Pelvic Anatomy - BGDA

Question 1

What are the 3 main joints of the pelvis?

Answer 1

Sacroiliac, sacrococcygeal and pubic symphysis

Question 2

What are the three ligaments of the sacroiliac joint?

Answer 2

Ventral sacroiliac ligament, dorsal sacroiliac ligament, interosseous sacroiliac ligament

Question 3

What is the pubic symphysis?

Answer 3

Midline fibrocartilaginous joint between the bodies of left and right pubis.

Question 4

Which ligaments strengthen the pubic symphysis?

Answer 4

Superior pubic ligament and inferior (arcuate) pubic ligament

Question 5

What are the vertebropelvic ligaments?

Answer 5

The sacrotuberous ligament (which extends from the sacrum and coccyx to the ischial tuberosity) and the sacrospinous ligament which extends from the sacrum and coccyx to the ischial spine.

Question 6

What do those two ligaments achieve together?

Answer 6

They convert the sciatic notches into respective sciatic foramina. These ligaments stop the sacrum from rotating due to pressure upon LV5 and the sacral promontary.

Question 7

What is the iliolumbar ligament?

Answer 7

This ligament extends from LV5 transverse processes to the iliac crest - prevent the downward displacement of the sacrum (due to pressure from body weight)

Question 8

List a reason for why male and female pelvis shapes differ.

Answer 8

The pubic bone is wider in females with greater separation of the pubic tubercles.

Question 9

List a reason for why male and female pelvis shapes differ.

Answer 9

The subpubic arch is wider in females and distance between ischial spines and tuberosities is greater.

Question 10

List a reason for why male and female pelvis shapes differ.

Answer 10

The subpubic angle in men is rather acute (about 60 degrees) while in females it can be greater than 80 degrees

Question 11

List a reason for why male and female pelvis shapes differ.

Answer 11

Men’s pelvic inlet is marked by a large sacral promontory. Women’s inlet does not have as prominent a sacral promontory.

Question 12

List a reason for why male and female pelvis shapes differ.

Answer 12

Men’s pelvises tend to be more robust with more substantial muscle attachment and thicker bone.

Question 13

What are the 4 pelvis shapes?

Answer 13

Gynecoid - optimal and round
Android - heart shaped
Anthropoid - elongated top to bottom
Platypelloid - elongated side to side

Question 14

What is the pelvic inlet?

Answer 14

The pelvic inlet is tilted at an angle of 50-60 degrees to the horizontal and is bounded by the sacral pormontory and alae, the arcuate line of the ilium and the pectineal line, pubic crest and pubic symphysis of the pubis.

Question 15

What is the pelvic outlet?

Answer 15

The pelvic outlet is tilted at an angle of 15 degrees to the horizontal and is bounded by the coccyx, sacrotuberous ligament, ischial tuberosity, ischiopubic ramus and pubic symphysis.

Question 16

What are the three levels of the true pelvic cavity?

Answer 16

The pelvic inlet, the mid-pelvic cavity and the pelvic outlet.

Question 17

What are the names of the diameters of each level?

Answer 17

Oblique, transverse and anteroposterior diameter.

Question 18

Describe the measurements of the pelvic inlet.

Answer 18

At the pelvic inlet, the transverse diameter is greatest (13.1cm), compared to anteroposterior (11.2cm) and oblique (12.5cm).

Question 19

Describe the measurements of the mid-pelvic cavity.

Answer 19

At the level of the mid-pelvic cavity, the oblique diameter is greatest (13.1cm), compared to anteroposterior (13.0cm) and transverse (12.5cm).

Question 20

Describe the measurements of the pelvic outlet.

Answer 20

At the level of the pelvic outlet, the anteroposterior diameter is greatest (12.5cm), compared to transverse (11.8cm) and oblique (11.8cm).

Question 21

What is the point of all this?

Answer 21

The baby, with its head flexed, corkscrews its way through the birth canal with the occiput facing transversely, then obliquely then anteriorly. This allows for a smooth transition through the birth canal as the baby negotiates the turn from the uterine axis to the vaginal axis.

Question 22

Which two muscles form the lateral walls of the pelvic cavity?

Answer 22

Piriformis and obturator internus.

Question 23

Outline key features of the piriformis muscle.

Answer 23

The piriformis muscle originates from the sacrum and passes through the greater sciatic foramen to insert on the femur.

Question 24

Outline key features of the obturator internus.

Answer 24

The obturator internus originates from the obturator membrane and pelvic bone, surrounds the obturator foramen and passes through the lesser sciatic foramen to insert on the femur.

Question 25

Which muscles form the pelvic diaphragm?

Answer 25

Ischiococcygeus and levator ani muscles.

Question 26

What is the role of the muscles of the pelvic diaphragm?

Answer 26

They support the pelvic viscera as well as oppose and/or control and/or augment micturition, parturition and defacation.

Question 27

Which three muscles form the levator ani?

Answer 27

Iliococcygeus, pubococcygeus and puborectalis muscles.

Question 28

Outline the key features of the iliococcygeus muscle.

Answer 28

The iliococcygeus muscle extends from the pelvic aspect of the ischial spine and the posterior part of the tendinous arch to the side of the coccyx.

Question 29

Outline key features of the pubococcygeus muscle.

Answer 29

The pubococcygeus muscle extends from the back of the pubis and anterior part of the obturator internus fascia to the coccyx. Can be said to have component muscles (levator prostatae in men, pubovaginalis in women - control of micturition)

Question 30

Outline key features of the puborectalis.

Answer 30

The puborectalis muscle is inferior to other muscles, forms a sling which originates at the pubis and encircles the anorectal junction. Posterior fibres mingle with those of the external sphincter or merge with the anococcygeal ligament.

Question 31

What is the anococcygeal ligament?

Answer 31

This is the ligament that is formed by the union of the levator ani muscles posteriorly. It attaches to the coccyx.

Question 32

Outline key features of the ischiococcygeus muscle.

Answer 32

• This muscle arises from the ischial spine and inserts into the last piece of the sacrum and coccyx
• it blends with the sacrospinous ligament - muscle fibres are embedded in and associated with the ligament

Question 33

What are the two fascia of the pelvic diaphragm?

Answer 33

The superior pelvic diaphragm fascia and inferior pelvic diaphragm fascia.

Question 34

What are the two triangles?

Answer 34

Diamond shape divided into two - upper portion is urogenital triangle and lower portion is anal triangle.

Question 35

What is the external anal sphincter?

Answer 35

This is a muscle that surrounds the anal canal and plays a role in controlling defacation.

Question 36

What is the space below the pelvic diaphragm?

Answer 36

Ischiorectal fossa

Question 37

Outline the ischiorectal fossa

Answer 37

The ischiorectal fossa is bounded by the sacrotuberous ligament, ischiopubic ramus and fascia of the obturator internus.
- Filled with liquid fat
- contains the pudendal canal (pudendal nerve, internal p. artery and internal p. vein)
- contains inferior rectal nerves and vessels
- anteriorly, the space extends between the levator ani and the urogenital diaphragm as the anterior recess of the ischiorectal fossa

Question 38

What fills the urogenital triangle?

Answer 38

The urogenital triangle is filled by the urogenital diaphragm

Question 39

What is the urogenital diaphragm composed of?

Answer 39

Sphincter urethrae (anteriorly), deep transversus perinei (posteriorly), and the superior and inferior fascia of the urogenital triangle (above and below the muscles)

Question 40

Where do the muscles of the diaphragm lie?

Answer 40

In the deep perineal space between the two fascia

Question 41

What separates the inferior pelvic diaphragm fascia from the superior UV diaphragm fascia?

Answer 41

Anterior recess of the ischiorectal fossa

Question 42

What is the superficial perineal space?

Answer 42

This is the space that lies inferior to the inferior urogenital diaphragm fascia aka the perineal membrane

Question 43

What does this space contain?

Answer 43

The superfical transversus perinei, bulbospongiosus and the ischiocavernosus

Question 44

What covers the superficial perineal space?

Answer 44

Superficial urogenital fascia

Question 45

Outline key features of the superficial transversus perinei

Answer 45

• passes medially from the ischial tuberosity to a fibromuscular node (the tendinous centre of the perineal body)
• this is located between the vagina and anus in the female, and between the membranous urethra and anus in the male

Question 46

What does the ischiocavernous muscle cover?

Answer 46

The crura of the penis or clitoris

Question 47

What does the bulbospongiosus muscle cover?

Answer 47

The bulb of the vestibule (female) or the bulb of the penis (male)

Question 48

Where else does the perineal body receive fibres from?

Answer 48

• levator prostatae
• pubovaginalis
• deep and superficial transversus perinei
• sphincter ani externus
• sphincter urethrae
• bulbospongiosus