Measurement of the pubic portion of the levator ani muscle in women with unilateral defects in 3-D models from MR images.
OBJECTIVE
Develop a method to quantify the cross-sectional area of the pubic portion of the levator ani muscle, validate the method in women with unilateral muscle defects, and report preliminary findings in those women.


METHODS
Multi-planar proton density magnetic resonance images of 12 women with a unilateral defect in the pubic portion of their levator ani were selected from a larger study of levator ani muscle anatomy in women with and without genital prolapse. Three-dimensional bilateral models of the levator ani were reconstructed (using 3-D Slicer, version 2.1b1) and divided into iliococcygeal and pubic portions. Muscle cross-sectional areas were calculated at four equally spaced locations perpendicular to a line drawn from the pubic origin to the visceral insertion using the I-DEAS computer modeling software.


RESULTS
The cross-sectional area of the muscle on the side with the defect was smaller than the normal side at all the four locations. The average bilateral difference was up to 81% at location 1 (nearest pubic origin). Almost all of the volume difference (13.7%, P=0.0004) was attributable to a reduction in the pubic portion (24.6%, P<0.0001), not the iliococcygeal portion (P=0.64), of the muscle.


CONCLUSIONS
A method was developed to quantify cross-sectional area of the pubic portion of the levator ani perpendicular to the intact muscle direction. Significant bilateral cross-sectional area differences were found between intact and defective muscles in women with a unilateral defect.
Chen
L
L
Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48109-2125, USA. luyunc@umich.edu
Hsu
Y
Y
Ashton-Miller
J A
JA
DeLancey
J O L
JO
D016022:Case-Control Studies; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D009130:Muscle, Smooth / Q000473:pathology*; D017773:Pelvic Floor / Q000473:pathology*; D011237:Predictive Value of Tests; D011336:Probability; D011630:Pubic Bone / Q000473:pathology*; D012016:Reference Values; D012307:Risk Factors; D012494:Sampling Studies; D012680:Sensitivity and Specificity