1. Akershus University Hospital; Department of Obstetrics and Gynecology; Sykehusveien 25 Lørenskog Akershus Norway 1478
2. Sahlgrenska Academy, University of Gothenburg; Institute of Neuroscience and Physiology, Department of Health and Rehabilitation/Physiotherapy; Gothenburg Sweden 405 30
3. Monash University; Monash Department of Clinical Epidemiology, Cabrini Hospital, Department of Epidemiology and Preventive Medicine, School of Public Health and Preventive Medicine; Malvern Victoria Australia
4. Monash University; Department of Epidemiology and Preventive Medicine, School of Public Health and Preventive Medicine; Malvern Victoria Australia
5. Oslo University Hospital; Department of Orthopaedics; Kirkeveien 166 Oslo Norway N-0407