hello anatomy friends this is dr alsup and we have made it through our good discussion of the
bones of the upper limb now we are going to talk about the specific joints that are found here and
we're going to start proximally and move our way distally so we'll start with the shoulder region
and really we're talking about two main joints we're talking about the acromioclavicular and
the true shoulder joint which is the glenohumeral but as i'm writing out definitely we will
talk about this being the shoulder joint but this kind of tells you exactly what is connecting here
so starting with the acromioclavicular joint this is actually going to be a joint between
the two bones of the pectoral girdle so you will have the acromion of the scapula articulating
with the clavicle and it is right here at that articulation that you have the acromioclavicular
joint so this is the one that i said that you could palpate that is close to the point
of the shoulder so follow your clavicle all the way laterally and then you should
feel a fairly prominent bump and that's about where these two bones are going to articulate
so kind of at that point of the shoulder region now this particular type of joint is synovial
but it is a plain joint which means that there is going to be gliding so slight gliding
of that acromion on the clavicle which will be a fairly small these are small movements
but they're important in terms of allowing that part of the scapula to move a little
bit in order for the full range of motion that occurs here at the shoulder joint
and if you've ever heard of the term shoulder separation you would think okay i'm talking about
the shoulder so i'm probably talking about the shoulder joint or the glenohumeral joint but that
is not the case shoulder separation is actually going to be associated with the acromioclavicular
joint so it's either disruption of the joint or a complete dislocation as you can see here
so this is the acromion this is the clavicle you can see that they've completely separated
in this particular image the shoulder separation is actually associated with the ac joint now this
can be caused either by a direct blow to the acromioclavicular joint say falling directly
on it or something hitting really hard there or it can even be caused by those FOOSH injury so that
fall from an outstretched upper limb and that can that force will kind of move its way up proximally
and it can cause a shoulder separation now the degree of the shoulder separation can vary to
something that is more of a disruption or slight disruption to a complete dislocation and usually
if there is a complete disruption of this ligament right here your coracoclavicular ligament you know
that that's going to be one of the more severe severe separations of this joint the ac joint
okay moving to the glenohumeral or the shoulder joint this is as you can see
pretty close to that ac joint it's going to be formed by the glenoid cavity or glenoid fossa
of the scapula and then of course the head of the humerus and so this is our first and one of our
best examples of a ball and socket joint and i want you to know while we're looking here how
shallow this glenoid cavity is in comparison to the size of the head of the humerus
and this lack of fit has a lot to do with the fact that there is going to be increased mobility
associated with this joint in fact the shoulder joint is going to be the most
mobile joint of the body and that's awesome think about it try to move your shoulder
joint you can move it in all kinds of different directions and we'll talk about that in a moment
but one really important concept when we're thinking about joints is that when you have
increased mobility what do you necessarily give up with that increased mobility
you're going to have less stability all right so you with mobility you have a lessening or
a decrease in stability so the glenohumeral joint is fairly unstable there are a lot of ligaments
and muscles that are going to play a role in terms of increasing the stability but the fact that this
is the most mobile joint in the body also means that it's going to be one of the most
injured joints as well so very clinically important region of musculoskeletal anatomy
all right so this is a ball and socket joint which means it can basically do all the movements that
are possible at a synovial joint so you can have flexion so this arm is flexing here or extension
this is extension here so this is extension pass anatomical position you can also have abduction or
moving away from the midline as well as adduction and that adduction can even go past midline
circumduction can occur here as well because you can flex extend abduct and
adduct if you add all four of those together we know that that can lead to circumduction
and then lastly medial and lateral rotation so think of that anterior portion of the humerus
medially rotating or laterally rotating so capable of all the joints this link here
should take you if you take you to some action videos that are showing these actions
okay now let's talk about a few of the structures that are associated with increasing the stability
of the shoulder joint you are going to have this fibrocartilaginous lip
so kind of going over and extending a little bit wider on this portion of the glenoid cavity you'll
even have one that's a little bit going to extend this way and this is the labra or the glenoid
labrum these are those lips that play a role in terms of fibrocartilaginous lips that play a
role in terms of deepening that glenoid cavity so you can see that it kind of extends out this way
to allow for that head to fit a little bit better in the glenoid cavity region to remember ball and
socket joints think labra also really importantly because this is such a complex area and there's a
lot of movement occurring at the glenohumeral joint you will have some very important bursi
that are associated with the joint i'm named two but they are certainly not the only ones
one right here that's just labeled bursa is going to be the subacromial bursa and this is going to
help facilitate movements of the supraspinatus tendon and so right here is the supraspinatus
muscle belly and you can see the tendon heading all the way over here to the greater tubercle
and so you're going to have this bursa here between the tendon
as well as between that ac joint clavicular region and the bone so it is very important in terms of
trying to reduce the friction that can occur in say full range abduction that would could
potentially lead to pinching or friction of this tendon on these more superior parts of these bones
now one bursa that is not here is so this is the sub scapular or subscapularis muscle
it's the only anterior rotator cuff muscle and we'll talk about those in a moment
um but its tendon is going to attach on this lesser tubercle over here and there will be a
bursa kind of underneath this tendon between kind of the neck of the scapula region which
would be right over here in the subscapularis tendon so help in terms of reducing the friction
associated with movement of the subscapularis and kind of that tendon could rub up against
the bone in those areas but you have that bursa there to help in terms of reducing that friction
so whereas the subacromial or subdeltoid is going to be more superiorly placed the subscapularis
will be more in or subscapular bursa will be more anteriorly placed and this one actually this bursa
is unique in the fact that it does communicate directly with the joint cavity usually they're
bursty like we have with the subacromial are completely separate from the joint cavity and
the joint capsule but the subscapular bursa does have a communication with it
now these are playing a role in terms of reducing friction in these areas but as there is a lot
of movement and a lot of times with people that have repetitive movements particularly abduction
flexion can have inflammation of these bursi and that these are common areas for bursitis so
that's why we're talking about these two because they come up a little bit more often clinically
okay you cannot talk about the shoulder joint even though we're not getting into
muscles quite yet but when you are talking about the shoulder joint in terms of what is really
uh creating the stability of the joint and keeping that humeral head where it
needs to be in the glenoid cavity it's really these rotator cuff muscles and this actually
brings up a really nice point that i think it's lost a lot of time in musculoskeletal anatomy
when you're talking about joints a lot of times you talk about ligaments
and that makes a lot of sense ligaments play a big role in terms of the stability in the
parts of connecting certain portions of bones to the other part of the bone or another bone
and kind of stopping unwanted movements or adding added protection but really tendons
can play this huge if not sometimes a more important role in the stability of joints and
it is certainly the case here when we're talking about the glenohumeral joint so the rotator cuff
muscles are going to be four muscles that are the main source of stability of the shoulder joint and
i'm not going to get into the the four different ones quite yet we will in the muscles video
but what i do want to note is that these four muscles will form an almost complete um encircling
of the glenohumeral joint region so it will play an important role in terms of enforcing
that articular capsule it will it will kind of go beyond that as well
so you almost completely surround the shoulder joint region because you have both anterior and
posterior rotator cuff muscles but one important note is that there will be an inferior weakness
in terms of the cuff so the the cuff is almost complete around the glenohumeral joint
except for um there's going to be an inferior weakness or an uh incompleteness of that cuff
and that has implications in terms of dislocations so when we're talking shoulder dislocation unlike
shoulder separation shoulder dislocation we are talking about the glenohumeral or shoulder joint
and so what will happen is that one part of the bone will dislocate from the other
and really it's this humeral head that will be the part that is going to do the majority of the
movement and typically and let me just kind of label things on this radiograph because i think
that can be helpful so there's the clip clavicle here's the acromion here's the coracoid process
glenoid cavity or fossa and then of course the humeral head so uh in a typical position that
humeral head should be up in this region right it should be articulating with the
glenoid cavity but if a shoulder dislocation occurs most commonly it will
occur in an inferior direction meaning that the humeral head will almost always move inferiorly
which you can certainly see is the case here but clinically uh very rarely are
shoulder dislocations described as an inferior dislocation even though you see a bit more of that
as well and you kind of add it to you but usually when a shoulder dislocation is described it's
either described as anterior or posterior and that has to do with the fact that did
the humeral head move anterior to kind of this bottom portion of the glenoid cavity or posterior
and it is almost always or certainly most commonly going to be anterior you can have
posterior dislocations for sure you can have all kinds of things pretty much anything can happen in
terms of the human body but by far the the higher frequency is going to be anterior dislocations
and this is often caused by excessive lateral rotation of the shoulder joint or hyperextension
of the arm and that will cause that humeral head to kind of move in this region here okay
so this is a a big concept and something that i hope we walk away with but tell me
true or false shoulder separation occurs at the glenohumeral joint all right so pause if you need
to i want you to focus on this term right here so where does shoulder separation occur at which
joint is it the glenohumeral joint no that is this is false shoulder separation is occurring at your
ac or acromioclavicular joint right whereas the glenohumeral joint you can have a dislocation
as well as many other um pathological considerations that we didn't get into in this
video but really sometimes people get the term shoulder separation shoulder dislocation mixed up
and this is really going to be more associated with the ac joint and shoulder dislocation is
more associated with the glenohumeral joint all right excellent we will continue our conversation
next with the joint the elbow joint the joints of the forearm and then of course the wrist joint or
the radiocarpal joint and then we will move into the muscles thanks for your time and attention
here as always please feel free to reach out with any questions and have a great rest of your day