[1] St Olavs Univ Hosp, Dept Neurosurg, Trondheim, Norway
[2] Norwegian Univ Sci & Technol, Dept Neuromed & Movement Sci, Trondheim, Norway
[3] Norwegian Univ Sci & Technol, Dept Publ Hlth & Nursing, Trondheim, Norway
[4] Unicare Helsefort Rehabil Ctr, Rissa, Norway
[5] Norwegian Univ Sci & Technol, Unit Appl Clin Res, Trondheim, Norway
[6] Univ Hosp Northern Norway, Dept Neurosurg, Tromso, Norway
[7] Norwegian Registry Spine Surg NORspine, Tromso, Norway
[8] St Olavs Univ Hosp, Natl Advisory Board Spinal Surg, Trondheim, Norway
[9] Norwegian Labour & Welf Adm NAV Trondelag, Trondheim, Norway