hello anatomy friends this is dr alsup and now that we have a pretty good understanding of what
the bones are that make up the pelvic girdle now we can talk a little bit about where these
bones articulate and what joints are going to be formed and what type of joints will be
associated and so the two main joints that we are going to discuss
are the paired sacroiliac joints and the pubic symphysis which is found in the midline region
then we'll talk a little bit about the ligaments associated with both of these joints
and what happens what would be the function of relaxation of some of
these ligaments particularly in terms of during pregnancy or the latter portions of pregnancy
okay so the sacroiliac joints these are going to be between the auricular surfaces of the coxal
bones as well as the auricular surfaces of the sacrum and honestly both of these
surfaces kind of look like little ears they look like this shape and they will articulate with the
auricular surface of the other bone and as you can see there are two sacroiliac joints so these are
paired because you have two coxal bones now what is neat nito about these sacroiliac joints are
that these are what's considered compound joints meaning that you really have two joints in one
uh and in this case you have two different structural types of joints in one area so you
will have a synovial portion of the sacroiliac joint that will honestly be the more anterior
portion which we can't see quite as well here and synovial really will make up the majority of it
and then this more posterior portion back here will actually be a synthesmosis and think back
to our conversations regarding uh the joint basics what type of joint is a syndesmosis
remember it's a good old fibrous joint so we um we have both a fibrous joint and a synovial
joint associated with the sacroiliac joint now it is a synovial joint synovial joints
as we know are freely movable but when we're talking about the sacroiliac joint we have
it's kind of pretty closely locked into place you have some very very strong ligaments that
really really really limit the movement that's allowed at sacroiliac joints you have a little bit
you want some flexibility in order to be able to move your hip a little bit
but you don't want too much because there is a lot of weight bearing that's associated with the
pelvic girdle so you don't want to have with with movement you often will lose stability
so this is a very st these are very stable joints and so with that very little movement is allowed
the pubic symphysis is exactly what you would think it is because it has it right here in its
name it is a symphysis which is a cartilaginous joint and so you'll have the two symphyseal
surfaces of the pubic bones articulating and then you will have the cartilaginous portion
that is actually attaching these two bones together so you only have the
one pubic symphysis and it's right here in the midline like most of the other symphyses
and little movement is allowed here as well okay so this is an old image it's a
it's i think it's from gray's anatomy a very very um older version but i really like how it's
showing the complexities and the amount of ligaments that you have in these areas
particularly in association with the sacroiliac joint there's a lot going on in that region
but with increased levels of hormones and particularly estrogen relaxin
is going to be an important one in that latter half of the pregnancy
these ligaments are going to become what we like to refer to as relaxed all right
so it's causing relaxation associated with the ligaments and that gives a bit more mobility
to the joints in this region and this can even allow an increase in diameter
of certain components of the pelvic girdle so particularly in terms of that pelvic outlet
if you have some flexibility in some of these ligaments down here that can really serve to widen
or increase the diameter of that pelvic outlet and this will help to facilitate the passage
of the fetus through the pelvic canal so anything that's kind of increasing that area will help
with that movement there all right so those are the joints associated with the pelvic girdle
again we will of course have the ball and socket hip joint but we'll talk about that with the lower
limb as it's really going to affect the movement of that region more but with the joints that we
were talking about here we have an example of all the main structural types of joints so we
had a fibrous joint a cartilaginous joint a synovial joint which one of these which one
of the joints did we discuss is cartilaginous is it the pubic symphysis or the sacroiliac joint
and hopefully you remember oops excuse me i'm so excited i can't wait to underline this
so you remember cartilaginous the symphysis
is a type of cartilaginous joint and so the pubic symphysis is cartilaginous the
sacroiliac is fulfilling the other two so that's syndasmosis so you have ascended syndicmatic part
which is fibrous joint as well as a synovial joint portion so you have that compound sacroiliac joint
all right excellent let's finish our conversation of the pelvis talking about certain muscles
particularly those that may play a role in terms of the lower limb some of the muscles
for this region will also be discussed in the reproductive section of the course thank you
for your time and attention and as always i hope you have a lovely rest of your day