Intra-rater reliability and diagnostic accuracy of a new vaginal dynamometer to measure pelvic floor muscle strength in women with urinary incontinence

Abstract

The first choice treatment in urinary incontinence (UI) is rehabilitation of the pelvic floor in order to improve muscle strength. However, no entirely reliable instruments for quantifying pelvic floor muscle (PFM) strength are currently available. Our aim was to test the intra-rater reliability and diagnostic accuracy of a new vaginal dynamometer for measuring PFM strength. Methods: Test-retest reliability study. One hundred and four women with stress urinary incontinence (SUI) were recruited. Patients were excluded if they had a history consistent with urge urinary incontinence or pelvic organ prolapse, pregnancy, previous urogynecological surgery, severe vaginal atrophy, or neurological conditions. The examination comprised digital palpation quantified by the modified Oxford scale and by two consecutive dynamometry measurements obtained using a new prototype dynamometer. This instrument comprises a speculum in which an inductive displacement sensor LVDTSM210.10.2.KTmodel, Schreiber) is attached to a spring of known stiffness constant (k). The intraclass correlation coefficient (ICC) was calculated to assess intra-rater reliability. Diagnostic accuracy was assessed using Receiver Operating Characteristics (ROC) curves analysis. Results: Of the 104 subjects included, 59.6% presented scores between 0–2 on the Oxford scale. Intra-rater reliability was 0.98 (95%CI: 0.97– 0.99). In the Bland & Altman plot, the distribution of disagreements was similar in the lowest and the highest strength values. The diagnostic accuracy of the dynamometer with regard to digital palpation showed an area under the curve of 0.85 (95%CI: 0.77–0.93). Conclusions: Our results suggest that this new vaginal dynamometer is a reliable and valid instrument for quantifying PFM strength.