Structure of the Pelvic Wall

Question 1

What is the Sacral Promontory?

Answer 1

The anterior-superior margin of vertebra S1 that projects forward

Question 2

What is the sacral canal?

Answer 2

Continuation of the vertebral canal

Contains the Cauda equina

Question 3

What is sacral hiatus?

Answer 3

The inferior opening to the sacral canal

Site of entry of needle for caudal injection/epidural

Question 4

What is the Coccyx?

Answer 4

4 coccygeal vertebrae fused together

Serves as site for muscle and ligament attachment

Question 5

What structures form the Pelvic Brim?

Answer 5

Promontory and ala of sacrum

Right and Left linea terminalis:

-arcuate line of the ilium, Pecten pubis, pubic crest

Question 6

What is the difference between the true and false pelvis?

Answer 6

True Pelvis - lies below the pelvic brim, contains lower GI tract and urogenital organs

False Pelvis - located above the pelvic brim, part of posterior wall of abdominal cavity

Question 7

Why are pelvic fractures associated with high mortality?

Answer 7

Pelvic organ damage and hemorrhage

One must assume damage to urinary bladder and urethra

Question 8

What is the sacroiliac joint?

Answer 8

Transmits the weight of most of the body to the hip bones

Held together by interosseous ligaments and anterior and posterior sacro-iliac ligaments

Question 9

What is the sacrotuberous ligament?

Answer 9

Broad attachment to sacrum and narrows inferiorly to attach to the ischial tuberosity

Located posterior to the sacrospinous ligament

Question 10

What is the sacrospinous ligament?

Answer 10

Triangular shape

Attaches to the lateral margin of sacrum and ischial spine

Question 11

What is the function of the sacrotuberous and sacrospinous ligament?

Answer 11

Prevent upward tilting of sacrum due to weight of trunk

Convert the greater and lesser sciatic notches into greater and lesser sciatic foramina

Question 12

What is the obturator membrane?

Answer 12

Covers obturator foramen, serves as a site of muscle attachment

Question 13

What are the three measurements for obstetrics?

Answer 13

Obstetric Conjugate

Diagonal Conjugate

Interspinous Distance

Question 14

What is the obstetric conjugate?

Answer 14

Minimum AP diameter of the lesser pelvis and narrowest fixed distance through which baby’s head must pass in a vaginal delivery

Sacral promontory to thickest margin of the pubic symphysis

Can’t be measured during pelvic exam*

Question 15

What is the diagonal conjugate?

Answer 15

Measured by palpating the sacral promontory with the tip of the middle finger while using other hand to mark the level of the inferior margin of the pubic symphysis on the examining hand

Question 16

What is the interspinous distance?

Answer 16

Distance between the ischial spines

Narrowest part of the pelvic canal

Question 17

What is the difference between the pelvic inlet, outlet, cavity and angle of pubic arches in males and females?

Answer 17

Pelvic inlet - F-oval, M - kidney shaped

Pelvic outlet - F-Large, M-Small

Pelvic cavity - F-Wide, M-Narrow

Angle of Pubic Arches - F-Wide, M-Narrow

Question 18

What are the walls of the true pelvis?

Answer 18

Lateral - Pelvic bones, Obturator Internus, Sacrospinous and Sacrotuberous ligaments

Anterior - Pubic symphysis and bodies of pubic bones

Posterior - Sacrum, coccyx, and piriformis muscle

Question 19

What is the pelvic diaphragm?

Answer 19

Thin muscle layer that forms the floor of the true pelvis

Contains urogenital hiatus for passage of urethra in both sexes

Supports pelvic viscera

Question 20

What are the origins and insertions of the Levator Ani?

Answer 20

Origin: Body of pubis, Tendinous arch, Ischial spine

Insertion: Coccyx, Anococcygeal body, Perineal body

Question 21

What is the significance of the perineal body?

Answer 21

Important for maintaining support of the pelvic viscera

If torn during childbirth, could result in organ prolapse

Question 22

What are the subdivisions off the Levator Ani?

Answer 22

Puborectalis

Pubococcygeus

Iliococcygeus

Question 23

What are the origin, insertion, and action of the coccygeus?

Answer 23

Origin: Ischial Spine

Insertion: Sacrum and Coccyx

Supports the pelvic viscera

Question 24

What is the endopelvic fascia?

Answer 24

Lines pelvic cavity and covers pelvic organs

Composed of parietal and visceral pelvic fascia

Parietal - covers muscles of pelvic wall

Visceral - located on surface of viscera

Question 25

What is the nervous supply provided by the Sacral Plexus?

Answer 25

Motor - lower limb muscles, pelvic diaphragm, muscles of perineum, pelvic viscera,

Cutaneous sensory to lower buttock and back of thigh

Question 26

What is the cause/result of compression of the sacral plexus?

Answer 26

Cause - pelvic tumor, compression by head of fetus during childbirth

Result - Pain to the lower limb (Sciatica)

Question 27

What composes the sacral plexus?

Answer 27

Anterior Rami of L4,L5 and S1-S4

Sacral nerves emerge from sacral canal via anterior sacral foramina

Question 28

What is the location of the sacral plexus (relative to a muscle)?

Answer 28

Anterior to the piriformis muscle

Question 29

What branches of the sacral plexus exit the true pelvis through the greater sciatic foramen?

Answer 29

Superior gluteal nerve - above piriformis*

Inferior gluteal nerve - below piriformis*

Sciatic Nerve - below piriformis*

Posterior Cuteaneous nerve of the thigh

Question 30

What branches of the sacral plexus pass through both the greater and lesser sciatic foramina?

Answer 30

Pudendal nerve

Nerve to Obturator Internus Muscle