Internal anal sphincter augmentation for fecal incontinence using injectable silicone biomaterial

A disrupted or weak internal anal sphincter can lead to passive fecal incontinence. This muscle is not amenable to direct surgical repair. Previous preliminary attempts to restore functional continuity have included a cutaneous flap to fill an anal canal defect, and injection therapy using polytetrafluoroethylene, collagen, or autologous fat. Urologists have also used injections of collagen or silicone to enhance bladder neck function. This pilot study aimed to assess the efficacy of single or multiple injections of the silicone-based product Bioplastique for the symptoms of passive fecal incontinence caused by an anatomically disrupted or intact but weak internal anal sphincter.

Ten patients (6 females; median age, 64, range, 41-80 years) with passive incontinence secondary to a weak (n = 6) or disrupted (n = 4) internal anal sphincter were injected either circumferentially or at a single site, respectively. Patients were assessed before and six weeks after treatment by clinical assessment, two-week bowel diary card, anorectal physiologic testing, and endoanal ultrasound. Patients failing to show improvement after the first injection were offered a second injection six weeks after the first injection. Clinical assessment was further repeated at six months, and five patients had a further ultrasound examination.

At six weeks, six of ten patients showed either marked improvement (n = 3) or complete cessation of leakage (n = 3). A further patient was greatly improved after a second injection. Three patients were not improved. At six months, two of the seven patients had maintained marked improvement, and one patient had maintained minor improvement; all of these three patients had circumferential multiple injections. Maximum resting and squeeze anal pressures did not differ significantly between before vs. six weeks after vs. six months after injection. At six weeks endoanal ultrasound (n = 9) confirmed the presence and correct position of the silicone in all but one patient who had experienced obvious external leakage of the product. At six months the silicone remained in the correct position in the five endosonographically assessed patients. Five of the initial patients experienced pain or minor ulceration at the injection site.

Although clinically effective immediately after injection, the benefit of an injectable biomaterial was maintained in only a minority of patients. This occurred despite the continued presence of material in the correct anatomical site. Patients with diffuse weakness treated by circumferential injection seemed to be the most responsive, but further studies are required to clarify this.