Transperineal ultrasound versus digital palpation: Identifying key parameters for objective pelvic floor muscle contraction assessment.

Abstract

Introduction: The assessment of pelvic floor muscle function is crucial for managing pelvic floor dysfunctions, yet digital palpation is subjective and lacks reproducibility. This study aimed to correlate pelvic floor muscle contractility assessed by digital palpation with transperineal ultrasound measurements and evaluate the reliability of the Modified Oxford Scale and key ultrasound-derived parameters. By comparing these methods, the study sought to establish transperineal ultrasound as a reliable, objective, and non-invasive tool for assessing pelvic floor muscle contractility.

Material and methods: A cross-sectional study was conducted at Shengli Provincial Hospital from November 2019 to July 2024. 442 of 512 screened women were included. Digital palpation was performed by two independent clinicians, and ultrasound measurements were conducted by two separate raters. Ultrasound raters were blinded to palpation (Modified Oxford Scale) findings. Transperineal ultrasound quantified multiple pelvic floor parameters, including proximal urethral axis angle change (maximal contraction-rest) and levator hiatus area. Inter-rater reliability was assessed using intraclass correlation coefficients for ultrasound measures and Cohen's kappa for MOS ratings. Correlations between ultrasound and palpation scores were analyzed using Spearman's rank. Cut-off values for key ultrasound parameters corresponding to palpation grades were determined via receiver operating characteristic curve analysis.

Results: Significant correlations (p < 0.001) were found between ultrasound parameters and MOS scores, with the strongest correlations observed for proximal urethral axis angle change (maximal contraction-rest) (r_s = 0.727) and proportional change in levator hiatus area (r_s = 0.717). Ultrasound assessments showed high inter-rater reliability (intraclass correlation coefficient = 0.92 for proximal urethral axis angle change), while palpation demonstrated moderate agreement (Cohen's kappa = 0.55). Cut-off values for key parameters were derived, such as proximal urethral axis angle change <9.5° for absent contraction and >16.5° for strong contraction.

Conclusions: Transperineal ultrasound demonstrated high reliability and provided an objective, non-invasive method for assessing pelvic floor muscle contractility. While digital palpation assessed functional strength, ultrasound visualized structural displacement during contraction. The two methods addressed complementary aspects of pelvic floor function, and their combined use enhanced clinical assessment.