4) Osteology of the Pelvis

Question 1

Which bones make up the pelvic girdle?

Answer 1

Right & Left hip bones (Ilium,Ischium & Pubis)

Sacrum (fusion of 5 sacral vertebrae)

Question 2

Where do the hip bones articulate with

a) each other
b) sacrum?

Answer 2

a) Pubic symphysis

b) Sacroiliac joint

Question 3

Describe the android (male) pelvis

Answer 3

Thick & heavy
Deep greater pelvis
Narrow & deep, tapering lesser pelvis
Heart-shaped, narrow pelvic inlet
Comparatively small pelvic outlet
Narrow pubic arch (<70 degrees)
Round obturator foramen
Large acetabulum
Narrow (-70 degree), inverted V greater sciatic notch

Question 4

Describe the gynecoid (female) pelvis

Answer 4

Thin & light
Shallow greater pelvis
Wide & shallow, cylindrical lesser pelvis
Oval & rounded, wide pelvic inlet
Comparatively large pelvic outlet
Wide pubic arch (>80 degrees)
Oval obturator foramen
Small acetabulum
Almost 90 degrees greater sciatic notch

Question 5

What is a good pelvis for childbirth?

Answer 5

Round inlet
Straight side walls
Ischial spines not too prominent
Well-rounded greater sciatic notch
Well-curved sacrum (fit with foetal head)
Sub-pubic arch >90 degrees

Question 6

What forms the pelvic inlet?

Answer 6

Promontory & ala of the sacrum posteriorly

Right & Left linea terminalis anteriorly (pubic crest, pectineal line & arcuate line)

Question 7

What forms the pelvic outlet?

Answer 7

Anteriorly - pubic arch
Laterally - ischial tuberosities
Posterolaterally - Inferior margin of sacrotuberous ligament
Posteriorly - Tip of coccyx

Question 8

Throughout pregnancy, how does the pelvic outlet increase?

Answer 8

Progesterone softens the sacrotuberous ligament
Increases size of pelvic outlet
Aids childbirth

Question 9

What is the anatomic conjugate of the pelvic inlet?

Answer 9

Sacral promontory to superior border of pubic symphysis

Question 10

What is the obstetric conjugate of the pelvic inlet?

Answer 10

Sacral promontory to midpoint of pubic symphysis

Shortest diameter in plane, pubic bone thickest

Question 11

What is the diagonal conjugate of the pelvic inlet?

Answer 11

Sacral promontory to inferior border of pubic symphysis

Reasonable approximation of antero-posterior diameter as cannot palpate pubic symphysis

Question 12

What is the greater pelvis?

Answer 12

Part of pelvis
superior to pelvic inlet
bounded by iliac alae posterolaterally
anterosuperior aspect of S1 posteriorly
Occupied by abdominal viscera (ileum & sigmoid colon)

No obstetrical significance

Question 13

What is the lesser pelvis?

Answer 13

Part of pelvis:
Bony canal, solid & immovable, between pelvic inlet & outlet
Bounded by pelvic surfaces of hip bones, saccrum & coccyx

Major obstetrical & gynaecological significance