1. Department of Anaesthesiology; Hospital Cologne-Merheim, University Hospital of the Witten/Herdecke University; Cologne; Germany
2. Department of Traumatology; Hospital Cologne-Merheim, University Hospital of the Witten/Herdecke University; Cologne; Germany
3. Department of Traumatology and Orthopedia; Hospital for Traumatology; Duisburg; Germany
4. Institute for Research in Operative Medicine (IFOM); Witten/Herdecke University; Cologne; Germany