Development of a novel acetabular cup component for large bearing total hip arthroplasty

Abstract

Total hip replacement (THR) is a successful procedure that demonstrates excellent long term survival rates in the elderly patient population. Resurfacing and large diameter bearing total hip components were introduced to improve survivorship in younger patients but problems associated with high levels of wear and component loosening has limited their acceptance in regular clinical practice. Aurora Medical Ltd (Southampton, UK) identified a need for a large diameter bearing hip replacement which offered high postoperative quality of life in the younger patient cohort through the development of a more biomechanically compliant acetabular component. Carbon fibre reinforced polyetheretherketone (CFRPEEK) has been identified as a potential bearing material for orthopaedic applications due to its proven mechanical and chemical properties, and its biocompatibility. This thesis outlines a preliminary design evaluation of a large diameter bearing CFRPEEK acetabular component, and focusses on four areas:

First, a novel cup design was investigated; the intention of the design was to provide more natural load transfer across the joint. The anatomic geometry of the acetabular load bearing surface was characterised, and incorporated into the design of a varying thickness acetabular cup.

Second, the relationship between the manufacturing processing parameters and the internal structure of CFRPEEK was investigated, assessing fibre orientation, distribution and defect population. It was found that the material injection location influenced fibre orientation and although a homogeneous fibre distribution was identified, the presence of porosity suggested that the injection holding pressure and/or the holding time were not adequate for successful moulding.

Third, implant fixation was considered; a primary fixation method was developed which involved creating a unique arrowhead structure onto the cup’s backing surface through two-stage moulding. The initial fixation provided by the moulded arrowheads was successfully verified through implantation and extraction investigations. However, further research needs to be conducted on the moulding procedure to ensure a consistent arrowhead shaped structure free from defects is formed. Two osseointegrative coating options to enhance secondary fixation of the cup were assessed. A hydroxyapatite on titanium coating exhibited the highest adhesion strength and did not compromise fatigue or tensile properties of the material.

Finally, studies were conducted to evaluate the feasibility of the digital volume correlation (DVC) technique to assess the change in the peri-prosthetic bone strain distribution as a result of implantation. It was found that bone was an ideal material candidate for DVC when imaged alone; however, the introduction of an acetabular component generated artefacts which compromised image quality and restricted the outcomes. A set of alterations to the image acquisition process were recommended to reduce these artefacts enabling the feasibility of the technique in calculating strains in the peri-prosthetic bone to be realised.

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Identifiers

ORCID for Martin Browne: orcid.org/0000-0001-5184-050X

ORCID for Philippa Reed: orcid.org/0000-0002-2258-0347

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