In this Cochrane review we aimed to assess the effects of single-incision sling (SIS) operations for treating stress urinary incontinence (SUI) in women compared to other mid-urethral slings.

Mid-urethral polypropylene mesh slings were the gold standard treatment option for female SUI from the 1990s, however increased reports of adverse outcomes led to high vigilance and restrictions on practice in many centres. SIS were originally developed as a less invasive alternative using shorter segments of mesh to try to reduce the risk of side effects while maintaining efficacy. This review collates the highest quality evidence to try and assess whether SIS achieve their intended purpose.

The Cochrane Incontinence Specialised Register (which contains trials identified from: Cochrane Central Register of Controlled Trials; MEDLINE; MEDLINE In-Process; MEDLINE Epub Ahead of Print; ClinicalTrials.gov; WHO ICTRP; and handsearched journals and conference proceedings) and reference lists of relevant articles were searched up to 20 September 2022.

Randomised or quasi-randomised controlled trials in women with SUI or stress-predominant mixed urinary incontinence in which at least one, but not all trial arms included a SIS were included in the review. 

The key comparisons of interest were: 
1.	SIS versus obturator slings; 
2.	SIS versus retropubic slings;
3.	SIS versus autologous fascial slings.

The primary outcome was subjective cure or improvement of urinary incontinence at 12 months. Key secondary outcomes were: patient-reported pain at more than 24 months; number of women with dyspareunia; number of mesh erosions in any area; number of women with urinary retention; quality of life at 12 months; and number of women requiring repeat continence/mesh revision surgery. 

The review, including all study selection, data extraction and analysis, was carried out according to the methodology outlined in the Cochrane Handbook for Systematic Reviews of Interventions. The certainty of the evidence for key comparisons and outcomes was assessed using the GRADE approach. TVT-Secur (a SIS with demonstrable inferiority) was withdrawn from the market in 2013. We presented results from trials using all other SIS for the key comparisons outlined.

In total, 62 studies (with 8051 women) were included in the review. 

Obturator slings:
Fifty-one studies compared SIS with obturator slings. There is no evidence of a difference between SIS and obturator slings for subjective cure or improvement of SUI at 12 months, (RR 1.00, 95% CI 0.97 to 1.03; 17 trials, 2359 women; high-certainty evidence). There is a slightly lower risk of mesh erosion with SIS compared with obturator slings (RR 0.61, 95% CI 0.39 to 0.96; 16 trials, 2378 women; high-certainty evidence). There is probably a reduced risk of patient-reported pain at 24 months with SIS compared with obturator slings (RR 0.12, 95% CI 0.02 to 0.68; 2 trials, 250 women; moderate-certainty evidence). The effect of SIS on the risk of dyspareunia is uncertain compared with obturator slings; the wide confidence intervals are consistent with possible benefit and possible harm (RR 0.78, 95% CI 0.41 to 1.48; 8 trials, 810 women; moderate-certainty evidence). SIS probably result in slightly fewer cases of postoperative urinary retention compared with obturator slings (RR 0.68, 95% CI 0.47 to 0.97; 23 trials, 2891 women; moderate-certainty evidence). At 12 months, women with SIS may have lower quality of life improvement compared with obturator slings (SMD 0.24, 95% CI 0.09-0.39; 8 trials, 698 women; low-certainty evidence). SIS may lead to slightly more women requiring repeat continence surgery or mesh revision compared with obturator slings; the wide confidence interval is consistent with no difference and possible harm (RR 1.42, 95% CI 0.94 to 2.16; 13 trials, 1460 women; low-certainty evidence). 

Retropubic slings:
Ten studies compared SIS with retropubic slings. There may be no difference between SIS and retropubic slings for subjective cure or improvement of SUI at 12 months (RR 0.99, 95% CI 0.91 to 1.07; 2 trials, 297 women; low-certainty evidence). It is uncertain whether SIS increase risk of mesh erosion compared with retropubic slings (RR 1.55, 95% CI 0.24 to 9.82; 3 trials, 267 women; low-certainty evidence). It is uncertain whether SIS cause fewer postoperative urinary retention episodes compared with retropubic slings (RR 0.47, 95% CI 0.12 to 1.84; 2 trials, 209 women; low-certainty evidence). It is uncertain whether SIS cause more episodes of repeat surgery (continence or mesh revision) compared with retropubic slings (RR 4.19, 95% CI 0.31 to 57.28; 2 trials, 182 women; very low-certainty evidence). One study reported on quality of life but not in a suitable format for analysis. No studies reported patient-reported pain at more than 24 months or dyspareunia.

Autologous fascial slings
One study (70 women) compared SIS to autologous fascial slings. It is uncertain if SIS have any effect on risk of dyspareunia or mesh erosions compared with autologous fascial slings. The study did not report on subjective cure or improvement of urinary incontinence at 12 months, patient-reported pain at 24 months or longer, number of women with urinary retention, quality of life at 12 months or the number of women requiring repeat continence surgery or sling revision.

Mixed comparison group
Two studies compared SIS with a mixed group of retropubic and obturator slings (SMUS). There may be similar or slightly fewer women with subjective cure or improvement in incontinence when undergoing SIS compared with SMUS at 12 months (RR 0.94, 95% CI 0.86 to 1.03; 2 trials 798 women). It was not possible to draw conclusions for other outcomes. 

Risk of bias
We assessed the evidence for key outcomes using GRADE; certainty of the evidence was mainly downgraded due to imprecision, inconsistency and risk of bias. Most studies were at low/unclear risk of bias; five studies were at high risk of outcome assessment bias.

SIS operations have been extensively researched; this Cochrane review update is substantial, incorporates a large number of randomised controlled trials and allows an up-to-date assessment on the safety and efficacy of SIS compared to other mid-urethral polypropylene slings. We can therefore be reasonably confident of the results demonstrated, though there are remaining uncertainties. 

SIS are as effective as obturator slings and may be as effective as retropubic slings for subjective cure or improvement of SUI at 12 months. It is uncertain whether SIS lead to better or worse rates of subjective cure or improvement compared with autologous fascial slings. There remain uncertainties regarding adverse events and we need further long term data to clarify the safety and effectiveness of SIS operations specifically regarding pain, dyspareunia, mesh erosion, quality of life and repeat surgery.

The clinical situation surrounding the use of synthetic polypropylene mesh in urogynaecology is complex and practitioners should adhere to guidance from relevant regulatory bodies. With this in mind, SIS (excluding TVT-Secur) may be as effective as obturator and retropubic slings at curing or improving SUI in the short and medium term. SIS are probably associated with similar or less pain than obturator slings in the short and medium term. However, longer-term data are less conclusive. The effects of SIS on reoperation rates or mesh revisions, patient-reported quality of life at 12 months or other adverse events compared with other mid-urethral sling surgeries are currently unclear. SIS remain a valid option for patients who have been appropriately counselled, bearing in mind the ongoing need for long-term follow-up data for all synthetic polypropylene mesh surgery and practice restrictions.

Continence 7S1 (2023) 100722
DOI: 10.1016/j.cont.2023.100722