1 Edinburgh Spinal Surgery Outcome Studies Group, Department of Neurosurgery, Royal Infirmary of Edinburgh, 50 Little France Crescent, Edinburgh, EH16 4SA, UK.
2 Centre for Clinical Brain Sciences, Chancellor's Building, The University of Edinburgh, 49 Little France Crescent, Edinburgh, EH16 4SB, UK.
3 Edinburgh Spinal Surgery Outcome Studies Group, Department of Neurosurgery, Royal Infirmary of Edinburgh, 50 Little France Crescent, Edinburgh, EH16 4SA, UK. andreas.demetriades@gmail.com.
4 Centre for Clinical Brain Sciences, Chancellor's Building, The University of Edinburgh, 49 Little France Crescent, Edinburgh, EH16 4SB, UK. andreas.demetriades@gmail.com.