Hypothesis/Aims of Study
To determine the relationship between POP-Q point Aa and maximum urethral straining angle (Q-tip strain) and if the relationship is affected by pelvic organ prolapse in a cohort of women with stress predominant urinary incontinence.
Study Design. Materials, and Methods
Maximum urethral straining angles and Aa measurements were obtained from 655 women with stress predominant urinary incontinence and urethral hypermobility who were enrolled in a multicenter randomised surgical trial comparing the retropubic urethropexy and the sling procedures. Respective Institutional Review Boards approved this study. Urethral hypermobility was measured with the Q-tip test, using a goniometer, and was defined by a resting angle or displacement angle at maximum valsalva effort, of >30º from the horizontal plane. Point Aa was measured relative to the hymen in the midline of the anterior vagina with a centimeter ruler with the subject in the supine position, straining maximally. This point of the POP-Q score represents the urethrovesical junction (UVJ). Pearson correlations and linear regression analyses were performed on baseline measures obtained prior to surgery. Q-tip values were treated as continuous variables and point Aa as ordinal data.
Subjects had a mean age of 51±10 years and mean BMI of 30±6.5 kg/m2. Seventy three percent were Caucasian, 11% Hispanic and 7% black. The median for point Aa was -1 cm (range –3cm to +3cm ) and the median Q-tipstrain value was 60o (range 10° to 130°). The distribution of point Aa is displayed in Figure 1. The distribution of overall stage of prolapse was 25% stage 0/I, 59% stage II, 16% stage III/IV. Fifteen percent reported prior anterior vaginal or incontinence surgery. Point Aa and Q-tipstrain were weakly correlated (o=0.34, p<0.0001). Results of a linear regression show that as maximum straining angle increases 1 degree, Aa increases 0.026 cm (p<0.0001). When POP-Q stage was held constant in the regression model, as Q-tipstrain increases 1 degree, Aa increases only 0.014 cm (p<0.0001). Therefore, the positive correlation between Aa and Q-tipstrain is not independent of prolapse stage. Age and prior anterior vaginal wall or incontinence surgery had no significant effect on the correlation between Aa and Q-tipstrain (p=0.07, p=0.64 respectively).
Interpretation of Results
There is a weak relationship between point Aa and Q-tipstrain angle in this sample of stress incontinent women. As the degree of urethral hypermobility increases, Point Aa becomes more prolapsed. However, one value does not predict the other. Twenty-nine percent of our cohort of stress incontinent women with urethral hypermobility appeared to have good UVJ support by visual inspection, with a point Aa of –2 or above. Our findings suggest that using the criterion of POP-Q point Aa ≥ –1cm to identify women with urethral hypermobility will exclude as many as 31% who meet the standard by Qtip test.
Point Aa of the POP-Q system provides the convenience of a non-instrumented measure of UVJ rotational descent. At values of –1 and more distal, point Aa can serve as a surrogate measure for the Q-tipstrain angle in identifying urethral hypermobility in stress incontinent women. When clinical care has the potential to be influence by the presence or absence of urethral hypermobility, a Q-tip test should be performed in women whose point Aa value is proximal to –1cm.