1. Department of Clinical Neuroscience, Karolinska Institute, 171 77 Stockholm, Sweden
2. Department of Biomechanical Engineering, Faculty of Mechanical Engineering, Delft University of Technology, 2627 Delft, The Netherlands
3. Department of Electrical Engineering, Eindhoven University of Technology (TU/e), 5612 Eindhoven, The Netherlands
4. Capio Spine Center Stockholm, Löwenströmska Hospital, 194 80 Upplands-Väsby, Sweden
5. Department of Medical Sciences, Örebro University, 701 85 Örebro, Sweden
6. Department of Surgical Sciences, Uppsala University, 751 35 Uppsala, Sweden