Clinical Anatomy of
the Female Pelvis
For the Obstetrician
Professor Hassan Nasrat
The Bony Pelvis
The ileopectineal line
divides the pelvis into
the false and the true
pelvis
The normal female
pelvis is described as
“gynecoid”
to
be
differentiated from the
male “android pelvis”.
The pelvic inlet “pelvic brim”
13 cm
12 cm
Antero-posterior
Transverse
Engagement of the fetal head usually occurs through the
transverse diameter
The Pelvic Cavity
The pelvic cavity:
Is the curved canal
between inlet and
outlet.
In the normal female
pelvis the cavity is
circular in shape and
curves forwards.
All its diameters
measureapproximate
ly 12 cm.
The Pelvic Outlet
the two pubic bones make the pubic arch, which in the normal female pelvis forms an
angle not less than 90°. A narrow angle will force the fetal head at delivery posteriorly and
thus increase the risk of perineal tear
Pelvic ligaments and
Diaphragm
The pudendal neurovascular bundle exits out of the greater sciatic foramen and reenters
the pelvis through the lesser sciatic foramen.
This is the site for administration of pudenal block for local anesthesia.
The two main muscles:
The levator ani muscle group:
Pubococcygeus, puborectalis, and iliococcygeus.
They muscles extend from the lateral pelvic walls
downward and medially to fuse with each other
posteriorly.
The levator hiatus lies anteriorly and accommodates the
urethra, vagina, and anus.
The coccygeus muscles
A triangular muscle arises from the ischial spine and
inserts onto the sacrum and coccyx
The Perineum
The Perineum
The perineum is divided into two parts (or
triangles):
Subdivided
into:
Anterior
or urogenital
triangle:
A superficial and deep perineal spaces by a
fibromuscular septum called the urogenital
diaphragm
Posterior or anal triangle:
The midline attachment forms the fibromuscular
perineal body. between the anal canal and the vagina
The Superficial Perineal Space
Boundaries of the
Superficial Perineal
Space
Note that the superfial muscles of the urogenital triangle and the muscles of the
anal triangle all converge in the midline at the central tendon of perineum
(perineal body) .
During episiotomy :It is important to
recognize superficial transverse perineilmuscle in order to ensure proper cooptation.
Is bounded by three sets of muscles:
•The ischiocavernosus:
•The bulbocavernosus (the sphincter of the Vagina):
•The superficial transverse perinei:
It also includes the Bartholin’s glands and the vestibular
bulbs.
The superfial muscles of the urogenital triangle and the
muscles of the anal triangle all converge in the midline.
The Deep Perineal Space
The Anal Triangle
The anal triangle is the area of the perineum behind an imaginary line that
extends between the ischial tuberosities.
The ischiorectal fossae :
•A potential space that allows distention of the rectum
during defecation and the vaginal wall during second
stage of labor.
•It is also a potential space for huge (up to one liter)
hematoma collection and abscess formation.
•The obturator nerve and internal pudendal vessels:
run alongside the lateral wall of the ischiorectal fossa
in the pudendal or Alcock’s canal. This canal is
formed from the splitting of the fascia on the lateral
wall of the ischiorectal fossa together with the
obturator fascia itself.
The external anal sphincter: The voluntary muscle which is responsible for
fecal continence is located within the anal triangle. Its total length is about 2 cm, and it
is composed
Tear of external anal sphincter is not uncommon during delivery particularly operative one
and should be carefully repaired. Failure to recognize tears of the external sphincter or
inappropriate repair can precipitate anal incontinence.
Nerve Supply of the Perineum
Ilioinguinal nerve (L1)
and genitofemoral nerve
(L1, 2)
The Pudendal
nerve
(S2-4)
Perineal branch of posterior
femoral cutaneous nerve
Coccygeal and last sacral
nerves (S4, 5)
The Uterus
In 75% the uterus is in the anteverted, anteflexed position.
On rare occasion a retro-verted gravid uterus may get entrapped within the pelvis and
beneath the sacral promontory, giving rise to anterior sacculatoin of the uterus.
Clinically this presents with acute retention of urine.
The Isthmus is the short constricted area that marks the junction of the uterine body
with the cervix.
The body of the uterus:
It has three layers: The endometrium, the myometrium and the perimetrium:
The myometrium: Has longitudinal, circular and oblique muscle fibers and
is very expansile. The oblique muscle fibers run “criss-cross” and compress the blood
vessels when the uterus is well contracted.
It is found mostly in the upper segment of the uterus, where the placenta normally
embeds.
The richness in muscle fibers and its criss-cross important to ensure proper hemostasis
following placental delivery.
In contrast to that is the lower uterine segment which is poor hemostasis following
placental delivery.
This explains why bleeding in the third stage is more difficult to control if the
placenta is implanted in the lower uterine segment as in cases of placenta praevia.
The Endometrium:
During pregnancy and childbirth, the endometrium is
referred to as the decidua.
The perimetrium:
Is a layer of peritoneum that covers the uterus except at
the sides where It extends to form the broad ligaments.
Significant bleeding and hematoma can extend whithin the layers of the broad
ligament into the extra peritoneal space with serious consequences
The Cervix:
Consists predominantly of collagenous connective tissue and
mucopolysaccaride ground substance.
It communicates with the uterine cavity through the internal os
and with the vaginal canal through the external os.
The endocervical canal is about 2.5 to 3 cm in length. It is lined
by a single layer of specialized columnar epithelium and secretes
mucus to facilitate sperm transport.
During pregnancy the glands secretion forms a plug of mucus
which helps protect against infection.
This plug of mucous comes away stained with some blood just
before labor commences. Many women refer to this as the
“show”.
Vascular Supply of the pelvis
Note the anastomsis between
the ovarian and uterine
artery.
Therefore the uterus receive
blood supply from two
sources on each side
Note the Ureter Crosses
below the Uterine Artery
about 1 cm from the cervix
Vessels and nerves of the
deep perineal space
Innervations of the Pelvis
Routes of Nerve Supply to
the uterus (visceral nerves).
Pain of uterine contractions
in the first stages is felt in the
abdomen, lower back
Routes of Nerve Supply to
cervix and upper vagina
(Somatic nerves)
In the second stage additional
source of pain from cervical
stretching and perineal
pressure.