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Quantification of Levator Ani Cross-Sectional Area Differences Between Women With and Those Without Prolapse

Hsu, Yvonne MD; Chen, Luyun MS; Huebner, Markus MD; Ashton-Miller, James A. PhD; DeLancey, John O.L. MD

doi: 10.1097/01.AOG.0000233153.75175.34
Original Research

OBJECTIVE: Compare levator ani cross-sectional area as a function of prolapse and muscle defect status.

METHODS: Thirty women with prolapse and 30 women with normal pelvic support were selected from an ongoing case-control study of prolapse. For each of the two groups, 10 women were selected from three categories of levator defect severity: none, minor, and major identified on supine magnetic resonance scans. Using those scans, three-dimensional (3D) models of the levator ani muscles were made using a modeling program (3D Slicer), and cross-sections of the pubic portion were calculated perpendicular to the muscle fiber direction using another program, I-DEAS. An analysis of variance was performed.

RESULTS: The ventral component of the levator muscle of women with major defects had a 36% smaller cross-sectional area, and women with minor defects had a 29% smaller cross-sectional area compared with the women with no defects (P<.001). In the dorsal component, there were significant differences in cross-sectional area according to defect status (P=.03); women with major levator defects had the largest cross-sectional area compared with the other defect groups. For each defect severity category (none, minor, major), there were no significant differences in cross-sectional area between women with and those without prolapse.

CONCLUSION: Women with visible levator ani defects on magnetic resonance imaging had significantly smaller cross-sectional areas in the ventral component of the pubic portion of the muscle compared with women with intact muscles. Women with major levator ani defects had larger cross-sectional areas in the dorsal component than women with minor or no defects.


Major levator ani defects resulted in smaller muscles in the ventral portion but larger muscles in the dorsal portion independent of pelvic support status.

From the University of Michigan, Ann Arbor, Michigan.

This study was sponsored by the National Institute of Child Health and Human Development (RO1 HD-38665) and the German Research Foundation (DFG, HU1502/1-1).

Corresponding author: Yvonne Hsu, 1500 East Medical Center Drive, Women's Hospital L4000, Ann Arbor, MI 48109-0276; e-mail:

© 2006 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.