Biomedical Engineering Reference
In-Depth Information
1
Introduction
The levator ani (LA) muscles, subdivided into the iliococcygues, pubococcygeus,
and puborectalis, form a dome-shaped muscular sheet that partially seals the pelvic
floor (PF), helps with pelvic organ support and plays a role in the second stage of
labour [
1
,
2
]. Childbirth-induced injuries to the LA muscles are considered as one
of the factors leading to PF muscle dysfunction, potentially causing pelvic organ
prolapse and stress incontinence [
3
-
5
]. Several imaging studies have demonstrated
that the damage to the LA muscle during vaginal birth occurs at the muscle/bone
interface, which manifests as a complete or partial detachment of the LA muscles
from the lateral pubic bones [
5
-
7
]. This type of damage, frequently referred to as an
avulsion injury, has been demonstrated in over 50% of women presenting with
significant pelvic organ prolapse [
8
]. Previous research has also shown that approx-
imately 10% of women who suffer from pelvic organ prolapse require surgical
correction [
9
]. The mechanism of the second stage of labour and its related
complications, including a reduction in the LA contractility and development of
stress incontinence, have been investigated by means of medical imaging and
biomechanical simulations; however, the injury mechanism of the vaginal delivery
still remains incompletely understood [
3
,
10
,
11
].
In light of this, a detailed three-dimensional representation of the LA muscle is
necessary to understand the effects of morphological variations on the mechanics
of vaginal delivery. The LA muscle shapes that are potentially more susceptible to
childbirth-induced trauma can be determined by analysing the LA muscle
response to vaginal delivery using a childbirth biomechanical simulation
framework.
Ultrasound and magnetic resonance imaging (MRI) are the two most commonly
used imaging modalities in diagnosing and researching the PF anatomy and physiol-
ogy [
3
,
12
]. Kruger et al. [
13
,
14
] utilised these imaging modalities to demonstrate
LA muscle hypertrophy in women involved in high-impact sport. This change
in the muscle morphology may be associated with complications during vaginal
delivery. However, the morphological parameters used to quantify LA muscle
geometry in those studies were likely to have been dependent upon the selection of
two-dimensional imaging planes. Furthermore, the scalar measurements were not
able to comprehensively describe the complex variations in LA muscle morphology
across the subjects. Singh et al. [
15
] have conducted a statistical analysis of the LA
muscle anatomy usingMRI in normal subjects and patients with prolapse, illustrating
variations in shape and orientation of the iliococcygeus among individuals. How-
ever, their measurements were based on qualitative observations and the authors did
not use computational models of the two populations. Lee et al. [
16
] also carried out a
statistical shape modelling study of the LA muscles in normal nulliparous women
and created an “optimised model” that represented the average morphology of the
LA in normal subjects. However, point-to-point correspondence of anatomical
features was not considered in this study, which brings into question the reliability
and applicability of the results.
