in the ischium and screws number 4-7 in the ilium. These conditions simulated a nominal load applied to the femoral head and a peak contact force on the femoral head during a complete gait cycle. The aim of the thesis was to identify which screws are important in achieving primary fixation under the applied load conditions. The results from this study provided evidence to suggest that supressing screws number 3 and 4 in the ischium and ilium respectively had the least effect on the transmission to the applied load in remaining screws. Omitting screws number 3 and 4 from the screw plan will aid in the restoration of bone quality without impacting the load transmitted into the remaining screws. Finally, this study proved that the screws with greater force per millimetre of length of screw while all screws were active (screws 2 and 5 under the peak contact force during a complete gait cycle), when removed, had potentially detrimental effect on the remaining screws and overall load transfer.

Keywords: Finitie element analysis, custom tri-flange acetabular cups, screw-bone interaction, screw loads

Subject: Engineering thesis

Thesis type: Masters
Completed: 2022
School: College of Science and Engineering
Supervisor: Professor Mark Taylor