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International Urogynecology Journal

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01-09-2014 | Original Article

Comparison of muscle fiber directions between different levator ani muscle subdivisions: in vivo MRI measurements in women

Authors: Cornelia Betschart, Jinyong Kim, Janis M. Miller, James A. Ashton-Miller, John O. L. DeLancey

Published in: International Urogynecology Journal | Issue 9/2014

Abstract

Introduction and hypothesis

This study describes a technique to quantify muscle fascicle directions in the levator ani (LA) and tests the null hypothesis that the in vivo fascicle directions for each LA subdivision subtend the same parasagittal angle relative to a horizontal reference axis.

Methods

Visible muscle fascicle direction in the each of the three LA muscle subdivisions, the pubovisceral (PVM; synonymous with pubococcygeal), puborectal (PRM), and iliococcygeal (ICM) muscles, as well as the external anal sphincter (EAS), were measured on 3-T sagittal MRI images in a convenience sample of 14 healthy women in whom muscle fascicles were visible. Mean ± standard deviation (SD) angle values relative to the horizontal were calculated for each muscle subdivision. Repeated measures ANOVA and post-hoc paired t tests were used to compare muscle groups.

Results

Pubovisceral muscle fiber inclination was 41 ± 8.0°, PRM was −19 ± 10.1°, ICM was 33 ± 8.8°, and EAS was −43 ± 6.4°. These fascicle directions were statistically different (p < 0.001). Pairwise comparisons among levator subdivisions showed angle differences of 60° between PVM and PRM, and 52° between ICM and PRM. An 84° difference existed between PVM and EAS. The smallest angle difference between levator divisions was between PVM and ICM 8°. The difference between PRM and EAS was 24°. All pairwise comparisons were significant (p < 0.001).

Conclusions

The null hypothesis that muscle fascicle inclinations are similar in the three subdivisions of the levator ani and the external anal sphincter was rejected. The largest difference in levator subdivision inclination, 60°, was found between the PVM and PRM.

In the rest of this paper we use the term muscle “fiber” instead of muscle fascicle because the term muscle “fiber” is more commonly used in the clinical literature. Given the assumption that the direction of the fiber is collinear with its fascicle as visualized on MRI this seems acceptable.

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Title: Comparison of muscle fiber directions between different levator ani muscle subdivisions: in vivo MRI measurements in women
Authors: Cornelia Betschart
Jinyong Kim
Janis M. Miller
James A. Ashton-Miller
John O. L. DeLancey
Publication date: 01-09-2014
Publisher: Springer London
Published in: International Urogynecology Journal / Issue 9/2014
Print ISSN: 0937-3462
Electronic ISSN: 1433-3023
DOI: https://doi.org/10.1007/s00192-014-2395-9

At a glance: The ONWARDS insulin icodec trials

Springer Medicine

Comparison of muscle fiber directions between different levator ani muscle subdivisions: in vivo MRI measurements in women

Abstract

Introduction and hypothesis

Methods

Results

Conclusions

At a glance: The ONWARDS insulin icodec trials

Springer Medicine

Abstract

Introduction and hypothesis

Methods

Results

Conclusions

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