Hello all this is Dr Alsup and in this learning objective video we will be discussing the muscles
of the rotator cuff as well as its close neighbor the teres major muscle. So a bit more
detail regarding what we will be discussing and expect you to understand upon review
of this learning objective so let's get right right into it.
So I do hope when you think of the rotator cuff you think of the shoulder region. And so it makes
sense that these muscles will have attachments on the major bones of the shoulder region.
So proximally they will all attach to the scapula. And they will literally be sitting on the body
of the scapula with the majority of them, so three out of four are sitting on the posterior portions
of the scapula and you can see that here, so this includes the supraspinatus the infraspinatus
on either side of the scapular spine and the teres minor so you can see the teres minor right here.
And there's only going to be one of the four muscles that will be more anteriorly placed
on the scapula and this is the subscapularis you can see a little bit of it here deep to that the
biceps brachii tendon. All of these posteriorly placed rotator cuff muscles will have a distal
attachment on the greater tubercle so you can see it here osteologically. And that one anterior
more anteriorly placed rotator cuff muscle the subscapularis will have its distal attachment on
the lesser tubercle which is going to be right about here-ish on that image and you can see
it clearly here. The lesser tubercle is going to be more anteriorly placed the greater tubercle
will be more laterally placed. So it makes sense now why the greater tubercle is bigger than the
lesser it is going to have three muscles attaching there whereas the lesser tubercle only has one.
As we discussed in the shoulder joint learning objective the rotator cuff is hugely important
in providing stability to the glenohumeral joint by forming that musculotendinous ring
around the joint with that little bit of an inferior deficiency.
I do want to note of clinical importance and will be discussed in more detail in the
upcoming shoulder clinical lecture that the most frequently injured or damaged rotator cuff muscle
is the supraspinatus muscle so this is going to come up over and over again. And this has much to
do with the location of its tendon between the coracoacromial arch so over here in this region
and being between that arch and the actual joint itself so if you imagine it can be really impinged
that tendon can be really impinged during repetitive movements of the shoulder in particular
things like full flexion or full abduction. If I were making this illustration I would have
this kind of more white this area more white to indicate the tendon of the supraspinatus muscle
so less like the the muscle belly, but you get what we're talking about here it's going to
kind of travel through this region in order to go attach on the greater tubercle. Okay three of the
four rotator cuff muscles play a role in rotation of the joint so both medial and lateral depending
on which muscle of the shoulder joint. I'm less concerned right now with you remembering which
one does what but I do hope you take away that these muscles play a role in rotation of the
shoulder joint. Now the supraspinatus does not it is going to play a role in initiating the first
15 degrees of abduction so kind of moving first moving the arm away from the body
before the deltoid muscle takes over so supraspinatus is going to initiate abduction.
All right let's spend our last few minutes discussing the teres major which while not
a rotator cuff muscle is very closely located to these posterior rotator cuff muscles so it's going
to be located just inferior here to the teres minor. And it's a pretty big muscle so we shouldn't
ignore it anyway I don't think this image does it justice. So the distal attachment will be on the
humerus but not directly on those tubercles that we just discussed it's going to be a little bit
inferior to those but with this type of attachment you know it's crossing the glenohumeral joint so
it'll affect the actions of the shoulder joint. As mentioned before teres major is robust
again this illustration I think is not doing it justice but you will see how large it is in
the laboratories. It can be visible and palpated particularly when contracting the teres major
on the inferior lateral portion of the posterior axilla so if you're looking kind of in the armpit
region you likely can see some of the teres major that's going to be deep to the skin.
The teres major antares minor muscles will form part of the boundaries for a space
in this general region referred to as the quadrangular space and this space
is important in understanding where the axillary nerve enters this region so how the axillary nerve
in its quest to reach the deltoid muscle how it's getting there. Also very closely related will be
the posterior circumflex humeral artery this nerve and artery travel very closely together.
The space is bounded by the teres minor superiorly so right here the teres major inferiorly
so those are going to be those two teres muscles there. Medially it will be bounded by the long head
of the triceps brachii muscle which is located on the posterior arm more to come on the triceps soon
and lastly medially it will be bounded by the actual humerus or the shaft of the humerus.
Again this area is important in allowing identification of where that axillary nerve
as well as its closely traveling artery will actually enter into this region
and it will innervate that important abductor of the arm the deltoid. Excellent we have reached the
summary slide. Please take time to review and I hope this particular slide helps in your studying.
Thanks again for your time and attention and have a great rest of your day