A cross-sectional study was designed in which patients serve as their own control by measuring the same variable using four different techniques. The study was approved by the ethics committee of the centre. Accepting an alpha risk of 0.05 and a beta risk below 0.1 in a one-sided test, 34 subjects are needed to detect a difference equal to or greater than 0.25 units. A follow-up loss rate of 10% has been estimated. Measurements were carried out by three independent investigators: a gynaecologist for digital evaluation, a physiotherapist for perineal tonometry, and another gynaecologist for 2D and 3D ultrasound assessment.
Volunteers with pelvic floor dysfunctions from pelvic floor clinics, as well as healthy volunteers, were included. During the first visit, the purpose and procedure of the study was explained, informed consent was obtained, and demographic data were collected. Volunteers were then scheduled for an appointment in a designated consultation room. All measurements were performed with the patient in the lithotomy position and with empty bladder.
First, digital evaluation of pelvic floor muscle contractility was performed using the modified Oxford scale. The gynaecologist inserted two fingers into the vagina, exerting slight pressure on the posterior vaginal wall, and asked the patient to perform a maximum contraction of the pelvic floor muscles. The procedure was performed three times, and the average score of the three attempts was calculated. Subsequently, the physiotherapist performed perineal tonometry of the pelvic floor muscles using a Phoenix tonometer (DPM®). Contractility was measured while maintaining for at least 5 seconds with the speculum open at 5° and 10°. This was repeated three times, and the average of the three maximum contractility values in g/cm2 was calculated. Finally, contractility was assessed using 2D and 3-4D ultrasound by another gynaecologist. A Voluson S10 ultrasound machine with a 4-8 MHz curved 3D/4D transabdominal probe, with a capture angle of 85° (GE Medical Systems, Zipf, Austria), was used. Both 2D and 3D assessments were performed by transperineal approach. The 2D measurement were performed in the mid-sagittal plane, obtaining the plane of minimal dimensions. The distance from the edge of the pubic symphysis to the internal point of the lowest area of the levator ani muscle at the anorectal angle was measured both at rest and on contraction. Muscle strength was calculated as a percentage using the formula: ((Rest Distance - Contraction Distance) / Rest Distance) x 100. The percentage of movement of the bladder neck on maximum contraction was also calculated. Finally, muscle strength was estimated by 3-4D ultrasound. An axial view of the levator hiatus was obtained in the plane of minimal dimensions. Hiatus area at rest and on maximum contraction was measured in rendered volume. The same formula as in the 2D technique was used. Additionally, it was assessed whether there were complete or partial defects of the fascicles of the levator ani muscle, as well as the area of the levator hiatus on maximum Valsalva manoeuvre.
Both measurements and clinical data of the patients were blinded to the three investigators conducting the tests.
Volunteers were invited to fill out a questionnaire about the degree of comfort, duration, and tolerance of each test (Figure 1).
Statistical analysis was performed using R software (version 4.3.1). Mean, standard deviation, minimum value, and maximum value were calculated for each variable. To measure test agreement, the percentage value was compared with the Pearson correlation coefficient being calculated for continuous quantitative variables with normal distribution, and the Spearman correlation coefficient for the Oxford scale, which is ordinal qualitative. A statistically significant value was accepted when p < 0.05. We also analyzed the correlation between tests within the subgroups: injury of the levator ani muscle, obesity, and presence of pelvic floor disorder.