1. Departments of Physical and Rehabilitation Medicine, Kuopio University Hospital, PB 100, KYS 70029, Kuopio, Finland
2. University of Eastern Finland, Kuopio, Finland
3. Neurosurgery, Kuopio University Hospital, PB 100, 70029 KYS, Kuopio, Finland
4. Neurosurgery, Oulu University Hospital, Kajaanintie 50, Oulu 90220, Finland
5. University of Oulu, Oulu, Finland