1. University Department of Orthopaedic Surgery, Glenfield General Hospital, Groby Road, Leicester LE3 9QP, UK.
2. Department of Orthopaedic Surgery, Leicester Royal Infirmary, Infirmary Square, Leicester LE1 5WW, UK.
3. Department of Epidemiology and Public Health, University of Leicester, 22-28 Princess Road West, Leicester LE1 6TP, UK.