The implantable bulking agents represent the most recent stage of development of a similar procedure which uses perianal injectable bulking agents. That procedure in turn was developed from use of injectable bulking agents in urology to treat urinary incontinence. Many different injectable materials have been used. The biggest problem with injectable materials is that they seem to have only a temporary effect. Over time the material is degraded and may migrate away from the injection site. For example, one study investigated the outcome and ultrasound appearance of 3 of the commonly used injectable bulking agents (Durasphere, PTQ, Solesta) after an average of 7 years. The researchers reported that typically about 14% of the original volume of material was still identifiable on ultrasound, and that complete disappearance of the materials on ultrasound was correlated with poorer clinical outcomes.[3]
Implantable bulking agents use multiple cylindrical HYEXPAN (polyacrylonitrile) implants. Marketed as "Gatekeeper" by Medtronic, Minneapolis, USA, it was first used to treat gastro-esophageal reflux disease.[1] Production of the implant system was transferred to THD S.p.A., Correggio, Italy. Gatekeeper now has a CE marking, and was registered for the treatment of fecal incontinence in 2010.[4] The first publication describing use of these implants in FI was in 2011.[5] Several other publications appeared and the results were initially promising.[6]
In the original description, Gatekeeper used four self-expandable, solid, thin cylinders.[4] Subsequently, six of the prostheses were used.[6] An advancement of the procedure was described in 2016, marketed as "SphinKeeper".[4] SphinKeeper uses 10 prostheses which are slightly thicker and longer compared to those used in the Gatekeeper implant system.[4] One publication stated that new generation SphinKeeper implant system has replaced use of Gatekeeper, and that the use of 10 prostheses represents change in the paradigm of injectable and implantable bulking agents.[3] SphinKeeper is a permanent implantable device rather than a bulking agent, and aims to create a kind of artificial neosphincter.[3] Previous techniques aimed to simply augment the internal anal sphincter.[3] The first systematic review on implantable bulking agents was published in 2022.[4] However, no randomized placebo controlled trials have been published yet.
Material
The implants are made of polyacrylonitrile (HYEXPAN). This material is inert, non-allergenic, non-immunogenic, nondegradable and noncarcinogenic.[1] The material is hydrophilic, which allows the implants to slowly absorb water and change in dimensions, which occurs within 48 hours once they are implanted in the tissues.[4]
This polyacrylonitrile material is thought to meet the criteria for the "ideal bulking agent", and therefore may overcome the disadvantages of other bulking agents.[1]
Indications
Implantable bulking agents are indicated for passive fecal incontinence, caused by interior anal sphincter dysfunction or damage.[1] The onset of incontinence should be at least 6 months ago.[6] It has been recommended that this procedure should be attempted only if non-surgical options have failed (such as pharmacologic, behavioral, pelvic floor rehabilitation),[6] and also if injectable bulking agents were unsuccessful.[1] Researchers are investigating the use of GK and SK in patients with a wider range of causes of fecal incontinence.[1]
Contraindications have been suggested by different authors, and include:
The surgeon identifies the interior anal sphincter and the intersphincteric groove while using an anal retractor such as the Eisenhammer retractor. 2 cm away from the anal verge a 2 mm incision is made in the perianal skin.[1] This location may minimize the possibility of contamination of the wounds during bowel movements.[6] The prostheses are implanted using a custom "gun" which consists of a delivery system and a dispenser which holds one prosthesis at a time.[1] This device is specific to the type of implant being used: Gatekeeper or SphinKeeper.[6] The needle (cannula / sheath) is inserted into the incision and pushed into the intersphincteric space through a short subcutaneous tunnel.[1][6] It is thought that the path of this created "tunnel" should not be a straight line, in order to prevent extrusion of the prosthesis along the insertion track.[6] The needle is advanced to a depth just beyond the level of the dentate line.[1] This will correspond to the upper part of the anal canal, at the level of the puborectalis muscle.[6] The exact position of the needle tip is confirmed by direct vision or with the guidance of endoanal ultrasound.[1] The procedure is described as relatively simple to perform from a technical perspective,[4] and one author stated that ultrasound guidance during placement is not necessary if the surgeon is experienced. Firing the "gun" causes the cannula to retract completely into the delivery system, leaving the prosthesis in the target location.[6] The prosthesis is then placed into the intersphincteric space.[1]
It is thought that placement of the implants in the intersphincteric space pushes the external anal sphincter outwards and the internal anal sphincter inwards. This may increase the length of the sarcomeres, which theoretically increases the contractility of the muscle. In terms of physiological measurements, the resting anal pressure and the length of the high pressure zone in the anal canal may be improved. In other words, the bulking effect may improve the seal of the anal canal and the length of the anal canal.[1]
The surgical procedure is almost identical for Gatekeeper and SphinKeeper. The difference between Gatekeeper and SphinKeeper is in the size and number of the individual prostheses. Gatekeeper uses 4-6 prostheses. SphinKeeper uses up to 10 prostheses.[1]
Within 48 hours of implantation, the implant material absorbs water from the tissues because of its hydrophilic properties. Each prosthesis becomes thicker and shorter in shape. This rapid increase in volume allows the prostheses to self-fix in position and prevents displacement and migration (in most cases).[1] The prostheses also become softer in consistency and compliant to external pressures, but are still able to maintain their original shape.[6]
In the dehydrated state, Gatekeeper prostheses are thin cylinders, 2 mm in diameter and 22 mm long. After implantation, they become 6.5 mm in diameter and 17 mm long. Their volume increases by 750% from 70 mm3 to 500 mm3.[1]
SphinKeeper prostheses are slightly thicker and longer cylinders. In the dehydrated state, SphinKeeper prostheses are 3 mm in diameter and 29 mm long. After implantation, they become 7 mm in diameter and 23 mm long.[1] SphinKeeper implants are long enough to restore the normal length of the anal canal.[6] They are also wide enough to make sure there is good filling ability. Therefore, SphinKeeper allows for surgical correction of larger defects of the internal anal sphincter or external anal sphincter.[6]
The process is repeated for each individual prosthesis, placing them into incisions made at the intersphincteric groove at equidistant intervals depending upon the total number of prostheses to be deployed.[1] For example, if 4 prostheses are to be used, incisions may be placed at 12, 3, 6, and 9 o’clock. If 6 prostheses are to be used, incisions may be placed at 1, 3, 5, 7, 9, and 11 o’clock.[6] The exact number of prostheses used is arbitrary, but placing 10 prostheses enables the creation of a circumferential ring of prostheses around the anal canal in the intersphincteric space. This effectively creates a situation similar to an artificial anal sphincter.[1] One publication reported improved outcome with Gatekeeper when more prostheses were used.[6]
Interestingly, it is thought that the exact spacing of the prostheses does not influence the outcome of the procedure, and the important factor appears to be that the prostheses are distributed equally around the anal canal.[6] This is the case even in the presence of tears of the external anal sphincter or internal anal sphincter.[6] Therefore, the implants are placed in the above locations for convenience of the surgeon, even for patients with a tear in a specific part of the sphincter.[6]
The incisions are closed with resorbable sutures. Endoanal ultrasound may be used to confirm the location of each prosthesis. A course of oral antibiotics (e.g. metronidazole) may be given after the procedure. Oral laxatives (e.g. lactulose) may be given, which prevents straining and constipation. Anal trauma (e.g. receptive anal intercourse) should be avoided for at least 72 hours after the procedure.[1] Patients are usually advised to rest in bed, with the aim of reducing the risk of dislocation of the prostheses.[6]
After healing, the implants continue to be palpable and are visible on endoanal ultrasound.[1] Each prosthesis appears as hyperechoic dot with a hypoechoic shadow behind it.[6] Three dimensional endoanal ultrasound has also been used to visualize the implants, wherein the prostheses appear as a continuous hyperechoic line.[6]
Complications
Compared to other surgical treatment options for fecal incontinence, implantable bulking agents appear to be safe.[6] Therefore, it is also suitable for elderly or frail patients.[6] However, complications are sometimes reported. For example, acute sepsis (infection) at the implantation site has been rarely recorded.[6]
The most important complication is displacement of a prosthesis (also referred to as migration / dislocation / dislodgement / extrusion).[6] The rate of displacement of at least 1 of the prostheses has been reported to be as low as 0%, or as high as 91% of cases.[4] The patient may report pain, swelling and/or no improvement in symptoms when there is prosthesis displacement.[6] This is potentially noteworthy,[7] since improved symptoms after use of injectable bulking agents have been attributed at least in part to the placebo effect.[8]
Placement in the intersphincteric space is thought to be less liable to extrusion or migration of the prostheses or other complications such as erosion, ulceration or fistula formation in the anal canal.[1][6] If the implants were in the submucosal layer, they would be more vulnerable to such complications.[1] Furthermore, displacement is less likely because of the rapid increase in size of the prostheses,[4] allowing them self-fix in position in most cases.[1]
A systematic review found that in total, migration / dislodgement / dislocation was reported in 41 out of 154 patients (26.6%) across 7 studies.[4] The same researchers reported that some kind of adverse event occurred in 48 out of 166 patients (28.9%).[4] Sometimes, a prosthesis had to be removed,[4] however it is possible to implant a new one in the correct position.[6]
Effectiveness
The first systematic review on GK and SK was published in 2022. It combined results from 8 studies published before 2020 – a total of 166 patients. All studies were judged to be at moderate to high risk of bias. The reviewers reported that severity of FI improved in 5 out of 7 of the studies which used the Cleveland Clinic FI Score and in 3 out of 5 of the studies which used the Vaizey score. Quality of life improved in 2 studies which measured that outcome. They concluded that GK and SK may be effective, safe and minimally invasive options for fecal incontinence in those cases where non surgical treatments have failed. The reviewers called for controlled trials to be conducted.[4]
Related Research Articles
Fecal incontinence (FI), or in some forms, encopresis, is a lack of control over defecation, leading to involuntary loss of bowel contents, both liquid stool elements and mucus, or solid feces. When this loss includes flatus (gas), it is referred to as anal incontinence. FI is a sign or a symptom, not a diagnosis. Incontinence can result from different causes and might occur with either constipation or diarrhea. Continence is maintained by several interrelated factors, including the anal sampling mechanism, and incontinence usually results from a deficiency of multiple mechanisms. The most common causes are thought to be immediate or delayed damage from childbirth, complications from prior anorectal surgery, altered bowel habits. An estimated 2.2% of community-dwelling adults are affected. However, reported prevalence figures vary. A prevalence of 8.39% among non-institutionalized U.S adults between 2005 and 2010 has been reported, and among institutionalized elders figures come close to 50%.
An anal fissure is a break or tear in the skin of the anal canal. Anal fissures may be noticed by bright red anal bleeding on toilet paper and undergarments, or sometimes in the toilet. If acute they are painful after defecation, but with chronic fissures, pain intensity often reduces and becomes cyclical.
A rectal prolapse occurs when walls of the rectum have prolapsed to such a degree that they protrude out of the anus and are visible outside the body. However, most researchers agree that there are 3 to 5 different types of rectal prolapse, depending on whether the prolapsed section is visible externally, and whether the full or only partial thickness of the rectal wall is involved.
A fecal impaction or an impacted bowel is a solid, immobile bulk of feces that can develop in the rectum as a result of chronic constipation. Fecal impaction is a common result of neurogenic bowel dysfunction and causes immense discomfort and pain. Its treatment includes laxatives, enemas, and pulsed irrigation evacuation (PIE) as well as digital removal. It is not a condition that resolves without direct treatment.
Anal fistula is a chronic abnormal communication between the anal canal and the perianal skin. An anal fistula can be described as a narrow tunnel with its internal opening in the anal canal and its external opening in the skin near the anus. Anal fistulae commonly occur in people with a history of anal abscesses. They can form when anal abscesses do not heal properly.
Stress incontinence, also known as stress urinary incontinence (SUI) or effort incontinence is a form of urinary incontinence. It is due to inadequate closure of the bladder outlet by the urethral sphincter.
An anal plug is a medical device that is often used to treat fecal incontinence, the accidental passing of bowel moments, by physically blocking involuntary loss of fecal material. Fecal material such as feces are solid remains of food that does not get digested in the small intestines; rather, it is broken down by bacteria in the large intestine. Anal plugs vary in design and composition, but they are typically single-use, intra-anal, disposable devices made out of soft materials to contain fecal material and prevent it from leaking out of the rectum. The idea of an anal insert for fecal incontinence was first evaluated in a study of 10 participants with three different designs of anal inserts.
Stapled hemorrhoidopexy is a surgical procedure that involves the cutting and removal of anal hemorrhoidal vascular cushion, whose function is to help to seal stools and create continence. Procedure also removes abnormally enlarged hemorrhoidal tissue, followed by the repositioning of the remaining hemorrhoidal tissue back to its normal anatomic position. Severe cases of hemorrhoidal prolapse will normally require surgery. Newer surgical procedures include stapled transanal rectal resection (STARR) and procedure for prolapse and hemorrhoids (PPH). Both STARR and PPH are contraindicated in persons with either enterocele or anismus.
Anorectal abscess is an abscess adjacent to the anus. Most cases of perianal abscesses are sporadic, though there are certain situations which elevate the risk for developing the disease, such as diabetes mellitus, Crohn's disease, chronic corticosteroid treatment and others. It arises as a complication of paraproctitis. Ischiorectal, inter- and intrasphincteric abscesses have been described.
Dextranomer is a cicatrizant used in dressings for wound healing, and in pharmaceutical products to treat fecal incontinence. It consists of dextran polymer chains cross-linked into a three-dimensional network.
A sacral nerve stimulator is a small device usually implanted in the buttocks of people who have problems with bladder and/or bowel control. This device is implanted in the buttock and connected to the sacral nerve S3 by a wire. The device uses sacral nerve stimulation to stop urges to defecate and urinate by sending signals to the sacral nerve. The patient is able to control their bladder and/or bowel via an external device similar to a remote control.
Lateral internal sphincterotomy is an operation performed on the internal anal sphincter muscle for the treatment of chronic anal fissure. The internal anal sphincter is one of two muscles that comprise the anal sphincter which controls the passage of feces. The procedure helps by lowering the resting pressure of the internal anal sphincter, which improves blood supply to the fissure and allows faster healing. The procedure has been shown to be very effective, with 96% of fissures healing at a median of 3 weeks in one trial.
Sacral nerve stimulation, also termed sacral neuromodulation, is a type of medical electrical stimulation therapy.
Overflow incontinence is a concept of urinary incontinence, characterized by the involuntary release of urine from an overfull urinary bladder, often in the absence of any urge to urinate. This condition occurs in people who have a blockage of the bladder outlet, or when the muscle that expels urine from the bladder is too weak to empty the bladder normally. Overflow incontinence may also be a side effect of certain medications.
Solitary rectal ulcer syndrome or SRUS is a chronic, benign disorder of the rectal mucosa. It commonly occurs with varying degrees of rectal prolapse. The condition is thought to be caused by different factors, such as long term constipation, straining during defecation, and dyssynergic defecation. Treatment is by normalization of bowel habits, biofeedback, and other conservative measures. In more severe cases various surgical procedures may be indicated. The condition is relatively rare, affecting approximately 1 in 100,000 people per year. It affects mainly adults aged 30–50. Females are affected slightly more often than males. The disorder can be confused clinically with rectal cancer or other conditions such as inflammatory bowel disease, even when a biopsy is done.
Anismus or dyssynergic defecation is the failure of normal relaxation of pelvic floor muscles during attempted defecation. It can occur in both children and adults, and in both men and women. It can be caused by physical defects or it can occur for other reasons or unknown reasons. Anismus that has a behavioral cause could be viewed as having similarities with parcopresis, or psychogenic fecal retention.
Obstructed defecation syndrome is a major cause of functional constipation, of which it is considered a subtype. It is characterized by difficult and/or incomplete emptying of the rectum with or without an actual reduction in the number of bowel movements per week. Normal definitions of functional constipation include infrequent bowel movements and hard stools. In contrast, ODS may occur with frequent bowel movements and even with soft stools, and the colonic transit time may be normal, but delayed in the rectum and sigmoid colon.
Fistulectomy is a surgical procedure where a surgeon completely removes a fistula, an abnormal tract that connects two hollow spaces of the body. In comparison to other procedural options of treating fistulae such as fistulotomies, where a fistula is cut open but not completely removed, and seton placement, where a rubber band seton is passed through the tract and left post-operation as a means to allow drainage of the fistula, fistulectomies are considered to be a more radical approach. The total removal of a fistula may damage nearby structures in the process.
In fecal incontinence (FI), surgery may be carried out if conservative measures alone are not sufficient to control symptoms. There are many surgical options described for FI, and they can be considered in 4 general groups.
These procedures aim to inject bio-compatible material into the walls of the anal canal, in order to bulk out these tissues. This may bring the walls of the anal canal into tighter contact, raising the resting pressure, creating more of a barrier to the loss of stool, and thereby reducing fecal incontinence. This procedure has many advantages over more invasive surgery, since there are rarely any serious complications.
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