Alterations in pelvic floor muscle (PFM) tone play a key role in the pathophysiology of various pelvic floor disorders, such as incontinence and vulvodynia. While various methods exist for evaluating PFM tone [1] digital palpation remains widely used in clinical practice as it is inexpensive, readily available, quick, and easy to perform. However, its clinimetric properties are not well supported empirically, with limited evidence available to substantiate its validity and sensitivity. No study has yet investigated a large number of participants with different PFM tone levels and compared subjective digital palpation measures with more validated, objective in vivo measurements. To address this gap in knowledge, this original study aimed to assess the validity of digital palpation in evaluating PFM tone using the Reissing scale by: (1) examining the association between palpation scores and both dynamometry and ultrasound imaging, and (2) determining whether the scale's levels can be distinguished using dynamometry and ultrasound imaging.

The cross-sectional data used for this study were derived from two large multicenter randomized controlled trials, which included nulliparous women with provoked vestibulodynia (PVD) and postpartum women with stress or mixed urinary incontinence (UI). PFM tone was evaluated via digital palpation at the 6 o'clock position (toward the posterior fourchette) using the Reissing scale, ranging from -3 (no resistance) to +3 (very firm resistance). Dynamometry evaluation included assessment of passive PFM forces at a 15 mm vaginal aperture and flexibility, defined as the distance between the device's branches at the maximal tolerated vaginal aperture. Transperineal 3D/4D ultrasound imaging was used to measure the levator hiatus area and anteroposterior diameter at rest.

The study sample included 528 women aged 18-45: 209 (40%) with PVD and 319 (60%) with UI. They were assessed by 34 physiotherapists with <1 to 31 years of experience (median 3.5 years). The Reissing scale scores ranged from – 3 to +3. All ultrasound and dynamometric measurements were significantly correlated with the Reissing scale (Spearman’s rank correlation coefficient absolute values rs=0.28 to rs=0.53; p<0.05). Since only one participant received a score of -3, this data was excluded from the subsequent analyses comparing dynamometry and ultrasound imaging across different palpation scores, as statistical comparisons could not be performed for a single-value group. A Kruskal-Wallis test indicated that all ultrasound and dynamometry measurements significantly differed across palpation score levels (p<0.05, η2 0.08-0.28 indicating medium to large effect sizes). For dynamometry, there was a significant difference in passive forces between the palpation scores: 3-1; 3-0; 3-(-1); 3-(-2); 2-0; 2-(-1); 2-(-2); and in flexibility between the scores: 3-2; 3-1; 3-0; 3-(-1); 3-(-2); 2-0; 2-(-1); 2-(-2); 1-0; 1-(-2) (post hoc p<0.05). In ultrasound evaluation of the levator hiatus area, a significant difference was observed for most palpation scores, except for 3 vs 2; 0-(-2); and (-1)-(-2) (post hoc p>0.05). For levator hiatus anteroposterior diameter, significant difference was obtained for the following Reissing scores: 3-1; 3-0; 3-(-1); 3-(-2); 2-1, 2-0; 2-(-1); 2-(-2); 1-(-1); 1-(-2) (post hoc p<0.05).

The findings of this study showed that PFM tone assessed with digital palpation was significantly associated with more objective tools, such as dynamometry and ultrasound imaging. While physiotherapists could discriminate between several levels of the palpation scale, the ability to distinguish between adjacent scale levels was lower, particularly at the negative scores of the scale (decreased tone scores).

Digital palpation may serve as a valid tool for providing an approximate assessment of PFM tone and can be useful in clinical practice. However, it lacks the sensitivity to detect small differences in PFM tone and may not be suitable for assessing treatment effects or for research purposes.

Worman R, Stafford RE, Cowley D, Hodges PW. Methods used to investigate tone of pelvic floor muscles in pelvic health conditions: A systematic review. Continence. 2023/06/01/ 2023;6:100593.