Wade, Abigail ORCID: https://orcid.org/0000-0002-7491-0248
(2023)
An Investigation into the Effect of Modular Taper Design in Total Hip Replacements on Engagement, Motion and Fretting Corrosion.
PhD thesis, University of Leeds.
Abstract
Modularity, and more specifically that between the head and stem in total hip replacements (THR), is ubiquitous in THR systems, with a key advantage of allowing surgeons to select components intra-operatively for restoration of natural hip function. However, modular interfaces are susceptible to fretting corrosion due to micro-scale motions in a corrosive environment that presents a crevice geometry, referred to in the field as mechanically assisted crevice corrosion. Mechanically assisted crevice corrosion or fretting corrosion has been, and continues to be, associated with higher than acceptable revision rates as a result of adverse soft tissue reactions to ion and debris generated at interfaces, such as the head-stem modular taper interface.
There is wide variation in modular taper design in THR, including taper length, taper angle, angular mismatch, surface topography and the head-stem material couple. However, decades of research into the effect of design on fretting corrosion has failed to draw consistent conclusions, save for high level conclusions such as long smooth tapers perform better than short rough ones.
The aim of this thesis was to systematically investigate the role of taper design variables on performance outcomes, in this case fretting corrosion. To start, fifty-one modular tapers from five manufactures were geometrically and topographically assessed to quantify intra and inter manufacturer variation. These observations, in conjunction with current national joint registry trends, were used to inform prototype samples using standard and beyond standard preclinical testing methodologies that better represent patient biomechanics. In-situ electrochemical and micro motion methodologies were also developed to quantify degradation processes in real-time. This study investigated the roles of angular mismatch and roughness on fretting corrosion, the effect of head assembly force was also studied.
Seating mechanics and disassembly force were largely found insensitive to angular mismatch and surface topography. An increase in current, subsidence (when the heads were assembled to low assembly forces) and micro motion was seen with increasing axial load during simulation studies. The use of a more complex biomechanical loading methodology (ISO 14242-1) did not result in an increase in current compared to a uniaxial loading methodology. At a greater head assembly force of 7 kN resulted in lower currents, subsidence and micro motion compared to when the heads were assembled to 2 kN . Generally, the samples with increased roughness presented greater currents than the smoother samples across the different loading scenarios (e.g. in the uniaxial study, the smooth matched samples presented an average current of 2.0 ± 0.6 µA compared to the rough smooth samples 14.7 ± 5.1 µA), indicating a higher susceptibility to fretting corrosion. This was not associated with a greater level of motion. Across the different simulation studies, the distally engaged samples (-0.089 ± 0.004 °) presented the lowest current compared to proximally engaged samples (0.118 ± 0.013 °) and matched samples (0.017 ± 0.004 °) of equivalent surface topography. Additionally, the distal samples presented a level of motion similar to the matched samples of equivalent surface topography.
Findings from this investigation suggests that taper design parameters of a rough male taper surface topography and a proximal angular mismatch, specified for ceramic heads, should not be directly translated over to metal head couples as per current clinical practice. Rather, this investigation suggests that smoother, distally engaged samples assembled to a high assembly force may help minimise degradation products generated at the head-stem taper modular interface in metal head couples. The inclusion of a more complex simulated walking gait loading scenario (ISO 14242-1) over the uniaxial simulated loading scenario may not be a valuable improvement to short-term, high throughput experimental studies.
Future work will investigate the effect of patient derived gaits and different daily living activities on the performance of modular tapers to better simulate that occurring in-vivo. The short-term test methodology developed in this project will also be used assess a greater number of samples in order to determine which combination of features best optimise the modular taper junction.
Metadata
Supervisors: | Bryant, Michael George and Beadling, Andrew |
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Related URLs: | |
Keywords: | Biotribocorrosion; Modular Hip Prostheses; Taper; Taper Interface. |
Awarding institution: | University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering (Leeds) > School of Mechanical Engineering (Leeds) > Institute of Engineering Thermofluids, Surfaces & Interfaces (iETSI) (Leeds) |
Depositing User: | Dr Abigail Wade |
Date Deposited: | 16 Jul 2024 11:05 |
Last Modified: | 16 Jul 2024 11:05 |
Open Archives Initiative ID (OAI ID): | oai:etheses.whiterose.ac.uk:35168 |
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