1. Department of Orthopedic Surgery, Harvard Medical School Orthopedic Trauma Initiative, Massachusetts General Hospital, Boston
2. Department of Surgery, University Medical Center Utrecht, Utrecht, the Netherlands
3. Department of Clinical Epidemiology, Leiden University Medical Center, Leiden, the Netherlands
4. Department of Surgery, St Antonius Hospital, Nieuwegein, the Netherlands
5. Department of Surgery, Luzerner Kantonsspital, Luzern, Switzerland
6. Department of Surgery, Diakonessenhuis Utrecht, Utrecht, the Netherlands