Cure of  urodynamically-proven stress incontinence (USI) by a Mid-urethral sling (MUS - tape) has been well recorded though the mechanism by which this occurs has not been clarified.We hypothesize that the intra-operative cure of stress incontinence by an MUS is achieved by bladder neck closure. To demonstrate this, we aim to correlate the perioperative reduction in the sign of stress incontinence with cystoscopic observations of increasing bladder neck closure.  We aim to prove, for the first time, that the mechanism of achieving continence with an MUS is an appropriate degree of bladder neck closure.

Forty consecutive women with USI were consented for: (i) MUS (Advantage Fit©- Boston Scientific) and pre/post-operative assessment of (ii) the sign of clinical stress leakage; (iii) bladder neck closure (by cystoscopy). Seven (18%) had undergone prior continence surgery. Thirty-one (78%) underwent concurrent pelvic organ prolapse (POP) surgery. Institutional ethical approval and patient consent had been obtained.
All assessments for SI were performed with patients under spinal block, in lithotomy position and asked to produce a maximum cough. The bladder had been emptied by short plastic catheter and was refilled to exactly 300mls prior to cough-testing. Cystoscopic assessment for bladder neck closure was at rest (no cough), with the cystoscope withdrawn 5mm (approx.) from a position where the full circumference of the bladder neck had been visualized. A minimum two observers (generally three) determined the following observations.
Stress incontinence grading (SIG): was scored: 0: cough, no SI; 1: cough, few drops SI; 2: cough, small SI leak; 3: cough, moderate SI leak; 4: cough, large SI leak; 5: no cough, large leak.
Bladder neck Closure (BNC): was scored: 1: 0-25%; 2: 25-50%; 3: 50-75%; 4: 75-100% closure. This represents the degree of reduction of the bladder neck aperture (full circumference having been visualized) by 5mm (approx.) cystoscopic withdrawal (see Figure 1).

Mean preoperative SIG was 3.6 (range 2-5); mean postoperative SIG was 0.5 (Range: 0-3) This indicates a mean reduction of SI from a moderate/ large leak with coughing to a few drops (max) with coughing. This correlated with clinical cure of SI at follow-up.
Mean preoperative BNC was 1.9 (Range 1-3); mean postoperative BNC was 3.9 (Range: 3-4). This indicates a mean improvement in bladder neck closure from 25-50% preoperatively to 75-100% postoperatively.
At the 6 week postop visit (26/40 so far), all patients were SI dry (2 patents required urodynamics for confirmation) with a mean postvoid residual of 5mL (Range 0-72mL). Two patients had a degree of urgency without urge incontinence.

The intraoperative cure of stress incontinence by MUS as judged by the reduction of the sign of SI is associated with increasing bladder neck closure (to over 75% BNC post-insertion). This is the first time that this finding has been clinically proven. The use of SIG and BNC offers two new methodologies to optimise the insertion of MUSs, particularly in combined SI-POP cases. Other continence procedures such as bladder neck elevatory procedures (e.g. colposuspension) and periurethral injectables have appeared to work by bladder neck closure, without similar confirmatory studies.

The intra-operative cure of stress incontinence by a MUS is achieved by bladder neck closure (generally more than 75% BNC post tape insertion). The use of the outlined SIG and BNC methodologies can optimise MUS insertion.