hello all this is dr alsup and we have reached my favorite video for the joints basics session
and this is where we really get to discuss what a synovial joint is and those particular structures
that make them unique and complex at the same time so you can see here with the learning objectives
that we have a lot to cover we're going to start with the structures you will have in every single
synovial joint and then talking through some of the structures that can be associated with
the synovial joint but not found in every single one such as menisci or labra or articular discs
lastly we'll have a discussion of what a bursa is and then something
pathological that can occur if there's inflammation of the bursa which is bursitis
all right there will be four structures that all synovial joints have the first is going to be
a synovial or articular capsule which is the way in which the bones actually connect so you can
see that the capsule kind of flanks the bone on either side and it will flank the second component
that all synovial joints have which is the synovial or articular or joint cavity and that's
what this blue area is right here even into this region now i want to note that the space between
the bones in this cartoonish image has been blown up to show you the basics and so you can
just kind of conceptualize it but realize those synovial cavities aren't that big you actually
have very little space in between the bones you do certainly have space and that's important in
terms of movement but it's not as large as what we're seeing on these cartoonish images within the
synovial cavity you will have synovial fluid which is the third thing found in all synovial joints
and lastly there will be articular cartilage which is number four and
we've mentioned articular cartilage in other videos these are going to be the ends
on the ends of the the articulating bones but not what actually is connecting the bones
so let's talk about each one of the three structures in a bit more detail starting with the
synovial or articular capsule we aren't going to spend time um on the articular cavity because it
is just a space although we will discuss certain structures that can be found within the cavity
the articular capsule or synovial capsule like i said you'll hear either way i've always have
a tendency to say articular i i like that word for some reason so it the articular
capsule has three main functions it will surround the synovial joint which also
allows it to enclose the synovial cavity as we mentioned in the subsequent slide
and this is the connective tissue that will actually unite or connect the articulating
bone so this is the part that is this is the connective tissue that's connecting the bones
it is actually composed of two separate layers the outer layer which you can see here in this
kind of light purple color is the fibrous capsule sometimes referred to as the fibrous membrane and
this layer is mostly composed of dense irregular connective tissue like we have here with a high
amount of collagen fibers and this will actually attach an intermingle with the periosteum
that surrounds the bone so you have that really tight connection the fact that there
is considerable collagen fibers that compose the dense irregular connective tissue really allows
for the notable movements that can occur at synovial joints in fact an individual
who is considered double jointed often just has greater flexibility in their articular capsule
and or their ligaments this outer layer is very often further fortified by capsular ligaments
or even sometimes completely replaced by tendons in certain areas like the anterior knee
the inner layer of the synovial capsule which is this kind of light blue right here is referred to
as the synovial membrane and this is going to be composed of areolar connective tissue with
elastic fibers and in some joints there may even be accumulations of adipose tissue at this layer
the knee as an example will have a an extensive fat pad uh associated around the synovial membrane
layer and i keep bringing up the knee which makes sense because it's one it's one of our
most complex joints and we'll spend a lot of time talking about the specifics of the knee
and also of very notable importance the synovial membrane will secrete synovial fluid and synovial
fluid is named after its similarity in appearance to an uncooked egg white thus the of in its name
and this fluid will form a film over most of the surfaces within the articular capsule
or within the cavity and this fluid serves many many functions including reducing friction that
can occur that will occur with movement at a joint so it's really lubricating the joint
it will absorb shock and we'll see that there are a lot of structures in synovial joints
particularly more complex ones that really play a role in terms of absorbing the shock that can
happen particularly in the action of running where you have all that weight of the body with every
step this is a really cool thing as well is that synovial fluid also can contains phagocytic cells
or cells that will remove debris that's sometimes found within the joint cavity due to normal wear
and tear of a joint so it can actually remove structures that you don't want in the synovial or
within the synovial joint and this is another huge one recall that cartilage is mostly a vascular
meaning that that articular cartilage that we we talked about on the ends of the bone it will
be it will be a vascular as well so synovial fluid will provide oxygen and nutrients to the articular
cartilage which is typically something that oxygenated blood carried by arteries would do but
since articular cartilage doesn't have that the synovial fluid is a nice substitute in terms of
being able to supply some of that to the articular cartilage now think about your last exercise
all right hopefully you've done that you know not not too distant past but when you exercise did
you warm up first one of the benefits of warming up is to allow for the synovial fluid to become
the right level of viscosity as well as stimulate production and secretion so it can
be very beneficial in reducing the amount of stress to your joints during exercise
the articular cartilage is located on the ends of the articulating bone so once again let's kind of
point it out on this image i went a little too far with that arrow it's really this right here
so it's located on the ends of the articulating bones and is composed of a thin layer
of hyaline cartilage but as i have mentioned numerous times at this point
because it doesn't and it doesn't hurt to say it one more time articular cartilage is not what is
binding the bones or connecting the bones that is that articular capsule so this is key here
many of the functions of the articular cartilage are similar to what we had with the synovial fluid
and you need numerous structures and joints particularly synovial joints which are freely
movable to reduce friction to absorb shock because all this movement is occurring here
now again articular cartilage is mostly a vascular and even though it can get some nourishment from
synovial fluid if there's an injury to this area it is very slow to heal and it may never depending
on how severe the the injury or damage is and it's here that it's with the articular cartilage that
wear and tear of a joint most typically occurs so osteoarthritis which we will talk about in a
bit more detail in a later video will be directly related to the health of the articular cartilage
all right let's spend some time on structures that won't be found in every synovial joint
but maybe in some of the more complex joints and we're going to start with an articular disc
which is a complete fibrocartilaginous disc located in the middle of a synovial cavity
and it really serves to divide the cavity into two halves and so this functionally can be important
because it can allow different types of movements to occur at the different halves of the cavity so
we are looking at the temporomandibular joint here and you can see the articular disc is this right
here in the middle and then you will have a space superior and inferior to it in this particular
case and so there will be different types of movements that can happen in the upper synovial
cavity or the lower synovial cavity because of the separation with the articular disc in the middle
very similar to the articular disc are the incomplete as in not a complete disc
so not completely circular and you can really see that here for the miniski
this these are the miniski or meniscus if you're only talking about one
and like the articular disc it is composed of fibrocartilage so fibrocartilage is uh back again
and the menisci will typically be found in areas with increased stress and and friction where that
occurs so think about the term meniscus have you heard it before you've likely heard of a meniscal
tear or injury and this will occur at the knee joint so the the most typical meniscus that you
hear are the menisci of the knee joint with both the articular discs and menisci during development
these structures are actually located between the fibrous and synovial membranes of the articular
capsule so this is during development but as the joint becomes functional particularly with walking
and during more considerable friction that can occur with with walking or running the synovial
membrane is worn off in that particular section of the joint and you are left with the miniski and
these meniscus will not be covered with synovial membrane so that synovial membrane will stop
on the other sides of the articular capsule and not make its way all the way to the meniscus
again another structure similar in composition is the labrum which are fibrocartilaginous so
fibrocartilages back lip located almost exclusively in ball and socket synovial
joints okay so this is a key here so this is where we will find the labra so what the labrum
will do is sit in the socket portion and serve to really deepen the socket and allow for a better
fit of the bone so our two main ball and socket joints are going to be the shoulder joint which
we're looking at here we're looking at the um a a view of the socket portion of the shoulder
joint as well as the hip the hip will also be a ball and socket joint and we'll have a labrum
a last stretcher i want to discuss are these little sac-like structures called bur-c or bursa
if we're talking singular and unlike the other accessory structures that we've just discussed
the miniski the labor and the articular disc that are located within the synovial capsule or in the
cavity mercy or not they're located outside of the joint capsule and located in strategic locations
in order to help alleviate friction in areas that experience quite a bit so all complex synovial
joints like the shoulder joint that we can see here the elbow hip the knee which we can see here
these will all have bursi and typically multiple bursi
the bursa resemble a little almost separate mini articular capsule with a little bit of
fluid and can be found in many locations such as between skin and bone tendon and bones
ligaments and bone and even muscles and bone so pretty much anywhere where you have an
increased amount of friction you may have a bursa and these can develop over time as well
in certain areas the bursi are very specialized in shape almost tube like
to wrap around long tendons or tendons that travel for a while without muscle coverings
or other structures so these are referred to as tendon or synovial sheaths you have examples of
these in the wrists with the long tendons from the forearm which have to travel all the way
to your fingers so very long indeed and these will be covered by synovial or tendon sheaths
with repeated or excessive exercise or say an infection enters the area of a bursa the bursa can
become inflamed and often will swell and this is referred to as bursitis and you can see an example
of an individual that has some very prominent swelling due to bursitis of their elbow joint
other causes include trauma to the area rheumatoid arthritis can cause bursitis
and symptoms will include pain mostly is kind of the big one swelling which you can see here
and this is an important one as well it can limit movement at that joint often in less severe cases
rest of the joint so not moving the joint as much will help in alleviating many of the symptoms
so we have discussed quite a bit and i hope we are feeling a bit of comfort with the structures of a
synovial joint as i mentioned as we talk about each individual major synovial joint we'll talk
about these specific structures in detail as it is as it is associated with those joints let's review
a question and um this question i love it's very similar to the type i would like to have on an
assessment so here we go a patient complains of continued pain in their knee region it is decided
that arthroscopic surgery is needed to explore the area with a focus on inspecting the incomplete
fibrocartilaginous structures associated with the knee what structures will be the focus here
all right so pause and take your time to answer this really work through that stem find the
pertinent things there and when you are ready unpause the video and we'll discuss together
so for me the key to the stem is this right here an incomplete fibrocartilaginous structure and
another key is that is associated with the knee so articular cartilage is hyaline cartilage so this
is out this is not correct articular discs are fibrocartilage but they are complete so um and
we haven't gotten into this detail yet but there's not an articular disc in the knee so this is out
burst c are five are not fibrocartilaginous structures even though they are associated
with the knee so that's out as well labra are our fibrocartilaginous lips but these are found on the
sockets of synovial ball and socket joints the knee is a hinge joint so this is not the correct
answer so that leaves miniski as the only answer left and it is in fact the correct one miniski
are incomplete fibrocartilaginous discs they sit these when we're talking about the knee
they sit on the articular surfaces of the proximal tibia which is part of the knee joint
alright thank you for your time and attention and please feel free to reach out with any questions