Pelvis and perineum

Question 1

When do the ischium, ilium and pubis fuse and where?

Answer 1

Adolescence and acetabulum

Question 2

What type of joint is the pubic symphysis?

Answer 2

Secondary cartilaginous

Question 3

What type of joint is the sacroiliac joint?

Answer 3

Plane synovial

Question 4

Which two ligaments are important in stabilising the pelvis?

What two spaces do the two ligaments form?

Answer 4

Sacrospinous - sacrum + coccyx to ischial spine

Sacrotuberous - sacrum to ischial tuberosity

Form two foramina - greater sciatic and lesser sciatic

Question 5

What structures pass through the greater sciatic foramen?

Answer 5

Sciatic nerve
Pudendal nerve
Superior and inferior gluteal nerves
Lateral rotator muscles of hip

Question 6

Which structure does piriformis pass through? O and I

Answer 6

Greater sciatic foramen

Originates from sacrum and inserts on greater trochanter

Question 7

What nerve provides motor and sensory supply to perineal region and external genitalia?

Answer 7

Pudendal nerve from sacral plexus

Question 8

Course of pudendal nerve? What accompanies it?

Answer 8

Posterior through greater sciatic notch, anterior through lesser sciatic notch.
Courses with internal pudendal artery and vein

Question 9

What does the conjugate diameter of the pelvic inlet refer to? What is it usually?

Answer 9

10.5-11cm from superior pubic symphysis to sacral promontory

Question 10

What does the transverse diameter refer to and how is it important in fetal delivery?

Answer 10

Perpendicular to the conjugate diameter

13.5cm so more space for fetus head, which can turn laterally to fit through the pelvic inlet

Question 11

What does the diagonal conjugate refer to? What is its significance clinically?

Answer 11

Used as an estimate for conjugate diameter. Insert fingers into vagina and measure length from middle finger touching sacral promontory to base of pubic symphysis
Approx 2cm greater than conjugate diameter

Question 12

What is the midpelvic diameter and rough length? Significance?

Answer 12

Diameter between ischial spines, ~11cm

Most likely place for foetus to get arrested

Question 13

What are the names of the two diameters of the pelvic outlet and what are their lengths? Significance for baby?

Answer 13

Intertuberous diameter (between ischail tuberosity) = 11cm
Anteroposterior diameter (inferior pubic symphysis to inferior coccyx) = ~13cm

Now that A-P diameter is longer, the foetal skull needs to rotate again so that it’s facing posteriorly (foetal skull longest A-P)

Question 14

Shape of male and female pelvic inlet + outlet?

Answer 14

Male = inlet heart shaped, outlet is narrow
Female = inlet is oval (widest transverse) and wide, outlet is round

Question 15

Shape of pelvic cavity female and male?

Answer 15

Male = funnel shaped
Female = cylindrical

Question 16

Subpubic angle of female and male?

Answer 16

Female = >80 degrees
Male = <70 degrees

Question 17

What are the borders of the pelvic inlet?

Answer 17

Posterior: Sacral promontory
Anterior: Pectineal line of pubis
Laterally: Arcuate line of ilium

Question 18

What is the region above and below the pelvic inlet called, and what organs do they contain?

Answer 18

Above = greater pelvis, abdominal organs
Below = lesser pelvis, reproductive and urinary organs

Question 19

What is the pelvic floor formed by?

Answer 19

Muscles:

• levator ani
• coccygeus

Question 20

What is the perineum and what separates it from the lesser pelvis?

Answer 20

Structures that lie inferior/superficial to the pelvic floor

Perineal membrane

Question 21

What muscles form levator ani?

Answer 21

Pubococcygeus

Iliococcygeus

Question 22

Innervation of pelvic diaphragm (muscles of pelvic floor)?

Answer 22

S3 and S4

Question 23

O of levator ani?

Answer 23

Tendinous arc of obturator internus

Question 24

What shape is the perineum and what defines the boundaries?

Answer 24

Diamond

Anterior: inferior pubic symphysis
Laterally: Ischial tuberosities
Posteriorly: Coccyx

Question 25

Attachment of perineal membrane? Related: where is the perineal body located and what is it?

Answer 25

Inferior border of pubic symphysis, lateral edges of ischial bones to Ischial tuberosities

PB dense mass of connective tissue that is attachment point for perineal and pelvic floor muscles found in the middle of the posterior edge of the perineal membrane

Question 26

What two structures pass through the perineal membrane?

Answer 26

Urethra and vagina

Question 27

What structures reinforce the sacroiliac joint?

Answer 27

anterior and posterior sacroiliac ligaments