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Origins, insertions, innervation and functions of the rotator cuff muscles.
Hello, everyone. This is Joao from Kenhub, and welcome to another anatomy. This time, we’re going to be focusing on one group of muscles that is quite well-known, the rotator cuff muscles.
So these muscles are found on your shoulder. They’re considered muscles of the shoulder.
Right now, we’re looking at a posterior view of your shoulder with the different muscles, and I’m just going to remove most of them to, then, just isolate the rotator cuff muscles.
Before I talk about the origins, insertions, innervation of the rotator cuff, and also some functions and related clinical anatomy, I’d like to list these muscles.
So, we’re going to be seeing the supraspinatus, the infraspinatus, the teres minor, and the subscapularis. These are the four muscles of the rotator cuff.
Now, before I continue on with details on the origins, insertions, functions, and all these details that are important to know about these muscles, I would like to just give you an overview. So an overview of the origin points.
These muscles will be originating from, as you can see here, from this bone here, a triangular-shaped bone known as the scapula.
Then, these muscles go all the way to insert at the humerus, as you can see here also, clearly, on this image.
Keep watching this video because we still need to cover the details.
Now, another overview that I would like to make, but this time on the different functions of the rotator cuff. The main function of the rotator cuff is to stabilize and center the humeral head.
As you know, the humerus is involved in the shoulder joint, so the function, one of the main functions of the rotator cuff is to stabilize and center the humeral head in the joint socket in the glenoid cavity of the scapula where the humerus will be articulating with to form the famous shoulder joint.
And in addition, the muscles will be tightening the joint capsule.
And also, as the name suggests, it plays… the rotator cuff will play a major role in internal and external rotation of the upper arm in the shoulder joint.
All the muscles mentioned earlier fulfill different functions that will be discusses individually throughout this tutorial.
We will move on and talk about the very first muscle that you see here highlighted in green.
Just added another couple of muscles here that we talked about before, the teres major and also the triceps, but highlighted, we have the supraspinatus muscle,
Which is a relatively small muscle of the upper back and is one of the four rotator cuff muscles, and the origin point for the supraspinatus will be, then, the supraspinous fossa of the scapula, which is a shallow depression in the body of the scapula above its spine.
So this is the spine of the scapula, and this is going to be then the supraspinous fossa where the supraspinatus will be originating from.
Now, the muscle runs from the supraspinous fossa to, then, insert to the greater tubercle of the humerus, as you can see here on the image.
Now, the supraspinatus muscle is going to be innervated by the suprascapular nerve, as you see here highlighted in green, which arises from the superior trunk of the brachial plexus.
A bit on the different functions or actions associated to the supraspinatus.
A contraction of the supraspinatus muscle will lead to abduction of your arm, as you see here represented on this image (so when you move your arm away from your torso). So, abduction of the arm at the shoulder joint.
And the supraspinatus also helps stabilize the shoulder joint by keeping the head of the humerus firmly pressed medially against the glenoid fossa of the scapula.
And you can actually see how the humerus is… or the head of the humerus is now forming this joint here with the glenoid cavity of the scapula and how this muscle even helps it hold these two together.
We’re now ready to move on to the next muscle that you see here highlighted in green, which is the infraspinatus. This one is a thick, triangular muscle which occupies the main part of the infraspinous fossa.
In terms of origin point for the infraspinatus, I already mentioned, yes, the infraspinous fossa of the scapula (just below the spine of the scapula) will serve as the origin point for the infraspinatus.
And like we’ve seen with the supraspinatus, the infraspinatus will go laterally to insert at the middle facet of the greater tubercle of the humerus, as you can see here.
The innervation of the infraspinatus is going to be provided by this nerve here as well, the suprascapular nerve.
So, remember that both the supraspinatus and the infraspinatus muscles are going to be innervated by the suprascapular nerve.
A little bit on the different functions or actions associated to the infraspinatus. The infraspinatus is the main external rotator of the shoulder, which you see here represented by this arrow.
And additionally, the infraspinatus reinforces the capsule of the shoulder joint and also assists in both abduction and adduction, as you see here indicated by these arrows.
So abduction is when you extend your arm to the side, away from your torso, and adduction is the opposite. So you bring your arm closer to your torso.
We’re ready to move on to the next muscle that you see here highlighted in green. Yes, this one is going to be, then, the teres minor.
The teres minor is a narrow, elongated muscle of the rotator cuff. It arises from the dorsal surface of the axillary border of the scapula, also known as the lateral border of the scapula, for the upper two-thirds of its extent,
And from the two aponeurotic laminae, one of which separates it from the infraspinatus muscle. The other, from the teres major muscle.
Now, the fibers of the teres minor muscle run obliquely upward and laterally. The upper ones end in a tendon which inserted… which is inserted into the lowest of the three impressions of the greater tubercle of the humerus, as you can see here.
Now, the lowest fibers of this muscle are inserted directly into the humerus, immediately below this impression.
Now, the muscle is going to be innervated by the posterior branch of the axillary nerve, which you see here highlighted in green, where it forms the pseudoganglion.
The pseudoganglion has no nerve cells, but nerve fibers are present here.
A little bit on the functions associated to the teres minor.
Now, the teres minor muscle’s functions consist primarily of external rotation, which you see here indicated by this arrow, and partially retroversion (so when you move your arm to the back, towards your back), and also adduction, which you see here indicated by this arrow (bringing your arm closer to your body).
We’re now ready to move on to the next muscle, the subscapularis, seen here highlighted in green.
Now, the subscapularis is a large, triangular muscle of the rotator cuff, and notice here that this is the only muscle that you can see from an anterior view.
We’ve seen all the other three from a posterior view. Right now, we’re looking at the shoulder joint and at the subscapularis from an anterior view.
Now, this muscle arises from its medial two-thirds and from the lower two-thirds of the groove of the subscapular fossa of the scapula of course. And this would be the subscapular fossa where the subscapularis is then originating from.
Now, the muscle goes all the way to, then, insert at the lesser tubercle of the humerus as you can see here.
When it comes to the innervation of the subscapularis muscle, this muscle is innervated by the upper and lower subscapular nerves, which are branches of the posterior cord of the brachial plexus.
And notice here the posterior cord of the brachial plexus where the two subscapular nerves are then branching off from.
As you’re expecting now, we’re going to move on to talk about the different functions and actions associated to the subscapularis.
The subscapularis is responsible for internal rotation of the head of the humerus, as you see here indicated by this arrow.
And when your arm is raised, it draws the humerus forward and also downward.
This is an important muscle as you can see here because it’s going to be able to stabilize the front of the shoulder joint by preventing displacement of the head of the humerus as you could probably guess by just noticing how it is placed over the shoulder joint.
This muscle also supports the upper arm during abduction and adduction, as you can see here indicated by these arrows.
Now, before we conclude this tutorial, I would like to give a word on clinical anatomy related to the rotator cuff. And we’ve seen, the anatomy of the rotator cuff muscles enables a lot of possibilities for complications.
We’re going to talk about two. One is impingement syndrome. The other one is rotator cuff tear.
Starting off with the very first one here, I just wanted to give a quick word on impingement syndrome.
The supraspinatus muscle, as you can see here highlighted in green, can have its tendon impinged at the acromion.
This process is commonly caused by a thickened tendon or an inflammation of the overlying bursa, leading to enlargement. Thus, compressing the subacromial space.
Now, a positive near sign, which is pain when elevating the shoulder above 120 degrees is characteristic in impingement syndrome.
The next one that we saw on the list was then the tear or rotator cuff tear, which happens during the rupture of one or more tendons of the rotator cuff muscles. This can happen due to trauma or by degenerative processes.
Since the rotator cuff plays an essential role in the stability and mobility of your shoulder joint, a rotator cuff tear leads then to, then, instability of the shoulder.
A rotator cuff tear can be treated with surgery, but sometimes, also with physical therapy when there is no major functional problem.