Anatomy of the Bony Pelvis in Relation to Labour Flashcards
What are the functions of the bony pelvis?
Support of upper body and transference of weight
Attachment of muscles and external genitalia
Protection of pelvic organs and passage for childbirth
What does the bony pelvis consist of?
Both hip bones, sacrum and coccyx
What makes up the pelvic inlet?
Sacral promontory, ilium, superior pubic ramus, pubic symphysis
What makes up the pelvic outlet?
Pubic symphysis, ischiopubic ramus, ischial tuberosities, sacrotuberous ligaments, coccyx
Where is the pelvic cavity located?
Lies within bony pelvis = continuous with abdominal cavity above, lies between pelvic inlet and pelvic floor
What are the bony landmarks of the pelvis?
Anterior = ASIS, iliac crest Posterior = PSIS, iliac crest
Where does the sacrotuberous ligament attach?
The sacrum and ischial tuberosity
Where does the sacrospinous ligament attach?
Sacrum and ischial spine
What are the functions of the pelvic ligaments?
Protection against sudden weight transfer
Relax during later pregnancy
What are the usual features of pelvic fractures?
Tend to be multiple or combined with joint dislocation
What can pelvic trauma cause?
Life threatening haemorrhage and damage to pelvic organs
What is moulding?
Movement of one bone over another to allow foetal head to pass through pelvis during labour
What are the borders of the vertex of the foetal skull?
Outlined by anterior and posterior fontanelles and the two parietal eminences
Why is the foetal head longer than it is wide?
The occipitofrontal eminence is longer than the biparietal diameter
How do the diameters of the pelvic inlet relate to each other?
Transverse diameter of pelvis is wider than the AP diameter
How should the foetus ideally enter the pelvic cavity?
Facing either left or right (transverse facing)
What does the station refer to?
Distance of foetal head from the ischial spines
What do the station numbers mean?
Negative number = head superior to spines
Positive number = head inferior to spines
What should happen while the foetus is descending through the pelvic cavity?
The foetal head should rotate and be in a flexed position
How do the diameters of the pelvic outlet relate to each other?
AP diameter is wider than the transverse diameter
What position should the foetus ideally leave the pelvic cavity in?
In the occipito-anterior position
What position should the foetal head be in during delivery?
Extension
What happens once the baby’s head has been delivered?
There is further rotation so that the shoulders and the rest of the baby can then be delivered
Where does the inguinal ligament attach?
Between ASIS and pubic tubercle
What position are the ischial spines palpable at on vaginal examination?
At approximately 4 and 8 o’clock positions
What are the differences between the male and female pelvises?
AP and transverse diameters of female pelvis are larger, both at the pelvic inlet and outlet
Suprapubic angle and pubic arch are wider in females
Pelvic cavity is more shallow in females
What is the anterior fontanelle called once it closes?
The bregma
When do the anterior and posterior fontanelles close?
Anterior = 18 months - 2 years Posterior = 6 months - 1 year
