1. Department of General Surgery, Shenyang Anorectal Hospital, Shenyang, Liaoning 110054, P.R. China
2. Department of General Surgery, The Second Hospital of Dalian Medical University, Dalian, Liaoning 116000, P.R. China
3. Department of General Surgery, Daqing Oilfield General Hospital, Daqing, Heilongjiang 163000, P.R. China