Some women experience voiding dysfunction after stress urinary incontinence (SUI) surgery. Increasing urethral resistance may cause obstruction mainly in women with previous voiding dysfunction and detrusor underactivity (DU). Some authors have found DU adversely affect voiding phase of micturition after TOT [1]. We explore if DU parameters found in urodynamic study (UDS) prior to SUI surgery using an adjustable Single Incision Sling (SIS) may be related to voiding dysfunction after surgery.

Retrospective, diagnostic, transversal and single center study to compare voiding dysfunction after SUI surgery with a SIS (Altis®) in women with detrusor underactivity (cases) and those with normal detrusor (controls) according to UDS pre-surgery. Inclusion criteria: women ≥18 years with SUI or Mixed UI (stress predominant) who were operated between June 2013 and December 2020 with a SIS (Altis®) at Urology Department (median follow-up 39 months). Exclusion criteria: women without UDS prior to surgery or without voiding phase in the P/Q, previous anti-incontinence surgery, POP stage ≥2, neurogenic conditions, other concomitant pelvic floor surgery. 
Preoperatively, all patients underwent a standardized urogynaecological work-up including: urogynaecological history, pelvic examination, cough stress test (stress test with a bladder volume at least 300 mL measured by ultrasonography), the Spanish validated version of the International Consultation on Incontinence Questionnaire Short Form (ICIQ-SF) and conventional urodynamic study (according to ICS good urodynamic practice) using a MMS Solar system with water-charged transducers. Urinary symptoms were evaluated during the UDS using a structured questionnaire evaluating the presence of storage (urinary incontinence, daytime frequency, urgency and nocturia) and voiding symptoms (hesitancy, slow- stream, intermittency, straining to void and feeling of incomplete emptying). 
Patients were divided into two groups according to detrusor contractility, which was assessed using the projected isovolumetric pressure (PIP) index [PdetQmax + maximum flow rate (Qmax)] with values of 30–75 cmH2O indicating normal contractility [2].
Altis® procedure was performed as standard description by 3 expert surgeons mostly by outpatient setting. Follow-up was carried out with physical examination, ICIQ- SF, TBS (treatment benefit scale), satisfaction visual scale (score 0–10), and cough stress test. Patients were evaluated postoperatively at 1, 6, 12 and 24 months. Voiding symptoms after surgery were actively recorded, as well as incidence of acute urinary retention, need of clean intermittent catheterization and need of des-obstructive surgery. Other adverse events, such as tape exposure and pain related to the procedure or the device, were evaluated at each visit.
To explore the statistical power of our sample, we calculated the necessary sample size based on a previous similar study [1]. We performed a confirmatory sample size calculation. To achieve a power of 85% to detect differences in the contrast of the null hypothesis H₀: p1 = p2 by means of a one-sided Chi-square test for two independent samples, taking into account that the significance level is 5%, and assuming that the proportion of de novo voiding dysfunction in the reference group is 2%, the proportion in the experimental group is 18%, and that the proportion of experimental units in the reference group with respect to the total is 80% [1], it was necessary to include 104 experimental units in the reference group and 26 units in the experimental group, totaling 130 experimental units in the study.

A total of 139 women met the inclusion and exclusion criteria, 29 (20.9%) in the DU group and 110 (79.1%) in the control group. Table 1 shows clinical and urodynamic characteristics of both groups. 
Acute urinary retention after surgery appeared in 4 (13,8%) of underactive patients and 9 (8,2%) of control group (p=0.377), requiring indwelling bladder catheter during 1-19 days (median 7 days). Only 2 patients needed clean intermittent catheterization for 1 week (underactive) and 3 months (control group). One patient in control group underwent sling section due to refractory urinary retention. Voiding symptoms increased after surgery in both groups (+20.7% DU group vs +8.1% normal group, p = 0.29). More voiding symptoms (persistent and de novo) were found in DU group vs normal group, but with no statistically significant differences. Both groups shown objective and subjective success with no statistical differences (table 2).

SIS (Altis®) maintained subjective and objective efficacy in both groups. We found more voiding symptoms in DU group, but no serious adverse event occurred. Patient satisfaction did not decrease in DU patients in spite of voiding symptoms after surgery. 
Natale et al [1] described that DU adversely affects the voiding phase of micturition after TOT, with a 18% increase of voiding dysfunction (very close to our 20.7%). Interestingly, they did not find worse subjective results (according to PGI-I) in DU group. We neither found treatment satisfaction differences between two groups. Both studies show that SUI surgery using TOT (Monarc®) or SIS (Altis®) increases the incidence of voiding symptoms in underactive detrusor group, but with no differences in objective-subjective success or treatment satisfaction compared with normal contractility group. 
Some limitations of the study are the single center and retrospective design; the definition of DU based on PIP is not universally accepted; results are only valid for SIS Altis® anti-incontinence surgery. 
Appropriate counselling prior to anti-incontinence surgery may be useful in women with DU parameters in UDS, explaining the higher  incidence of voiding symptoms but with no impairment on success.

Voiding symptoms increases in DU women after SIS (Altis®) anti-incontinence surgery, but without impairment in objective or subjective success, or treatment satisfaction.

Natale F, Illiano E, Zucchi A, Balzarro M, La Penna C, Costantini E. Transobturator mid-urethral sling in females with stress urinary incontinence and detrusor underactivity: effect on voiding phase. Int Urogynecol J. 2019 Sep 4;30(9):1519–25.
Griffiths D. Detrusor contractility: order out of chaos. Scand J Urol Nephrol Suppl. 2004 Jan 9;38(215):93–100.