 This is going to be a demonstration of the rotator cuff muscles. So let's first point out which are the rotator cuff muscles. This is the prone cadaver. I am standing on the left side of the cadaver. The camera person is on the head end of the cadaver. And we have cut and reflected the deltoid muscle here. We have disarticulated the acromioclavicular joint. We have reflected the trapezius muscle here. So this is the orientation. Let's start off with the rotator cuff muscles. Let's first name them. This muscle that we see here, this is the supraspinatus. The second muscle that we see, this is the infraspinatus. The third muscle, this is the t-rease minor. These are three of the rotator cuff muscles. S-I-T. There's a fourth muscle which is present on the anterior surface of the scapula that is called the subscapularis, which we cannot see because this is a prone cadaver. The tendon of insertion of each of these muscles, they fuse with the capsule of the shoulder joint and they also pump a cuff or a sleeve around the head of the humerus. That is why they are called cuff, but not all of them are responsible for rotating the humerus. The supraspinatus muscle, it takes origin from the supraspinatus posa of the scapula. This is the spine of the scapula. So this is the supraspinatus posa where it's taking origin from and the tendon then goes under the chromium process where my finger is gone in and it gets inserted onto the greater tuberosity of the humerus in this region. At the point of insertion, just proximal to the insertion is the site, the so-called danger zone of the supraspinatus, where it is likely to undergo rupture due to wear and tear in degenerative tendonitis or supraspinatus tendonitis, leading to what is known as rotator cuff syndrome. I'm going to mention more of that a little later. Now, let's come to the intraspinatus. The intraspinatus takes origin from this big area of the scapula behind on the posterior aspect below the spine of the scapula. This is the intraspinatus posa. So it takes origin and it was covered by a very thick fascia, which part of which we have retained here and part of which we can see on this side just like the supraspinatus and the fibres then converge and we can see one set of fibres here, middle set of fibres and another set of fibres. And all of them they converge and then they go under the chromium process and they get inserted under the posterior aspect of the greater tuberosity of the hubris. That is the intraspinatus. Now, let's take a look at the t-rease minor. The t-rease minor takes origin from the lateral border of the scapula above the origin of the t-rease major, which I shall mention just a little later. And the fibres then go up and they get also inserted onto the lower part of the greater tuberosity. So, we have supraspinatus, intraspinatus, t-rease minor, all of them getting inserted. Now, let's take a look at the action. These are called the rotator cuff muscles, but there are some exceptions to the rule. The supraspinatus does not rotate the hubris. It is only responsible for initiating abduction from 0 degrees to about 10 or 15 degrees. That is the supraspinatus. Therefore, that is also used as a test for the supraspinatus. The intraspinatus and the t-rease minor, they are the ones which are the lateral rotators of the humerus. So, therefore, they are the true rotator cuff. And the subscapular is, which we cannot see, which arises from the subscapular fossa in front of the scapula and gets inserted onto the lesser tubercle of the humerus. That is responsible for medial rotation. So, therefore, that is also a true rotator. So, these are the actions of the supraspinatus, intraspinatus, t-rease minor, and subscapular is. Coming to the nerve supply. The supraspinatus and the intraspinatus is supplied by a nerve which runs where my finger has gone in, deep. It runs through the suprascapular notch. That is the suprascapular nerve. It is a branch of the brachial plexus, and it supplies the supraspinatus, and then it winds around the neck of the scapula, and it supplies the intraspinatus. The t-rease minor is supplied by the axillary nerve, which is the branch from the posterior core of the brachial plexus. And the subscapular is supplied by the upper and the lower subscapular nerve, which also arises from the brachial plexus. So, that is about the nerve supply. Now, let's mention the very important clinical aspect about the supraspinatus. There is a very important clinical condition known as the rotator cuff syndrome. Though it is called the rotator cuff syndrome, it essentially most commonly involves the supraspinatus tendon. The supraspinatus tendon is located where my finger has gone in. We cannot see it. Though we have disarticulated the clavicle from the acromion, it goes under. And there is a bursa under the supraspinatus tendon, which is known as the supraspinatus bursa. That is the region where the supraspinatus tendon is most prone to degenerative wear and tear, and it is known as the danger or the critical zone of supraspinatus rupture. It is preceded by supraspinatus tendonitis, which occurs in old age. And that is what leads to the rotator cuff syndrome. In such situation, the patient will not be able to initiate abduction. And if this condition progresses, then it can also involve the shoulder joint. It can involve this structure that we, where my finger has gone in. This is the sub-deltoid subacromial bursa. It can produce subacromial bursa. That can get inflamed and it can also produce inflammation and degeneration of the shoulder joint and other structures within the shoulder joint. So therefore, the rotator cuff syndrome is not just one entity. It is a composite entity involving many features. So these are a few quick points about the rotator cuff muscles. This muscle that we see here, this is the T.D.'s major muscle. The T.D.'s major muscle takes origin from the lateral margin border of the scapula near the angle of the scapula. And the fibers then go up and they get inserted onto the medial lip of the inter tubercular sulcus of the humerus. The action of the T.D.'s major is extension, adduction and medial rotation of the humerus. The T.D.'s major is not a part of the rotator cuff. It's the invention as an addendum to this generation just to complete the picture.