1. Department of Orthopedics, Radboud University Medical Center, Nijmegen, The Netherlands;
2. Department of Orthopaedic Surgery, VU University Medical Center, Amsterdam, The Netherlands;
3. Spine Surgery Unit, Hospital Universitari Vall d’Hebron, Barcelona, Spain;
4. Spine Unit, Bordeaux University Hospital, Bordeaux, France;
5. Department of Orthopedics and Traumatology, Ankara Spine Center, Ankara, Turkey;
6. Department of Orthopedics and Traumatology, Acıbadem Mehmet Ali Aydınlar University, Istanbul, Turkey;
7. Spine Surgery, Schultess Clinic, Zurich, Switzerland; and
8. Spine Surgery Unit, Hospital Universitario La Paz, Madrid, Spain