1. Department of Health, University of Witten/Herdecke, Witten, Germany
2. Department of Orthopedics and Trauma Surgery, Kreisklinikum Siegen, Siegen, Germany
3. Institute of Biology, University of Siegen, Siegen, Germany
4. Department of Anaesthesia and Intensive Care Medicine, Clinique Bénigne Joly, Talant, France
5. Department of Orthopaedics and Rheumatology, University of Marburg, Baldingerstraße, Marburg, Germany
6. Department of Statistics an Econometrics, University of Siegen, Siegen, Germany
7. Joint Center Hilden, Hilden, Germany
8. Ruhr-University Bochum, Bochum, Germany