When subjects were divided into groups based on distal anterior vaginal wall support, the mean straining Q-tip values for the 190 (29%) subjects judged to have a “well supported” distal anterior vaginal wall (Aa –2 cm or less) was 51.5±14.6º compared with 64±18.6º in the 454 (69%) women with a “poorly supported” distal anterior vaginal wall (Aa –1 cm or greater) (P<.001).
The overall stage of prolapse in the POP-Q examination is determined by the lowest presenting part of the vagina or cervix (points Ba, Bp, or C). To explore the influence (potential distortion effect) that “overall” stage of prolapse had on the relationship of Aa and straining Q-tip angle, we performed a (linear, multivariable) regression analysis with POP-Q stage held constant. In this analysis, POP-Q stage was significantly associated with Q-tip straining angle (P=.01), such that women in stage II had the greatest straining angle compared with women in the other two stage groups (0/I and III/IV), but the relationship between point Aa and straining angle was essentially unchanged. As point Aa increased by 1 cm, Q-tip straining angle increased 4.3º on average, when stage of prolapse was held constant (P<.001). When we restricted the analysis to those women with point Aa between –3 and +1 (n=608), the strength of the association between point Aa and straining angle was similar. In this subgroup, as point Aa increases by 1 cm, straining angle increased 5.7 degrees (r=0.35, P=.001).
Nearly a third of stress-incontinent women with urethral mobility by Q-tip test visually appeared to have a well-supported urethrovesical junction with Aa values of –2 cm or less in this large prospective study. The position of the anterior vaginal wall only weakly correlated with the maximum Q-tip straining angle. The position of the urethrovesical crease (point Aa) on POP-Q and straining angle on Q-tip test do not appear to reflect the same anatomic support and cannot be used to predict one another. No Aa value can rule out urethral hypermobility.
Our findings are consistent with others who attempted to identify a “cutoff” value for point Aa, which could reliably diagnose urethral hypermobility. Montella et al18 found that point Aa values less than +2 were neither sensitive nor specific for predicting urethral hypermobility in 111 women with prolapse or urinary incontinence or both. Similarly, Cogan et al7 found that 95% of patients with stage II or greater prolapse met criteria for hypermobility with straining angles of more than 30º. However, small numbers of women with stage 0/I prolapse limited the conclusions. In a study of 134 consecutive women referred for an urogynecology evaluation, women with stage 0 prolapse met criteria for urethral hypermobility 6% of the time, stage I prolapse 91%, and stage II or greater prolapse 100%. When point Aa was stage I or less, point Aa had a positive predictive value of 82% for urethral hypermobility (Q-tip angle of 30º or more) and a negative predictive value of 94%. The authors concluded that women with stage 0 or I prolapse required a Q-tip test to assess urethral mobility whereas those in higher stages did not.16 Our study findings reinforce this advisory.
Urethral mobility, as defined by the Q-tip test, is considered a selection criterion and prognostic factor for incontinence procedures such as the retropubic urethropexy and the rectus fascial sling. The optimal method for determining urethral mobility remains unclear because both Q-tip and POP-Q have intrinsic flaws. Both measurements are influenced by straining effort as well as the accuracy of the examiner's gross visual measurements. Assessing urethral mobility by POP-Q has the advantage of avoiding discomfort from urethral probing and the variability of correct swab positioning at the bladder neck. Additionally, interobserver and intraobserver reliability of the POP-Q examination components has been established.14 However, anterior vaginal wall morphology is influenced by numerous factors such as muscularis hypertrophy, rugae, obstetric lacerations, surgical distortion, and urethral diverticula. Caputo and Benson8 reported on the use of perineal ultrasonography as an alternative to more accurately measure proximal urethral mobility, but access to ultrasonography in the ambulatory setting and its associated expense has limited its utility.
All of the women enrolled in the SISTEr trial had urethral hypermobility by Q-tip; therefore, we are unable to determine an Aa value that assures the presence of urethral hypermobility and circumvents the need for a Q-tip test. Regrettably, we did not standardize our method for obtaining Q-tip straining angles in women with advanced (stage III/IV) prolapse. Examiners variably reduced and maintained support of the uterus and vaginal walls during the Q-tip angle measurements so that the prolapsing vaginal wall or cervix did not deflect the swab. This variability in technique may explain the wider range of Q-tip values and the lack of correlation between Q-tip angle and positive Aa values in women with advanced prolapse. We recommend that a standardized technique for prolapse reduction be used by future investigators because reduction method and loss of apical support may influence urethral mobility.
Our findings suggest that clinicians who visually ascertain urethral mobility by watching descent of the distal anterior vagina during Valsalva efforts may underestimate the presence of hypermobility. The Urinary Incontinence Treatment Network is currently conducting a randomized trial comparing the outcomes after transobturator and retropubic polypropylene mesh midurethral slings. Preoperative urethral mobility will be analyzed as a prognostic variable in the continence outcomes of both procedures. Until clinical trials specifically define the prognostic value of point Aa in incontinent women undergoing surgery, clinicians should not use this anatomic landmark as a selection criterion for procedures.
This study confirms that, although there is a positive correlation between the POP-Q measurement point Aa and the Q-tip straining angle, point Aa of –1 cm or less should not be used as a surrogate for good urethral support and does not predict the absence of urethral hypermobility.
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Urinary Incontinence Treatment Network Steering Committee
William Steers, MD, Chair (University of Virginia, Charlottesville, Virginia); Ananias C. Diokno, MD (William Beaumont Hospital, Royal Oak, Michigan); Salil Khandwala MD, Veronica Mallett, MD (Oakwood Hospital, Dearborn, Michigan; U01 DK58231); Linda Brubaker, MD, Mary Pat FitzGerald, MD (Loyola University Medical Center, Maywood, Illinois; U01DK60379); Holly E. Richter, PhD, MD, L. Keith Lloyd, MD (University of Alabama, Birmingham, Alabama; U01 DK60380); Michael Albo, MD, Charles Nager, MD (University of California, San Diego, California; U01 DK60401); Toby Chai, MD, Harry W. Johnson, MD (University of Maryland, Baltimore, Maryland; U01 DK60397); Halina M. Zyczynski, MD, Wendy Leng, MD (University of Pittsburgh, Pittsburgh, Pennsylvania; U01 DK 58225); Philippe Zimmern, MD, Gary Lemack, MD (University of Texas Southwestern, Dallas, Texas; U01DK60395); Stephen Kraus, MD, Thomas Rozanski, MD (University of Texas Health Sciences Center, San Antonio, Texas; U01 DK58234); Peggy Norton, MD, Lindsey Kerr, MD (University of Utah, Salt Lake City, Utah; U01 DK60393); Sharon Tennstedt, PhD, Anne Stoddard, ScD (New England Research Institutes, Watertown, Massachusetts; U01DK58229); John W. Kusek, PhD, Leroy M. Nyberg, MD, PhD, Debuene Chang, MD (National Institute of Diabetes and Digestive and Kidney Diseases); Anne M. Weber, MD (National Institute of Child Health and Human Development).