Bony Pelvis Anatomy

Question 1

List the bones that make up the pelvis (4)

Answer 1

1. 2 hip bones - one on either side
2. sacrum
3. coccyx

Question 2

Which bones fuse together to form the hip bones

Answer 2

1. ilium
2. ischium
3. pubis

Question 3

Functions of the bony pelvis

Answer 3

Support of the upper body when sitting and standing

Transference of weight from the vertebral column to the femurs to allow standing and walking

Attachment for muscles of locomotion and abdominal wall

Attachment for external genitalia

Protection of pelvic organs, their blood & nerve supplies, their venous and lymphatic drainage

Passage for childbirth

Question 4

pelvic girdle vs bony pelvis

Answer 4

Coccyx is not part of pelvic girdle

Sacrum is part of pelvic girdle

Question 5

Other names for hip bone

Answer 5

oscoxa

innominate

Question 6

Which bones of the hip bone fuse first?

Answer 6

Ischium and pubis at around age 4

Question 7

What is the significance of acetabulum?

Answer 7

formed by fusion of three hip bones - ‘triradiate”

Question 8

Bony landmarks of ilium

Answer 8

Iliac crest
ASIS
AIIS
PSIS
PIIS

Question 9

Bony landmarks of ischium

Answer 9

ischio-pubic ramus: where ischium and pubis join together

ischial spine

Ishicial tuberosity - attachment of hamstring

Question 10

Bony landmarks of pubis

Answer 10

ischio-pubic ramus

superior pubic ramus

pubic tubercle - protrusions in the front

pubic symphysis - joint between the two

pubic arch - forms the sub

pubic angle

Question 11

What are the boundaries of the pelvic inlet/brim?

Answer 11

1. Sacral promontry (sounds like prominent)
2. ilium - arcuate line
3. superior pubic ramus
4. Pubic symphysis

Question 12

What are the boundaries of the pelvic outlet?

Answer 12

1. pubic symphysis
2. ischiopubic ramus
3. ischial tuberosities
4. sacrotuberous ligaments
5. coccyx

Question 13

Features of pelvic cavity

Answer 13

lies within the bony pelvis

continuous with abdominal cavity above

lies between pelvic inlet and pelvic floor

contains pelvic organs and supporting tissues

Question 14

Significance of pelvic floor

Answer 14

Divides pelvis from perineum

Question 15

Palpable surface landmarks of the pelvis (anterior)

Answer 15

1. Iliac crest
2. ASIS
3. pubic symphysis - important for fundal height
4. pubic tubercle
5. inguinal ligamnet: between pubic tubercle and ASIS

Question 16

palpable surface landmarks of the pelvis (posterior)

Answer 16

1. iliac crest
2. PSIS
3. Sacrum
4. Ischial tuberosity
5. Coccyx

Question 17

Joints of the pelvis (location and type)

Answer 17

1. hip joint: acetabulum and head of femur - synovial
2. Pubic symphysis - secondary cartilaginous
3. Sacroiliac joint - synovial anteriorly, syndesmoses posteriorly

Question 18

Ligaments of the pelvis

Answer 18

Cross joints
Stabilise the joints of the pelvis

1. Sacro-tuberous (post) - from sacrum to ischial tuberosity
2. Sacro-spinous (ant) - sacrum to ischial spine

Question 19

Function of pelvic ligaments

Answer 19

1. Ensure the inferior part of the sacrum is not pushed superiorly when weight is suddenly transferred vertically through the vertebral column (e.g. when jumping or during late pregnancy)
2. The presence of these 2 ligaments also forms 2 foraminae, the greater and lesser sciatic foraminae

Question 20

Notch vs foramen

Answer 20

Notch is the hole without ligament

Question 21

Clinical relevance of bony landmarks

Answer 21

• TRAUMA to bony pelvis can result in life threatening haemorrhage and/or damage to pelvic organs
  a) common iliac artery and vein
  b) sacral plexus in close approximation with bones
  c) organs - bladder, rectum, uterus
• CHILDBIRTH - pelvis, foetal skull, labour

Question 22

Male Pelvis vs Female pelvis

Answer 22

1. AP and transverse diameter of female pelvis > male pelvis at both inlet and outlet
2. Female sub-pubic angle and arch > male
3. Depth of female pelvic cavity < male

Question 23

Foetal skull and childbirth

Answer 23

Fontanelles: anterior and posterior (clinically important)

Moulding: movement of one bone over another to allow the foetal head to pass through the pelvis during labour.
The presence of the sutures and the fontanelles allows the bones to do this

Question 24

Important terms related to foetal skull

Answer 24

Vertex: between the two parietal eminences & the anterior and posterior fontanelles (diamond) - identification of vertex helps identify fetal position

Occipitofrontal diameter: should be longer than bi-parietal diameter (skull is longer than it is wide) - allows ease of delivery

Question 25

Describe foetal positioning in relation to pelvic inlet during labour

Answer 25

At pelvic inlet: transverse diameter > AP diameter

In fetal skull: occipitofrontal diameter > biparietal diameter

Therefore, foetus should ideally enter pelvic cavity in the transverse direction (facing either right or left)

Question 26

Explain the meaning of “station” in childbirth

Answer 26

The distance of the foetal head from the ischial spines .

A negative number - head is superior to the spines

A positive number means the head is inferior to the spines.

Question 27

Describe foetal positioning in relation to pelvic cavity during labour

Answer 27

While descending through the pelvic cavity, the foetal head should:

• rotate
• be in a flexed position, i.e. chin on chest

Question 28

Describe foetal positioning in relation to pelvic outlet during labour

Answer 28

At the pelvic outlet, the AP diameter is wider than the transverse diameter

baby should ideally leave the pelvic cavity in an occipitoanterior (OA) position

During delivery the foetal head should be in extension