Vaginal palpation of pelvic floor muscle strength: inter-test reproducibility and comparison between palpation and vaginal squeeze pressure

Background. Vaginal palpation is commonly used in clinical practice to teach and evaluate pelvic floor muscle strength, and several grading systems have been developed. The aim of the present study was to test inter-rater reproducibility of the modified Oxford grading system and compare results from vaginal palpation with squeeze pressure measurement. Methods. Twenty female physical therapy students, mean age 25.1 years (range 21-38) participated in the study. Two experienced physical therapists conducted the palpation test in random order. Muscle strength was classified according to a 6-point scale (modified Oxford grading system). Results from the palpation test were compared with measurement of vaginal squeeze pressure using a vaginal balloon connected to a fiberoptic microtransducer (Camtech AS, Sandvika, Norway). To ensure validity of pressure measurement only contractions with simultaneous observation of inward movement of the perineum were registered. Results. The inter-rater reliability for vaginal palpation was 0.70 measured by Spearman's rho (p<0.01). Cohen's Kappa was <kappa>=0.37 (SEM 0.16). There was agreement between the physical therapists in nine subjects (45%). In all but one subject the disagreement was one category. Mean maximal strength for the group was 19.7 cm H2O (95% CI: 16.5-22.9). There were no differences between weak, moderate, good and strong muscle contraction classified by palpation test when comparing results from the vaginal squeeze pressure (p=0.66). Conclusions. Vaginal palpation is mandatory when teaching correct pelvic floor muscle contraction. However, the present results indicate that the method is not reproducible, sensitive and valid to measure PFM strength for scientific purposes.