Week 1 - The Bony Pelvis Flashcards
What does the bony pelvis consist of?
2 innominate bones, sacrum and coccyx
The pelvic girdle (bony ring) does not include which part of the bony pelvis?
Coccyx
Each innominate bone is a fusion between what other bones?
Ilium, ischium and pubis
The two sides of the bony pelvis connect where:
a) anteriorly?
b) posteriorly?
a) Pubic symphysis
b) Sacro-iliac joints
Which bone is this describing - ‘the flattened, superior, fan-shaped part of the hip bone’?
Ilium
Where does the iliac crest pass from?
ASIS to PSIS
The iliac fossa is an attachment for which muscle?
Iliacus
What sits in the left iliac fossa?
Sigmoid colon
What are the two parts of the ischium?
Body and ramus
The body of the ischium forms the posterior part of what structure?
Acetabulum
The ramus of the ischium forms the posterior part of what structure?
The inferior obturator foramen
The ischiopubic ramus is located where in relation to the ischial ramus?
Medial
What part of the ischium do we sit on?
The ischial tuberosity
Which group of muscles originate from the ischial tuberosity?
Hamstrings
The pubis is an angulated bone, which is formed of the superior pubic ramus that forms the anterior part of which structure?
Acetabulum
The inferior pubic ramus forms the inferior border of what structure?
Obturator foramen
The pubic tubercle is the attachment for which ligament?
Inguinal ligament
The two pubis bones are connected where?
Pubic symphysis
Which bone of the pelvis is most different between males and females?
Pubis
What is the different in the pubic arch in males and females?
This has a wider angle and flares out more in females than males
What are the 3 joints of the pelvis?
Hip joint, sacroiliac and pubic symphysis
What is the stability and movement of the sacroiliac joints?
Small amount of movement but overall are very stable
What type of joint is the pubic symphysis?
Cartilagenous
Why does the pubic symphysis need to have more mobility than the sacroiliac joints?
To allow it to expand during pregnancy
What type of joint is the hip?
Synovial ball and socket
Where does the inguinal ligament attach between?
ASIS and pubic tubercle
Which structures of the pelvis are palpable on vaginal examination, at approx 4 and 8 o clock positions?
Ischial spines
Why are the ischial spines clinically relevant?
For administering a pudendal nerve block, and assessing how far through the pelvis a foetal head is
The iliac crests are at what spinal level?
L4
What is the role of the sacrospinous and sacrotuberous ligaments?
To ensure that the inferior part of the sacrum is not pushed superiorly when weight is suddenly transferred through the vertical column
What happens to the ligaments of the pelvis in pregnancy?
Hormones are released which cause them to relax to allow for the foetus to grow
The presence of the sacrospinous and sacrotuberous ligaments forms what other structures?
Greater and lesser sciatic foraminae
Structures which pass through the sciatic foraminae are heading towards where?
Perineum or lower limb
What structures form the pelvic inlet?
Sacral promontory, ilium, superior pubic ramus and pubic symphysis
What is the sacral promontory?
S1 vertebral body
What structures form the pelvic outlet?
Pubic symphysis, ischiopubic ramus, ischial tuberosities, sacrotuberous ligaments and coccyx
Above the pelvic inlet there is an area known as the ‘false pelvis’ - this is part of what cavity?
Abdominal cavity
What is the main difference between the structures forming the pelvic inlet and outlet?
Inlet is completely bony while the outlet is formed of bones and ligaments
Where does the pelvic cavity lie within?
The bony pelvis
The pelvic cavity lies between which two structures?
Pelvic inlet and pelvic floor
What muscle forms the inferior parts of the pelvic cavity, and is also known as the pelvic floor?
Levator ani
What is found below the pelvic cavity?
Perineum
In terms of mechanics, how do fractures tend to occur in the pelvis?
They are usually multiple, or combined with a joint dislocation
Trauma to the bony pelvis can result in what?
Life threatening haemorrhage +/- damage to the pelvic organs
Disruption to any vasculature in the pelvis will cause what?
Internal bleeding
What is the difference in the diameters of the pelvis in males vs. females?
All diameters of the pelvis are larger in the female
What is the difference in the pelvic cavities between males and females?
Shallower in females (i.e. less distance between inlet and outlet)
What is ‘moulding’?
The bones of the baby’s skull moving over each other to allow the foetal head to pass through the pelvis in labour
The presence of what in a baby’s skull allow moulding?
Fontanelles and sutures
What is the following a sign of:
a) bulging fontanelles?
b) depressed fontanelles?
a) Raised ICP
b) Malnutrition
How long does it take for each type of fontanelle to close?
Posterior takes around 3-6 months while anterior takes 9-18 months
What is the vertex?
An area of the foetal skull which is outlined by the anterior and posterior fontanelles and the parietal eminences
Which diameter of the foetal skull is the largest?
Occipitofrontal
Which diameter of the pelvis is largest at the pelvic inlet? As a result of this, how should the foetus ideally enter the pelvic cavity?
Transverse - ideally facing either to the right or left (transverse) direction
While descending through the pelvic cavity, what should happen to the foetal head?
Rotate, and be in a flexed position
Which diameter of the pelvis is largest at the pelvic outlet? As a result of this, how should the foetus ideally leave the pelvic cavity?
AP diameter - ideally in an occipitoanterior (OA) position
During the delivery, should the foetal head be extended or flexed?
Extended
What movement of the baby needs to occur once the head has been delivered?
Further rotation to allow one shoulder out and then another
Where does the sacrospinous ligament attach between?
Ischial spines and sacrum
Where does the sacrotuberous ligament attach between?
Ischial tuberosities and sacrum
What is the difference in the shape of the pelvic outlet in males and females?
Males = more heart shaped, females = more oval shaped
What is the difference in the sacral promontory between males and females?
More anterior in males
