Implantable bulking agent

Did You Know?

• The polyacrylonitrile material is hydrophilic and absorbs water, changing dimensions within 48 hours of implantation.
• The material is considered to meet criteria for an ideal bulking agent and may overcome disadvantages of other agents.

History

Implantable bulking agents are the most recent stage of a procedure that began with perianal injectable bulking agents, which in turn were developed from injectable bulking agents used in urology for urinary incontinence. Many injectable materials have been tried, but they tend to have only a temporary effect because the material degrades and may migrate over time. One study found that after an average of 7 years, only about 14% of the original volume of three commonly used injectable agents (Durasphere, PTQ, Solesta) remained visible on ultrasound, and complete disappearance correlated with poorer outcomes. Implantable bulking agents use multiple cylindrical HYEXPAN (polyacrylonitrile) implants. Marketed as Gatekeeper by Medtronic, Minneapolis, USA, the system was first used for gastro-esophageal reflux disease. Production later transferred to THD S.p.A., Correggio, Italy. Gatekeeper received CE marking and was registered for fecal incontinence in 2010, with the first publication on its use for that condition appearing in 2011. The original Gatekeeper used four self-expandable solid thin cylinders; later six were used. An advancement described in 2016, marketed as SphinKeeper, uses 10 prostheses that are slightly thicker and longer. One publication stated that SphinKeeper has replaced Gatekeeper and that the use of 10 prostheses represents a paradigm change, aiming to create an artificial neosphincter rather than simply augment the internal anal sphincter. The first systematic review on implantable bulking agents was published in 2022, but no randomized placebo-controlled trials have been published yet.

Indications

Implantable bulking agents are indicated for passive fecal incontinence due to internal anal sphincter dysfunction or damage, with onset at least 6 months prior. The procedure is recommended only after non-surgical options (pharmacologic, behavioral, pelvic floor rehabilitation) and injectable bulking agents have failed. Contraindications include active perianal sepsis, inflammatory bowel diseases involving the anorectum, active anal/rectal/colon cancer treatment, rectal bleeding of unknown cause, rectal prolapse, uncontrolled coagulation disorders, pelvic radiotherapy, immunosuppression, pregnancy or planned pregnancy within 12 months, a lesion involving more than 60° of the internal anal sphincter or more than 90° of the external anal sphincter on ultrasound, and severe anal scarring. Diabetes mellitus, pudendal neuropathy, and previous sacral nerve stimulation are not contraindications.

Procedure

The procedure is performed under local or regional anesthesia (spinal) with or without sedation or general anesthesia, takes 30 to 40 minutes, and may be done as an outpatient day case. Intravenous antibiotics may be given at the start. The patient is usually placed in the lithotomy position. The surgeon identifies the internal anal sphincter and intersphincteric groove using an anal retractor such as the Eisenhammer retractor. A 2 mm incision is made in the perianal skin 2 cm from the anal verge to minimize wound contamination during bowel movements. The prostheses are implanted using a custom delivery system and dispenser specific to Gatekeeper or SphinKeeper. The needle is inserted into the incision and pushed into the intersphincteric space through a short subcutaneous tunnel; the tunnel path should not be straight to prevent extrusion. The needle is advanced just beyond the dentate line, corresponding to the upper anal canal at the level of the puborectalis muscle. Tip position is confirmed by direct vision or endoanal ultrasound, though one author stated ultrasound guidance is unnecessary for experienced surgeons. Firing the device retracts the cannula, leaving the prosthesis in the intersphincteric space. Placement pushes the external anal sphincter outward and the internal anal sphincter inward, potentially increasing sarcomere length and contractility, and may improve resting anal pressure and high-pressure zone length.

Complications

Implantable bulking agents appear safe compared to other surgical options for fecal incontinence and are suitable for elderly or frail patients. Acute sepsis at the implantation site has been rarely recorded. The most important complication is prosthesis displacement (migration, dislocation, dislodgement, extrusion), with reported rates ranging from 0% to 91% of cases. Patients may report pain, swelling, or no symptom improvement when displacement occurs. Placement in the intersphincteric space is thought to reduce the risk of extrusion, erosion, ulceration, or fistula formation compared to submucosal placement. Displacement is less likely because the prostheses rapidly increase in size and self-fix in position. A systematic review found migration or dislodgement in 41 of 154 patients (26.6%) across 7 studies, and some adverse event in 48 of 166 patients (28.9%). Sometimes a prosthesis must be removed, but a new one can be implanted in the correct position.