1. Department of Neurosurgery, University of Thessaly, Larissa, Greece
2. Care of the Elderly Department, Watford General Hospital, Edinburgh, UK
3. Department of Clinical Neurosciences, Royal Infirmary of Edinburgh, Edinburgh, UK
4. Edinburgh Spinal Surgery Outcome Studies Group, Leiden, The Netherlands
5. Department of Neurosurgery, University of Leiden, Leiden, The Netherlands