[1] Oslo Univ Hosp, Dept Phys Med & Rehabil, Oslo, Norway
[2] Univ Oslo, Fac Med, Oslo, Norway
[3] Oslo Univ Hosp, Res Support Serv, Oslo Ctr Biostat & Epidemiol, Oslo, Norway
[4] Oslo Univ Hosp, Div Emergencies & Crit Care, Dept Pain Management & Res, Oslo, Norway