Determining the displacement of the pelvic floor and pelvic organs during voluntary contractions using magnetic resonance imaging in younger and older women.

OBJECTIVES: To: (i) visualize the effect of sustained voluntary contractions on the anatomical configuration of the pelvic floor (PF) muscles using magnetic resonance imaging (MRI); (ii) examine the effect of ageing on the range of displacement of the PF contents secondary to contraction and simulating incontinence exercises; and (iii) introduce the concept of contractile change in volume (DeltaPF-V) using three-dimensional (3D) reconstruction from axial, sagittal and coronal MRI. SUBJECTS AND METHODS: Two groups of continent women volunteers, familiar with correct PF contraction, were evaluated. The mean (sd) age in group I was 34 (6) years and that of group II 55 (9) years; the mean parities were 0.7 and 2.2, respectively. MRI was conducted with the women supine and data were obtained in the axial, sagittal and coronal planes. In each plane, images were obtained with the PF relaxed and subsequently with the PF contracted over 10-20 s. Image processing was used to enhance the anatomical boundaries of the pelvic organs and to measure the displacement produced by the contraction. Displacements, observed between each image pair, were colour-coded to highlight the geometric differences between a relaxed and contracted PF and to facilitate measuring displacement. Data measured from each group were pooled and the range of motion expressed as the mean (sd), compared using Student's t-test.
RESULTS: Digitally processed imaging allowed an accurate comparison between the relaxed and contracted PF, and highlighted the differences between them. From these views, the levator ani displaced the vagina asymmetrically in nine of the 11 older subjects, and in six of the 17 younger subjects. The values from the imaging in the sagittal and coronal plane for the two groups were: levator ani displacement, 7.4 (1.1) and 1.4 (0.2) cm (P < 0.002), superior bladder wall, 4.2 (0.5) and 1.0 (0.1) cm (P < 0.002). There were also significant differences in the range of displacement produced by voluntary PF contraction in the internal structures; external outlines did not reflect these changes. The maximum displacement of the gluteal surface in the coronal plane did not change significantly; in group I it was 3.9 (1.8) to 2.9 (0.7) cm. From the 3D re-construction, DeltaPF-V for the younger women was significantly larger, at 23.3 (3.9) mL (P < 0.01) than in the older women, at 9.1 (4.4) mL. CONCLUCION: The range of motion over which voluntary PF contractions displace the bladder and vagina is age-dependent, being higher in younger than in older subjects. It remains to be established whether range of movement is a limitation caused by neuronal factors, decrease in muscle strength/mass, or the substitution of spaces with fat (restricting free movement), or other factors.