1. Department of Neurosurgery, Hospital Central Dr Ignacio Morones Prieto, San Luis Potosi, San Luis Potosí, Mexico
2. Department of Spine Surgery, University Hospital Cologne Clinic and Polyclinic for Orthopaedics and Emergency Surgery, Koln, Nordrhein-Westfalen, Germany
3. Department of Spine Surgery, Sana Klinikum Offenbach GmbH, Offenbach, Hessen, Germany