Factors Influencing Press-fit Acetabular Cup Failure: an Experimentally Validated Finite Element Study
Author(s)
Clarke, SG
Type
Thesis
Abstract
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.
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.
Date Issued
2011
Date Awarded
2011-07
Citation
PhD Thesis, 2011
Journal / Book Title
PhD Thesis
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Jeffers, Jonathan
Phillips, Andrew
Bull, Anthony
Sponsor
Finsbury Orthopaedics Ltd and EPSRC
Creator
Clarke, Susannah G.
Publisher Department
Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)