1. Department of Orthopaedics, University College Hospital, 235 Euston Road, London NW1 2BU, UK.
2. Imperial College London, Charing Cross Hospital Campus, Fulham Palace Road, London W6 8RF, UK.
3. Royal National Orthopaedic Hospital, Brockley Hill, Stanmore HA7 4LP, UK.
4. North Tees Hospital, Hardwick, Stockton-on-Tees, Cleveland TS18 9PE, UK.
5. Norfolk and Norwich University Hospital, Colney Road, Norwich NR4 7UY, UK.
6. Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Nuffield Orthopaedic Centre, Windmill Road, Headington, Oxford OX3 7LD, UK.
7. Musculoskeletal Research Unit, Avon Orthopaedic Centre, Southmead Hospital, Westbury-on-Trym, Bristol BS10 5NB, UK.