Is urethral mobility really being assessed by the pelvic organ prolapse quantification (POP-Q) system?

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.

A total of 274 patients with pelvic organ prolapse 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.

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).

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.