Flashcards in Lecture 17 RH Deck (36)
What are the divisions of the pelvis?
True 'lesser' pelvis
False 'greater' pelvis
What is the difference between the pelvic divisions?
True pelvis is the part of the pelvis that contains most the pelvic viscera and bone anteriorly. (closed)
False pelvis is superior and has no anterior bone. (more open)
What does the true pelvis contain?
True pelvis contains the termination of the GI tract, the urinary tract and genital tract.
what divides the true and false pelvis from each other?
the iliopectineal line
What are the main differences between male and female pelvises?
Female pelvis is wider than it is longer.
Female pelvis underneath pubic bone is wide and narrow in a male.
Males have a heart shaped inlet whereas females have a wide inlet mediolaterally.
In males ischial spine projects medially but in females it doesn't project as far medially.
Outlet is narrow in males but both males and females have diamond shaped outlets
What is the variation of the pelvis in females?
30% of females have android pelvises. (not ideally suited for childbirth and more funnel shaped)
50% of females have gynaecoid pelvis. (Inlet is wide mediolaterally)
the remaining 20% have eitehr anthropoid (similar to primates) and platypelloid ( in 2% of females and is flattened in shape)
What is the common pelvis shape among males?
most males have an android pelvis. (funnel shaped going down)
How is the sacrum and the pelvis orientated relative to the rest of the body?
Sacrum and upper pelvis is tilted forward so that the pubis is inferior compared to the upper part of the pelvis. Pubis is in line with lumbosacral joint.
What is different in females compared to males about the tilt of the lumbar spine and pelvis?
Females have a more exaggerated lumbar lordosis and pelvic tilt than males.
What fills the obturator foramen?
What happens to the pelvic bones at the acetabulum?
Ischium posterior to pubis
Ilium meets the other bones at the acetabulum
What is the function of the obturator membrane?
Membrane gives rise to muscles that pass through pelvic cavity and some to the lower limb.
Why are the sciatic notches important?
2 sciatic notches important for transmission of nerves and blood vessels.
What is the pelvic outlet divided into? What are the kinds of boundaries they contain?
outlet contains the urogenital triangle (anteriory) and the anal triangle (posteriorly).
urogenital triangle contains bony boundaries and anal triangle is ligamentous.
What are the boundaries of the pelvic inlet?
from the top of the pubis to the sacroiliac joint
What are the boundaries of the narrow pelvic plane?
from S4 to inferior pubis
What is the narrow pelvic plane?
It is an important point that the fetus has to pass through for the pelvis
What is the average size of the pelvic inlet and outlet in females?
average pelvic inlet size is 11 - 13.5cm
average pelvic outlet size is 11 - 11.5
*fetal skull is about 9.5cm in diameter
How does the fetus present itself when moving through the narrow pelvic outlet?
pelvic floor rotates the fetus so that it faces anteroposteriorly in a way that makes it form the smallest possible diameter called vertex presentation.
If this doesn't work out the skull can narrow itself to fit through outlet via fetonelles*.
What happens to the pubic symphysis with aging?
ridges and grooves on pubic symphysis are smoothened with age.
What are the arches of the pelvis and when are they important?
acetabuli to sacrum form the arch that bears weight during standing.
between pubic bones is important when sitting
How does bone structure assist in weightbearing?
bones are organised in trabeculae from pelvis passing through upper femur which resist weightbearing forces. Other trabeculae for to the pubis to resist sitting forces.
How is weight distributed when standing?
when standing weightbearing from above and below the pelvis follow the pelvic ring structure.
Where is the center of rotation of the pelvis?
What ligaments resist movement of the pelvis?
Sacrospinous between sacrum and ischial spine.
sacroiliac between ilium and sacrum
sacrotuberous between sacrum and ischial tuberosity
Describe the reverse keystone effect:
Sacrum sinks forwards and downwards into the pelvis and posterior ligaments tighten and pull the iliac blades with them and so they stabilise the joint.
What are the 2 joints that are important for connecting hip bones?
2 joints that connect hip bones:
What are the features of the sacroiliac joint?
part synovial (anteriorly), part fibrous (posteriory)
Contain auricular surfaces
Held together by powerful ligaments (interosseus, sacroiliac, sacrospinous, sacrotuberous ligaments, some ligaments from lumbar spine as well)
They resist nutation
What is the degree of movement of the sacroiliac joint? When does this occur?
2 - 8 degrees; majority of movement at sacroiliac joint occurs when gettng up from bed.
Mothers may have a higher degree due to relaxin.