Association between 2D trans-perineal ultrasound and physical examination in evaluation of ani function

Abstract

Purpose

To compare the correlation between 2D transperineal ultrasonography and physical examination (intravaginal palpation) for assessing pelvic floor and levator ani function.

Methods

Due to symptoms of pelvic floor disorder, 40 women between the ages of 29 and 75 were enrolled in this study as candidates for urodynamic and structural evaluation of the pelvic floor. A pelvic floor gynaecologist and radiologist assessed the levator ani function via physical examination (graded based on the Oxford Grading System) and transperineal 2D ultrasound, respectively.

Results

The ultrasound parameters for calculating the Levator Ani Index (LAI) demonstrate a difference between the anteroposterior dimension of the levator hiatus (r = 0.691, p < 0.001) and the cranial shift of muscle (r = 0.499, p < 0.001) at rest and during a squeezing manoeuvre in the mid-sagittal plane. Reduced anteroposterior diameter of the hiatus and increased cranial shift were associated with a higher Oxford Physical Examination Score (OPES). The association between LAI and OPES was independent of baseline variables such as age, BMI, number of births, and the presence of incontinence symptoms.

Conclusion

Measures such as the LAI can be used to quantify the function of the levator ani muscle, which may be useful for evaluating the efficacy of pelvic floor physiotherapy and exercise.

Introduction

The levator ani muscle is the primary pelvic organ stabiliser, and it plays a significant role in pelvic floor dysfunctions such as faecal/urinary incontinence and pelvic organ prolapse [1]. Physiotherapy is one of the primary treatment options for strengthening the levator ani muscle and is an effective alternative to surgery for patients with mild to moderate pelvic organ prolapse. For years, intravaginal palpation was used to assess the function of the levator ani muscle during various manoeuvres [2–4]. However, the potential limitations of this method, such as its limited repeatability and operator dependence, have led researchers to seek a more efficient and accurate method for assessing and quantifying the functioning of the levator ani muscle [5, 6]. Ultrasonography has been introduced in recent years as a potential method for evaluating pelvic floor muscle (PFM) morphology and function [7]. When comparing the accuracy of 2D mid-sagittal ultrasound and intravaginal palpation for assessing PFM strength, some studies demonstrate a significant correlation between the two methods [8]. Transperineal ultrasound using a 3D/4D probe enables direct visualisation of the muscles and can be used to assess muscular morphology and function [9]. Recent studies have attempted to standardise 2D ultrasound for pelvic floor evaluations, as it is more accessible, less expensive, and does not require advanced expertise [10]. The assessment of levator ani function via physical examination is subjective and requires gynaecologists with a subspecialty in pelvic floor disorders to have extensive clinical experience. However, 2D ultrasonography permits the quantitative assessment of the functional state of the levator ani. The purpose of the present study was to evaluate the correlation between 2D ultrasonography and physical examination for assessing pelvic levator function.

Materials and methods

Patient selection

This cross-sectional study was conducted on 40 women aged 29–75 years who were candidates for urodynamic and structural evaluation of the pelvic floor due to symptoms of PFM dysfunction, such as stress urinary incontinence, tissue protrusion from the vagina, faecal incontinence, or obstructed defecation. Women with cognitive impairment, physical impairment, or any psychological conditions that prevented their full cooperation during the ultrasound examination were excluded from the study. The institution’s ethics committee approved the study, and all patients signed a consent form prior to participation. Data on age, parity (number of deliveries of a foetus older than 24 weeks), weight, and height (body mass index measured by dividing weight in kilogrammes by height in metres squared), as well as symptoms such as stress incontinence (defined as urinary incontinence when coughing, laughing, or lifting heavy weights) or urge incontinence (defined as an uncontrollable desire to void and labile bladder control), prolapse (vaginal tissue protrusion), obstructed defecation (inability to evacuate the faeces completely), or faecal or gas incontinence, were obtained through an interview with a trained general practitioner. The patients were also briefly instructed in PFM contractions for the study.

Ultrasound technique and physical examination

Physical examination and 2D ultrasound with a curved array probe (3.5–5 MHz) in a mid-sagittal view were used to evaluate the functional status of PFMs. First, the maximal strength of the PFM was evaluated by vaginal examination and graded according to the Oxford Physical Examination Score (OPES) as follows: 0 (no discernible PFM contraction); 1 (very weak PFM contraction); 2 (weak PFM contraction); 3 (moderate PFM contraction); 4 (good PFM contraction); and 5 (strong PFM contraction). All assessments were conducted by a gynaecologist with a subspecialty in pelvic floor disorders who was blind to the imaging reports.

Second, 2D mid-sagittal transperineal ultrasonography was performed at rest and following a squeezing manoeuvre in a semi-recumbent position with the hip slightly flexed and abducted. The preference was for a partially full bladder. If faecal impaction made imaging difficult, the study was repeated after the bowel was evacuated. The probe was covered with thin plastic wrap, wiped with alcohol, and placed in the labial area (against the pubic symphysis) with a cranial tilt of approximately 75°. A minimal amount of pressure was applied to the perineum so as not to conceal the descent of the pelvic organs. The patients were asked to cough to reduce air bubbles. The images were taken in the mid-sagittal plane with a 2D curved array 3.5–5 MHz probe. Two parameters were used to quantify the functional status of the levator ani muscle. First, the anteroposterior dimension of the levator hiatus was determined by drawing a line from the inferior margin of the pubic symphysis to the insertion site of the levator muscle’s central plate just posterior to the anorectal junction (Fig. 1). The central plate of the levator muscle is visible as an echogenic area just posterior to the anorectal junction (see the asterisk shown in Figs. 1 and 3). The anteroposterior dimension of the levator hiatus decreases during squeezing in relation to the resting position, and there is a direct correlation between the dimension and the strength of the levator ani muscle (Figs. 2 and 3). Second, the cranioventral shift was calculated as the distance between the internal urethral meatus at the bladder neck and the inferior margin of the pubic symphysis (Fig. 1). More cranial shifts during the squeezing manoeuvre result in increased levator muscle activity in this method.

Fig. 1.

Schematic view of the mid-sagittal plane on a transperineal ultrasound

Fig. 3.

2D mid-sagittal view at the level of the urogenital hiatus during a squeezing manoeuvre; the AP diameters reach 6.6 cm with a cranial shift of 3 mm, indicating satisfactory levator ani function

Fig. 2.

2D mid-sagittal view of the urogenital hiatus in a resting position; Line A demonstrates the anteroposterior (AP) diameter of the urogenital hiatus, measured from the inferior margin of the pubic symphysis to the posterior aspect of the anorectal junction at the insertion site of the levator ani central tendon (7.8 mm in this patient). Line B, which is drawn from the bladder neck to line A, represents the cranial shift

To better quantify the levator ani function, the levator activity index was defined as the decrease in hiatal anteroposterior (AP) diameter (millimetres) multiplied by the cranial shift (millimetres).

An experienced radiologist who was unaware of the results of the clinical examination performed the ultrasound examination.

Data analysis

For quantitative variables, the results were presented as mean ± standard deviation (SD), while categorical variables were summarised as frequencies (per cent). The normality of the data was determined using the Shapiro–Wilk test. The correlation between physical and ultrasound examination parameters was evaluated using Pearson’s correlation test or the non-parametric Spearman’s correlation test. The linear regression model was used to examine the adjusted relationship between physical and ultrasound functional parameters after adjusting for baseline variables. In regression models, the assumptions of normality of residuals, consistency of error variance, and co-linearity problem were evaluated and, if necessary, confirmed by an appropriate transformation. IBM SPSS Statistics 23.0 (SPSS Inc., Chicago, IL) was used for all statistical analyses, and p-values < 0.05 were considered statistically significant.

Results

This study included a total of 40 women with suspected PFM dysfunction. The mean ages and BMIs of the participants were 49.90 ± 10.08 years and 25.10 ± 1.93 kg/m², respectively. The mean parity was 3.42 ± 1.72, and only 5.0% of the participants were primiparous. Regarding clinical symptoms, 9 subjects (22.5%) exhibited stress incontinence, 5 (12.5%) exhibited urge incontinence, and 8 (20.0%) exhibited both symptoms. Table 1 summarises the results of both physical and ultrasound examinations. The mean Oxford Physical Examination Score was 2.80 ± 0.97, indicating levator ani muscle strength (scores 2–5) in 95.0% of patients, while only 2.5% had no muscular contraction (Fig. 5). The mean levator ani hiatal dimension at rest and in the squeezed position was 62.45 ± 6.74 mm and 49.40 ± 7.79 mm, respectively, with a mean difference of 13.05 ± 7.39 mm. The mean cranial shift of the muscle was 5.83 ± 4.83 mm. The calculated mean levator activity index was 87.53 ± 104.9. Using the correlation coefficient test (Table 2), moderately positive correlations were found between the Oxford Physical Examination Score and the levator ani AP dimension difference during rest and squeeze (r = 0.691, p < 0.001), cranial shift (r = 0.499, p = 0.001), and the levator activity index (r = 673, p < 0.001). As demonstrated in Fig. 4, an increase in the Oxford Physical Examination Score is associated with an increase in the levator ani hiatal dimension difference during rest and squeeze (Fig. 4a) and the levator index (Fig. 4b). The results of adjusted regression analysis revealed a positive relationship between the Oxford Physical Examination Score and the levator ani AP hiatal dimension (β = 4.77, p < 0.001) and the levator activity index (β = 1.15, p < 0.001). To maintain the regression assumptions, the levator activity index, as the dependent variable, was transformed into a natural logarithm (LN [levator index]) in the model. In regression models, baseline variables such as patients’ age, BMI, number of births, and presence of incontinence symptoms were adjusted (Table 3).

Table 1.

The descriptive statistics of vaginal examination and ultrasonic assessments of levator ani function

Indicator	Mean ± SD	Minimum	Maximum
Oxford physical score	2.80 ± 0.97	0.0	4.0
Levator ani AP dimension at rest	62.45 ± 6.74	51.0	82.0
Levator ani AP dimension at squeezing	49.40 ± 7.79	32.0	68.0
Difference in levator ani AP dimension at two positions	13.05 ± 7.39	1.00	33.00
Cranial shift	5.83 ± 4.83	0.0	19.0
Levator index	87.53 ± 104.9	0.00	408.0

Fig. 5.

2D mid-sagittal view of the urogenital hiatus in a patient with urinary incontinence a at rest, b during squeezing manoeuvre, and c during maximal strain. The AP diameter of the urogenital hiatus and the cranial shift of the bladder neck range from 69 and + 17.5 mm at rest to 52 and + 18.8 mm during squeezing and then to 73 and − 29.2 mm during maximal straining when a cystocele is present

Table 2.

The correlation between Oxford physical score and ultrasonic parameters

Variable	r coefficient	P-value
Levator-ani AP diameter at rest	0.203	0.21
Levator-ani AP diameter at squeezing	−0.480	0.002
Difference in levator-ani AP diameter at two positions	0.691	< 0.001
Cranial shift	0.499	0.001
Levator index	0.673	< 0.001

Fig. 4.

Scatter plot for the Oxford Physical Examination Score. a difference in urogenital hiatus AP diameter at rest and during the squeezing manoeuvre; b levator activity index: the AP diameter difference and levator activity index increased as the Oxford Physical Examination Score increased

Table 3.

The association between the change in AP diameter of urogenital hiatus and levator index with Oxford score adjusted for baseline variables

	Change in levator-ani AP dimension		Levator activity indexa
Variable	β (95% CI)	P-value	β (95% CI)	P-value
Age	−0.08 (−0.30 to 0.14)	0.48	−0.01 (−0.04 to 0.03)	0.75
BMI	0.72 (−0.28 to 1.71)	0.15	−0.05 (−0.11 to 0.21)	0.53
Parity	−0.33 (−1.62 to 0.97)	0.61	−0.08 (−0.14 to 1.29)	0.48
Incontinence	0.21 (−3.25 to 3.67)	0.90	−0.45 (−0.12 to 0.09)	0.11
Oxford score	4.77 (2.86 to 6.68)	< 0.001	1.15 (0.76 to 1.55)	< 0.001

^aNatural logarithm transformed to hold the regression assumptions

Discussion

Traditionally, a vaginal examination has been used to assess the functional state of PFMs; however, the subjective nature of this method necessitated the development of a quantitative method for the precise evaluation of pelvic floor function. Although various modalities, such as magnetic resonance imaging or 3D/4D ultrasonography, have now been developed to accurately evaluate the pelvic floor’s muscular morphology and function, the unavailability and expense of these modalities have prompted clinicians to utilise cost-effective tools that are readily available. Using 2D ultrasonography as an available and affordable tool facilitated the evaluation of PFMs; however, the diagnostic accuracy of this method compared to physical examination remains unknown. The current study found that intravaginal palpation and 2D transperineal ultrasonography had moderate concordance in assessing levator ani hiatal dimension, cranial shift, and levator activity index during rest and squeezing manoeuvre. However, levator hiatus area and thickness can only be measured with a 3D/4D probe and not with 2D ultrasonography. The diagnostic performance of 2D ultrasonography has been compared to other imaging modalities to assess pelvic floor dysfunction in terms of urinary, sexual, or defecatory dysfunction. The accuracy of 3D/4D versus 2D ultrasonography was compared by van Gruting et al. [11], who found that the former method was not superior. Similar to our findings, Albrich et al. [12] demonstrated a significant correlation between subjective digital assessment of PFM strength and 2D and 3D ultrasound parameters as an objective diagnostic tool, whereas Lone et al. [12] demonstrated that the accuracy of pelvic floor ultrasound staging is limited and that clinical assessment is still the gold standard for assessing pelvic organ prolapse in women. The pelvic floor ultrasound images of a 50-year-old woman with urinary incontinence are displayed in Fig. 5. As demonstrated in Fig. 5, the anteroposterior diameter of the urogenital hiatus decreased by approximately 17 mm (from 69 to 52 mm) during the squeezing manoeuvre, while the caudal shift of the bladder neck increased by approximately 1.3 mm (from 17.5 to 18.8 mm). During maximal straining, the AP diameter of the levator hiatus increased by approximately 4 mm (from 69 to 73 mm), accompanied by a caudal shift of the bladder neck of approximately −29.2 mm and the development of a cystocele; these findings are suggestive of severe pelvic floor dysfunction, as predicted by clinical examination. Overall, our observations revealed a correlation between 2D ultrasound results and physical examinations, and it is a cost-effective tool that can be used in conjunction with a physical examination. Especially in patients with pelvic floor dysfunction who are treated non-surgically (e.g., pelvic floor physiotherapy), ultrasound with quantitative parameters such as the Levator Ani Index (LAI) can be used as an objective tool for a more accurate assessment of treatment response. Clearly, additional research on a larger patient population is required to better standardise quantitative measures for defining the presence and severity of pelvic floor dysfunction.

Conclusion

Pelvic floor ultrasound employing objective measures such as the LAI is a low-cost, widely accessible diagnostic tool that can provide quantitative measures for pelvic floor muscular function assessment in non-surgically treated patients and correlate with a subjective physical examination.

Abbreviations

PFM

Pelvic floor muscles

SD

Standard deviation

LAI

Levator Ani Index

BMI

Body mass index

OPES

Oxford Physical Examination Score

Author contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by AA, ZG, SR, MA-A, SNMY. The first draft of the manuscript was written by SR and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data availability

Related data is available from corresponding author upon reasonable demand.

Declarations

Conflict of interest

The authors declare that there is no conflict of interest.

Ethical statements

The study was approved by institutional ethics committee and all the patients signed an informed written consent before their participation.

Consent to publish

The authors affirm that research participants provided informed consent for publication of the images in Figs. 2 and 3.