A physical simulation to investigate the effect of anorectal angle on continence

This paper investigates the effect of the anorectal angle on continence using a physical model of the anatomical system. A method to fabricate, measure and control a physical model for the simulation of human faecal continence is presented. A model rectum and associated soft tissues, based on geometry from an anonymised CT dataset, was fabricated from silicone and showed behavioural realism to ex vivo tissue. Simulated stool matter with similar rheological properties to human faeces was developed. Instrumentation and control hardware are used to regulate injection of simulated stool into the system, define the anorectal angle and monitor stool flow rate, intra-rectal pressure and puborectalis force. A study was then conducted in which simulated stool was introduced to the system for anorectal angles between 80° and 100°. Results obtained from the study give insight into the effect of the anorectal angle on continence. Stool leakage was reduced as the angle became more acute. Conversely, intra-rectal pressure increased. These data demonstrate that the anorectal angle is fundamental in maintaining continence. This work is valuable in helping improve our understanding of the physical behaviour of the faecal system. It has particular relevance facilitating improved technologies to treat or manage severe faecal incontinence.