Bony Pelvis & Pelvic Diaphragm

Question 1

What bones make up the bony pelvis?

Answer 1

Pelvic bone, sacrum, and coccyx

Question 2

What bones make up the pelvic bone? Where do they fused?

Answer 2

Three fused bones: ilium, ischium, and pubis.

They fuse in the acetabulum, which is the socket for the head of the femur

Question 3

What two regions does the ischial spine demarcate?

Answer 3

Greater sciatic notch - Superior to ischial spine in the ilium
Lesser sciatic notch - Inferior to ischial spine, in the ischium

Question 4

What makes up the ischiopubic rami and what does it surround?

Answer 4

The ramus of the ischium and the inferior pubic ramus. It surrounds the obturator foramen on one side

Question 5

What bones form the obturator foramen?

Answer 5

Only the ischium and pubis bones

Question 6

What bone is the pectineal line part of? What is it also called?

Answer 6

Pubis, also called pectin pubis

Question 7

What is the linea terminalis and what areas does it define?

Answer 7

It is the sharp marginal line defining the pelvic inlet. It defines the boundary between true pelvis and false pelvis

Question 8

What is the lining of the linea terminalis from anterior to posterior?

Answer 8

Pubic crest, pectineal line, arcuate line, margin of ala, promontory

Question 9

What is the false pelvis?

Answer 9

Part of abdominal cavity, defined as region contained by pelvic bones but lying superior to linea terminalis

Question 10

What is the true pelvis?

Answer 10

Region inferior to linea terminalis but superior to pelvic diaphragm

Question 11

What is the bone you sit down on?

Answer 11

The ischial tuberosity

Question 12

What borders define the pelvic outlet?

Answer 12

The inferior aspect of the pubic symphysis to the tip of the coccyx. Bordered by coccyx, medial boundary of sacrotuberous ligament, ischial tuberosity, ischiopubic rami, and pubic symphysis.

Question 13

What are gynecological conjugates and how is the inlet diameter measured?

Answer 13

Ways of measuring the pelvic inlet and outlet to see if the baby will fit. The inlet diameter is measured from the superior surface of the pubic symphysis to the promontory of the sacrum

Question 14

How is the pelvis oriented in the vertical plane?

Answer 14

The anterior superior iliac spines are in the same vertical plane as the pubic tubercles

Question 15

What are the two shapes of the pelvic outlet between sexes? How can you determine the difference by X-ray?

Answer 15

Males: Android (heart-shaped). denser pelvic bone, pronounced promontory + ischial spine
Females: Gynocoid (Circular / oval), wider ala and less prominent promonotory.

X-ray: pubic angle is 50-60 degrees in males, and 80-105 degrees in females

Question 16

How is the femur / acetabulum different between males and females?

Answer 16

Female: acetabulum displaced anteriorly to position the neck of the femur to be anterior to the coronal plane.

Male: Femur is 15-20 degrees posterior to female

Question 17

What ligaments are above and below the pubic symphysis?

Answer 17

Superior and inferior pubic ligaments

Question 18

What is the obturator membrane and what passes through it?

Answer 18

It is the tendinous membrane which almost fully encloses the obturator foramen.

Superiorly, there is an opening which allows the passage of the obturator nerve, artery, and vein from pelvis into adductor compartment of thigh

Question 19

What is the sacrotuberous ligament?

Answer 19

Ligament attaching from posterior aspect of sacrum to ischial tuberosity. Lies posterior to sacrospinous ligament

Question 20

What is the sacrospinous ligament? What does it divide?

Answer 20

Ligament anterior to sacrotuberous ligament, connecting from lower margin of sacrum to ischial spine. Demarcates the greater and lesser sciatic foramen.

Question 21

What is the function of the greater sciatic foramen and what muscle exits there?

Answer 21

Foramen accommodating outflow of blood vessels, nerve, and piriformis muscle from pelvis to gluteal region. It functions to facilitate communcation between pelvis and gluteal region.

Question 22

What is the lesser sciatic foramen? What is the only structure that exits the pelvis here?

Answer 22

Communication between the gluteal region and the perineum through the pudental canal.

Only structure to exit pelvis into gluteal region here is the tendon of the obturator internus muscle.

Question 23

What is the origin, insertion, innervation, and action of the obturator internus muscle?

Answer 23

Origin: Internal surface of obturator membrane, superior pubic and inferior ischiopubic rami
Insertion: Tendon bends 90 degrees thru lesser sciatic foramen to greater trochanter of femur
Innervation: Nerve to obturator internus (lumbosacral plexus)
Action: Lateral rotation of femur

Question 24

What is the origin, insertion, innervation, and action of the piriformis muscle?

Answer 24

Origin: Pelvic surface of sacrum
Insertion: Tendon through greater sciatic foramen to greater trochanter of femur
Innervation: Small branch of lumbosacral plexus
Action: Lateral rotation of femur

Question 25

What two fascial thickenings form on the obturator internus muscle?

Answer 25

Pelvis: Tendinous arch
Perineum: Pudental canal

Question 26

What is the tendinous arch and where does it extend?

Answer 26

Thickening of obturatur internus fascia which divides the true pelvis from the perineum by serving as attachment to the pelvic diaphragm muscles.

Attach: Superior pubic rami (just lateral to pubic tubercle) and extending in an arc to the ischial spine

Question 27

What is the anococcygeal ligament?

Answer 27

Central ligament suspending the anal canal to the tip of the coccyx. It is the place where the right and left halves of the pelvic diaphragm fuse posterior to the anal canal

Question 28

What is the median raphe?

Answer 28

The spot beneath the anococcygeal ligaments where the pelvic diaphgram is actually fused

Question 29

What is the urogenital hiatus?

Answer 29

The opening in the pelvic diaphragm anterior to the anal canal where it splits on each side to allow midline passage of urethra in both sexes + vagina in females.

Question 30

What forms the inferior boundary of the abdominal cavity?

Answer 30

Pelvic diaphragm + urogenital diaphragm around urogenital hiatus, which prevents abdominal and pelvic viscera from escaping the pelvis into the perineum

Question 31

What two muscles make up the pelvic diaphragm

Answer 31

1. Levator ani - 3 muscles on each side

2. Coccygeus muscle - 1 muscle on each side

Question 32

What muscles make up the levator ani?

Answer 32

Puborectalis, pubococcygeus, iliococcygeus

Question 33

What is the puborectalis muscle? Where is it best seen? What is its function?

Answer 33

Levator ani muscle attaching laterally to pubic symphysis and wrappign around rectum posteriorly to form a sling with its partner. It is inferior to the pubococcygeus muscle so it is best seen from the perineum

Function: Maintain anorectal flecture and the anorectal junction. It is normally contracted, putting an 80 degree bend in alignment of rectum with anal canal to maintain fecal continence.

Question 34

What is the pubococcygeus muscle?

Answer 34

Levator ani muscle attaching to anterior half of tendinous arch, forming lateral margins of urogenital hiatus. Form part of the median raphe posteriorly, which attaches to superior surface of anococcgeal ligament.

Question 35

What is the iliococcygeus muscle?

Answer 35

Levator ani muscle attaching to posterior half of tendinous arch and ischial spine to insert on posterior portion of anococcygeal ligament and tip of coccyx.

Question 36

What is the coccygeus muscle? What is the major attachment?

Answer 36

Thin, triangular muscle with origin from ischial spine attaching to coccyx and lateral margin of sacrum at SV5 level. It attaches to the anterior surface of the sacrospinous ligament.

Question 37

What innervates the pelvic diaphragm?

Answer 37

Ventral sacral rami on floor of pelvis, plus inferior rectal nerve (a branch of pudental nerve)

Question 38

Where does the urogenital (UG) diaphragm extend?

Answer 38

Occupies the space between the two ischiopubic rami (IPR) up to the ischial tuberosities. Forms a physical boundary to close of the urogenital hiatus of levator ani, and forms foundations here.

Question 39

Where do the pelvic diaphragm and UG diaphragm fuse?

Answer 39

Along margin of UG hiatus.

Question 40

What forms the borders of the anterior recess of the ischioanal fossa and what is it?

Answer 40

It is a potential space between the pelvic diaphragm and UG diaphragm. It is filled with fat normally, and is felt when you go above the UG diaphragm but beneath the tendinous arch demarcating the levator ani.

Medially / Superiorly : Levator ani
Inferiorly: UG diaphragm
Laterally: Obturator internus muscle and ischiopubic rami