[1] Oslo University Hospital Rikshospitalet,Department of Neurosurgery
[2] University of Oslo,Faculty of Medicine
[3] Oslo University Hospital Rikshospitalet,Department of Neuroradiology
[4] St. Olavs Hospital,National Advisory Unit of Spinal Disorders and Department of Orthopaedic Surgery, Clinic of Orthopaedics and Rheumatology
[5] Trondheim University Hospital,Department of Neuroscience, Faculty of Medicine
[6] Norwegian University of Science and Technology,Department of Biostatistics, Epidemiology and Health Economics
[7] Oslo University Hospital,National Advisory Unit of Spinal Disorders
[8] University Hospital of Trondheim (St Olavs Hospital HF),Department of Neurosurgery
[9] University Hospital of Trondheim (St Olavs Hospital HF),Department of Neurosurgery
[10] University of Trondheim,Department of Neurology and FORMI
[11] Haukeland University Hospital,undefined
[12] Oslo University Hospital Ullevaal,undefined