1. Department of Neuromedicine and Movement Science, Norwegian University of Science and Technology, Trondheim, Norway;
2. Department of Neurosurgery, St. Olavs Hospital, Trondheim, Norway;
3. Department of Clinical Medicine, Faculty of Health Sciences, UiT the Arctic University of Norway, Tromsø, Norway;
4. Department of Public Health and General Practice, Norwegian University of Science and Technology, Trondheim, Norway;
5. National Advisory Unit on Spinal Surgery, St. Olavs Hospital, Trondheim, Norway;
6. Department of Neurosurgery, Leiden University Medical Centre and Spaarne Hospital, Haarlem/Hoofddorp, The Netherlands;
7. Institute for Clinical Medicine, UNN The Arctic University of Norway, Tromsø, Norway;
8. Department of Neurosurgery and the Norwegian Registry for Spine Surgery, University Hospital of North Norway, Tromsø, Norway