Biomedical Engineering Reference
In-Depth Information
Effects of Levator Ani Muscle Morphology
on the Mechanics of Vaginal Childbirth
Xiani Yan, Jennifer A. Kruger, Martyn P. Nash, and Poul M.F. Nielsen
Abstract Childbirth-induced trauma is one of the leading factors that cause pelvic
floor (PF) muscle dysfunction. There is preliminary evidence to suggest that the
morphology of the levator ani (LA) muscles influences the progress of the second
stage of labour. Three-dimensional modelling of the LA muscle shape variations
can help to identify structures that are potentially susceptible to labour-induced
injuries. The first aim of this study was to use finite element modelling to study the
geometrical variations of the normal PF muscles, using sets of magnetic resonance
images from 12 normal nulliparous women. The effects of PF muscle shape
variation on the mechanics of vaginal childbirth was then investigated using
biomechanics simulations. During construction of the individual-specific PF
models, point-to-point correspondence of anatomical features was achieved
through a series of mathematical transformations. A principal component analysis
(PCA) method was applied to the fitted PF models to compute the PF shape
variations. The results were then used to construct the mean PF shape, plus four
further PF models derived from the mean model and the first two primary modes of
variation. These PCA-derived models were analysed using a biomechanical frame-
work of the second stage of labour. The maximum principal stretch ratios and the
forces required for delivery of a foetal head were quantified and analysed with
respect to the geometry of each derived mode, to extract features of the PF muscles
that are potentially susceptible to childbirth-induced injuries. The statistical shape
analysis approach presented here may be extended to extract patterns of PF muscle
morphological changes that are involved in PF dysfunction.
X. Yan ( * ) • J.A. Kruger
Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand
e-mail: xyan075@aucklanduni.ac.nz ; j.kruger@auckland.ac.nz
M.P. Nash • P.M.F. Nielsen
Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand
Department of Engineering Science, The University of Auckland, Auckland, New Zealand
e-mail: martyn.nash@auckland.ac.nz ; p.nielsen@auckland.ac.nz
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