This is a tutorial on the rotator cuff. The rotator cuff are a group of muscles which
are important in supporting the glenohumeral joint. They are important in shoulder movements
and maintaining stability of this joint. So if we just have a look at the glenohumeral
joint over here, you can see that the head of the humerus sits in this very shallow glenoid
fossa. So the shoulder joint essentially sacrifices stability for mobility. So the rotator cuff
muscles are a group of muscles that originate on the scapula and insert onto the head of
the humerus and provide stability across this joint. So I've just added in the muscles here
and we'll just take a look at the muscles that make up the rotator cuff, and a look
at their function. So this big muscle sitting over here - so we're looking at a lateral
view of the left side of this model. So this is the big, powerful deltoid muscle. I'll
just get rid of that so we can have a good view of the rotator cuff muscles. And then
we've got the trapezius here, so I'll get rid of that as well. And we've got the powerful
pectoralis major here. So just having a look at the rotator cuff muscles now, there are
four rotator cuff muscles and you can remember them with the acronym SITS - S I T S. So "S"
is Supraspinatus, "I" infraspinatus, "T" teres minor, and the final "S" is subscapularis.
So we'll just work our way through those muscles to begin with. So the supraspinatus is this
muscle which sits at the top of the scapula, so if you think of the name "supraspinatus",
"supra" means "above", "spinatus" refers to the spine of the scapula, so it's sitting
above the spine of the scapula which you can see here. So this is the supraspinatus. And
if we look at where it inserts onto the humerus, you can see that it attaches superiorly on
the head of the humerus, on the, at the top of the greater tuberosity. So if we just imagine
this muscle contracting we can see that it will bring the humerus up in this kind of
motion, so it will abduct the arm. So the supraspinatus is responsible for the initiation
of abduction, and the supraspinatus is innervated by the suprascapular nerve. So the next muscle
we're looking at is this one here, the infraspinatus, and again this sits below the spine of the
scapula - so "infra", and "spinatus" referring to the spine, so "infraspinatus". And this
muscle attaches slightly inferiorly and posteriorly on the greater tuberosity of the humerus.
So again it's always useful to try and think logically about how these muscles act if they
contract, rather than just memorising different functions of muscles. So just looking at where
it inserts, you can see if it were to contract, it would pull the humerus round in this way.
So it would externally rotate the humerus - you can see that by the position of where
it inserts. So this muscle inserts on the posterior facet of the greater tuberosity
slightly inferiorly and posteriorly to the insertion point of the supraspinatus. So that's
the infraspinatus. And then we've got the teres minor here - this is the third rotator
cuff muscle and this has...you can see by the same, by the point of insertion slightly
inferiorly to the infraspinatus you can see that it will also have the same action, so
that it externally rotates the humerus. And the teres minor is innervated by the axillary
nerve. So I'll just get rid of this muscle quickly, so you can actually have a look at
where it sits on the scapula. So you can, I don't know if this is the best illustration,
but the teres minor originates on the middle half of the lateral border of the scapula,
and if we remove this muscle, we can see the teres major, which isn't a rotator cuff muscle,
but which lies just beneath the teres minor - so I'll just bring that back. There we go.
Okay, so the last muscle of the rotator cuff is the subscapularis, but unfortunately it
isn't actually included on this muscle, but the subscapularis as the name suggests lies
underneath the scapula. So if I were to remove...it literally lies on the underside of the surface
of the scapula, so you would ordinarily be able to see it from this view, sitting under
the scapula, and this muscle, if I just get rid of the biceps, this muscle would come
round from under the scapula to insert on the lesser tuberosity of the humerus. So whereas
the infraspinatus and teres minor insert on the greater tuberosity and cause external
rotation of the humerus, the subscapularis inserts on the lesser tuberosity here. So
if you can just see this sort of lump here, that's the lesser tuberosity of the humerus,
and that's where the subscapularis inserts. So it internally rotates the arm, so it brings
the humerus round this way - medial rotation. And the subscapularis is innervated by the
upper and lower subscapular nerves. So those are the four muscles of the rotator cuff.
And the rotator cuff muscles are an important set of muscles to know about because they're
quite frequently injured, you can get tears in the actual muscle itself, or you can get
damage to the tendons. And injury is quite commonly seen in people who have a job, or
hobby that involves a lot of throwing. You'll see it in people who go to the gym a lot and
bench press, so it's quite a common source of... So yeah, a common source of shoulder
pain is often related to the rotator cuff and you'll come across something called impingement
syndrome, so this is where, or shoulder impingement, so the name quite suggests the cause of the
pain, so you get impingement of the tendons as they run under this subacromial space.
So this acromion process of the scapula sticks out here, and you've got the tendons - so
you can see the supraspinatus tendon running underneath this space, and if this space is
narrowed for any reasons, so for instance in osteoarthritis you get bony outgrowths,
osteophytes, and they narrow the space where this tendon runs and put pressure on it and
cause a lot of pain, they cause weakness, and a loss of shoulder movement. So that's
a particular condition to be aware of. So that's the rotator cuff muscles - four muscles,
remember it by the acronym "SITS": supraspinatus, infraspinatus, teres minor, and subscapularis.
And if you try and remember the points of insertion you can relate that to the function.
So the supraspinatus initiates abduction, the infraspinatus externally rotates, and
so does the teres minor, and the subscapularis, which inserts on the inferior...on the lesser
tuberosity, causes internal rotation. So that's the rotator cuff.