1. Department of Neurosurgery, University Hospital Erlangen, Erlangen, Germany
2. Department of Neurosurgery, University Hospital Augsburg, Augsburg, Germany
3. Department of Orthopedic Surgery, Malteser Waldkrankenhaus St. Marien, University Hospital Erlangen, Erlangen, Germany
4. Institute for Medical Engineering, OTH Technical University of Applied Sciences Amberg-Weiden, Amberg, Germany
5. Department of Spine Surgery, Kliniken Dr. Erler GmbH, Nürnberg, Germany