Anal canal to pubis angle: a novel clinical ultrasound technique for the assessment of the anorectal region

Posterior compartment prolapse is associated with severe morbidity including faecal incontinence and defaecation dysfunction. The aim of this study was to develop and validate a novel ultrasound marker (anal canal to pubis angle) for the assessment of the anal axis in the context of posterior compartment prolapse in women and in controls (healthy, nulliparous, non-pregnant volunteers). Anal canal to pubis (AC/Pubis) angle is measured with 2D transperineal ultrasound in precisely the midsagittal plane. The image was inverted and zoomed out and the angle opened to 107° (maximum). The image includes the pubis, urethra and anal canal. The angle measurement starts from the anal canal, pivots on the anorectal junction and ends at the shadow of the pubis. Inter- and intra-observer agreement in AC/Pubis angle measurement was assessed and the angles measured in the two groups compared. Forty women with posterior prolapse and 17 controls were included. Close agreement was observed in inter- and intra-observer AC/Pubis angle measurements assessed with Bland-Altman analysis. AC/Pubis angle is significantly wider in prolapse patients compared to controls (t-test, p < 0.001), with mean AC/Pubis angle in prolapse patients 122.9° (SD 15.6°) and controls 98.2° (SD 15.9°). The AC/Pubis angle is a novel validated 2D ultrasound technique for the assessment of the anorectal axis that potentially can be performed using equipment that is widely available in routine clinical practice. The AC/Pubis angle is significantly wider in prolapse patients compared to controls.