1. Musculoskeletal Research Unit, School of Clinical Sciences, University of Bristol, 1st Floor Learning & Research Building, Southmead Hospital, Bristol, BS10 5NB, UK
2. Cardiff & Vale University Health Board, University Hospital Llandough, Penlan Road, Llandough, Penarth, Vale of Glamorgan, CF64 2XX, UK
3. Centre for Hip Surgery, Wrightington Hospital, Lancashire, WN6 9EP, UK