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What is the function of the pelvis?

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!


Where did the pattern of forelimb and hindlimb develop first?

in the hindlimb


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

Ilium ~ scapula
Ischium ~ coracoid
Pubis ~ clavicle


Who has wider pelvises males or females?

which increases the tilt of their femora relative to their tibiae


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

ilium, ischium, and pubis
all contribute to the acetabulum connected by the triradiate cartilage


What are the secondary ossification centers of the pelvis?

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


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

as muscle attachment points are subject to avulsion fractures.


When does the secondary ossification centers fuse?

late teens and early 20s.


What is the sacrum formed from?

stack of fused vertebrae


What are the ala of the sacrum formed from?

formed by enlarged and fused transverse processes


What are ossification centers of the sacrum?

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


What are the cornea of the sacrum and coccyx?

zygapophyses (articular facets).
They are often vestigial and may fail to articulate


What is the sacral canal?

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


What is the roof of the sacral canal?

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


What is the sacral hiatus?

end of the bony roof over the sacral canal.
Its position is variable


how is the sacral hiatus formed?

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


How is spina bifida formed?

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


Is spina bifid a usually asymptomatic?

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.


What are the ossification centers of the sacrum?

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


When does the ossification of the sacrum fuse?

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.


How does the sacral vertebrae fuse?

from the bottom up


When does the sacral vertebrae fuse?

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


when does the joint between S1 and S2 fuse?

open long after the others have fused.


how many vertebral segments does the cossyx have?

commonly 4
may have 3 or 5


How does the coccyx fuse?

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


What is not fused on sacral vertebrae?

the pedicles


Where does the spinal nerve roots exit on the sacrum?

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


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

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.


What are the boundaries of the pelvic outlet?

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


What is below the linea terminals?

true pelvis, or pelvic bowl, mostly enclosed by the
pubes, ischia, sacrum, and coccyx.