[1] Turku Univ Hosp, Dept Neurosurg, Div Clin Neurosci, PB 52, Turku 20521, Finland
[2] Univ Turku, Fac Med, Dept Clin Med, Turku, Finland
[3] Natl Inst Hlth & Welf, Ctr Hlth & Social Econ, Helsinki, Finland
[4] Univ Oulu, Unit Clin Neurosci, Neurosurg, Oulu, Finland
[5] Oulu Univ Hosp, Med Res Ctr, Oulu, Finland
[6] Univ Eastern Finland, Inst Clin Med Neurosurg, Kuopio, Finland
[7] Kuopio Univ Hosp, Dept Neurosurg, Kuopio, Finland
[8] Helsinki Univ Hosp, Dept Orthoped, Helsinki, Finland
[9] Welf Dist Forssa, Forssa, Finland
[10] Orton Orthopaed Hosp, Helsinki, Finland