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Female Pelvic Anatomy
• The hip bone is originally made up of
three bones that have fused: 1)ilium,
2)ischium and 3)pubis. These come
together at the acetabulum.
• The pelvic brim extends from
promontory of the sacrum, arcuate
line of the ilium, pectineal line and
pubic crest. Some people divide the
pelvis into a greater (or false) pelvis
and lesser (or true) pelvis.
• No muscle crosses the pelvic brim. If
they did, they would be in the way
during childbirth.
Ligaments of the Pelvis
The sacrotuberous and sacrospinous ligaments
complete the greater and lesser sciatic foraminae
The inlet to this canal is at the level of the sacral
promontory and superior aspect of the pubic bones.
The outlet is formed by the pubic arch, ischial
spines, sacrotuberous ligaments and the coccyx.
The ideal or gynaecoid pelvis is recognised
by its well-rounded oval inlet and similarly
uncluttered outlet
The inlet has its longest dimension from
side to side, whereas at the outlet the
longest dimension is anteroposteriorly
The upper sacrum is stabilised by the
illiolumbar ligaments via its attachment
to the fourth and fifth lumbar vertebra
and
the
lower
sacrum
by
the
sacrospinous
and
sacrotuberous
ligaments attachments to the posterior
iliac spines and ischial tuberosities.
During pregnancy, the elevated
levels of oestrogen, progesterone
and relaxin play a major role in
increasing the laxity of the pelvic
girdle joints. The hormonal levels do
return to normal in the weeks
following childbirth, but the time
taken will also be affected by
breastfeeding. By 3 to 6 months
postnatal, the pelvic girdle should
return to its prepregnant state; it
may need external stabilisation
during this period.
An increase has been found in the
width of the symphysis pubis from 4
mm to 9 mm in asymptomatic women
on X-ray . The separation of less than
1cm should be considered normal, a
greater separation being considered
a partial or complete rupture; this
may be up to 12 cm. resulting in
tension and pain at the sacroiliac
joints or symphysis pubis, or both.
in the full squatting position; it
has been estimated that the
area of the outlet can be
increased by as much as 28% in
this way . In squatting, the
femora apply pressure to the
ischial and pubic rami, thus
producing separation outward at
the symphysis pubis and an
upward and backward rotation
of the sacrum.
THE PELVIC FLOOR AND
MUSCLES OF THE PELVIS
The puborectalis is actually a part of the
pubococcygeus
muscle
that
wraps
around the posterior aspect of the rectum
forming a sling that holds the rectum
forward in the pelvis.
The pubococcygeus and iliococcygeus
muscles make up the levator ani. The
muscles of the levator ani are important
supportive muscles for the midline organs
of the pelvis. Any weakness in these
muscles can cause clinical problems of
urinary or fecal incontinence.
The levator ani muscles otherwise known as the
pelvic
diaphragm
or
pubovisceralis
(pubococcygeus)
and
iliococcygeus,
are
composed of striated muscle fibre. They are
covered by fascia on their superior and inferior
aspects. The anterior midline cleft in the
muscles is known as the urogenital hiatus,
through
which
the
urethra,
vagina
and
anorectum pass.
The perineal membrane is sometimes called the
urogenital diaphragm, or the triangular ligament.
It lies inferior to the levator ani and attaches the
edges of the vagina to the ischiopubic ramus,
provides lateral attachments for the perineal
body and assists in the support of the urethra. It
is suggested that it has a greater supportive
function when the levator ani muscles are
relaxed.
levator ani is considered as several separate
muscle parts:
•pubovaginalis
•coccygeus
•iliococcygeus
•pubococcygeus
•Puborectalis
origin:
from a tendinous arch between the pubis and
ischial spine on the internal surface of the pelvis
insertion:
perineal body
external wall of anal canal
anococcygeal ligament
coccyx
Pubovaginalis
originate from the posterior pelvic surface of the body of the pubis
bone. Fibres pass inferiorly, medially and posteriorly.
inserts into the central perineal tendon posterior to the vagina.
The levator ani muscle
seen from above looking
over
the
sacral
promontory
(SAC)
showing the pubovaginal
muscle
(PVM).
The
urethra,
vagina,
and
rectum
have
been
transected just above
the pelvic floor. PAM =
puboanal muscle; ATLA =
arcus tendineus levator
ani;
and
ICM
=
iliococcygeal muscle
The arcus tendineus
levator ani (ATLA);
external
anal
sphincter
(EAS);
puboanal
muscle
(PAM); perineal body
(PB) uniting the 2
ends
of
the
puboperineal muscle
(PPM); iliococcygeal
muscle
(ICM);
puborectal
muscle
(PRM).
The arcus tendineus fascia of the pelvis (ATFP) is a linear
fascial thickening of the obturator fascia attached anteriorly to
the pubic bone and posteriorly to the ischial spine and is
believed to be of great importance in the continence mechanism
levator ani Muscle showed that it was made up of large
diameter type I (slow twitch) and type II (fast twitch)
striated muscle fibres, with muscle spindles observed.
Muscle activity may be recorded by electromyograph (EMG)
from the levator ani muscle ‘at rest’ and even in sleep;
presumably the type I fibres are responsible for this. By
contrast, type II fibres are highly fatiguable but produce a
high order of power on contraction.
All these facts support the contention that the levator ani
muscle is a skeletal muscle adapted to maintain tone over
prolonged periods and equipped to resist sudden rises in
intra-abdominal pressure, as for example on coughing,
sneezing, lifting or running.
It has been shown that there is reflex activity such that a
fast-acting contraction occurs in the distal third of the
urethra, which contributes to the compressive forces of the
proximal urethra during raised intra-abdominal pressure
The perineal body is a central cone-shaped
fibromuscular structure which lies just in front of the
anus. The cone is about 4.5 cm high and its base,
which forms part of the perineum, is approximately 4
cm in diameter. Anteriorally it fuses with the vaginal
wall, the superficial transverse perineal muscles, the
perineal membrane and the levator ani muscles
insert into it. The perineal body also affords support
to the posterior wall of the vagina. The integrity of
the perineal body and its connections have been
thought to be of considerable importance in the
supportive role of the pelvic floor. This explains the
concern that obstetricians have had for the welfare
of the perineal body in labour, particularly in the
second stage when, toward delivery, the pelvic floor
stretches considerably and provides a gutter to guide
the foetal head towards and down the birth canal.