Metal-on-Polyethylene Total Hip Arthroplasty: Exploring wear and corrosion resistance through visual analysis techniques

Project Introduction
Metal-on-Polyethylene (MoP) is currently the most widely used bearing combination in total hip arthroplasty (THA) devices, accounting for 87.1% of cemented primary hip implants in the UK in 2017. MoP is typically used in small diameter devices in order to limit the production of Polyethylene (PE) wear debris, which causes osteolysis leading to aseptic loosening and failure. These small diameter bearings are widely used but these devices limit patient hip functionality and are susceptible to dislocation; this is the second leading cause of revisions following wear related failures such as osteolysis. These limitations are largely acceptable in older patients who tend to have relatively low functionality prior to implantation, but are problematic for younger patients who are usually more active. Larger diameter bearings combat these limitations, but the accompanying increase in surface area of the bearing results in increased wear debris production and possibly corrosion.

Therefore if it can be shown that, when using modern materials and manufacturing techniques, a large diameter MoP device can perform within acceptable wear and corrosion tolerances compared to existing devices, then the new large-bearing technology could be widely adopted. This would deliver the benefits of large diameter bearings such as larger range of motion and reduced risk of dislocation, , and would increase knowledge of orthopaedic wear and corrosion resistance in general, which could be applied to other implant technologies.

Objectives
The project will investigate and improve corrosion and wear resistance of a novel MoP THA device. This will involve experiments testing the wear resistance, corrosion resistance and fatigue life of sample implants. The main objectives of the project are summarized below:
Year 1: Literature review, design of experiments, manufacture of fixture and hip components, preliminary tests and review paper writing.
Year 2: Wear and corrosion studies, learning and developing XPS sample analysis knowledge, interim paper publication and conference presentation.
Year 3: Design and implement novel upgrades to hip simulator to provide enhanced testing parameters, validation paper publication, conference attendance and thesis commencement.
Year 4: Thesis preparation and finishing experiments, paper publication on updated experimental results, conference attendance and preparation of ISO and ASTM testing body recommendations.

The research undertaken in this project should aid wider adoption of large diameter MoP THA devices, delivering the advantages discussed previously to patients. Additionally, the knowledge gained from this project should improve understanding of wear and corrosion methods, which would lead to the production of hip implants that are more resistant to these; this could also be applied to other orthopaedic devices. To aid in this outcome new testing methodologies will be produced, to be shared with the orthopaedic community. Other outcomes include an assessment of the suitability of modern PE materials for use in large diameter MoP THAs, and the design of a surface analysis sample assessment protocol, for contribution to the National Joint Registry.

Why Newcastle University?
Newcastle University is a Leading UK research centre in the field of bioengineering. The research group is housed in the school of engineering, but also benefits from strong ties with the university's medical school, as well as the NHS, medical charities and leading industrial partners. The research group also benefits from the expertise of multiple leading academics in the field, as well as having an array of equipment and facilities such as NEXUS that will aid the progress of the project.