[1] Univ Groningen, Univ Med Ctr Groningen, Dept Surg, Anorectal Physiol Lab, Groningen, Netherlands
[2] Med Ctr Leeuwarden, Dept Surg, Leeuwarden, Netherlands
[3] Univ Groningen, Univ Med Ctr Groningen, Dept Surg, Div Abdominal Surg, Groningen, Netherlands
[4] Martini Hosp, Dept Surg, Groningen, Netherlands
[5] Antonius Hosp, Dept Surg, Sneek, Netherlands
[6] Tjongerschans Hosp, Dept Surg, Heerenveen, Netherlands
[7] Nij Smellinghe Hosp, Dept Surg, Drachten, Netherlands
[8] Univ Groningen, Univ Med Ctr Groningen, Dept Surg, Div Pediat Surg, Groningen, Netherlands
[9] Univ Groningen, Univ Med Ctr Groningen, Dept Surg, Anorectal Physiol Lab, Hanzepl 1,POB 30 001, NL-9700 RB Groningen, Netherlands