1 Department of Neurosurgery, Helsinki University Hospital and University of Helsinki, Helsinki 00014, Finland. Electronic address: rahul.raj@hus.fi.
2 Department of Neurosurgery, Helsinki University Hospital and University of Helsinki, Helsinki 00014, Finland.
3 Department of Orthopaedics and Traumatology, Helsinki University Hospital and University of Helsinki, Helsinki 00014, Finland; Finnish Centre for Evidence-Based Orthopaedics, University of Helsinki, Helsinki, Finland.