1. Center for Rheumatology and Spine Diseases, Rigshospitalet Glostrup;
2. Department of Clinical Medicine, University of Copenhagen;
3. Department of Orthopedic Surgery, Regionshospitalet Silkeborg;
4. Center for Spine Surgery and Research, Middelfart Hospital, Middelfart; and
5. Department of Regional Health Research, University of Southern Denmark, Odense, Denmark