pelvic overview

Question 1

What is the function of the pelvis?

Answer 1

1. Transmit the weight of the body to the lower extremities
2. Transmit digestive, urinary, and reproductive “pipes” to the pelvic outlet.
3. Transmit nervous and vascular supply from the trunk to the lower extremity and perineum.
4. Support abdominopelvic viscera.
5. Anchor pelvic diaphragm muscles (closely related to previous function!).
6. Anchor body wall muscles from the trunk.
7. Anchor lower extremity muscles.
   …all at the same time!

Question 2

Where did the pattern of forelimb and hindlimb develop first?

Answer 2

in the hindlimb

Question 3

What are the homologous bone structures in the hindlimb and forelimb?

Answer 3

Ilium ~ scapula
Ischium ~ coracoid
Pubis ~ clavicle

Question 4

Who has wider pelvises males or females?

Answer 4

females

which increases the tilt of their femora relative to their tibiae

Question 5

What are the three primary ossification centers of the os coxa?

Answer 5

ilium, ischium, and pubis

all contribute to the acetabulum connected by the triradiate cartilage

Question 6

What are the secondary ossification centers of the pelvis?

Answer 6

triradiate cartilage, 
crest of ilium, 
anterior inferior iliac spine,
 ischial tuberosity,
pubic symphyses

Question 7

What does the secondary ossification centers of the pelvis serve as?

Answer 7

as muscle attachment points are subject to avulsion fractures.

Question 8

When does the secondary ossification centers fuse?

Answer 8

late teens and early 20s.

Question 9

What is the sacrum formed from?

Answer 9

stack of fused vertebrae

Question 10

What are the ala of the sacrum formed from?

Answer 10

formed by enlarged and fused transverse processes

Question 11

What are ossification centers of the sacrum?

Answer 11

S1 and S2, they include costal elements that ossify separately from the vertebral bodies.

Question 12

What are the cornea of the sacrum and coccyx?

Answer 12

zygapophyses (articular facets).

They are often vestigial and may fail to articulate

Question 13

What is the sacral canal?

Answer 13

corresponds to the neural canal (= vertebral foramen) of more cranial vertebrae.

Question 14

What is the roof of the sacral canal?

Answer 14

roofed by the fused laminae, zygapophyses, and spinous processes of the sacral vertebrae.

Question 15

What is the sacral hiatus?

Answer 15

end of the bony roof over the sacral canal.

Its position is variable

Question 16

how is the sacral hiatus formed?

Answer 16

At some level of the sacrum, the paired neural arch elements will fail to fuse.
This disunion produces the sacral hiatus.

Question 17

How is spina bifida formed?

Answer 17

all of the neural elements of the sacrum may fail to unite, and the sacral canal has no bony roof.

Question 18

Is spina bifid a usually asymptomatic?

Answer 18

Sacral spina bifida is usually asymptomatic. The sacral canal is still covered by the dense network of ligaments, fascia, and other connective tissues, and there is little risk to the lowest branches of the cauda equina.

Question 19

What are the ossification centers of the sacrum?

Answer 19

usually five:
one for the centrum or body of the vertebra,
two for the neural arch,
in S1 and S2, two costal elements.

Question 20

When does the ossification of the sacrum fuse?

Answer 20

Epiphyseal plates for the costal processes—including the sacroiliac joint surfaces—and the ends of the vertebral bodies appear at puberty, and fuse in the mid-20s.

Question 21

How does the sacral vertebrae fuse?

Answer 21

from the bottom up

Question 22

When does the sacral vertebrae fuse?

Answer 22

18th year and ending between the 25th and 30th

Question 23

when does the joint between S1 and S2 fuse?

Answer 23

open long after the others have fused.

Question 24

how many vertebral segments does the cossyx have?

Answer 24

commonly 4

may have 3 or 5

Question 25

How does the coccyx fuse?

Answer 25

commonly found in three pieces, corresponding to segments 1, 2, and 3+4.
The coccyx may fuse to the sacrum late in life

Question 26

What is not fused on sacral vertebrae?

Answer 26

the pedicles

Question 27

Where does the spinal nerve roots exit on the sacrum?

Answer 27

sacral foramina
nerves are in place before the cartilaginous precursors of the bones; the skeleton forms around the nervous system, not vice versa.

Question 28

What are the boundaries of the pelvic inlet or line of terminalis?

Answer 28

1. Sacrum: sacral promontory, margin of ala
2. Ilium: arcuate line
3. Pubis: pecten pubis (= pectineal line), pubic crest

Note that the ischia are not involved in forming the pelvic inlet.

Question 29

What are the boundaries of the pelvic outlet?

Answer 29

1. Pubis: pubic symphysis, pubic arch (= ischial ramus of the pubis)
2. Ischium: pubic ramus (of the ischium), ischial tuberosities
3. Sacrotuberous ligament
4. Coccyx

Question 30

What is below the linea terminals?

Answer 30

true pelvis, or pelvic bowl, mostly enclosed by the

pubes, ischia, sacrum, and coccyx.

Question 31

What is above the line terminalis?

Answer 31

false pelvis, partially enclosed by the wings of the ilia.