Can we rely on palpation to assess pelvic floor muscle tone? A validity study comparing palpation to ultrasound and dynamometry.

The 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 transperineal ultrasound imaging as well as dynamometry; 2) evaluating whether the levels of the scale can be discriminated against ultrasound imaging and dynamometry. 

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

The study sample included 529 women assessed by 34 physiotherapists with 0 to 31 years of experience (median 3.5 years). The Reissing scale scores ranged from -2 to +3. All ultrasound and dynamometric measurements were significantly correlated with the Reissing scale (Spearman’s rank correlation coefficient absolute value r_s=0.28 to r_s=0.53; p0.05). A Kruskal-Wallis test indicated that all ultrasound and dynamometry measurements significantly differed across palpation score levels (p0.05). 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 p0.05). 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 p0.05). 

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. Palpation may serve as a valid tool for providing an approximate assessment of PFM tone. While physiotherapists could discriminate between several levels of palpation, the ability to distinguish between adjacent scale levels was lower, particularly at the bottom of the scale. 

Digital palpation 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.