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

Abstract

To assess the validity of digital palpation in evaluating pelvic floor muscle (PFM) tone by: (1) examining the association between palpation scale and both dynamometry and ultrasound imaging measures, and (2) determining whether the palpation scale levels can be distinguished when compared with dynamometry and ultrasound imaging measures. Cross-sectional validation study. Two research laboratories. Women aged 18-45 (n=528) with provoked vestibulodynia (n=209) and urinary incontinence (n=319). Not applicable. Digital palpation, dynamometry and transperineal 3D/4D ultrasound imaging. PFM tone was evaluated by 34 physiotherapists via vaginal digital palpation at the 6 o'clock position using the Reissing scale, ranging from -3 (no resistance) to +3 (very firm resistance). Dynamometry evaluation included assessment of passive forces and passive elastic stiffness (vaginal aperture of 15 mm), as well as flexibility (distance between the dynamometric speculum branches at the maximal tolerated aperture). Transperineal ultrasound imaging was used to measure the levator hiatus area and anteroposterior diameter at rest. All dynamometric and ultrasound measurements were significantly correlated with the Reissing scale (Spearman's rank correlation |r_s|=0.28-0.53; p<0.05). A Kruskal-Wallis test indicated that all dynamometry and ultrasound measurements significantly differed across palpation score levels (p<0.05, η² 0.08-0.28, medium to large effect sizes). While physiotherapists could discriminate between several levels of palpation scale, the ability to distinguish between adjacent scale levels was lower, particularly for the negative scores of the scale (decreased tone scores). PFM tone assessed with digital palpation using the Reissing scale is associated with objective measurements using dynamometry and ultrasound imaging. Digital palpation may serve as a valid tool for providing an estimated assessment of PFM tone in clinical practice. However, the considerable variability and overlap in values across palpation scores highlight some limitations, hindering precise assessment and limiting its suitability for research purposes.