There is sexual dimorphism of the pelvis or
gender differences in how the pelvis is constructed.
Here, we see two pelves which would be plural
of pelvis. The upper one is a woman. The lower
one is associated with a typical male pelvis
and there are going to be differences between
men and women with respect to the dimensions
of the inlet and the dimensions of the outlet.
And if we take a look, first, at the inlet,
here is the pelvis of a woman. And if we follow
the landmarks or boundaries of the inlet,
we see that they are fairly round in appearance.
If we shift our attention down below to a
male pelvis and follow the boundaries, these
boundaries form a more heart-shaped structure.
Thus, this male pelvis has a narrower inlet.
The outlet in a woman is going to be larger
than in a man. The ischial spines are going
to have greater separation. The dimension
between the coccyx and the pubic symphysis
will be longer in a woman than in a male.
And you can appreciate the dimensional differences
here from coccyx to pubic symphysis, shorter
distance than above and the dimension between
the ischial spines is shorter in a male pelvis
than in a woman's pelvis. And the purposes
of the sexual dimorphism relates to childbearing.
A woman needs a larger inlet and a larger
outlet for the birth of a child.
There is also a difference in a region called
the subpubic angle between a male pelvis and
a female pelvis. The subpubic angle is shown
right in through here and you can appreciate
the angle in this example versus the angle
that's formed over here. The pelvis with the
wider subpubic angle belongs to a woman and
then the subpubic angle that is narrow in
appearance would belong to a man. However,
the sexual dimorphism that we just went through
is not always black and white. In some cases,
those lines can become somewhat blurred.
Now, we'll shift our focus to the joints of
the pelvis. And when we think about the pelvis
and its articulations, we're going to highlight
three of those, a lumbosacral articulation,
a sacroiliac articulation and the pubic symphysis.
All three of those articulations are demonstrated
in these two slides that we see here. We have
a male pelvis and a female pelvis.
And if you take a look at the subpubic angle
here versus the subpubic angle here, the pelvis
below may has a much wider angle. So, that would
be a female pelvis with the male pelvis above.
The joints that are demonstrated here would
be between the 5th lumbar vertebra and we
see the transverse processes of it at this
level and then the 5th lumbar vertebra will
articulate with the sacrum.
The sacroiliac joints are here and here, or
here and here, and then the pubic symphysis
is where the two pubic bones will meet in
the anterior midline as well, as here in the
female pelvis. These are very very strong
articulations because of the tension, stress
and weight that's placed upon them.
To help with structural integrity of these
articulations, there are several ligaments
of the pelvis. Some of these are much more
important in providing for structural integrity
of the articulations. Others, we've mentioned
before, in creating notches into apertures.
But, some of the ligaments to highlight here
that would be found in the pelvis would be
the lumbosacral ligament. This one is really
not well identified, but if we look at the
transverse process here of the 5th lumbar
vertebra and look at this ligament that's
attached to it and then attached to the superior
aspect of the ala of the sacrum, this is your
lumbosacral ligament. The iliolumbar ligament
would run from this same transverse process.
It would course more horizontally and then
run on the superior aspect to the posterior
iliac crest. That is also not well shown here.
The sacroiliac joints are very very strong
ligamentous structures because of the forces
placed upon them. We have the anterior sacroiliac
ligament here and then on the posterior aspect,
we would have the posterior sacroiliac ligament.
Anteriorly, here, we have the inguinal ligament.
This is not really supporting any of the articulations,
but represents the inferior attachment of
the aponeurosis of the external abdominal
Underneath it, you have some aisles
and that will allow for the passage of muscles
into the thigh and will allow for the passage
of neurovascular structures in and out of
The sacrotuberous ligament is seen here. Sacrospinous
ligament is shown there.
That brings us to our summary slide and the
key take-home messages from this lecture are
The pelvis is composed of the sacrum, coccyx
and the pelvic bones.
The false pelvis is the inferior part of the
abdominal cavity whereas the true pelvis defines
the pelvic cavity itself.
The pelvis is bounded by lateral walls and
The pelvis wall is formed by bony structures,
ligaments and muscles and presents three apertures.
The pelvic diaphragm and the deep perineal
pouch and the perineal membrane constitute
Sexual dimorphism of the pelves is necessary
to facilitate childbirth in women.
The lumbosacral, sacroiliac and pubic symphysis
represent joints of the pelvis and these joints
are strengthened or reinforced by strong ligaments.
Thank you for joining me on this lecture on