1. Department of Surgery, Anorectal Physiology Laboratory, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
2. Division of Abdominal Surgery, Department of Surgery, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
3. Department of Surgery, Martini Hospital, Groningen, The Netherlands
4. Department of Surgery, Medical Centre Leeuwarden, Leeuwarden, The Netherlands
5. Department of Surgery, Antonius Hospital, Sneek, The Netherlands
6. Department of Surgery, Tjongerschans Hospital, Heerenveen, The Netherlands
7. Department of Surgery, Nij Smellinghe Hospital, Drachten, The Netherlands
8. Division of Pediatric Surgery, Department of Surgery, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands