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Tension free vaginal tape (TVT) is used widely for the treatment of stress urinary incontinence. Because this procedure was introduced only 10 years ago, most papers have focused on success rates and subsequent complications1, 2; to date there have been no reports with relevant data about the complex changes of the lower urinary tract after this procedure, although various studies of the mechanism of TVT have been published3–13.
Ultrasound is one of the methods used in monitoring the lower urinary tract, especially to assess the position and mobility of the bladder neck14–16. It permits visualization of the tape, which is highly echogenic and can be identified easily posterior to the urethra. The TVT operation was designed to support the middle and distal urethra17. To evaluate the effect of this operation it is important to assess the position and mobility of the whole urethra before and after surgery.
The aim of our study was to evaluate changes of the lower urinary tract after a successful TVT operation (especially changes in the mobility of the whole urethra), to evaluate these changes in women with different degrees of urethral mobility, to evaluate the changes of the proximal urethra (funneling) and of the thickness of the urinary bladder wall, and to evaluate the relationship between the position and mobility of the tape and the mobility of the urethra.
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This prospective study included 52 women after a successful TVT procedure. Stress urinary incontinence was confirmed urodynamically before surgery. Transperineal and introital ultrasound examinations were performed by a single operator before the TVT procedure and approximately 3–6 months after surgery using an Acuson 128 XP 10 (Acuson, Mountain View, CA, USA) ultrasound machine, equipped with a 5–3.5-MHz curved array probe for the perineal examination and a 7–5-MHz sector probe for the introital examination. Surgery in all women was performed in the same way by either J.M. or A.M. After surgery, a urodynamic examination, stress test and pad weight test were performed, to exclude de novo urge incontinence, urgency or persistent stress incontinence. This study was approved by the local ethics committee and each patient who enrolled provided written informed consent and agreed to each procedure.
The most accurate ultrasound assessment of the lower urinary tract is based on the use of x, y coordinates in the orthogonal system in accordance with the guidelines of the German Urogynecology Working group18 (Figure 1). However, direct measurement of x, y coordinates during ultrasound examination is highly complicated. The position of any point in the plane can be expressed in either orthogonal (x, y) or polar (p,γ) coordinates. We chose the latter as they are easier to measure during ultrasound examination (most ultrasound machines allow measurement of distance and angle). The orthogonal coordinates (x, y) can then be calculated easily from p and γ: x = p × (cos(180°− γ/180°) × π); y = p × (sin(180°− γ/180°) × π).
Figure 1. Ultrasound parameters according to the German Urogynecology Working Group. γ (gamma), angle between the inferior edge of the symphysis and the urethrovesical junction (UVJ); h, distance between the UVJ and the horizontal; p, distance between the inferior edge of the symphysis and the UVJ; x and y, distance between the UVJ and the x- and y-axes; X, axis of the symphysis, with 0 at its lower edge; Y, axis perpendicular to that of the symphysis.
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The coordinate system was defined as follows: the x-axis is the axis of the symphysis, with 0 at the lower edge of the symphysis. The y-axis is perpendicular to x. Following this system the rotational angle gamma (γ) and distance (p) between the lower edge of the symphysis (origin of the system) and bladder neck (or the other points in the system) were measured.
For all women, changes in position and mobility of the whole urethra during maximal Valsalva maneuver were measured, as were changes induced by the surgery. The mobility was expressed as the vector and direction of the movement from rest to maximal Valsalva maneuver. The measurements were taken transperineally with the woman in a supine position at rest and during maximal Valsalva. Before the ultrasound examination the urinary bladder was filled to 300 mL with sterile saline.
Because the anatomical length of the urethra varies, measurements of the urethra were taken at four defined points: at the urethrovesical junction (UVJ), 17 mm below the UVJ (middle of the urethra; point M) and 1 cm above and below this point (upper and lower third points; UT and LT) (Figure 2). To evaluate the changes of the position and mobility of the posterior bladder wall, measurements were taken at a point 1 cm from the posterior part of the bladder neck (points P and B) (Figure 2). After surgery the position of the tape, the upper and lower tape margins, was assessed (Figure 2). We correlated the position of the tape and the lower urethral segment—the orthogonal distance of the upper and lower edges of the tape from the lower urethral segment (i.e. the distance of these two points in the orthogonal system from a line which is formed by M and LT). The shift of the tape to urethral reference points M and LT between rest and maximal Valsalva was described. The width and orientation of the tape and orientation of the urethra at rest, and their changes at maximal Valsalva, were calculated.
Figure 2. (a) Line diagram indicating reference points used in measurement of ultrasound parameters. 1, urethrovesical junction (UVJ); 2, upper third of the urethra (UT); 3, middle of the urethra (M); 4, lower third of the urethra (LT); 5, posterior part of the bladder neck (P); 6, bladder wall 1 cm from P (B); 7, upper tape margin; 8, lower tape margin. Single arrow indicates the tape. Double arrows indicate the axis of the symphysis pubis, the line end at the lower edge of the symphysis pubis (0 in the polar and orthogonal systems). The ultrasound images show measurement of the reference points at rest (b) and at maximal Valsalva (c).
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To achieve a better understanding of the changes after the surgery, the women were subdivided according to their preoperative urethral mobility (division according to quartiles, i.e. those with low mobility in the first quartile, those with intermediate mobility in the second and third quartiles and those with high mobility in the fourth quartile). For three mobility groups (women with low, intermediate and high urethral mobility before surgery) we compared the changes induced by the operation and the typical position and mobility of the tape after surgery.
For evaluation of the proximal urethra, the distance between the inner edges and depth of visible opening (funneling) was measured introitally at rest and at maximal Valsalva19, 20. After the bladder had been emptied, its thickness was measured at three points21 (anterior part, trigone and dome).
The reliability of the ultrasound measurements was tested prior to the study via an F-test in a mixed model ANOVA. The measure of reliability used was intraclass correlation coefficient; absolute typical error and typical error were expressed as the coefficient of variation.
Data were summarized as mean and median, with SD and quartile range for measures of variability. Depending on the character of the data, either a matched pairs t-test or the Wilcoxon test was used to evaluate the changes that occurred during Valsalva maneuver or that had been induced by the operation. For comparisons between the three mobility groups, an ANOVA F-test or Kruskal–Wallis test was used where appropriate. The level of significance was set to 0.05. All analyses were performed using open source statistical environment R, version 1.7.122.
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The intraclass correlation coefficients for the single operator for measurements at rest and at maximal Valsalva, respectively, were 0.86 and 0.86 for gamma, 0.84 and 0.84 for p, 0.88 and 0.90 for x and 0.81 and 0.78 for y. The typical error of measurements at rest for gamma was 3.58°; for p it was 0.95 mm. The absolute difference between the two measurements was 2.1 (SD, 1.5) mm. At maximal Valsalva the typical error for gamma was 6.23°; for p it was 1.45 mm, and the absolute difference was 2.5 (SD, 2.0) mm. These data indicate the high accuracy of the ultrasound measurements.
The mean age of the women in the study was 57.2 (SD, 11) years, the mean body mass index was 27.5 (SD, 4.6), and the mean parity was 1.9 (SD, 0.6). Mobility of the urethra was described as the vectors of movement from rest to maximal Valsalva. Preoperative ultrasound showed urethral mobility in all patients. The highest mobility was observed in the upper parts of the urethra, and mobility decreased in the lower parts. The mean vector length of the movement for the UVJ was 19.3 (SD, 7.8) mm, for UT it was 18 (SD, 6.9) mm, for M it was 15.5 (SD, 5.8) mm, for LT it was 14.6 (SD, 5.7) mm, for P it was 21.3 (SD, 9.2) mm and for B it was 24.1 (SD, 11.8) mm. The direction of movement from rest to maximal Valsalva was described as the angle of divergence from the horizontal measured clockwise, where the horizontal from left to right represents zero shift. Before surgery the upper points (UVJ, P, B) shifted to the right and slightly downwards (around 30°), the upper part of the urethra (UT) turned diagonally to the right (40–45°), the middle part (M) turned diagonally to the right and down (60°) and the lower part (LT) turned practically vertically downwards (80°).
The position of the urethra at rest was not influenced by surgery (it remained in the same position as before, Figure 3a). However, the operation significantly decreased the mobility of all parts of the urethra during Valsalva (Figure 3b). The mean vector length of the movement for UVJ was 14.2 (SD, 6.9) mm, for UT it was 12.1 (SD, 5.5) mm, for M it was 9.5 (SD, 4.2) mm, for LT it was 9.4 (SD, 4.4) mm, for P it was 16.3 (SD, 8) mm and for B it was 18.6 (SD, 9.7) mm. Women with high mobility before surgery had high mobility afterwards. The direction of movement of all parts was similar to that before surgery.
The average orthogonal distance of the superior margin of the tape from the urethra at rest was 10 mm and that of the inferior margin was 8 mm. At rest the superior margin was 1.3 mm over reference point M, and the inferior margin was 0.9 mm over point LT. The mean vector length of the movement from rest to maximal Valsalva for the upper tape margin was 10.1 (SD, 5.1) and for the lower margin it was 8.6 (SD, 4.7). At maximal Valsalva the distance between the superior margin and the urethra was practically unchanged, and it decreased between the inferior margin and the urethra, indicating rotation of the tape. In comparison with the reference points (M and LT), the tape was 4–5 mm higher at maximal Valsalva, indicating slippage of the urethra. At maximal Valsalva the tape was slightly slimmer (shorter), indicating bending of the tape (Table 1). At rest the tape was parallel to the lower urethra. At maximal Valsalva the angle of divergence of the tape from the urethra increased; the tape rotated approximately 30° and the urethra 20° (Table 2).
Table 1. Position and orientation of the tape and lower urethral segment
Table 2. Changes of the length and rotation of the tape and of the rotation of the lower urethral segment during Valsalva
| ||Mean difference||t-test||Median difference||Wilcoxon test|
|Lower CI||Upper CI||P||Lower CI||Upper CI||P|
|LT-R & LT-V (mm)||1.04||0.49||1.59||0.0004||1.01||0.47||1.64||0.0011|
|IT-R & IT-V (°)||30.5||21.4||39.7||0.0000||28.1||21.1||35.2||0.0000|
|IU-R & IU-V (°)||20.0||9.4||30.5||0.0004||15.7||9.1||23.4||0.0000|
|DU-R & DU-V (°)||− 10.6||− 23.6||2.5||0.1095||− 11.2||− 18.4||− 3.1||0.0065|
For the different mobility groups there was no difference in the direction of movement during Valsalva maneuver preoperatively (Figure 4). Postoperatively, the resting position of the tape with respect to the lower urethral segment was the same for all groups; hence, preoperative mobility type did not influence the position of the tape (Figure 4). The absolute changes of the vector of the urethral movement differed according to the mobility group: the average decrease was 6 mm; for women with low, intermediate and high mobility, respectively, it was 2–3 mm, 4–6 mm and 9 mm. The percentage change in relative mobility was the same in all groups, and increased in the lower parts of the urethra. The relative decrease of mobility for the UVJ for patients with low, medium and high mobility, respectively, was 15%, 25% and 32%, and for the middle of the urethra these values were 19%, 36% and 43%.
The operation did not influence the proximal urethra at rest and significantly decreased funneling during maximal Valsalva (width and depth) (Table 3). After surgery there was an increase in the thickness of the bladder wall (0.64 mm (P < 0.0001) and 0.73 mm (P = 0.0004), respectively, for the anterior dome and trigone).
Table 3. Correlation of visible opening of the proximal urethra (width and depth) before and after surgery
| ||Before surgery||After surgery||Mean difference||P (t-test)|
|WFR0 & WFR3 (mm)||4.57||1.65||4.58||1.81||− 0.01||0.9710|
|DFR0 & DFR3 (mm)||4.35||1.59||3.76||1.25||0.58||0.0417|
|WFV0 & WFV3 (mm)||7.84||1.55||6.53||2.94||1.30||0.0085|
|DFV0 & DFV3 (mm)||9.51||2.31||6.77||3.75||2.74||0.0001|
|DWF0 & DWF3 (mm)||3.27||1.64||2.06||2.16||1.21||0.0042|
|DDF0 & DDF3 (mm)||5.16||2.27||3.01||3.58||2.15||0.0019|
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Ultrasound is an excellent method for the investigation of the lower urinary tract15, 16, 23–25. The use of the orthogonal system of x, y coordinates allows high accuracy of measurement and permits a comparison of the effects of anti-incontinence procedures on the lower urinary tract; this system should be used for measurements at any point. The prolene tape is highly echogenic, and its margins can be identified easily26; it is possible to compare its position and mobility with that of different parts of the urethra and, based on the findings, explain the function of the TVT procedure.
When assessing morphological changes after the TVT procedure, it is important to understand and clarify its mechanism of action. The position of the urethra and bladder neck after the TVT procedure has been demonstrated in different studies by different imaging techniques (ultrasound1, 2, 3, 8, 11–13, 26, 27, magnetic resonance imaging10 and X-ray28) or by Q-tip test7.
All ultrasound studies used in the explanation of the effect of the TVT operation have monitored changes in the position and mobility of the bladder neck. Some of these studies found no changes in bladder-neck mobility3, 8 and some described reduced mobility11, 12. One of the first studies reported not only a decrease in bladder-neck mobility, but also its elevation after the TVT procedure12. Sarlos et al.3 did not find a significant difference between pre- and postoperative bladder-neck mobility. In their study the mean vector length of bladder-neck descent (i.e. of movement of the UVJ) was 14.8 mm, which reduced to 12.7 mm after surgery. In comparison, our study found that the mean mobility was higher, at 19.3 mm before surgery and 14.2 mm after. To achieve a better understanding of the changes after the surgery, the women included in our study were subdivided (using quartiles) into three groups: low, intermediate and high urethral mobility before surgery. For these groups we then compared the changes induced by the operation and the typical position and mobility of the tape after surgery. The first quartile was set at 14.1 mm, the cut-off value for low mobility; the average postoperative decrease in bladder neck mobility in this group was 2 mm. Our data for women with low mobility were very similar to the data of Sarlos et al.3. A study using the Q-tip test7 also found no change in urethral mobility. However, due to this method's lower sensitivity, it was impossible to examine precisely all the subtle changes induced by surgery; it was possible only to say that women with high mobility before surgery had high mobility afterwards.
In their MRI study Halaska et al.10. found reduced mobility after a computer analysis of the changes of the whole urethra at three points (inner and outer meatus and middle of the urethra). However, dynamic MRI cannot visualize the tape and this is a disadvantage when trying to explain the mechanism of TVT.
The position of the tape may play a key role in the effectiveness of the operation. The TVT procedure was designed to support the middle and distal urethra. According to some studies for restoring continence and avoiding voiding disorders, it is not necessary to fix the tape in a mid-urethral position8, 13, 28. The location of the tape in the proximal third of the urethra is also effective for restoring continence and is not a cause of a higher rate of voiding disorders28. From our data we could not confirm that different placement of the tape did not influence the effect of surgery. All of our operations were performed in the same manner, with the tape being located in practically the same position in relation to the lower urethra.
Also important for understanding the TVT mechanism is the description of the movement of the tape during increasing intra-abdominal pressure (dynamic changes of position during Valsalva, coughing or physical activity). For description of the tape movement, one point is used, the upper margin8, 25. The average tape movement was assessed relative to the inferioposterior symphyseal margin and showed narrowing of the distance between the tape and the symphysis and downward displacement of the tape. The mechanism of how the tape influenced the urethra can be explained by the ‘iris effect’25: dynamic compression of the urethra against the symphysis during Valsalva. Ultrasound determination of the position and mobility of the tape relative to the inferioposterior margin of the symphysis pubis13, 25, 26 described well the position and mobility of the tape, but did not reflect the fact that in different patients, the position of the tape was influenced by the different positioning and mobility of the urethra. From our work it was apparent that the tape moved differently and less in comparison with the urethra. The tape influenced the mobility of the middle parts of the urethra more than it did other areas. Kinking was more evident in women with higher preoperative mobility of the urethra (again, the tape influenced the lower parts more; the upper part tended to move as it had before surgery, bending around the tape).
In terms of the effect of the tape on bladder-neck opening at rest and funneling, most studies found reduced evidence of funneling after the TVT procedure13, 29, although in some patients it persisted. Most investigators did not quantify funneling, providing only an evaluation of whether it was present. Ultrasound contrast medium has been used to prove that the depth and diameter of urethral dilation can be measured in all women20; the same study exhibited urethral dilation during Valsalva in all incontinent women. It seems that the methodology of imaging of the proximal urethra is a key factor preventing comparison between different studies. In our study we compared the changes of visible opening of the proximal urethra at rest and at maximal Valsalva, and did not use a cut-off value30 to determine whether funneling was occurring.
Based on our work we can suggest several important clinical implications. A successful TVT procedure does not influence the position of the urethra and proximal urethra at rest but significantly decreases the mobility of the urethra during Valsalva maneuver. From these results we can suppose that after a successful procedure there is no evidence of the urethral obstruction at rest. TVT works as a dynamic elastic closing mechanism, which affects the urethra during increasing intra-abdominal pressure (cough, Valsalva, physical activity): the urethra moves in the same direction as before surgery, but less so. Increasing intra-abdominal pressure compresses the urethra and surrounding tissue against the tape (which appears similar to compression of the urethra with the tape against the symphysis). If the distance between the tape and the inferioposterior margin of the symphysis at rest and at maximal Valsalva is correlated, the distance during Valsalva is shorter than that at rest. We suppose that the elasticity and mobility of the tape allow progressive closure of the urethra. The action of the tape is more complex than simply the compression of the urethra. There is a decrease of mobility of all parts of the urethra and also a decrease of funneling at maximal Valsalva (for patients with low and intermediate mobility this is like standing on a swing—the tape allows only partial descent—while for those with higher mobility there is evidence of kinking around the tape). From our results we can summarize that the effect of the tape is not only the sling mechanism, otherwise it would be impossible to explain the fact that there was a proportional influence of urethral mobility and rotation of the tape in the different urethral mobility groups. This effect is apparently dependent on the elasticity, tension and structure of the entire tape, not only the suburethral part.
It is important for the surgeon about to perform the TVT procedure to be informed about the type of urethral mobility of the patient. Reduced anterior vaginal wall mobility has been associated with TVT failure and postoperative voiding dysfunction31. Dietz et al.32 recently described higher mobility of the tape in a group when the cough test was not used for adjustment of the tape, without any negative impact on the effect of the procedure (the cough test may lead to over-tightening of the tape; pers. observ.). The highest incidence of complications is likely to be in the group of patients with a marginal type of urethral mobility (i.e. high or low).
The results of our study are limited by the fact that we have no correlation between successful and unsuccessful procedures, and the examination was performed a relatively short time after surgery, but the time-dependent decline in cure rates of this procedure is slow27. Due to the relatively low incidence of complications after this procedure, more patients are needed for its accurate description and statistical evaluation. For these purposes it is necessary to perform a prospective longitudinal observational multicenter study.