In Vitro Investigation into the use of Dual Mobility for Partial Revision of a Failed Metal Hip Resurfacing

Abstract

The aim of this work is to investigate whether a failed MOM total hip resurfacing arthroplasty (THRA) can be converted to a successful total hip arthroplasty (THA) during partial revision surgery using an alternative bearing surface for the femoral bearing surface only. It is estimated that around 10% of primary hip replacements will fail each year and with a large number of patients receiving hip replacements at a younger age, as well as living longer, it is essential that the quality of options for revision surgery is as high as possible.
The alternative femoral component used in this study was the Biomet Dual Mobility (DM) femoral bearing, comprising of a small head and a mobile bearing Vitamin-E infused UHMWPE liner which is completely free to move between the head and cup.
DM bearings are suggested in this project for use during partial revision procedures because one of the main reasons for implant failure after revision surgery is joint instability and DM bearings are reported to improve joint stability and prevent component dislocation.
This thesis is structured with four main results sections:
Firstly, retrieved CoCrMo components from failed THA were analysed and the surface features were characterised using zygo non-contacting profilometry, optical microscopy and scanning electron microscopy. The average surface roughness across the explanted CoCrMo cups was 0.031 ± 0.03 μm with a corresponding surface skewness of -5.04 ± 4.68 μm. Microscopy images showed a wide range of surface features including multidirectional scratching and carbide removal.
Secondly, MOM biotribological studies using the Durham hip simulator were undertaken in order to generate physiologically scratched CoCrMo acetabular cups in vitro that were similar to the retrievals. This was done through two methods; one simulation used ISO-standard wear conditions whilst another simulation investigated the effect of clinically relevant third-body particles on the MOM articulation. The aim was to produce CoCrMo cups with the desired surface roughness from multirdirectional abrasive scratching combined with negative surface skewness.
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Thirdly, DM biotribological studies using the ProSim hip simulator were then carried out using the previously scratched CoCrMo cups under aggressive testing conditions in order to fully assess the performance of the DM joint and its suitability for use in partial revision procedures. This project has tested a wide variety of CoCrMo cups with worn features similar to that seen in vivo from failed MOM bearings against DM heads and all vitamin-E infused UHMWPE liners have experienced very low wear rates in comparison to UHMWPE, from 0.23 – 5.15 mm3/MC depending on the test conditions.
Finally, test serum from the MOM ISO-standard simulation was analysed and compared to digested test serum from the DM simulations. Problems encountered with isolating CoCr particles from the DM test serum raised important concerns about the initial test set up which would have to be modified in order for future work to produce clinically relevant wear debris.
Overall this research has successfully increased the understanding of DM bearings for application in partial revision procedures and the results indicate that DM heads are indeed a viable solution for the conversion of a failed MOM THRA into a successful THA.