1. Department of Trauma and Orthopaedic Surgery, The Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne, Tyne and Wear NE2 4HH, UK.
2. Department of Orthopaedic Surgery, Freeman Hospital, Freeman Road, High Heaton, Newcastle upon Tyne, Tyne and Wear NE7 7DN, UK.
3. Department of Primary Care and Population Sciences, Royal Free and University College Medical School, Royal Free Campus, Rowland Hill Street, London NW3 2P, UK.
4. South Tees Acute Hospitals NHS Trust, Middlesbrough General Hospital, Ayresome Green Lane, Middlesbrough, Cleveland TS5 5AZ, UK.