1. Department of Neurosurgery, Charité–Universitätsmedizin Berlin, Freie Universität Berlin, Humboldt-Universität zu Berlin and Berlin Institute of Health, Berlin;
2. Department of Neurosurgery, School of Medicine, Klinikum rechts der Isar, Technical University of Munich;
3. Department of Neurosurgery, Universitätsmedizin Göttingen;
4. Department of Neurosurgery and Interdisciplinary University Spine Center, Universitätsklinikum Hamburg-Eppendorf, Hamburg;
5. Department of Trauma and Orthopedic Surgery and Interdisciplinary University Spine Center, Universitätsklinikum Hamburg-Eppendorf, Hamburg, Germany;
6. Department of Neurosurgery, Hôpitaux Universitaires de Genève, Switzerland; and
7. Department of Neurosurgery, Medizinische Universität Innsbruck, Innsbruck, Austria