1. Center for Spine Surgery and Pain Therapy, Center for Orthopedics and Traumatology of the St. Elisabeth Group—Catholic Hospital Rhein-Ruhr, St. Anna Hospital Herne/Marien Hospital Herne University Hospital of the Ruhr University of Bochum/Marien Hospital Witten, Herne;
2. Center for Rheumatology, Rheumazentrum Ruhrgebiet, Ruhr University of Bochum, Herne;
3. Clinic for Orthopaedics and Orthopaedic Surgery, University Medicine Greifswald;
4. Center for Orthopedics and Traumatology of the St. Elisabeth Group—Catholic Hospital Rhein-Ruhr, St. Anna Hospital Herne/Marien Hospital Herne University Hospital of the Ruhr University Bochum/Marien Hospital Witten, Herne; and
5. Center for Spine Surgery and Pain Therapy, Center for Orthopedics and Traumatology of the St. Elisabeth Group—Catholic Hospital Rhein-Ruhr, St. Anna Hospital Herne, University of Witten/Herdecke, Herne, Germany