1. Haukeland University Hospital; Centre for Pain Management and Palliative Care & Regional Centre for Excellence in Palliative Care; Bergen Norway N-5021
2. Rigshospitalet and Copenhagen University; Department of Anaesthesia 4231; Centre of Head and Orthopaedics Blegdamsvej 9 Copenhagen Denmark 2100
3. University of Oxford; Pain Research and Nuffield Department of Clinical Neurosciences (Nuffield Division of Anaesthetics); Pain Research Unit Churchill Hospital Oxford Oxfordshire UK OX3 7LE
4. Helsinki University Central Hospital; Department of Anaesthesia, Intensive Care Medicine, Emergency Medicine and Pain Medicine; Helsinki Finland