Bones and Joints of Pelvis

Question 1

What demarcates the true pelvis from the false pelvis and what muscle attaches to it?

Answer 1

Iliopectineal line.

Pectineus muscle attaches to it.

Question 2

Describe the 4 types of pelvis and their shape.

Answer 2

50% of females have a Gynaecoid pelvis, which is designed to accommodate fetus, and for the fetus to pass through the pelvis into the birth canal.

30% of females however, have the android type, not well suited for child birth, because its narrower from side to side and longer from front to back and funnel shaped in the true pelvis so they may have complications while in females that diameter stays the same all the way through

• Remaining 20% of females are of 2 other types:

1. 18% Anthropoid pelvis: similar to the apes, very narrow medial - lateral, elongated in anterio-posterior direction
2. 2% Platypelloid pelvis: flattened much like the beak of a pelvis.

Question 3

What does our lordotic curvature allow?

Answer 3

Lordotic curvature - tilts the pelvis forwards and allows the lumbar spine and pelvis to accommodate to the line of gravit

Question 4

What bones is the hip bone made out of?

Answer 4

Illium, Ischium, Pubis.

Question 5

What do the 3 hip bones form?

Answer 5

The 3 bones join together to form the acetabulum, and they have an epiphyseal plate.

Question 6

What do we use the coccyx as a landmark for?

Answer 6

→ We use the coccyx as a landmark for viscera. E.g. the ovaries in the females is located on a line that runs between the tip of the coccyx and the top of the pubic symphysis.
→ Therefore the ovary can be palpated at the line.
→ In males, the seminal vesicles are also located on that line.

Question 7

What is the main limitation of the pelvis and where is this plane?

Answer 7

Runs from S4, to the inferior aspect of the pubic symphsys - the narrow pelvic pain (narrowest part of the pelvis) where the largest part of the head of the baby needs to pass during child birth.

The main limitation is the narrow pelvic pain.

Question 8

What happens to the foetus as it descends through the pelvis and how does the pelvic floor allow this?

Answer 8

As the fetus descends into the pelvis, the head is located transversely and then it can then fit through the pelvic inlet, because the average diameter of the skull is 9.5cm.
What it does is rotate the head and body of the fetus, so by the time we get to the true pelvis, the head is an antero-posterio direction and the babies chin gets tilted to its head, so it presents the smallest diameter called the vertex presentation.

Question 9

If the foetus presents in the ‘brow presentation’ how can the head accommodate for this?

Answer 9

The head can accommodate to this, there are space in the head, call ‘fontanels’ = ‘window’, and they stay open until about 18 months, allowing the cranial bones to slide along each other, making this birth process much easier, and quite often you see babies that the head is quite distorted, but this changes after birth.

Question 10

What are the 5 apertures of the pelvis?

Answer 10

1. Pelvic Inlet - from the abdomen
2. Anterior sacral foraminae - to back
3. Obturator canal - to lower limb
4. Greater sciatic foramen - to lower limb
5. Lesser sciatic foramen - to perineum and gluteal region

Question 11

Where do the 2 arches of the pelvis travel and how do they aid in the transfer of weight inferiorly?

Answer 11

1. From acetabulum, through to the top of the sacrum, and to the other acetabulum on the other side.
   It is this arch that bears weight in stance ‘standing’
2. Between the two ischial bones, bearing weight in sitting.

Question 12

What do the pubic bones allow for in terms of the mechanism of the pelvis?

Answer 12

They allow for movement and load transfer and absorption of force between trunk and limbs

Question 13

Where is the centre of rotation on the sacrum?

Answer 13

S2

Question 14

Nutation is resisted by which ligaments?

Answer 14

Interosseus sacroiliac
Sacrospinous
Sacrotuberous

Question 15

What are the 2 joints of the pelvis?

Answer 15

• Sacroilliac Joint

- Pubic symphysis

Question 16

Describe the sacroilliac joints

Answer 16

Synovial  + Fibrous
* Secondary Cartilaginous* 
 Held together by powerful ligaments: Interssous sacroiliac 
Iliolumbar 
Sacrotuberous
Sacrospinous

Question 17

When does the most amount of movement occur at the scare-illiac joint?

Answer 17

When you go from recumbent position to standing up .

Question 18

What is the name of the hormone that relaxes pelvic ligaments and when is it released?

Answer 18

Relaxin. Mid- Late stages of pregnancy. To allow for the exit of baby.

Question 19

What acts as an intermediary in transferring loads between tank and lower limbs?

Answer 19

Posterior layer of lumbar fascia

Question 20

Describe the Pubic Symphysis.

Answer 20

2nd Cartilaginous joint.
Ligaments that support it : Superior, arcuate(resisting vertical forces) and anterior
Reinforced by criss crossing fibres from rectus abdomens and transversus (+ adductor longs and internal oblique)

Question 21

What is Ring Phenomena?

Answer 21

Concept that if there is a fracture at one side, there will also be another fracture at its diametrically opposing section. - Occurs in pelvis.