1. Department of Anaesthesia, Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK
2. Pain Research Fellow, The Royal Marsden Hospital/The Institute of Cancer Research, London SW3 6JJ, UK
3. Specialty Registrar, Barts and the London School of Anaesthesia, London E1 1BB, UK
4. Consultant, East & North Hertfordshire NHS Trust, Stevenage SG1 4AB, UK