Evaluation of polyetheretherketone as a candidate material for cemented total knee replacement

Abstract

Total knee replacement (TKR) is an increasingly prevalent procedure for the treatment of knee joint degeneration. Aseptic implant loosening remains a predominant cause of revision surgery. Traditional metallic implants can cause stress shielding of the surrounding tissues in-vivo, which may lead to compromised implant support. The success rate of contemporary TKR has plateaued; alternative bearing materials may be an effective research focus to address the shortcomings of metallic TKR.

Poly-ether-ether-ketone (PEEK) is bioinert, with promising wear resistance and mechanical properties for implant applications, principally, an elastic modulus similar to that of bone. A novel cemented PEEK femoral component is currently in development as part of an all-polymer TKR. The fixation for such a concept is critical in determining its success in-vivo, but this may be compromised should the increased structural compliance cause higher interfacial stress. This is the first study to assess PEEK femoral fixation using bone cement and was carried out as part of a consortium project, led by Invibio Ltd.

PEEK-cement interface strength tests were performed under adverse shear loading conditions. The results showed that the interface strength is governed by the mechanical interlock alone; a hierarchical surface texture on PEEK achieved the highest interfacial shear strength with cement. This is also the first study to show that surface activation of PEEK by oxygen plasma treatment significantly improves the cement adhesion strength. Evidence of bending at the PEEK-cement lap-shear interface demonstrated the concern that increased compliance could lead to higher interfacial strains and compromise fixation, compared to metal-cement interfaces.

Digital Image Correlation (DIC) was employed to measure periprosthetic bone strains. CoCr implants produced low strains in the central metaphyseal region of the lateral bone surface compared to the intact case, indicative of stress shielding. The PEEK implant induced a strain distribution closer to that on the intact bone surface, suggesting that PEEK could promote the strains required for bone maintenance. This study demonstrates the need for rigorous DIC protocol in the biomechanics community and is presented to guide future studies for valid comparison of results.

Finally, Digital Volume Correlation (DVC) was used to demonstrate the concept of strain measurement at the bone cement fixation region of the PEEK TKR construct. With optimal ?CT scan setup and DVC parameter selection, measurements may be obtained which characterise full-field cement strain with sufficient resolution, accuracy and precision. The work presented in this thesis, extended according to the suggested further work, should support future polymer orthopaedic implant developments by ensuring more robust pre-clinical analysis, with a closer representation of the unique response to the experienced in vivo conditions.

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Identifiers

ORCID for Katy Rankin: orcid.org/0000-0002-8458-1038

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

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