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Synthetic midurethral slings for stress urinary incontinence
Introduction
Synthetic midurethral slings (MUSs) have become the most popular surgical procedures performed for the treatment of stress urinary incontinence (SUI) in the twenty-first century. Few operations in gynecology or urology have been as well studied or have gained such wide acceptance. These procedures generally have been shown to be minimally invasive, and have high efficacy, low morbidity, and a relatively quick recovery. This chapter discusses synthetic retropubic, transobturator (TOT), and single-incision MUSs. Because the efficacy data are few, we do not discuss variations that use biologic materials for the slings. A complete discussion of autologous fascia bladder neck slings is found in Chapter 16 .
Retropubic midurethral slings
Retropubic MUSs were developed in the mid-1990s in an attempt to create a minimally invasive surgical treatment for SUI. Until this time, incontinence procedures aimed at suspending or supporting the proximal urethra and bladder neck. described a rationale for a more distally placed suburethral sling based on concepts they termed the “integral theory.” This theory was based on the presumption that the pubourethral ligaments support the midurethra and attach to the pubic bones, acting as a backboard for the midurethra. This backboard allows for compression of the midurethra against it when intraabdominal pressure increases, thus maintaining continence. The theory states that the absence of the backboard support causes a loss of this watertight seal, and SUI develops. By passing a strip of supportive material (loosely woven polypropylene) under the midurethra in women with SUI, this “backboard” action could theoretically be replicated. The strip of polypropylene is left loose or “tensionless,” and direct compression of the urethra is avoided. In its earliest configuration, placement of the MUS was achieved through an anterior vaginal wall dissection at the level of the midurethra. Placement of the sling material was accomplished by passing the arms of the tape (sling) in a retropubic fashion through the anterior abdominal wall with the aid of specially designed trocars. Available data from anatomic dissections, ultrasound, and magnetic resonance imaging do not necessarily support Ulmsten and Petros’ description of the role of the pubourethral ligaments in urinary continence; nevertheless, MUSs have been shown through clinical studies to be the safest and most effective surgical treatment for SUI currently available. The primary mechanism of action for MUS is thought by most to be midurethral kinking against or around the sling with increased intraabdominal pressure.
The first commercially available retropubic MUS was tension-free vaginal tape (TVT; Ethicon, Somerville, NJ; Fig. 17.1 ), which consisted of a narrow polypropylene mesh strip with two specially designed trocars. The trocars were inserted through a small vaginal incision and passed on each side of the urethra through the retropubic space to two exit locations in the suprapubic area of the anterior abdominal wall. Passage of the trocars from the vaginal incision to the anterior abdominal wall has been described as the “bottom-up” approach. Several other retropubic sling “kits” with minor modifications also are available, including a “top-down” approach whereby the trocars are passed retropubically from the anterior abdominal wall to the vaginal incision, and the tape is attached to the vaginal end of the trocar and then pulled back up through the retropubic space to the abdominal wall.
Indications, patient selection, and types of slings
The indications for retropubic MUS placement include symptomatic SUI or occult stress incontinence significantly affecting the patient’s quality of life. Patients should have failed conservative treatments for SUI. Initial studies assessing functionality of the retropubic MUS mostly included “ideal” women—those who were not obese (body mass index [BMI] >35 kg/m 2 ), who had stress-predominant incontinence with a mobile urethra, and who had no prolapse. In time, studies also documented excellent outcomes in women who were overweight, had recurrent or mixed urinary incontinence, had intrinsic sphincter deficiency (ISD), and in whom the procedure could be performed in conjunction with a vaginal prolapse repair. Retropubic anatomy, prior surgery, body habitus, and surgeon experience are important variables to consider in surgical planning.
Absolute contraindications to the procedure include any important structure potentially in the path of the trocars or sling, such as a pelvic kidney or vascular graft, low ventral hernias, pregnancy, and active oral anticoagulation. Relative contraindications include any previous condition that would put the patient at high risk for significant pelvic adhesions, creating the risk for small bowel to be firmly adhered to the back of the pubic bone, such as a history of a ruptured appendix with peritonitis or stage 4 endometriosis. In such circumstances, a TOT sling would be a preferred procedure, because the retropubic space would be completely avoided.
Other patients in whom a synthetic sling is probably inappropriate include those with contraindications to permanent mesh implantation, including prior mesh complications or prior pelvic irradiation. Smoking also increases the risk of mesh complications and should be considered when choosing the type of continence surgery. Additionally, MUSs should generally be avoided in those who are undergoing concurrent or have undergone prior urethral reconstruction. Examples of this clinical situation include urethral diverticulectomy, urethrovaginal fistula repair, or urethral injury secondary to prior sling placement or pelvic fracture. Although there are few reports of MUS use in this setting, experience with synthetic material in the setting of urethral reconstruction has demonstrated a high rate of erosion ( ). In contrast, excellent outcomes have been reported with the use of a biologic pubovaginal sling (see Chapter 16 ) in the setting of reconstruction, with an 88% cure rate after diverticulectomy in 16 patients and an 86% cure rate after genitourinary fistula repair in seven patients, with no reported erosions ( ). Also, a synthetic MUS is not the preferred procedure in the case of neurogenic incontinence, such as in a patient with spina bifida. Because patients with neurogenic incontinence are already dependent on clean intermittent self-catheterization, a tension-free MUS may not provide the necessary compression to achieve continence between catheterizations. Biologic pubovaginal slings have been used successfully in patients with neurogenic causes of SUI, successfully providing occlusion at the bladder neck, with continence rates of 95% in one study ( ).
Surgical technique
Bottom-to-top (see 
)
- 1.
Preoperative considerations. Single-dose intravenous perioperative antibiotics are given for skin and vaginal flora coverage. The antibiotic classes commonly used include intravenous cephalosporins and fluoroquinolones. Antiembolic prophylaxis is given as indicated. Sterile urine should be confirmed before the procedure; some physicians postpone surgery if an active urinary tract infection is documented.
- 2.
Patient positioning and preparation. The patient is positioned in the dorsal lithotomy position, with legs supported in Allen or candy cane stirrups and all pressure points padded appropriately. The perineum and vagina are prepared, and surgical draping is placed to allow access to the vagina and suprapubic area.
- 3.
Anesthesia. We prefer to use general anesthesia; however, some surgeons prefer intravenous sedation with local anesthesia to allow the cough stress test to be performed to facilitate appropriate tensioning of the sling. Because approximately 50% of cases are done in conjunction with a prolapse repair, all surgeons need to be well versed in tensioning techniques under general anesthesia (see step 8).
- 4.
Vaginal dissection. The anterior vaginal wall is hydrodissected with a combination of lidocaine and epinephrine, with the goal of completely blanching the anterior vaginal wall at the level of the mid- to distal urethra. A scalpel is used to make an incision from just below the external urethral meatus to the level of the midurethra. The vaginal wall is sharply dissected with Metzenbaum scissors off the posterior urethra, creating small tunnels to the inferior pubic ramus ( Fig. 17.2 ). Sharp dissection is required, because the distal anterior vaginal wall and posterior urethra are fused at this level. Some physicians prefer to hydrodissect along the trocar trajectory bilaterally before passing the trocars.
- 5.
Trocar passage. A catheter guide is placed in the indwelling Foley catheter so that the urethra and bladder neck can be displaced away from where the trocar is inserted. The trocar tip is inserted into the previously dissected tunnel on each side, lateral to the urethra, and advanced to the undersurface of the pubic bone. The tip of the trocar should be sandwiched between the index finger of the surgeon’s nondominant hand placed in the anterior vaginal fornix and the undersurface of the interior pubic ramus. Care is taken not to “button-hole” into the vaginal lumen at the fornix. The tip of the needle is carefully advanced through the endopelvic fascia into the retropubic space ( Fig. 17.3 ). When the resistance of the endopelvic fascia is overcome, and the tip of the needle is in the retropubic space, the handle of the trocar is dropped, and the needle is advanced through the retropubic space as it hugs the back of the pubic bone ( Fig. 17.4 ). The next resistance felt is the rectus muscle and anterior abdominal fascia. The needle is advanced through these structures to exit through the previously made suprapubic stab wound (see Fig. 17.4 ). Fig. 17.5 illustrates the appropriate passage of the needle through the retropubic space when viewed from above, as well as examples of incorrect passage of the trocar.
- 6.
Cystoscopy. Careful cystoscopy is performed with a 70-degree scope to evaluate the bladder for inadvertent trocar injury with the trocar in place. If such an injury were to occur, it would generally be visualized in the anterolateral aspect of the bladder (usually the area between 1 o’clock and 3 o’clock on the left side and 9 o’clock and 11 o’clock on the right side). If the trocar is seen, or if there is any creasing of the bladder mucosa that does not disappear with bladder distention, the trocar should be withdrawn and repassed. When the bladder is perforated (which occurs in approximately 3%–5% of cases), it is most often because the surgeon has allowed the trocar to migrate too medially, or away from the back of the pubic bone in a cephalad direction (see Fig. 17.5 A and C). During repassage of the trocar, great care should be taken to hug the back of the pubic bone. In such cases, the patient may still proceed with the postoperative voiding trial without the need for discharge with an indwelling catheter, because the bladder perforation is very small and usually in a high, nondependent portion of the bladder. If excessive hematuria is present, or if the base or trigone of the bladder is perforated, postoperative bladder drainage should be continued for at least a few days. If bladder perforations occur on multiple attempts, the surgeon should consider another approach that avoids the retropubic space, such as TOT MUS.
- 7.
For passage of the sling, the trocar tips are disconnected from the handle, and the mesh and its plastic sheath are pulled up through the suprapubic stab wound along the trocar trajectory.
- 8.
Tensioning. Sling tensioning is very subjective. It may be done using a No. 8 Hegar dilator, Mayo scissor, or surgical clamp, such as a right-angled clamp, inserted between the posterior urethra and the suburethral portion of the sling if the patient is receiving general anesthesia ( Fig. 17.6 ). Some surgeons prefer to perform the procedure using a local anesthetic and use a cough stress test. Regardless of tensioning technique, the ultimate endpoint is to create a laxity in the mesh manifested by a ricochet of the mesh back toward the urethra if it is pulled on vaginally using a right-angled clamp, as well as avoiding direct contact of the mesh with the underside of the urethra. Then the plastic sheaths covering the mesh, if present, are removed, and tension of the mesh is rechecked. The mesh is suprapubically resected flush with the skin, making sure the skin is mobilized away from the mesh ends before skin closure.
- 9.
The vaginal wound is copiously irrigated and closed with a running 2-0 or 3-0 polyglycolic acid suture. The suprapubic stab wounds are closed with an absorbable suture or liquid tissue adhesive.
- 10.
The catheter may be removed in the recovery room, and the patient is discharged after confirming voiding efficiency. If unable to void, the patient is taught intermittent self-catheterization, or an indwelling Foley catheter is placed.
Top-to-bottom
- 1.
Vaginal dissection. The vaginal incision should be larger than that described for the bottom-to-top technique, because the dissection must allow the index finger of the surgeon’s nondominant hand to be placed into the incision to pick up the tip of the needle as it passes into the vaginal incision.
- 2.
Top-to-bottom trocar passage. Before passage of the trocars, complete drainage of the bladder is ensured. At the previously marked puncture sites in the suprapubic region, a stab incision is made on each side. The incisions should be well within the pubic tubercles bilaterally. A trocar is inserted into the first of the suprapubic incisions, aligned with the sagittal axis of the body, and then carefully punctures through the anterior rectus sheath. By angling caudally and “walking off” the superior posterior edge of the pubic bone, the trocar is advanced into the retropubic space, maintaining close contact with the posterior surface of the pubic bone. Concurrently, the surgeon’s finger is inserted into the previously dissected periurethral space on the ipsilateral side to control the distal tip of the trocar. In a controlled manner, the trocar is progressively advanced until the tip is visible in the vaginal incision. Cystoscopy, as previously described, is performed to confirm that the needle did not penetrate the bladder. The same maneuver is performed on the contralateral side ( Fig. 17.7 A and B).
- 3.
Loading the mesh. The mesh is attached to the trocars, and the trocars are withdrawn through the suprapubic stab wounds. The sling is tensioned as previously described for the bottom-to-top technique ( Fig. 17.6 ).
Transobturator midurethral slings
Indications, patient selection, and types of slings
Because retropubic MUS require blind passage of a trocar through the retropubic space, inadvertent bladder perforation occurs in 3% to 5% of cases. Also, vascular and bowel injuries that resulted in significant morbidity and mortality have been reported, albeit very rarely. In the hope of avoiding these complications, DeLorme described the TOT technique for MUS placement in 2001; this was published by . The inside-out variation was described by .
As with retropubic synthetic slings, this is a minimally invasive MUS using a synthetic tape; however, it is placed using a TOT approach rather than a retropubic one, almost eliminating any potential for bladder or bowel perforation and major vascular injury. Specially designed needles are passed either from the inner groin into the vaginal incision (outside-in technique) or from the vaginal incision into the inner groin (inside-out technique). When the procedure is performed in an appropriate fashion, the needle, and subsequently the sling, pass through (from the outside in) the subcutaneous fat, gracilis tendon, adductor brevis, obturator externus, obturator membrane, and obturator internus ( ). TOT slings use the basic concept of midurethral support with the sling placed underneath the urethra; resistance against the urethra is generated when intraabdominal pressure increases, which increases outlet resistance and prevents SUI.
TOT slings have become a popular surgical treatment for SUI. The technique has been shown to be a low-risk procedure with effectiveness comparable to most other surgical options. TOT slings are associated with a lower risk of urethral obstruction, urinary retention, and subsequent need for sling release compared with retropubic slings. For primary cases, a TOT sling demonstrates similar rates of cure compared with retropubic synthetic slings, with fewer bladder perforations and postoperative irritative voiding symptoms ( ). Also, as mentioned, rare but catastrophic bowel and major vessel injuries are almost eliminated. The tradeoff is that patients experience more complications referable to the groin, such as pain and leg weakness or numbness, with the TOT approach. Retropubic slings may be more effective for recurrent incontinence and in women with ISD, although the data supporting this statement are difficult to interpret because of controversy regarding how best to define and diagnose ISD.
Indications for TOT sling placement are the same as for retropubic MUS, with the possible exception of recurrent incontinence or ISD. Contraindications include pregnancy, groin abscesses, chronic infection or pain, and active anticoagulation. TOT slings are also commonly placed in women undergoing repair of pelvic organ prolapse in the hope of preventing the de novo development of SUI (occult incontinence).
Surgical technique
As previously mentioned, TOT slings can be placed inside-to-outside or outside-to-inside. The indications, effectiveness, and frequency of complications seem to be similar between the two groups ( ; ; ). At the present time, the decision regarding which approach to use is based mostly on the preference and experience of the surgeon.
Inside-out (see )
- 1.
Preoperative considerations. Single-dose intravenous perioperative antibiotics are given for skin and vaginal flora coverage. The antibiotic classes commonly used include intravenous cephalosporins and fluoroquinolones. Antiembolic prophylaxis is given as indicated. Sterile urine should be confirmed before the procedure; some physicians postpone the surgery if an active urinary tract infection is documented.
- 2.
Patient positioning and preparation. The patient is positioned in the dorsal lithotomy position, with legs supported in Allen or candy cane stirrups and all pressure points padded appropriately. The perineum and vagina are prepared, and surgical draping is placed to allow access to the vagina and inner groin.
- 3.
Anesthesia. Although we prefer to perform these procedures using a general anesthetic, they can be performed using intravenous sedation with local infiltration of the vaginal and groin tissue, which allows the use of a cough test to assist in appropriate tensioning of the sling.
- 4.
The exit site of the needle is marked. It should be 2 cm above the level of the urethra and 2 cm lateral to the labial fold ( Fig. 17.8 ).
- 5.
Vaginal incision. Anterior retraction of the vaginal mucosa with an Allis clamp facilitates visualization. We prefer to hydrodistend the anterior vaginal wall with either a combination of epinephrine and lidocaine or injectable-grade saline. A scalpel is used to make a distal incision in the anterior vaginal wall under the midurethra.
- 6.
Vaginal dissection. Sharp dissection is used to mobilize the anterior vaginal wall off the underlying urethra. Some physicians prefer to hydrodissect the trocar trajectory bilaterally before placing the sling and its trocar.
- 7.
Trocar passage. The trocar tip is inserted into the previously dissected vaginal incision lateral to the urethra and advanced gently while rotating the trocar handle. This insertion is done while hugging the pubic rami, knowing that the obturator canal, which houses both the obturator nerve and vessels, is at the opposite anterolateral margin of the foramen. The tip should emerge at the exit site generated previously at the level of the clitoris. The vaginal sulcus is inspected to ensure that no perforation or mucosal damage has occurred. Certain TOT sling kits (TVT-Transobturator [TVT-O] and TVT-Abbrevo; Ethicon, Somerville, NJ) have a winged guide introducer that helps facilitate appropriate passage of the needle through the obturator membrane, easily guiding the trocar into position ( Fig. 17.9 ). Some surgeons prefer perforating the membrane with Metzenbaum scissors before passing the trocar. Once the membrane is penetrated with the tip of the trocar, the surgeon’s hand is lowered or dropped toward the patient to allow the helical passer to rotate around the ischiopubic ramus and exit in the inner thigh ( Fig. 17.10 A and B).
- 8.
Cystourethroscopy. Careful cystoscopy of the urethra and the bladder should be performed to visualize any damage. If the trocar were to perforate the bladder, it would generally be visualized in the anterolateral aspect of the bladder (usually the area between 3 o’clock and 5 o’clock on the left side and 7 o’clock and 9 o’clock on the right side). If not detached yet, the offending trocar can be withdrawn and reinserted. Occurrence of bladder or urethral perforation or injury is extremely rare during TOT placement.
- 9.
Tensioning. The sling should lay flat against the urethra (without a gap at rest), easily allowing a right-angled clamp to be passed between the sling and the posterior urethra. We prefer to tension TOT slings slightly tighter than retropubic MUSs ( Fig. 17.11 ). The plastic sheaths covering the mesh, if present, are removed, and tension of the mesh is rechecked. The mesh at the groin incisions is resected flush with the skin, making sure the skin is mobilized away from the mesh ends before skin closure.
- 10.
The vaginal wound is copiously irrigated and closed with a running 3-0 polyglycolic acid suture. The groin stab wounds are closed with an absorbable suture or covered with liquid tissue adhesive.
- 11.
The catheter may be removed in the recovery room, and the patient is discharged after documenting voiding efficiency. If unable to void, the patient is taught intermittent self-catheterization, or an indwelling Foley catheter is placed.
The TVT-Abbrevo is a more recent version of the inside-out TOT sling. It differs from earlier slings in that the sling is only 12 cm long (versus the traditional 18- to 19-cm–long TOT sling). The shorter mesh traverses only the obturator internus, obturator membrane, and obturator externus, avoiding all the other inner groin muscles. Nonabsorbable polypropylene sutures are attached to the lateral edges of the mesh to allow for adjustments in mesh tensioning. Also, a midline placement loop serves as a visual aid to help center the mesh. Both the loop and the polypropylene sutures are removed after the sling is tensioned to the surgeon’s satisfaction ( ).
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