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Obstetrics & Gynecology:
Original Research

Is Urethral Mobility Really Being Assessed by the Pelvic Organ Prolapse Quantification (POP‐Q) System?

Cogan, Stephanie L. MD; Weber, Anne M. MD, MS; Hammel, Jeffrey P. MS

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Author Information

Department of Gynecology and Obstetrics and Department of Biostatistics and Epidemiology, Cleveland Clinic Foundation, Cleveland, Ohio.

Address reprint requests to: Stephanie L. Cogan, MD, Cleveland Clinic Foundation, Department of Gynecology and Obstetrics, 9500 Euclid Avenue A81, Cleveland, OH 44195; E‐mail: cogans@ccf.org.

Presented in abstract form at the 2000 Annual Meeting of the American Urogynecologic Society, Hilton Head, South Carolina, October 26–28, 2000.

Received May 25, 2001. Received in revised form October 5, 2001. Accepted November 1, 2001.

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Abstract

OBJECTIVE: To estimate the relationship between Q‐tip measurement of urethral hypermobility and visual assessment of the urethrovesical junction as assessed by points Aa and Ba of the pelvic organ prolapse quantification (POP‐Q) system.

METHODS: A total of 274 patients with pelvic organ pro‐lapse or urinary incontinence had preoperative Q‐tip test straining angles and POP‐Q staging measurements. By the Q‐tip test, urethral hypermobility was defined as a straining angle of 30 degrees or greater relative to the horizontal. As defined in the POP‐Q system, point Aa is located in the midline of the anterior vaginal wall 3 cm from the external urethral meatus and represents the urethrovesical junction. Point Ba represents the most dependent position of the anterior vaginal wall. The correlation between point Aa of the POP‐Q system and the Q‐tip test was assessed using the Spearman correlation coefficient. Similar assessments were made for point Ba.

RESULTS: Mean age of the 274 subjects was 58.5 ± 11.8 years; mean parity was 3.1 ± 1.6. A total of 104 patients reported prior surgery for prolapse or incontinence. Mean Q‐tip straining angle was 61 ± 20 degrees; 258 (94%) had urethral hypermobility. Values of point Aa ranged from −3 cm to +3 cm, with median 0 cm. The correlation coefficient between the Q‐tip straining angle and point Aa was r = 0.47 (P < .001). Urethral hypermobility was observed in 95% of patients with stage II prolapse at point Aa and in 100% of patients with stages III and IV prolapse at point Aa. The correlation coefficient between the Q‐tip straining angle and point Ba was r = 0.32 (P < .001).

CONCLUSION: Although the correlation between the Q‐tip straining angle and point Aa of the POP‐Q was moderately strong, one value cannot be predicted from the other. The Q‐tip test may be unnecessary in patients with stages II, III, and IV prolapse at point Aa as virtually all such patients demonstrate urethral hypermobility.

Since its accidental discovery in 1971,1 the Q‐tip test has become a commonly used measure of urethral mobility in patients with urinary incontinence. With the patient in dorsal lithotomy position, a lubricated Q‐tip is inserted to the level of the urethrovesical junction, and the degree of excursion relative to horizontal is assessed at rest and with increased intra‐abdominal pressure. Urethral hypermobility has been defined as a straining angle of 30 degrees or greater. Although initially employed for the differentiation of stress incontinence previously classified as type I and type II, it remains a measure of the support at the urethrovesical junction and the mobility of the urethra that occurs with increases in intra‐abdominal pressure.2 Although simple to perform and inexpensive, it is uncomfortable for the patient. In addition, the measurement itself is subject to considerable variation and requires correct placement of the Q‐tip at the bladder neck.3

In 1996, the International Continence Society accepted the pelvic organ prolapse quantification (POP‐Q) system for standardized staging of pelvic organ pro‐lapse.4 The POP‐Q system has good interrater and intrarater reliability. In a prospective study, reliability was studied in 48 subjects who underwent pelvic examinations by two investigators, each blinded to the results of the other's examination. The reproducibility of the nine site‐specific measurements was analyzed with the Spearman correlation coefficient, and the reproducibility of the staging and substaging with the Kendel τ B correlation coefficient. The POP‐Q examination was also performed at two different times by one examiner on 25 patients to assess for intraobserver reliability. The correlations for each of the nine measurements were highly significant for both groups; the staging and substaging demonstrated high reproducibility in both groups. In both studies, the stage never varied by more than one in any of the patients; in the interobserver study, 69% of the stages were identical, and in the intraobserver study, 64% were identical.5 Based on physical examination, the locations of defined points in the vagina are measured relative to the hymen. Point Aa, located in the midline of the anterior vaginal wall 3 cm from the external urethral meatus, corresponds to the approximate location of the urethrovesical crease.4 Point Ba represents the most dependent position of the anterior vaginal wall. If the POP‐Q system provides accurate assessment of the anterior vaginal wall, and point Aa truly represents the urethrovesical junction, it may not be necessary to perform the Q‐tip test as a separate measure of urethral mobility. The POP‐Q is less invasive and more tolerable to patients than the insertion of a Q‐tip into the urethra.

The objective of the current study was to estimate the relationship between the Q‐tip test measurement of urethral hypermobility and visual assessment of the urethrovesical junction by point Aa of the POP‐Q system. An assessment was also made to determine the relationship between point Ba and the Q‐tip test.

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MATERIALS AND METHODS

Data for this study were obtained from subjects enrolled in either a randomized trial of anterior colporrhaphy techniques (study 1) or a prospective cohort study of outcomes after prolapse or incontinence operations (study 2). Patients were selected from a database. Subjects from the randomized trial of anterior colporrhaphy techniques were randomized to three different techniques of anterior colporrhaphy. Biostatistics prepared the randomization envelopes. Women with urinary incontinence requiring a retropubic urethropexy were excluded. In the prospective cohort study of outcomes after prolapse or incontinence operations, women with utero‐vaginal prolapse and/or urinary incontinence requiring surgical correction were selected; there were no exclusion criteria in this group. The source used for patient recruitment for both studies was the surgery schedule. Patients were identified before their preoperative visit. The length of enrollment for the anterior colporrhaphy study was 3 years (June 14, 1996 to May 26, 1999); that of the cohort study was 4 years (June 10, 1996 to August 16, 2000). The initial observations were made before the day of surgery. Patients underwent a preoperative examination including the POP‐Q and Q‐tip tests as well as 12 and 24 months after surgery. Questionnaires were also done at the time of each examination. Both studies were approved by the Institutional Review Board at the Cleveland Clinic, and all subjects provided written informed consent. A research nurse experienced in using the prolapse staging system of the International Continence Society examined all women in the supine lithotomy position in stirrups on a standard gynecologic examination table. With this staging system, six sites of the vagina are measured in centimeters in relation to the hymen. Negative numbers represent locations above the hymen; positive numbers, beyond the hymen. By definition, point Aa may assume values of −3 cm to +3 cm. Stage 0 is defined as point Aa at −3 cm; stage I, point Aa at −2 cm; stage II, point Aa at −1, 0, or +1 cm; stage III, point Aa at +2 cm; and stage IV, point Aa at +3 cm. Vaginal examinations were performed with Sims speculums; the maximum descent of prolapse was demonstrated by the Valsalva maneuver or cough and confirmed by the patient to be the most severe protrusion that occurred. Methods, definitions, and descriptions conform to the standards recommended by the International Continence Society except where specifically noted.4

The Q‐tip test was performed by inserting a lubricated cotton‐tip applicator transurethrally and withdrawing to the point of resistance, presumably indicative of the urethrovesical junction. The angle relative to horizontal was measured at rest and with straining. Urethral hyper‐mobility was defined as a maximum straining angle of 30 degrees or greater relative to the horizontal plane.

Statistical analyses were performed with centimeter measurements of point Aa as an ordinal variable; ruler measurements taken to the nearest half centimeter were rounded away from zero to the nearest integer value for consistency. Median and quartiles were used as the measures of central tendency for points Aa and Ba. Continuous variables were presented with mean and standard deviation. Effective sample sizes do not always equal the total sample size because of missing data. Strengths of association between the Q‐tip and POP‐Q tests were determined by Spearman correlation coefficients; P values for these tests refer to a test of the hypothesis that the correlation is zero. Comparisons of groups based on prior surgical history with respect to POP‐Q measurements were performed with Wilcoxon rank sum tests. A multivariable model with straining angle as the outcome and with point Aa, age, prior pelvic surgery, menopausal status, and use of hormone replacement therapy as predictors was constructed. A significance level of α = 0.05 was used for each statistical test. Also, 95% confidence intervals were computed for the percentage of women with urethral hypermobility according to the stage of prolapse at point Aa. Exact confidence intervals were used. A receiver operating character (ROC) curve was used to assess prediction of the Q‐tip straining angle based on different values of point Aa.

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RESULTS

Patient demographics are as in Table 1. The mean age of the patients in study 2 was younger (P < .001). Mean Q‐tip angle at rest was 13 ± 5 degrees; mean Q‐tip straining angle was 61 ± 20 degrees. A total of 258 women (94%) had urethral hypermobility. In patients with prior prolapse or incontinence surgery, 92 (88%) had urethral hypermobility, with mean straining angle 56 ± 24 degrees; in those without prior surgery, 151 (97%) had urethral hypermobility, with mean straining angle 65 ± 17 degrees. Values of Aa in all groups ranged from −3 cm to +3 cm. In patients with prior surgery for prolapse or incontinence, median and quartiles of point Aa were 0 (−1, 2). In patients with no prior pelvic surgery, median and quartiles were 0 (−1, 1). In all patients, median and quartiles for point Ba were 0 (−1, 2).

Table 1
Table 1
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There was a moderately strong correlation between the Q‐tip straining angle and point Aa, with r = 0.47, P < .001 (Figure 1). The correlation was higher in patients with previous surgery (r = 0.57) compared with those without surgery (r = 0.41), though the difference was not statistically significant. Table 2 shows the percentage of patients with urethral hypermobility according to the stage of prolapse at point Aa. When patients with stages III and IV prolapse are considered together, the confidence bound becomes 0.96. Analysis for point Ba and Q‐tip straining angle revealed a Spearman correlation coefficient of r = 0.32 (P < .001). When considering the multivariable model, point Aa was discovered to explain 29% of the variability in straining angle after already accounting for the other variables; this does not represent a substantial increase in predictive ability when compared with a univariable model.

Figure 1
Figure 1
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Table 2
Table 2
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An ROC curve was plotted for predicting urethral hypermobility using the point Aa measurement (Figure 2). The ROC curve demonstrates that at a cutoff of 3 cm, there is good specificity (100%) but poor sensitivity (28%). A cutoff of 2 cm provides good sensitivity (91%) but poor specificity (44%). There is no cutoff at which both sensitivity and specificity are acceptable.

Figure 2
Figure 2
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DISCUSSION

We conclude from our findings that the landmarks of anterior vaginal topography do not necessarily represent the dynamics of the urethrovesical junction. However, in those with prolapse of stages II, III, and IV at point Aa, urethral hypermobility is virtually assured. In this patient population, the more invasive Q‐tip test does not offer additional clinical information and can be safely eliminated from the evaluation.

Although we anticipated a very strong correlation between the POP‐Q and the straining angle of the Q‐tip test, our results failed to demonstrate this. The scatter‐plots do not reveal any obvious trends that would enable prediction of Q‐tip straining angle measurements based on POP‐Q point Aa findings; this supports the previous findings of Montella et al.7 However, the absolute value of the Q‐tip straining angle may not be that important when a dichotomy is used to describe urethral hypermobility as present or absent by Q‐tip straining angle greater than or equal to 30 degrees.

The Q‐tip test, despite its limitations, remains a commonly used measure of urethral mobility. It is important to recognize that the selection of 30 degrees as the cutoff between the presence or absence of urethral mobility is arbitrary, based on the findings of Crystle et al1 and Caputo and Benson.6 An ROC curve constructed on point Aa cutoff points for all patients and their predictive ability for a positive Q‐tip test revealed that no cutoff point allowed for prediction of a positive Q‐tip test. Other modalities to assess proximal urethral support and their correlation with the Q‐tip test have been investigated, but a gold standard still remains to be defined.

A limitation of the current study is that the majority of patients in the study population had urethral hypermobility and prolapse, so that there were only small numbers with stages 0 and I prolapse at point Aa. The data indicate that the higher the stage, the greater the likelihood of urethral hypermobility; similarly, the lower the stage, the lesser the likelihood of urethral hypermobility. However, the confidence intervals are wide for stages 0 and I because of smaller numbers of patients in those groups. This underscores the importance of further research. Nevertheless, because assessment of urethral mobility is clinically relevant in patients with advanced prolapse who are undergoing surgery, the results of this study are valuable in the management of those patients.

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REFERENCES

1. Crystle CD, Charme LS, Copeland WE. Q-tip test in stress urinary incontinence. Obstet Gynecol 1971;38:313–5.

2. Walters MD, Diaz K. Q-tip test: A study of continent and incontinent women. Obstet Gynecol 1987;70:208–11.

3. Karram MM, Bhatia NN. The Q-tip test: Standardization of the technique and its interpretation in women with urinary incontinence. Obstet Gynecol 1988;71:807–11.

4. Bump RC, Mattiasson A, Bo K, Brubaker LP, DeLancey JOL, Klarskov P, et al. The standardization of terminology of female pelvic organ prolapse and pelvic floor dysfunction. Am J Obstet Gynecol 1996;175:10–7.

5. Hall AF, Theofrastous JP, Cundiff GW, Harris RL, Hamilton LF, Swift ST, et al. Interobserver and intraobserver reliability of the proposed International Continence Society, Society of Gynecologic Surgeons, and American Urogynecologic Society pelvic organ prolapse classification system. Am J Obstet Gynecol 1996;175:1467–71.

6. Caputo RM, Benson JT. The Q-tip test and urethrovesical junction mobility. Obstet Gynecol 1993;82:892–6.

7. Montella JM, Ewing S, Cater J. Visual assessment of urethrovesical junction mobility. Int Urogynecol J 1997;8:13–7.

© 2002 The American College of Obstetricians and Gynecologists

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