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Title: Factors influencing press-fit acetabular cup failure : an experimentally validated finite element study
Author: Clarke, Susannah G.
ISNI:       0000 0004 2705 042X
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2011
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The work undertaken in this thesis uses finite element analysis to investigate the most critical causes of acetabular cup implant failure. To enable accurate conclusions from finite element analysis, three studies have been carried out to strengthen understanding and confidence in finite element model outcomes. Two of these are sensitivity studies, which inform the required level of model definition to enable repeatable results. The third study is an in vitro experimental validation of finite element strains, displacements and cup-bone micromotions; therefore validating the use of the finite element model to predict physical situations. Metal on metal press-fit acetabular cups are the worst performing acetabular cup type with severe failure consequences compared to cups made from more inert materials such as polyethylene or ceramic. The cause of failure of these cup types is widely acknowledged to be multi-factorial, therefore creating a complex scenario for analysis through clinical studies. A factorial analysis has been carried out using finite element analysis to investigate the relative influence of five input factors associated with acetabular cup implantation on output parameters indicating potential failure of the implantation. The factorial analysis concluded that the most significant influences on failure are cup positioning and the interference fit between the acetabular bone and implanted cup; and that these influences have a higher potential to cause failure than the design of the implant used, within the boundaries of the implant design parameters investigated here. Errors in these aspects of surgery may result in acetabular cup failure. It is therefore paramount to reduce errors in the surgical process to enable accurate levels of positioning and interference fit. Time and resources may therefore be best spent developing surgical instrumentation which can increase the accuracy of the implant positioning and fit, and ascertaining the optimal levels of both, rather than designing new implants.
Supervisor: Jeffers, Jonathan ; Phillips, Andrew ; Bull, Anthony Sponsor: Finsbury Orthopaedics Ltd ; EPSRC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral