Measurement of the pubic portion of the levator ani muscle in women with unilateral defects in 3â D models from MR images

Abstract

ObjectiveDevelop a method to quantify the crossâ 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.MethodMultiâ 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. Threeâ dimensional bilateral models of the levator ani were reconstructed (using 3â D Slicer, version 2.1b1) and divided into iliococcygeal and pubic portions. Muscle crossâ sectional areas were calculated at four equally spaced locations perpendicular to a line drawn from the pubic origin to the visceral insertion using the Iâ DEAS® computer modeling software.ResultsThe crossâ 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.ConclusionsA method was developed to quantify crossâ sectional area of the pubic portion of the levator ani perpendicular to the intact muscle direction. Significant bilateral crossâ sectional area differences were found between intact and defective muscles in women with a unilateral defect.