Is urethral kinking a confounder of the association between urethral closure pressure and stress urinary incontinence?

Intact urethral support and normal sphincter function are deemed important for urinary continence. We aimed to test whether the location of urethral kinking (as the likely anatomical correlate of maximal pressure transmission) is associated with stress urinary incontinence and/or urodynamic stress incontinence.

This was a retrospective study on women seen in a tertiary urogynecological center in 2017. Patients had undergone an interview, multichannel urodynamic testing and 4D translabial ultrasound. Volume data was used to assess urethral mobility using a semi-automated Excel® urethral motion profile program. Mobility vectors were calculated using the formula SQRT [(xval_ xrest )2 + ( yval_ yrest )2 ]. Location of urethral kinking was identified as a concave contour of the urethra on the vaginal side on maximum Valsalva in the midsagittal plane. The distance between the center of the kink and the bladder neck is measured and represented as centile using the formula: Distance from bladder neck ÷Length of urethra.

Of 450 women seen, 61 were excluded due to previous incontinence surgery and 82 for missing data, leaving 307, of which 227(74%) complained of stress urinary incontinence and 211(69%) complained of urgency urinary incontinence. 190 (62%) were diagnosed with urodynamic stress incontinence. On multivariate analysis maximum urethral pressure (36 vs 50 cmH2O, P<0.001), mid-urethral mobility (2.27 vs 2.03cm, P=0.003) and location of urethral kinking (63.1th vs 59.7th centile, P=0.002) were significantly associated with urodynamic stress incontinence. Location of urethral kinking was associated with stress urinary incontinence on univariate analysis (P=0.026) but not on multivariate analysis (P=0.21).

The location of urethral kink is associated with urodynamic stress incontinence. The further urethral kinking is from the mid-urethra, the more likely is urodynamic stress incontinence. This provides circumstantial evidence for the pressure transmission theory of stress continence. This article is protected by copyright. All rights reserved.

Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 2020 Jul 16 [Epub ahead of print]

C Ling, K L Shek, M Gillor, J Caudwell-Hall, H P Dietz

Suzhou Municipal Hospital, The Affiliated Suzhou Hospital of Nanjing Medical University, Jiangsu, China., Nepean Clinical School, University of Sydney, Australia.

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