1. Clinic for Technical Orthopedic Surgery and Rehabilitation, University Hospital of Münster, Münster, Germany
2. Department of Surgery, Hospital Group Twente, Almelo, the Netherlands
3. Department of Rehabilitation Medicine, Center for Rehabilitation, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands
4. Clinic for Spinal Cord Injuries, Bad Wildungen, Germany