Osteology of the Pelvis

Question 1

Which bones is the pelvis made of?

Answer 1

4 bones:
- 2 innominate bones
- Iliac crest
- (Arcuate line + pectineal line + pubic crest) = linea
terminalis
- Ischial spine - greater & lesser sciatic notches
- Ischial tuberosity
- Sacrum
- Promontory - Anterior superior edge of 1st sacral
vertebra
- Coccyx

Question 2

What is a “good” pelvis for child birth?

Answer 2

Gynecoid pelvis

• Round inlet
• Straight side walls
• Ischial spines not too prominent
• Well-rounded greater sciatic notch
• Well-curved sacrum
• Sub-pubic arch > 90°

Question 3

What is the “false” pelvis?

Answer 3

Greater pelvis (no obstetric relevance)

Question 4

What is the “true” pelvis?

Answer 4

Lesser pelvis

• Bony canal
• SOLID & IMMOBILE

Question 5

What are the 4 pelvic planes?

Answer 5

Pelvic inlet
Plane of greatest diameter
Plane if least diameter
Pelvic outlet

Question 6

What are the different clinical assessments of the pelvis in regards to childbirth?

Answer 6

Pelvic inlet
- Anteroposterior diameter
Mid-pelvis
- Check for straight side walls
- Bispinous diameter
Pelvic outlet
- Infrapubic angle
- Distance between ischial tuberosities

Question 7

What are the pelvic conjugates?

Answer 7

Antero-posterior diameter of pelvis
-Anatomical conjugate

-Obstetric conjugate
- Measured from the sacral promontory o the midpoint
of the pubis symphisis
- Can’t palpate

• Diagonal conjugate
  
  • Measured from the sacral promontory to the inferior
    border of the pubic symphisis
  • Can palpate

Question 8

Why do we use the diagonal conjugate of the pelvis instead of the obstetric conjugate?

Answer 8

Because we can palpate the diagonal conjugate, but can’t palpate the obstetric conjugate

Question 9

What is special about the pelvic outlet in reference to childbirth?

Answer 9

It is slightly less rigid
This is due to ligaments:
- Sacrotuberous ligament
And these ligament soften under the influence of progesterone.