Lecture 15: Bones & Joints of Pelvis

Question 1

What separates the true (lesser) and false (greater) pelvis?

Answer 1

Iliopectineal line - top of pubis along bony ridge to lieum

Question 2

How is the female pelvis different to the male pelvis?

Answer 2

Wider than it is longer, narrower in height, wide subpubic arch, ischial spine does not project far medially, round pelvic inlet

Question 3

What are the 4 types of female pelvis and the occurrence of these?

Answer 3

Gynaecoid - 50%
Android - 30%
Anthropoid - 18%
Platypelloid - 2%

Question 4

What is characteristic of a gynaecoid pelvis?

Answer 4

Designed to allow foetus to move through

Question 5

What is characteristic of an android pelvis?

Answer 5

Not ideally suited for childbirth, narrower side to side and longer, funnel shaped in midpelvis

Question 6

What is characteristic of the anthropoid pelvis?

Answer 6

Narrow medial to lateral, elongated anteroposterioly (related to head shape of ape)

Question 7

What is characteristic of the platypelloid pelvis?

Answer 7

Flattened

Question 8

What are the features of the male pelvis?

Answer 8

Tall and narrow, heart shaped inlet, narrow subpubic angle, ischial spine projects medially into mid pelvic region

Question 9

How is the pelvis tilted?

Answer 9

Tilted forwards so pubis is more inferior than rest of pelvis.

Question 10

Which gender has greater lumbar lordosis?

Answer 10

Females - more pelvic tilt

Question 11

What is the shape of the pelvic outlet and how does it differ between genders?

Answer 11

Diamond shaped, narrowed in both directions in males

Question 12

What is the pelvic outlet divided into?

Answer 12

Urogenital triangle and anal triangle

Question 13

What are the boundaries of the urogenital triangle?

Answer 13

Bony

Question 14

What are the boundaries of the anal triangle?

Answer 14

Ligamentous

Question 15

What is the narrow pelvic plane?

Answer 15

Plane of least dimensions in the pelvis. Passes through ischial spine, S4 and pubic bones

Question 16

What is the average diameter of foetus skull at birth?

Answer 16

9.5cm

Question 17

What is the average diameter of the female pelvis?

Answer 17

10.5-11.5cm

Question 18

How does the foetus move through the pelvis?

Answer 18

Head is transverse and fits through pelvic inlet, then pelvic floor rotates head of baby so that when it reaches the true pelvis the head is in an anteroposterior direction and the chin is on the chest, moves through pelvic outlet in same posture

Question 19

What is the vertex presentation?

Answer 19

When the baby is moving through the true pelvis and the head is tilted down - smallest diameter 9.5cm

Question 20

What happens if the baby presents with a brown presentation, how is this accommodated for?

Answer 20

Head is up (13.5cm diameter) and delivery is made difficult.

Baby has fontanels in skull that allow cranial bones to slide across each other

Question 21

When does the frontal fontanel close?

Answer 21

18 months

Question 22

What is characteristic of the pubic symphysis in younger individuals?

Answer 22

Has ridges and grooves - these are worn away with age

Question 23

What are the two bony arches in the pelvis and what do they do?

Answer 23

• Acetabulum to acetabulum, bears weight when standing

- Between ischial bones and pubis, bears weight when sitting

Question 24

How is weight transferred when standing?

Answer 24

Weight transmitted from trunk to pelvis and causes pelvis to rotate forwards

Question 25

What does the pelvis rotate relative to?

Answer 25

S2

Question 26

Why does little rotation actually occur at the pelvis?

Answer 26

Strong ligamentous support - interosseous, sacroiliac, sacrospinous, sacrotuberous

Question 27

What is the reverse keystone effect?

Answer 27

Sacrum sinks forwards and downwards into the pelvis, posterior ligaments tighten and draw iliac bones together

Question 28

What are the features of the sacroiliac joint?

Answer 28

Synovial anterior and fibrous posterior, held together by powerful ligaments that resist tendency of sacrum to rotate, auricular and iliac surfaces, only 2-8 degrees of movement – usually when you get up from lying down, movements may increase during mid-late stages of pregnancy

Question 29

What happens when the ligaments supporting the SIJ are damaged in pregnancy?

Answer 29

SIJ pain L5-S2 posteriorly, L3-S1 anteriorly, pain referred to medial and lower bum

Question 30

What is the function of the posterior layer of lumbar fascia?

Answer 30

Acts as an intermediary in transferring loads between trunk and lower limb muscles (lat dorsi and gmax)

Question 31

What are the features of the pubic symphysis?

Answer 31

Midline secondary cartilaginous joint, superior, arcuate and anterior (resist vertical forces) ligaments, reinforced by criss crossing fibres from rectus abdominus and transversus (+ adductor longus and internal oblique) – tie beam, prevent lateral separation, site of pubic symphysitis

Question 32

What is nutation and counter nutation?

Answer 32

Pelvis tilting forwards and backwards

Question 33

What is characteristic of a pelvic fracture, and what is unique in kids?

Answer 33

Because it is a ring it fractures in multiple places, in kids the ligament is stronger than bone so common to get avulsion fractures