Øivind Jans1,2, Henrik Kehlet3,4. 1. Section of Surgical Pathophysiology 4074, Copenhagen University Hospital, Rigshospitalet, Blegdamsvej 9, 2100, Copenhagen, Denmark. 2. The Lundbeck Foundation Centre for Fast-Track Hip and Knee Arthroplasty, Copenhagen, Denmark. 3. Section of Surgical Pathophysiology 4074, Copenhagen University Hospital, Rigshospitalet, Blegdamsvej 9, 2100, Copenhagen, Denmark. henrik.kehlet@regionh.dk. 4. The Lundbeck Foundation Centre for Fast-Track Hip and Knee Arthroplasty, Copenhagen, Denmark. henrik.kehlet@regionh.dk.