Single-Incision Sling Versus Polyacrylamide Hydrogel During Transvaginal Prolapse Surgery for Occult Stress Urinary Incontinence: A Retrospective Cohort Study

Abstract

Objective:

This study compared the outcomes of the bulking agent polyacrylamide hydrogel (PAHG) with a single-incision sling (SIS) for treating occult stress urinary incontinence (SUI) in association with vaginal prolapse surgery.

Methods:

This was a retrospective study of patients who underwent transvaginal surgical correction of pelvic organ prolapse and received either SIS or urethral bulking with PAHG for occult SUI. Demographic and perioperative data were extracted from the charts. The primary outcomes were Urinary Distress Inventory–6 (UDI-6) scores, Incontinence Impact Questionnaire–7 (IIQ-7) scores, and incontinence episodes documented by 3-day bladder diaries collected 24 months after surgery. Secondary outcomes included complications such as adverse events, rates of urine retention with prolonged catheterization, and urinary-tract infections.

Results:

Thirty patients had the bulking agent using PAHG with the prolapse surgery for occult incontinence and 23 patients has SIS. Twenty-two patients from each group completed the postoperative questionnaires. UDI-6 scores were low in both groups with bulking versus SIS value (19 versus 11; p = 0.096). The stress subscale median value for bulking versus SIS was 33 versus 0; p = 0.009. IIQ-7 median value was 0 for both groups. The median Foley catheter duration for the bulking group versus the SIS group was 1 versus 5 days (p = 0.015).

Conclusions:

SIS and PAHG were equally satisfactory for treating occult SUI with similar total UDI-6 and IIQ-7 scores; yet, the UDI-6 stress subscale was significantly better for the SIS group, but with more short-term voiding dysfunction. (J GYNECOL SURG 20XX:000)

Introduction

Stress urinary incontinence (SUI) that occurs only with pelvic organ prolapse (POP) reduction is known as occult SUI. The incidence of occult SUI ranges from 35% to 68% of women with high-grade prolapse.^1,2 On examination, occult SUI can be demonstrated by a cough-stress test with a full bladder after reducing the prolapse using a half speculum, cotton swab, or pessary.

A meta-analysis showed that adding midurethral slings (MUS) to prolapse surgery is beneficial for patients with occult incontinence.³ The percentage of SUI operations performed simultaneously with POP surgeries rose from 38% to 47% between 2001 and 2009 in the United States.⁴ However, the use of MUS can result in adverse events, such as pain, mesh erosion, and urine retention.⁵ With the increase in mesh litigation, the ban of MUS in the United Kingdom⁶ and the 2016 U.S. Food and Drug Administration (FDA) reclassification of transvaginal mesh kits into class III devices, some physicians are not using MUS in mild cases of SUI and opting for a step-by-step selective approach based on the patient's symptoms after POP surgery. As a result, concomitant MUS procedures dropped from 46% to 35% from 2011 to 2019, according to a review published in 2022.⁷

There is still a need for a less-invasive treatment for mild-to-moderate incontinence that may be used with POP procedures. Single-incision slings (SIS) and urethral bulking agents are both minimally invasive approaches that have been studied extensively to treat SUI. SIS is becoming a more-popular option, as it is associated with fewer complications, compared to conventional MUS (retropubic slings [RP] and transobturator transvaginal slings (TVT).⁸ Some studies showed positive sustained results in comparison to conventional MUS.^9,10 Different urethral bulking agents have been used to address SUI with varying efficacy.¹¹ Macroplastique^® was used for occult incontinence and the objective cure rate was 87%.¹²

In June 2020, the Bulkamid^® Urethral Bulking System, Axonics, Irvine, CA, USA) received FDA approval to be used in the United States as a urethral bulking agent. A randomized trial showed inferior outcomes for SUI treatment, compared to TVT, but with a high satisfaction and cure rate, and fewer complications, in comparison to TVT.¹³

This article reports a retrospective cohort study that included the current authors' experiences using either SIS or PAHG for addressing occult SUI during POP surgery, with follow-ups on patients on their urinary incontinence symptoms after surgery. The hypothesis is that urethral bulking is as effective as SIS for addressing occult SUI.

Materials and Methods

This was a retrospective, cohort comparative study. After obtaining institutional review board (IRB) approval (IRB# 21-53) from The Christ Hospital, in Cincinnati, OH, USA, the study was registered at ClinicalTrials.gov (ClinicalTrials.gov Identifier: NCT05210738). From June 2019 to June 2021, all medical records of women with POP who underwent surgical prolapse correction were reviewed. Preoperatively, each patient had undergone a standardized history taking and physical examination that included evaluation of her prolapse and lower urinary-tract symptoms, examination for prolapse grading, and a cough-stress test with reduction and without reduction to assess for occult SUI.

The inclusion criteria were patients with POP and occult SUI (positive cough-stress test only with reduction performed by the surgeon preoperatively), and who had transvaginal surgical correction for POP with a SIS or bulking agent to treat documented occult SUI.

The exclusion criteria were patients who had abdominal or laparoscopic surgeries, women who had prior anti-incontinence procedures, and women with outright SUI demonstrated without prolapse reduction.

A chart review was performed to collect demographic, preoperative, operative, and postoperative data. Demographic data included age, body mass index (BMI), race, menopause status, smoking status, medical morbidity, POP stage, and previous hysterectomy. Operative and postoperative data included blood loss amount, procedure time, type of prolapse surgery performed, blood transfusion, organ injury, duration of hospital stay, voiding trial results, need for catheterization (in case a patient did not pass a voiding trial), urinary-tract infection (UTI) after surgery, any subsequent need for an additional procedure to treat SUI, and any other late complications such as mesh extrusion.

All surgeries were performed by the same surgeon with the patients under general anesthesia. Each prolapse was corrected surgically in a normal fashion, using only native tissue. An apical prolapse was corrected by either uterosacral suspension or sacrospinous suspension according to the surgeon's preference, anterior and posterior vaginal-wall prolapses were corrected via standard anterior and posterior colporrhaphy. Attention was then directed toward correcting the occult SUI with either an SIS or a bulking agent. Prior to the FDA's approval of Bulkamid in 2020, SIS was the standard treatment for occult SUI during POP surgery, regardless of the type of apical prolapse. After the FDA approval, PAHG was then incorporated into these procedures.

For SIS, the Altis^® Single Incision Sling system, (Coloplast, Minneapolis, MN, USA) was used. The Altis is a microporous, knitted, monofilament polypropylene sling (7.75 cm) that spans between the obturator membrane complexes. The surgical technique for SIS was performed in a standard fashion.¹⁴

For the PAHG procedures, Bulkamid, a homogenous gel without particles, was used. It is made of a PAHG (2.5% polyacrylamide and 97.5% water) that is nonbiodegradable.¹⁵ A standard 2 cc of PAHG was used. Bulkamid was injected transurethrally into the submucosa under cystoscopic guidance. A 4-point injection plan at 2, 5,7, and 10 o'clock positions was followed with the material (0.2–0.8 mL per injection site) placed ∼1 cm distal to the bladder neck. The material was injected until the deposit visually reached the midline of the urethra, creating a coaptation of the urethral lumen. A 12F Foley catheter was then placed after the PAHG injection and was left until the postoperative voiding trial.

Each patient typically underwent a voiding trial before discharge. A successful voiding trial was defined as the patient's ability to void at least 200 mL of the 300 mL instilled into the bladder within 30 minutes. Subjects with failed voiding trials were offered intermittent self-catheterization at home until a postvoid residual volume <80 mL on 2 consecutive measurements was obtained. Alternatively, patients were discharged with an indwelling Foley if they could not tolerate intermittent self-catheterization and had another voiding trial within a week in an office visit.

Standard postoperative evaluations and examinations were performed at the 2- and 6-week follow-ups. The presence of UTIs was monitored for 6 weeks after surgery. A UTI is defined as a patient reporting UTI symptoms with at least 1 documented positive urine culture (> 10² K colony forming units/mL).

The study's primary outcomes were Urinary Distress Inventory–6 UDI-6 score,¹⁶ Incontinence Impact Questionnaire short form–7 (IIQ-7) score,¹⁶ and incontinence episodes objectively documented by a 3-day bladder diary.¹⁷ These outcomes were assessed at 24 months after surgery. Patients were contacted by telephone calls, during which the patients completed the UDI-6 and IIQ-7 questionnaires. The voiding diary was mailed to the patient and the patient filled out the voiding diary and mailed it back.

The UDI-6 is a 6-item symptom inventory, specific to symptoms associated with lower urinary-tract dysfunction, that combines information on irritative, stress, and obstructive/discomfort symptoms. The IIQ-7 is a 7-item life-impact assessment instrument specific to urinary incontinence and covers separate domains of physical activity, travel, social/relationships, and emotional health. Patients rate the extent to which they experience impaired urinary function (incontinence) and the extent to which the urinary incontinence affects their daily functioning on a 4-point scale: 0 = “not at all”; 1 = “slightly”; 2 = “moderately”; and 3 = “greatly.” The mean score of items is multiplied by 33 1/3 to convert to a 0–100 scale. Higher scores indicate more symptom distress (UDI-6), or more impact on daily life (IIQ-7).

The 3 subscales of the UDI-6 (irritative, stress, and obstructive) were analyzed further for each group to compare each symptom individually. The bladder diary was used to provide an objective measure of response to treatment as recommended by the International Continence Society.¹⁷

Secondary outcomes included the rates of complications in both groups, which included adverse events, rates of urine retention with prolonged catheterizations, and development of UTIs.

Statistical methods

Based on a 2020 study,¹³ the predicted success rate is 95% and 60% for tension-free vaginal slings and PAHG, respectively, for treating stress incontinence. At a power of 80% and a significance level of 0.05, the sample size estimate was 21 patients per group. The cases of all patients who had the required surgeries from June 2019 to June 2021 were included.

IBM SPSS Statistics for Windows, version 23.0 (Statistical Package for the Social Sciences, IBM Corp., Armonk, NY, USA) was used for data analysis. Numerical variables were tested for normality for appropriate selection of descriptive estimates and test statistical selection. A comparison of means of the 2 study groups was performed using a parametric t-test (with mean ± standard deviation) and a nonparametric test-test (Wilcoxon rank-sum test) with median and range. χ² and Fisher's exact tests were used for testing proportion independence. Significance was set at a p-value of 0.05 and was always 2-tailed.

Results

A review of charts revealed that 275 patients underwent vaginal prolapse correctional operations between June 2019 and June 2021. Of these,143 patients underwent prolapse surgeries without anti-incontinence procedures, while 132 had prolapse surgeries with anti-incontinence procedures. Among these 132 patients, 53 had anti-incontinence procedures for occult incontinence and 30 patients received urethral bulking, while 23 patients received SIS. Figure 1 is the study flow diagram. The charts of all patients with occult incontinence who had anti-incontinence procedures were reviewed, and data were extracted from these charts.

FIG. 1.

Flow chart of the number of patients in each group, with 30 patients each receiving a bulking agent for occult stress urinary incontinence (SUI) and 23 patients each receiving a single-incision sling (SIS) for occult SUI.

Several attempts were made to contact patients for their questionnaires. Twenty-two patients from each group completed their questionnaires. Eleven patients from the bulking group returned their bladder diaries while 8 patients from the SIS group returned their bladder diaries. The median follow-ups were 20 months (range: 16–26) for the bulking group and 26 months (range:18–30) for the SIS group.

Table 1 lists the patients' characteristics. There were no difference between the 2 groups regarding age, BMI, degree of prolapse, and menopausal status.

Table 1.

Baseline Characteristics of Women with Occult Incontinence

Characteristics	Urethral bulking group (n = 30)	SIS group (n = 23)	p-Value^*
Age (mean ± SD)^a	61 ± 10.5	66 ± 8.9	0.063
BMI (kg/m²)^a	29 ± 7.0	27 ± 3	0.103^b
Post menopause	24 (80%)	21 (91.3%)	0.441^c
HRT	2 (6.7%)	0 (0%)	0.499^c
Smoker	1 (3.3%)	0 (0%)	1.00^c
Previous hysterectomy	16 (53.3%)	9 (39.1%)	0.305^c
Advanced prolapse (Grade III–IV)	16 (53.3%)	17 (73.9%)	0.126^c
DM	4 (13.3%)	1 (4.3%)	0.374^c

Normal data are expressed as mean ± SD.

p-Value <0.05 is considered significant.

Age and BMI are expressed in mean ± SD; other data are expressed in percentages.

Student's t-test.

χ²test.

SIS, single-incision sling; SD, standard deviation; BMI, body mass index; HRT, hormone-replacement therapy; DM, diabetes mellitus.

Table 2 shows the patients' operative characteristics with no significant differences between the 2 groups.

Table 2.

Operative Characteristics of the 2 Groups

Procedures	Urethral bulking (n = 30)	SIS (n = 23)	p-Value
Apex repair	24 (80%)	21 (91.3)	0.441
Posterior repair	28 (93.3%)	23 (100%)	0.499
Anterior repair	29 (96.7%)	23 (100%)	1.000
Hysterectomy	12 (40%)	11 (47.8%)	0.590
Duration of hospital stay (d)	1 (0–3)	1 (0–5)	0.477

Data are expressed in numbers (percentages).

Duration of hospital stays are expressed in medians (ranges).

SIS, single-incision sling; d, day(s).

Table 3 shows some perioperative morbidities and postoperative complications. In the SIS group, there was 1 case of a cystotomy that was related to the prolapse surgery. There were no significant differences, respectively, between the bulking and SIS groups in overactive bladder (OAB) symptoms after surgery, 9 (30%) versus 10 (43.5%); rates of UTIs, 6 (20.7%) versus 3 (13.6%); or blood losses, 75 mL (range: 50–150) versus 75 mL (range: 50–1500). The bulking group had 3 admissions, compared to 1 admission in the SIS group. Two admissions were for pain from a hematoma formation from the prolapse repair that was treated conservatively, 1 for pyelonephritis treatment and 1 readmission from the SIS group owing to the sling release due to significant voiding dysfunction 30 days after her primary surgery. Postoperatively, in the SIS group, 1 patient had a vaginal mesh extrusion that occurred 9 months after primary surgery that was repaired surgically. One patient in the bulking group had an RP sling for persistent SUI.

Table 3.

Perioperative Morbidities and Postoperative Complications

Complications	Urethral bulking (n = 30)	SIS (n = 23)	p-Value
Bladder/ureteral injury	0 (0%)	1 (4.3%)	0.434
Blood loss (mL)	75 (50–150)	75 (50–1500)	0.532
Passed voiding trial	17 (56.7%)	7 (30.4%)	0.057
Foley catheter duration (d)	1 (0–15)	5 (0–31)	0.015
UTI	6 (20.7%)	3 (13.6%)	0.714
Readmission	3 (10%)	1 (4.3%)	0.624
Another anti-incontinence surgery	1 (3.3%)	0 (0%)	1.000
OAB treatment	9 (30%)	10 (43.5%)	0.311
Mesh erosion	0 (0%)	1 (4.3%)	0.434

Blood loss and Foley duration are expressed in medians (ranges); other data are expressed in numbers (percentages).

SIS, single incision sling; UTI, urinary-tract infection; OAB, overactive bladder.

Patients in the bulking group were more (borderline significantly) likely to pass their voiding trial before discharge, with 17 (56.7%) passing, compared to 7 (30.4%) in the SIS group, with a p-value of 0.057. As a result, the median Foley duration was 1 day (range: 0–15) for the bulking group, compared to 5 (range: 0–31) days for the SIS group (p = 0.015).

The results of the UDI-6 scores are shown in Table 4. UDI-6 scores were low in both groups with a p-value of 0.096. The median score for the bulking group was 19 (range: 0–60), compared to 11 (range: 0–55) for the SIS group. The UDI-6 scores were broken down further into 3 subscales that examined irritative, stress, and obstructive/discomfort symptoms. The irritative subscale median value was 33 (range: 0–66) for the bulking group and 16 (range: 0–99) for the SIS group (p = 0.400). The stress subscale median value was 33 (range: 0–99) for the bulking group versus 0 (range: 0–49) for the SIS group (p = 0.009). The obstructive subscale median value was 0 (range: 0–16) for the bulking group versus 0 (range: 0–0) for the SIS group (p = 0.150).

Table 4.

Urinary Distress Inventory–6 Scores for Urethral Bulking and Single Incision Sling Groups

UDI-6 score	Study groups		p-Value
UDI-6 score	Urethral bulking (n = 22)	SIS (n = 22)	p-Value
Total score	19 (0–60)	11 (0–55)	0.096
Subscale—irritative	33 (0–66)	16 (0–99)	0.400
Subscale—stress	33 (0–99)	00 (0–49)	0.009
Subscale—obstructive	00 (0–16)	00 (0–0)	0.150

Data are expressed in medians (ranges).

SIS, single incision sling; UDI-6, Urinary Distress Inventory–6.

Table 5 shows the results of the IIQ-7 questionnaires between the 2 groups. The median value was 0 (range: 0–66) for both groups (p = 0.47).

Table 5.

Incontinence Impact Questionnaire Short Form–7 Scores for Urethral Bulking and Single Incision Sling Groups

IIQ-7 Score	Study groups		p-Value
IIQ-7 Score	Urethral bulking (n = 22)	SIS (n = 22)	p-Value
Total score	0 (0–66)	0 (0–66)	0.47

Data expressed in median (range).

SIS, single incision sling; IIQ-7, Incontinence Impact Questionnaire short form–7.

Table 6 shows the comparison of both groups' bladder diaries. The bulking group had 11 patients, while the SIS group had just 8. For simplicity, these patients were instructed to track only urgency, incontinence episodes, and nocturia. The median and range for both groups are shown in the table, with no significant differences seen in any of the diary components.

Table 6.

Bladder Diary Parameters for Urethral Bulking and Single Incision Sling Groups

Parameters	Study groups		p-Value
Parameters	Urethral bulking (n = 11)	SIS (n = 8)	p-Value
Nocturia	1 (1–2)	1 (1–-2)	0.815
Urgency	6 (5–8)	7 (6–9)	0.001
Urinary incontinence	0 (0–2)	1 (0–2)	0.058

Data are expressed in medians (ranges).

SIS, single-incision sling.

Discussion

Occult SUI remains a challenging problem, due to the unpredictability of incontinence symptoms after a prolapse is fixed surgically. The majority of studies have focused on treatments such as urethropexy or slings with only 1 study reporting the results of urethral bulking for treating occult SUI.¹² Most of the studies have compared concomitant conventional MUS versus staged procedure treatments for women undergoing prolapse surgery. However, there is currently no standard algorithm in place to advocate for one path over another. The argument between universal versus selective strategy is still ongoing among surgeons, mainly because of the risks and costs involved with conventional MUS. A different method to address occult SUI that is less-complicated and produces good outcomes would transform the approach to dealing with this issue. Urethral bulking and SIS offer 2 less-invasive options to conventional slings.

In a randomized trial comparing TVT to urethral bulking for primary SUI, at a 1-year follow-up, both groups in the trial showed significant improvements in their quality of life, with the TVT group having a better outcome in incontinence score. However, the TVT group experienced more pain than the bulking group.¹⁸ Another systematic review of bulking agents, in 2021, found PAHG, when used to treat SUI, to have a better safety profile, and long-term efficacy up to 70% for as long as 96 months, compared to other bulking agents, including Coaptite,^® Durasphere,^® and Macroplastique.¹¹ In another study, SIS were found to be associated with shorter operating times, and less intraoperative bleeding and voiding dysfunction, compared to conventional MUS.⁸ SIS were also found to be comparable to conventional MUS in a 2022 randomized trial, with both groups reporting similar success rates at 36 months.¹⁹

The current study examined results of 2 minimally invasive alternatives (bulking and SIS) for treating occult incontinence. The primary outcomes measured were the UDI-6 and IIQ-7 scores. According to a 2021 study that sought to establish cutoff values for UDI-6 and IIQ-7, scores >33.33 indicated greater discomfort caused by urinary incontinence symptoms.²⁰

The current study's findings revealed that UDI-6 scores for both groups were significantly lower, indicating that the treatment was generally successful. Both groups' UDI-6 scores were low, with a median of 0, indicating that patients were satisfied with either kind of treatments.

Further examination of the UDI-6 results, with subscales breakdown revealed that the SIS had significantly a lower score on the UDI-6 stress subscale than the PAHG group did. These findings were unsurprising, given that they are consistent with prior research showing that bulking has a lower cure rate for SUI than MUS does.¹³ Both groups had low UDI-6 subscale scores for obstructive symptoms, while irritative symptoms scores were better for SIS patients but without a statistical difference. Comparison of the bladder diaries for both groups confirmed the findings collected by the questionnaires. There was no statistical difference between the incontinence and urgency episodes in both groups.

Although postoperative Foley duration is influenced by many factors, such as the degree of prolapse, type of prolapse surgery performed, and performance of anti-incontinence procedures, the current study found that postoperative voiding trials using bulking were more successful than those trials with SIS; there was shorter postoperative Foley durations in the bulking group. This study has practical implications, because most patients find self-catheterization or the use of a catheter after surgery to be inconvenient. More studies are needed to confirm this finding with proper study samples, as this was not the current study's primary outcome. Short-term urine retention is a well-known risk factor with MUS and incomplete bladder emptying has been reported in patients who received MUS with POP surgery.^1,21

SIS carries a low risk of voiding dysfunction and complications.⁸ However, 2 patients in the SIS group required reoperations: 1 for sling release for voiding dysfunction and the other for sling extrusion. In the bulking group, 1 patient had a sling placed for SUI. Although SIS problems are uncommon, it is important to consider the safety profile of slings versus the effectiveness of bulking to treat occult SUI.

The current study's relative long-term follow-up of patients is one of its strengths. The investigation examined both subjective and objective outcomes. Patients were treated for occult SUI in blocks, with the first group receiving SIS and the second group receiving urethral bulking. This lowered any potential for provider-selection bias that could occur by favoring less-severe occult SUI to 1 group over another.

This study's limitations included the fact that it was conducted at a single center, limiting the generalizability of the findings. As with most retrospective studies, some patients were unable to be reached for follow-ups; however, the results met the sample-size requirements. Because fewer patients were willing to complete bladder diaries, we had fewer bladder diaries' outcomes, resulting in limitations to form a reliable objective conclusion. If patients who could not be reached sought care elsewhere during their postoperative courses, this study's results may have been underreported.

Conclusions

Urethral bulking and SIS are reasonably safe and effective treatment options for patients with occult stress incontinence in conjugation with POP surgeries. SIS resulted in less SUI with better UDI-6 stress subscale scores but had more short-term postoperative voiding difficulty than urethral bulking. Randomized trials are needed with longer follow-ups to confirm these findings.

Footnotes

Acknowledgments

This study was registered at (ClinicalTrials.gov Identifier: NCT05210738).

Authors' Contributions

All of the authors were personally and actively involved in substantial work leading to this article.

Author Disclosure Statement

No financial conflicts of interest exist for Drs. Abdelaziz and Walters. Dr. Karram is a consultant and speaker for Biote, Inmode, Pathnostics, Allegran, Astellas, Urovant, Colpoplast, and Caldera.

Funding Information

No funding was provided for this study.

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