The Pelvis

Question 1

Which bones fuse to form the hip (innominate) bone?

Answer 1

The ilium, ischium and pubis.

Question 2

What are the 3 joints of the pelvis and what type of joint is each one?

Answer 2

The sacroiliac (synovial); intervertebral disc (fibrous); and pubic symphysis (cartilaginous).

Question 3

What are the various diameters (conjugates) of the pelvis and between what bony
landmarks do they extend?

Answer 3

Diagonal conjugate: sacral promontory to inferior aspect of pubis; obstetric (true) conjugate: 2 cm shorter than the diagonal; midpelvic (transverse) congugate: distance between ischial spines.

Question 4

Which one, measured per vagina, is considered critical in obstetrics? Why?

Answer 4

The diagonal conjugate is measured per vagina from which the smaller - and more critical - obstetric conjugate is derived. The shortest diameter however, is the transverse conjugate.

Question 5

Define the attachments of the sacrotuberous and sacrospinous ligaments.

Answer 5

Sacrotuberous: dorsal aspect of sacrum to ischial tuberosity; sacrospinous: lateral aspect of the sacrum to the ischial spine.

Question 6

What two foramina are formed by these structures?

Answer 6

Greater (via sacrospinous lig.) and lesser (via sacrotuberous lig.) sciatic foramena.

Question 7

Name the muscles that form the walls of the pelvis?

Answer 7

Obturator internus and piriformis.

Question 8

What are the attachments of the muscles that form the walls of the pelvis?

Answer 8

Obturator internus: rim of obturator foramen to greater trochanter; and piriformis: vertebrae S1-3 to greater trochanter.

Question 9

What is the innervation of the obturator and piriformis muscles?

Answer 9

Obturator internus: n. to obturator internus (L5, S1.2); and piriformis: (S1,2).

Question 10

What muscles form the floor of the pelvis?

Answer 10

Coccygeus and levator ani mm. (pubococcygeus + iliococcygeus - deeper fibers of the latter = puborectalis)

Question 11

Where do the muscles of the pelvic floor arise?

Answer 11

Coccygeus: ischial spine to lateral margin of sacrum & coccyx; and levator ani: pubis and tendinous arch of obturator internus to coccyx.

Question 12

What is the innervation of the coccygeous and levator ani?

Answer 12

S2,3,4.

Question 13

What do these muscles form a sling around?

Answer 13

Lower rectum/upper anal canal.

Question 14

What is the perineal body?

Answer 14

A connective tissue mass.

Question 15

Where is the perineal body located?

Answer 15

Between the anus and the base of the scrotum in the male or the posterior aspect of the vagina in the female.

Question 16

Why is the perineal body clinically important?

Answer 16

It is either incised, or avoided, in episiotomies during childbirth.