1. Nuffield Orthopaedic Centre, Windmill Road, Headington, Oxford OX3 7LD, UK.
2. Alfred Hospital, PO Box 315, Prahran, 3181 Victoria, Australia.
3. Stoke Mandeville Hospital, Mandeville Road, Aylesbury, Buckinghamshire HP21 8AL, UK.
4. Department of Public Health and Primary Care, University of Oxford, Radcliffe Infirmary, Woodstock Road, Oxford OX2 6HE, UK.