Download obstetric anatomy midw 201

OBSTETRIC ANATOMY
MIDW 201
BY
ESTHER A. M. ANYIDOHO
17TH NOV., 2014
COURSE OBJECTIVES
By the end of the course students should be
able to:
1. Describe the female and male reproductive
systems
2. Describe the physiology of ovulation and
fertilization
3. Describe the placenta and its functions
4. Describe the various types of female pelvis
and their relationship in labour and delivery
THE FEMALE PELVIS
• Objectives: By the end of the session, students
should be able to:
a. List the parts of the female bony pelvis
b. Describe each component part of the bony
pelvis
c. List the types of the female bony pelvis
d. List 2 effects of each type of the female bony
pelvis on labour and delivery
Female Bony Pelvis cont’d
• General description:
 The bony pelvis is located between the trunk and
the lower limbs of the body.
 It articulates superiorly with the 5th Lumbar
vertebra
 It articulates inferiorly with the coccygeal
vertebrae which form part of it
 It articulates laterally with the left and right
femoral heads in a depression called the
Acetabulum
The Female Bony Pelvis cont’d
The anterior border is the Symphysis Pubis.
 Bones of the Bony Pelvis is made up of 4
bones:
1. The Sacrum
2. The Cocyx
3. Two Innominate bones
These bones together make the bony pelvis the
largest bone formation in the human body
The Female bony Pelvis cont’d
The Sacrum: It is made up of 5 fused vertebrae. It is
triangular in shape with the apex pointing
downwards.
It lies between the right and left innominate bones
It articulates with the 2 innominate bones
It has 4 pairs of foraminae (windows or holes).
These communicate with the sacral canal. The
foraminae serve as exit for nerves from the spinal
cord at the level, blood vessels and lymphatic
channels as well.
The Female Bony Pelvis cont’d
The Sacrum has a hollow which is the anterior
concave surface. The concavity of the hollow
increases the capacity of the pelvis.
It has a widened portion on each of the first sacral
vertebra which are referred to as alae
(wings).
The Promontory is the centre point of the upper
border of the first sacral vertebra. This protrudes
over the hollow with the fifth lumbar vertebra.
The Female bony Pelvis cont’d
• The Sacral canal runs longitudinally through the
sacrum and opens at the level of the fifth lumbar
vertebra. The spinal nerves fan out through the
canal at the level of the 2nd and 3rd sacral
vertebrae to form the Cauda equina
• Obstetric Importance:
Anaesthetic agent is introduced through the caudal
canal to relieve pain from uterine contractions
during labour. This causes temporal paralysis of
the nerves leading to the relief of the pains.
The Female Bony Pelvis cont’d
• The Cocyx (Tail): This is four tiny fused vertebrae.
It is also triangular in shape. The base articulates
superiorly with the inferior aspect of the 5th
sacral vertebra. It serves as an attachment for
muscles and ligaments.
• Obstetric importance:
In the female, during the second stage of labour,
the cocyx tips backwards to widen the exit of the
birth canal for the head of the baby to pass
through.
The Female Bony Pelvis cont’d
 The Innominate Bones: These bones form the
lateral aspects of the bony pelvis.
 Each bone developed from 3 primary centres
of ossification. This formed three bones thus –
Ilium, Ischium and Pubis.
 The 3 bones meet in cup-shaped depression
called Acetabulum
The Female Bony Pelvis cont’d
• The ILIUM is the biggest and the uppermost of
the innominate bones. The uppermost end is
called the Iliac crest which is easily palpable
(the waist) by the hands resting on the hips. It
has four projections, two anterior and two
posterior called spines.
• The ilium articulates anteriorly with the
antero-superior iliac spine and posteriolry,
with the postero-superior iliac spine.
The Female Bony Pelvis cont’d
• The Antero-inferior lies approximately 2.5cm
below the antero-superior iliac spine. The
postero-superior iliac spines are located in the
dimples at the lower back of the individual.
The postero-inferior iliac spines mark the
upper border of the Greater Sciatic Notch
through which the Sciatic Nerves pass.
• The ilium forms the upper two-fifth of the
Acetabulum.
The Female Bony Pelvis cont’d
• The inner concave surface is smooth and the
outer surface is rough for attachment of the
gluteal muscles forming the buttocks.
• The ISCHIUM is the lowest portion of the
innominate bone. It forms the lower two-fifth
of the acetabulum. It has two projections
called the Ischial spine and the Ischial
Tuberosity respectively. The Ischial spine
terminates into the Lesser Sciatic Notch.
The Female Bony Pelvis cont’d
• The Ischial Tuberosity is the thickened portion
of the Ischium on which the weight of the
body rests in a sitting position.
• The Ischial spine separates the Lesser Sciatic
Notch from the Greater Sciatic Notch.
• The PUBIS is the smallest bone of the
innominate bone. It forms the lowest one-fifth
of the Acetabulum.
The Female Bony Pelvis cont’d
• There are two Pubic bones which are united
anteriorly to form the a square-shaped pubic
bones. The two bones are fused together by a
pad of cartilage in the middle, called the
Symphysis Pubis.
• The Superior Pubic Ramus forms the upper
portion. It unites with the ilium to form the
Iliopectineal eminence.
The Female Bony Pelvis cont’d
• The right and left descending Rami form the
Pubic Arch. Its importance is during the birth
of the baby, it widens out.
• The Ischium and the Pubis surround a
foramen called the Obturator Foramen
The Female Pelvis cont’d
• Types of Pelves: The classification of the pelvis is made
according to shape of the brim. The pelvic brim has
measurements which allow the passage of the foetal head
with no difficulty.
• However, if any of the measurements is reduced by 1cm,
then there will be difficulty for the passage of the foetal
head.
The Female Bony Pelvis cont’d
• There are four main types of pelves
1. Gynaecoid
2. Android
3. Anthropoid
4. Platypelloid
 The Gynaecoid pelvis is said to be the ideal
for childbearing. It is the true female pelvis
Female bony pelvis cont’d
• Features:
The Brim – rounded
Fore pelvis is generous
Cavity – the sacrum is well curved with straight
walls
Outlet –Ischial spines are rounded and blunt, not
prominent
Effect on labour: It enables the foetus to present
with its most rounded part of the head - occiput
The female bony pelvis cont’d
Anteriorly, because of the rounded brim. This
position is most favourable at the start of labour.
 The Android Pelvis: This resembles the male
pelvis. The bones are heavier than the that of the
Gynaecoid pelvis.
• Features:
The Brim – heart-shaped, making the fore pelvis
narrow. The transverse diameter does not cross
Female Bony pelvis cont’d
The centre of the Anteroposterior (AP) diameter,
but it is much more nearer the sacrum. It is
funnel-shaped.
The Cavity – it is deep with straight hollow of the
sacrum and side walls. The sacrum is longer than
that of the Gynaecoid pelvis. The Greater Sciatic
Notch too is narrower than that of the Gynaecoid
pelvis.
The Outlet – The available space is reduced due
to the acute subpubic angle.
Female bony pelvis cont’d
The Ischial spines are sharp and turn inwards
leading to the reduction of the transverse
diameter.
Effect on labour: Because the pelvis is more
rounded in the posterior angle, the foetus
tends to lie with its occiput in the right or left
posterior quadrant of the pelvis. This makes
labour to be prolonged.
Female bony pelvis cont’d
It may result in deep transverse arrest of the
head as it is caught up in the deep posterior
pelvis. Internal rotation becomes difficult, due
to the prominent ischial spines. This pelvis can
be found in 20% of women population.
 The Anthropoid Pelvis: This is seen in very tall
long-legged women; especially, the whites and
South African women.
Female Bony Pelvis cont’d
The Brim – Oval in shape. Long AP diameter.
Reduced transverse diameter.
The Cavity – It is deep. Fore pelvis is narrow,
with divergent sidewalls and blunt ischial
spines. Transverse diameter is reduced with
wide Sciatic notch.
The Outlet is adequate in all diameters. The
subpubic angle is greater than 90 degrees.
Female bony Pelvis cont’d
Effects on labour: The foetus lies in the AP of the
pelvic brim. The occiput tends to lie in the
hollow of the sacrum rather than directly
anterior. The foetus remains in that position
till delivery. Thus unreduced occipito posterior
position that is face-to-pubis instead of faceto-perineum. It has a higher incidence of OPP
and breech presentation. Can be found in 25%
of women.
Female Bony Pelvis cont’d
 The Platypelloid Pelvis – Flat pelvis.
The Brim – Kidney-shaped. AP is reduced and
transverse diameter is increased.
The Cavity – It is flat and shallow.
The Outlet – Subpubic angle is more acute
with reduced available space, because the
inferior pubic rami are in a much more
sharper angle which is wider. The ischial
spines are too blunt. Found in 5% of women.
Female bony pelvis cont’d
Effect on labour: The engagement of the foetal
head is difficult. The foetus usually presents
with the long diameter of the head –
biparietal diameter across the transverse
diameter of the pelvic brim which is roomy.
There is early rupture of the membranes due
to the high presenting part. There is a
possibility of cord prolapse. Engagement of
the head may lead to lateral tilting of the
head,
Female Bony Pelvis cont’d
b. Face presentation
c. Delivery by Caesarean Section as a result of the
floating high head.
Other types of Pelves:
1. Justo-minor Pelvis: Miniature Gynaecoid pelvis.
All the diameters are proportinately reduced.
Mostly found in women with small stature – 1.5m
in height. They can deliver normally if the foetus
is proportionate to the pelvis otherwise, is C/S.
Female bony pelvis cont’d
2. Robert Pelvis- The sacrum has no alae and
therefore contracted in all diameters. Delivery
is by C/S
3. Naegele Pelvis – The sacrum has only one ala
giving it its obliquity. It may be due to
congenital abnormality or injury. Delivery is
C/S.
JOINTS AND LIGAMENTS OF THE
PELVIS
• There are four pelvic joints with their supporting
ligaments.
 Two Sacro-iliac joints
 The Symphysis Pubis
 The Sacrococcygeal joint
The Sacro-iliac joints lie between the bodies of the
first and second sacral vertebrae and the articular
surfaces of the ilium each side. These joints have
the body weight transmitted through them and
are subjected to great strain.
Pelvic Joints and Ligaments
• Supporting Ligamentsa. Strong sacro-iliac ligaments surround the
joints.
b. The Sacrotuberous ligament stretches from
the lower border of the sacrum to ischial
spine. They aid in the restriction of sacral
movement.