Pelvic floor muscle training (PFMT) is widely applied to women with pelvic organ prolapse (POP). It is the first-line treatment for POP recommended by International continence society (ICS) as Grade B. Pelvic floor muscle (PFM) function is thought to play a significant role in the pathogenesis of POP. PFM kinesiologic function is assessed by using relatively reliable measurements, such as digital examination, perineometer, electromyography with a vaginal prove. However, they are considered to be slightly invasive method as the tool is inserted into vagina. There are some patients feel discomfort and pain, for example immediately after transvaginal surgery or vaginal delivery. Ultrasonography has developed to become an alternative method and a more practical alternative for both anatomical and functional assessment. Although 3 dimensional (3D) ultrasonography, assessing levator hiatus area, strength and endurance parameters was associated with vaginal pressure in women with POP, 3D ultrasonography has been used in some medical institutions only due to comparatively higher price than 2 dimensional (2D) ultrasonography. The previous study showed that 2D ultrasonography measuring the distance of anterior-posterior diameter (APD) of levator hiatus during PFM voluntary contraction can be used to assess both the supporting function and the contractile function of the pelvic floor in postpartum women[1]. Nevertheless, to date, few reports on APD for the patients with POP were published reliability with 2D transperineal ultrasnography both before and after PFMT. The aim of this study is to clarify the feasibility of 2D transperineal ultrasonography in women with POP.

Thirty-one patients with POP were participated in this study. The sample size calculation based on the significant change of PFM strength after PFMT compared to before PFMT, and we set a final sample size of 27 including dropouts. The patients who have been diagnosed with POP (stage II or III) were included in this study. The research ethics committee of our institution approved this study. All participants were given written information.
One physiotherapist performed the perineometer and 2D transperineal ultrasonography examination for PFM functions. We conformed that all patients could perform correct PFM contractions before starting examination. The maximum voluntary contraction (MVC) of PFM was assessed by perineometer. All women were tested three times of maximum voluntary contraction of the PFM. The maximal value was recorded from three contractions each patient. The APD was defined as the minimal distance between the hyperechogenic posterior aspect of the pubic symphysis and the anterior border of the heyperechogenic pubovisceral muscle in the mid-sagittal plane by using 2D transperineal ultrasonography (figure 1) [2]. The image of APD was obtained by placing a curved array ultrasonography transducer on perineum in mid-saggital plane. The APD were measured at rest (APD at rest) and during PFM contraction (APD at contraction) in the supine position. The dynamic images were obtained during PFM contractions and at rest. PFM contractions and relaxation were recorded at least three times. The formula used to calculate the difference in values of distance between at rest and maximum vaginal contraction as follows: ΔAPD (mm) = (APD at rest – APD at contraction).
All participants visited 6 times routinely during PFMT period. They were given one-to-one PFMT and lifestyle advises by physiotherapist. Statistical analysis was performed for the following data analysis. Twenty-eight women out of 31 participants who completed PFMT were included in this study. Wilcoxon signed-rank test was used to compare the pelvic function before and after PFMT. Spearman’s rank correlation coefficient was used to compare MVC and ΔAPD. The significance level was set at p-value <0.05.

Thirty-one outpatients visited a department of urology from November 2013 to May 2014 were assessed. Twenty-eight women with POP (Stage1-3) were compered (age: 66.0±7.4 years). The MVC of PFM increased after 4-month PFMT compared with before, 24.0±13.9 and 31.2±14.5 cmH2O, respectively (p<0.05). The ΔAPD also significantly increased from 8.8±5.1 to 12.1±4.5 mm (p<0.01). Moreover, the current study showed that there was a moderate correlation between MVC and ΔAPD both before (R=0.53) and after PFM training (R=0.68) (p<0.01) (Figure.2).

This is the first prospective study indicating that there was a significant correlation between ΔAPD and vaginal pressure before and after 4-month PFMT in patients with POP. It suggests that ΔAPD can be used for an alternative parameter of vaginal pressure in daily clinical settings. Ultrasonography has been used by a number of clinician, researchers because relatively easy to learn and high reliability. APD measured by two/ three/ four-D ultrasonography have been reported in nulliparous, primiparous and POP patients. However, to our knowledge, APD by using 2D transperineal ultrasonography has not been clarified in patients with POP only. Using 2D transperineal ultrasonography, the displacement of anorectal junction was obtained during PFM contraction in healthy women. We hypothesized that 2D transperineal ultrasonography detect the change of PFM contractility before and after PFMT in POP patients. As a result of this study, 1) the ΔAPD and vaginal pressure significantly increased before and after PFMT, 2) the ΔAPD was significantly associated with vaginal pressure before and after PFMT. The previous study demonstrated that PFMT improved PFM strength, and prolapse symptoms compared to control group [3], and pubovisceral muscle thickness increased by 15.6%, and levator hiatus area in the axial plane narrowed by 6.3% in PFMT group. It could suggest that the change of PFM contractility can be detected by ΔAPD, using 2D transperineal ultrasonography in daily clinical settings. 
The limitation of present study included that the sample size was small. Larger research will be required to solve this problem in future.

We propose that APD could be an alternate parameter as a non-invasive tool to assess PFM function in clinical settings. Moreover, dynamic 2D transperineal ultrasonography could be a method to study functional changes of POP patients.

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