1. Department of Orthopaedic Surgery and Traumatology (Affiliated to Institute of Clinical Research, University of Southern Denmark, Denmark), Odense University Hospital, Sdr. Boulevard 29, 5000, Odense C. Denmark
2. Odense University Hospital, Sdr. Boulevard 29, 5000, Odense C. Denmark
3. Department of Orthopaedic Surgery, Lillebaelt Hospital, Kolding, Skovvangen 2-8, 6000, Kolding Denmark
4. Institute of Regional Health Research, University of Southern Denmark and Odense Patient data Explorative Network (OPEN), Odense University Hospital (Affiliated to: The Danish Twin Registry, Institute of Public Health, Denmark), Odense University Hospital, Sdr. Boulevard 29, 5000, Odense C. Denmark
5. Spinesection, Hamlet Hospital, Copenhagen Denmark
6. Spinesection, Department of Orthopaedic Surgery, Lillebaelt Hospital, Middelfart, Østre Hougvej 55, 5500, Middelfart Denmark