Rotator Cuff Tutorial – Anatomy Tutorial

Rotator Cuff Tutorial – Anatomy Tutorial


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.

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