© Royal College of Obstetricians and Gynaecologists Anatomy of the female pelvis and vaginal birth.

© Royal College of Obstetricians and Gynaecologists

Anatomy of the female pelvisand

vaginal birth


Take a look at the bony pelvis you have been given.

View it from the front.

In the following slides, the bony landmarks will be described.


Innominate bone


Sacrum


Coccyx


Sacroiliac joint


Sacrococcygeal joint


Symphysis pubis


Ischial spine


Ileopectineal line


Obturator foramen


Pubic arch


Sacral promontory


Anterior foramina


Now look at the pelvis from one side.

In the following slides, more landmarks will be shown.

You will also see how the pelvis is orientated when a woman is standing up straight.


Anterior superior iliac spine

Symphysis pubis

Vertical plane


Pubis

Ileum

Ischium


Obturator foramen

Acetabulum


Look at the pelvis from the front again.

In the following slides, you will be shown a little more anatomy.

Look at the position of the sacrotuberous and sacrospinous ligaments.


Sacrotuberous ligament


Sacrospinous ligament


Look at the pelvis from behind.

Look at the position of the sacrotuberous and sacrospinous ligaments.

These delineate the greater and lesser sciatic foraminae.


Greater sciatic foramen

Lesser sciatic foramen


We are now going to add in some muscles.

You will see piriformis from front and back.

You will see obturator internus from the back.


Piriformis


Obturator internus


We are now going to add in blood vessels and nerves.



Internal Iliac A

Common Iliac A


External Iliac A


Internal Iliac V

Common Iliac V


The Lumbosacral Plexus


Sciatic nerve


Pudendal nerve


Obturator nerve


Look at the pelvis from the side.

We will look at the muscles and ligaments on the side wall of the pelvis.

You will see where the levator ani muscles originate.

You will also see the critical dimensions of the pelvis.


Obturator canal


Obturator internus

Muscle

Covered by

Fascia


Line of attachment of levator ani


Pelvic inlet

Critical pelvic dimensions


Pelvic midplane



Pelvic outlet



Pelvic outlet

Pelvic inlet

Pelvic cavity

Pubic arch

Female Male



Imagine a ‘coronal’ plane through the middle of the pelvis.

You will see the rectum coming through the pelvis.

You will see where the levator ani muscles originate.

You will see which structures form the pelvic diaphragm.


Iliac crest

Pelvic brim

Ischial tuberosity


Rectum


Obturator

Internus

With Fascia


Levator ani

Plus coccygeus

Makes

Pelvic diaphragm


There are some structures above the pelvic diaphragm.

There are some structures below the pelvic diaphragm.


Peritoneum


Subperitoneal space


Contains:

Pubocervical

Trans cervical

Sacrocervical

Ligaments


Perineum

everything under pelvic diaphragm


Ischiorectal fossae


Now look at the pelvis from below.

Look at the layout of the bones and the ligaments.

They define the pelvic outlet.


Obturator membrane

Obturator canal


Pubic arch

Inferior pubic ramus

Ischial ramus

Symphysis pubis



Sacrum / coccyx

Ischial tuberosity


Pelvic outlet


Urogenital triangle

Anal triangle


Keep looking at the pelvis from below.

Imagine the anatomy above the pelvic diaphragm.

The following slides show the structures encountered as you descend through the pelvis.


Rectum

Cervix

Bladder

Above the

Pelvic diaphragm


Pubocervical ligament Above the

Pelvic diaphragm


Transverse cervical ligament

Above the

Pelvic diaphragm


Sacrocervical ligament

Above the

Pelvic diaphragm


Levator ani:

Pubococcygeus

Iliococcygeus

Ischiococcygeus

Pelvic diaphragm

Coccygeus



Imagine the anatomy as you descend below the pelvic diaphragm.

The following slides show the structures encountered as you continue to descend through the pelvis.


Superior layer

of fascia

Urogenital diaphragm


Sphincter urethrae


Deep transverse peroneal muscles


Perineal membrane


Clitoris & crus

Structures in

Superficial pouch

Bulb of vestibule

Vestibular glands


Ischiocavernosus

Muscles in

Superficial pouch

Bulbospongiosus

Supl transverse peroneal muscles


Perineal body



You have now reached the most superficial level.


Labium minus

Labium majus


Prepuce of clitoris

Mons pubis

Vestibule

vagina

Fourchette


Here is the female abdomen and pelvis viewed from one side.

The structures shown should now be familiar to you.


Peritoneum


Pubocervical ligament

Sacrocervical ligament


Pelvic diaphragm


Here is the rectum.

Look at its anatomical relations.


Perineal body

Sacrum

Anococcygeal body

Rectum


Puborectalis

Deep

Superficial

Subcutaneous


Take your fetal skull and view it from above.

Note the near central position of the anterior fontanelle.


occiput

posterior fontanelle

parietal eminence

saggital suture

anterior fontanelle

frontal bones

coronal sutures

lambdoid sutures


The following slides will demonstrate the orientation of the fetal skull as it passes through the pelvis in normal

labour.


passenger

the head flexes as the uterus contractsthe head descends and engages in the pelvis

the leading part approaches the ischial spines


passenger

the occiput starts to rotate anteriorlythe occiput reaches the pelvic floor (levator ani)

internal rotation continues to achieve an occipito-anterior position


passenger

the occiput clears the symphysis pubisthe head extends to deliver


passenger

the head sits on the maternal perineum


passenger

the fetal head realigns itself with the fetal shoulders - restitution


passenger

the shoulders contact the pelvic floor and rotate so that the bisacromial diameter lies in an anteroposterior orientation

the head therefore continues to rotate - external rotation

© Royal College of Obstetricians and Gynaecologists Anatomy of the female pelvis and vaginal birth.

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Transcript of © Royal College of Obstetricians and Gynaecologists Anatomy of the female pelvis and vaginal birth.