Received: 30 August 2019
Accepted: 19 January 2020
First Online: 31 January 2020
Ethics approval and consent to participate
: Ethical approval was sought from the local research ethics committee with formal approval deemed unnecessary under the National Health Service research governance arrangements. The study was done in agreement with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments.
: Not applicable
: HRM reports the Henni Mester Scholarship from University of Oxford, Royal College of Surgeons research grant and the Goodfellow Fellowship. JAK reports a grant to the University of Oxford from Zimmer Biomet. CAD and DM report royalties, consultancy payments related to knee replacements and a grant to the University of Oxford from Zimmer Biomet. AJ and SJM have no potential conflict of interest.