1. Department of Neurological Surgery, University of Washington, Seattle, Washington, USA;
2. Department of Orthopedics and Trauma Surgery, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne, Germany;
3. College of Osteopathic Medicine, Nova Southeastern University, Fort Lauderdale-Davie, Florida, USA;
4. Department of Orthopedics and Trauma Surgery, Krankenhaus Porz am Rhein, University of Cologne, Cologne, Germany;
5. Department of Neurosurgery, University of Michigan, Ann Arbor, Michigan, USA;
6. Department of Neurosurgery, Geisinger Neuroscience Institute, Danville, Pennsylvania, USA;
7. Texas Back Institute, Plano, Texas, USA;
8. Department of Neurosurgery, Warren Alpert Medical School, Brown University, Providence, Rhode Island, USA