1. Department of Neurosurgery, National Hospital for Neurology and Neurosurgery, University College London, London, United Kingdom
2. Departments of Neurosurgery and Orthopedic Surgery, Thomas Jefferson University and Hospitals, Philadelphia, Pennsylvania
3. Department of Neurosurgery, Medical Center Haaglanden, Haaglanden, the Netherlands
4. Department of Orthopedic Surgery, L'Institut Mutualiste Montsouris, Paris, France
5. Department of Orthopedic Surgery, University Hospital of Aarhus, Aarhus, Denmark
6. Departments of Orthopedic and Neurological Surgery, Washington University, St. Louis, Missouri
7. Department of Neurosurgery, Groningen, the Netherlands
8. Division of Neurosurgery, University Hospital Leuven, Leuven, Belgium
9. Division of Neurosurgery and Spinal Program, University of Toronto and Toronto Western Hospital, Toronto, Ontario, Canada
10. Department of Orthopedic Surgery, Kanazawa Medical University Hospital, Kanazawa, Japan
11. Spinal Unit, Hospital Universitario Dr Peset, Valencia, Spain
12. Department of Orthopedic Surgery, University Medical Center Utrecht, Utrecht, the Netherlands
13. Department of Neurosurgery, Leiden University Medical Centre, Leiden, the Netherlands
14. Centre for Spine Studies and Surgery, Queens Medical Centre, Nottingham, United Kingdom
15. Department of Orthopaedic Surgery, Nihon University School of Medicine, Japan
16. Department of Orthopedic Surgery, Kanazawa University, Kanazawa, Japan
17. Department of Neurosurgery, Jackson Memorial Hospital, University of Miami, Miami, Florida