ANATOMY AND PHYSIOLOGY:
PELVIC BONE AND FETAL SKULL
BY: HN MULUNDU
WALVIS BAY CAMPUS
OBJECTIVES
At the end of the session, student should be able to:
Outline the structures of the pelvis
Mention the bones of the pelvis
Explain the joints of the pelvis
 Explain the ligaments of the pelvis
Describe the muscles of the pelvic floor
Discuss the types of pelvis and their effects on labour
 Describe the areas or zones of the true/gynaecoid pelvis
 Explain the landmarks of the pelvis.
 identify and plain different types of pelves
INTRODUCTION
The bones of pelvis is combine to form the
pelvic canal, were the fetus pass during birth.
The shape and size of pelvic bones determines
whether the fetus of the average size will pass in
it.
The gynaecoid pelvis is the normal female
shaped pelvis that is suitable for a normal child
birth
Four bony structure of pelvis
 two innominate bones
 sacrum
 the coccyx
THE INNOMINATE BONES
 the ilium
The ischium
 pubic bone
THE ILIUM
 Is the strongest
 heavy superior bone
 the upper part of ilium forms the false pelvis
the posterior joins to the ala of the sacrum at
sacroiliac joint.
 upper curved boarder is know as iliac crest.
 the iliac crest ends posteriorly in the posteriorsuperior iliac spine
THE ILIUM
And anteriorly in the anterior – superior iliac spine.
the lower portion of the ilium forms the part of the
Of the ischium posteriorly and the pubic bone
anteriorly.
 the upper and lower portion of the ilium forms a
ridge which divides the false and true pelvis.
true pelvis, which meets the inferior boarder
 the rigde is named the iliopectineal line.
 the iliopectineal line forms the lateral border of the
pelvic brim or inlet of the true pelvic cavity.
THE ISCHIUM
 Lower part of innominate bone.
 the thicker lower boarder is the ischial tuberosity.
 the body mass is taken on by these bones.
 these bones form the part of pelvic outlet.
 the thin inferior ramus projects forward and
upwards from, that joins with the inferior of the
pubic
THE ISCHIUM
Bones, to form an arc.
 superiorly the ischium widen and joins the
ilium, in the posterior portion of the
acetabulum.
PUBIC BONE
 consist of two arms.
 superior and inferior rami.
The body of two pubic bone meet inferiorly to form
symphysis pubis.
 upper and superior ramus form pubic crest.
The two arms meet the ischium inferiorly and ilium
superiorly, which forms the oval window.
 Or hole in inferior pelvic wall, known as obturator
foramen.
 THE SACRUM
 Strong and heavy bone.
Forms posterior part of pelvis.
 articulate on both sides with ilium at the
sacroiliac joint.
made up of five fused vertebrae.
PELVIC JOINTS
Sacroiliac joint
 Between sacrum and ilium
 Strongest joint in the body
Sacrococcygeal joint
 Sacrum and coccyx
 Enable coccyx to bend backward allowing fetal
head to negotiate the outlet of pelvis canal.
PELVIC JOINTs
Lumbosacral joint
 lies posterior aspect of pelvis between 5th
lumbar vertebrae and sacrum
 PELVIC LIGAMENTS
Ligaments are fibrous strong connective tissues,
the ligaments of the pelvis strengthen or
connects the joints of the pelvis.
They are partially cartilaginous, Or partially
fibrous
 Sacrospinous ligament
Sacrotuberous ligament
 SACROSPINOUS LIGAMENTS
 is from lower sacrum and coccyx towards
ischial spines.
 it surrounds the lower boarder of sciatic notch.
 it is covered by coccygeus muscle of a pelvic
floor.
SACROSPINOUS CONTINOUES…
 SACROTUBEROUS LIGAMENT
 It covers the lesser sciatic notch and runs from
lower sacrum coccyx to the ischial tuberosity.
TRUE PELVIS
True pelvis is crucial in obstetrics, because is were the
fetus pass during delivery.
It is divided into 3 areas/ zones.
PELVIC ZONES
 pelvic brim or inlet
 pelvic cavity/ mid-pelvis
 pelvic outlet
TRUE PELVIS CONTINUES….
 PELVIC INLET/BRIM
 significant area zone,
since it must adequate for the fetal head to pass
through,
if not labour becomes obstructed
 engagement of the fetal head
 Takes place if the fetal head goes through the pelvic
brim.
PELVIC BRIM CONTINUES
LAND MARKS OF PELVIC BRIM
 posteriorly: promontory of the sacrum, the
alae of the sacrum and sacro- iliac joints.
 laterally: illio-pectineal lines, and ilio-pectineal
eminences.
 anteriorly: pubic crest and symphysis pubis
 MEASUREMENT OF PELVIC BRIM
MEASUREMENTS OF PELVIC BRIM
CONTINUES……
ANTERO- POSTERIOR DIAMETERS.
 obstric conjugate of 11 cm.
- Measured from central sacral promontory to
posterior symphysis pubis
 the anatomical or true conjugate of 12cm.
- From central tip sacral promontory to the summit of
symphysis pubis
MEASUREMENTS OF PELVIC BRIM
CONTINUES….
 the diagonal conjugate of 12cm.
- Can be assessed during vaginal examination.
- from tip of promontory of sacrum to bottom of
symphysis pubis.
MEASUREMENTS OF THE PELVIC BRIM
CONTINUES
OBLIQUE DIAMETERS.
 all oblique diameters of pelvic brim measure 12cm.
 from left or right sacro-iliac joint to pectineal
eminence.
TRANSVERSE DIAMETERS
 transverse diameter of pelvic brim measure 13cm.
- Measured from the widest part of pelvic brim
MEASUREMENT OF PELVIC BRIM
CONTINEUS….
 the sacro- cotyloid dimension measures 9,5cm
- Measured from central sacral promontory to the
ilio- pectineal eminence.
PELVIC CAVITY/ MIDPELVIS
 Area between inlet and outlet of the pelvis.
LAND MARKS
 Anterior wall: formed by pubic bones and it’s
depth is 4 cm.
 posterior wall: formed by curve of sacrum, length is
12cm.
 lateral wall: covered by obturator Internus muscles
and sciatic notch.
MEASUREMENT OF PELVIC CAVITY
MEASUMENTS OF PELVIC CAVITY
ANTERO- POSTERIOR, OBLIQUE AND
TRANSVERSE DIAMETERS.
 All measurements of the pelvic cavity are 12cm
ISCHICIAL BI-SPINOUS MEASUREMENT.
 Is only 10 cm to 10.5 cm.
 measured between ischial spines.
 PELVIC OUTLET
 Is the lower circumference of the true pelvis.
 it is described in terms of anatomical and
obstetrical outlet.
LAND MARKS
 POSTERIORLY: coccyx and sacro-tuberous
ligaments.
 LATERALLY: ischial tuberosities.
 ANTERIORLY: the pubic arch.
MEASUREMENT OF PELVIC OUTLET
MEASUREMENTS OF PELVIC OUTLET
CONTINUES
ANTERO-POSTERIOR DIAMETER
- It measures 13 cm, when coccyx is bend forward.
- measures from apex of pubic arch to the tip of
coccyx.
OBLIQUE DIAMETER
- measures 12cm.
- measured from Centre of sacro-tuberous ligament
to the junction of ischial ramus of pubis.
MEASUREMENT OF PELVIC OULET
CONTINUES.
TRANSVERSE DIAMETER
- Measures 11 cm.
- measured between widest point of ischial
tuberosities.
TYPES OF PELVIS
 gynaecoid pelvis-TRUE PELVIS
 android pelvis-FALSE
 anthropoid pelvis-FALSE
 patypelloid pelvis-FALSE
 justo minor pelvis-FALSE
DETECTION OF DIFERRENT TYPES OF
PELVES
 Race and stature of a women.
 taking history, of obstetric history.
 pelvic assessment during vaginal examination
 ultrasound scanning.
 x-ray/ radio graphical pelvimetry.
 GYNAECOID PELVIS
 Is the ideal pelvis, because of it’s features make it
more suitable for a normal child birth of an average
sized baby.
CRITERIA
BRIM
 round or oval transversely.
 no inappropriate projection of sacral promontory.
GYNAECOID PELVIS CONTINUES…..
CRITERIA
BRIM
 round or oval transversely.
 no inappropriate projection of sacral
promontory.
Antero-posterior diameter measures 12cm.
 transverse diameter measures 12.5cm
GYNAECOID PELVIS CONTINUES
PELVIC CAVITY
 Shall and straight side walls.
no excessive projection of ischial spines.
OULTLET
 Round pubic arch, with angle of 85%.
 inter-tuberous diameter measures10.5 cm.
 mobile coccyx.
 ANDROID PELVIS.
 It resembles the male pelvis.
CRITERIA
BRIM
 heart shaped
 narrow anterior
 is common in African women/ tall women with
narrow hips.
ANDROID PELVIS CONTINUES
PELVIC CAVITY AND OUTLET
 Narrow, straight and long sacrum.
 reduced pubic arch.
 mid-cavity and outlet contracture.
 ischial bi-sponous diameter is narrowed,
because ischial spines are prominent and
reduced diameter of inter-tuberous
ANDROID PELVIS CONTINUES..
EFFECT ON LABOUR
Occipito-posterior position are common
Deep transverse arrest can occur
Delay in second stage of labour
 ANTHROPOID PELVIS
CRITERIA
BRIM
 Oval
 greatest diameter is antero-posterior, transverse
diameter is reduced.
PELVIC CAVITY
 slight narrow in transverse diameter.
OUTLET
 Antero-posterior is the largest, with reduced
diameter of inter-tuberous
ANTHROPOID PELVIS CONTINUES…….
EFFECT ON LABOUR
if the fetal head engage in occiput anterior, there
will be no problem.
 in Occipito- posterior position, the occiput will
have difficulty in rotating,
causing labour to prolong.
 PLATYPELLOID PELVIS
CRITERIA
BRIM
 kidney shaped.
 sacrum moves forward, which causes reduction in
antero-posterior diameter.
CAVITY
 shallow pelvis
 slightly narrow in antero-posterior diameter
PLATYPELLOID PELVIS CONTINUES
OUTLET
 increased angle of pubic arch.
 transverse/ inter-tuberous diameter increase.
 anteroposterior diameter reduced.
Outlet is capacious.
PLATYPELLOID PELVIS CONTINUES
EFFECT ON LABOUR.
fetal head difficulty in entering The brim, causing
prolonged labour or obstructed labour.
 increase incident of face or brow presentation.
 if the head enter the brim and mid-cavity as a
normal, vertex presentation, there will be no
further difficulty.
 JUSTO MINOR PELVIS
 has the criteria of the gynaecoid pelvis, but the
diameters are reduced with 0.5 – 1cm.
common in Indian women, women under 1.5
height and small shoe size.
EFFECT ON LABOUR.
 the effect depend on fetal size.
 Indian bear small babies, therefore have no
difficult labour
JUSTO MINOR PELVIS CONTINUES……
 European and African women with this type of
pelvis results in difficult labour,
which results in cephalo-pelvic disproportion.
INFLUENCES WHICH CAN AFFECT THE
SHAPE OF PELVIS
Accidents
Congenital abnormalities
Disease e.g. poliomyelitis
Low socio-economic conditions
Incorrect dieting and anorexia nervosa
PELVIC FLOOR
 Pelvic floor is made up by the soft
tissues, that covers the pelvis outlet.
It keeps the pelvic and abdominal content in
place and provide support.
To allow access to the outside for the bladder,
uterus and rectum.
it controls fetus in the birth canal
MUSCLES OF PELVIC FLOOR
 Deep layer
 Middle layer
 Superficial layer
FETAL SKULL
Longitudinal diameters
6 longitudinal diameters namely:
•SOB:-sub-occipito-bregmatic 9.5cm
•Sof:- Sub-occipito-frontal
10.cm
•OF:- Occipito-frontal
5cm
•MV:-Mento-Vertical
13.5cm
•SMV-Sub-mento-bregmatic
9.5cm
FETAL SKULL
Bones
 Two haves frontal
 Two parietal
 One occipital
Sutures
 Frontal suture- bisect frontal bone
 Sagittal suture- Divide skull into halves
FETAL SKULL
 Coronal suture- separate frontal from parietal
 Lambdoidal suture- divide parietal from occipital
 Temporal sutures- between temporal, frontal and
parietal
Two important fontanelles
 anterior fontanelle or bregma (diamond shaped)
 Posterior fontanelle or lambda (triangular)
FETAL SKULL
• Sub-Occipito-bregmatic ( SOB) diameter (9.5cm)
measured from below the occipital to the centre
of the anterior fontanelle or Bregma.
• Sub-Occipitofrontal (SOF) 10cm measured
below the occipital protuberance to the centre
of the frontal
REFERENCES
 Franser,
D and Cooper M. A (2009).MYLES
textbook of MIDWIVES ( 15th edition)
 Sellers, P.M (2018). Sellers’ midwifery (3rd)