Scapulohumeral Muscles – Anatomy of the Shoulder

00:00 Okay. Now let's move on to what are known as scapulohumeral muscles.

00:05 These are muscles that are running from the scapula and passing towards the humerus.

00:11 We can see we have a whole series of them that are running from the scapula to the humerus.

00:17 We have deltoid. We have supraspinatus, infraspinatus. We have some teres muscle teres minor teres major and we have subscapularis. And we can see we will go over the various attachments and functions. So let's start with deltoid. We can see we have got the deltoid muscle here coming from three different parts of the appendicular skeleton. We have the clavicular part. We have the acromial part and we have the spinal part. So we have the anterior, we have the middle and we have the posterior part of the deltoid. And these are all running together to the deltoid tuberosity which remember we saw on the lateral aspect of the humerus.

01:04 The deltoid, the anterior part comes from the clavicle, the lateral part comes from the acromion and the posterior part comes from the spine of the scapula and they all converge down onto the deltoid. We can see that in this table here. Clavicular head, acromial head, spinal head, coming from those places, runs the deltoid tuberosity of the humerus on the lateral surface and is innervated via the axillary nerve and this comes from C5. The clavicular head is important in flexing and medially rotating the shoulder joint. So it flexes the shoulder joint. It is important in medially rotating, so it turn the shoulder joint internally. The acromial head is important in abducting the shoulder, so moving the arm outwards. And the spinal head extends and laterally rotates the shoulder joint. So because of the wide attachment of the muscles, their wide spread origin, they can have a number of functions. This one is important. The ability for the acromial head, this middle part of deltoid to abduct the shoulder. Because this works alongside supraspinatus.

02:21 We can see here in the table supraspinatus helps to initiate abduction. So the initiation of abduction is not actually carried out via deltoid. The initiation of abduction is carried out by supraspinatus. It then assists deltoid when it takes over abduction. So starting abduction is supraspinatus. Deltoid then carries on abduction beyond the first initial 15 degrees of abduction. We can see that here. Here we have supraspinatus. Supraspinatus running from the supraspinous fossa of the scapula. Supraspinous fossa remember above the spine of the scapula passes towards the humerus, specifically passing towards the greater tubercle of the humerus here. When this muscle contracts the scapula is going to remain stable and the humerus is going to move out where it is going to abduct. So it is going to move in this direction, move outwards. It moves the first 15 degrees via the action of supraspinatus and then middle portion of deltoid carries on the movement of abduction. If we now go to other muscles, other scapulohumeral muscles running from the scapula to the humerus we find we have a muscle coming from the infraspinatus fossa that is passing from inferior to the spine of the scapula and that passes also to the greater tubercle of the humerus. We then find we have teres minor and we have teres major. All these muscles running from the scapula to the humerus. We can see this is on the posterior aspect of the humerus. And we also have muscles which were on the anterior surface of the humerus.

04:12 Sorry, have a muscle on the anterior surface of the scapula and this muscle in between the scapula and the chest wall is subscapularis. Subscapularis we can see here is running towards the lesser trochanter of the humerus, the lesser tubercle a bigger part of the humerus we can see the lesser tubercle receiving subscapularis. So if we look at the detail of this, then here we can see infraspinatus, we can see infraspinatus originating from the infraspinous fossa and it passes to the greater tubercle of the humerus. This is innervated via the suprascapular nerve. We can also see we have teres minor passing across from the lateral border of scapula and the middle portion of the infraspinous fossa. We can see it is passing again to the greater tubercle. And what we have is we now have three muscles that are going to the greater tubercle. We have the supraspinatus which is going to the greater tubercle. We then have the infraspinatus going to the greater tubercle. We have teres minor going to the greater tubercle. And these goes to the specific parts of the greater tubercle. We can see the supraspinatus passes to the superior facet on the greater tubercle. We can see the infraspinatus passes to the middle facet and teres minor passes to the inferior facet. So it pass to specific regions of the greater tubercle. They won't pass to the same place. They pass to specific regions. Teres minor is innervated via the axillary nerve. Remember we saw that supplying deltoid. These two muscles infraspinatus and teres minor helps to laterally rotate the shoulder joint and they hold the head of the humerus in the glenoid cavity and this is really important. They help to hold the head of the humerus in the glenoid cavity. I mentioned previously that these muscles that the glenohumeral joint was relatively weaker compared to say the hip joint allowing for greater range of movements. But what actually stabilizes the joint as well as some ligaments of these muscles passing from the scapula to the humerus and they help to stabilize the joint. They are known as rotator cuff muscles. Here we can see these rotator cuff muscles or some of the rotator cuff muscles infraspinatus, teres minor and subscapularis. What we could add on to here is supraspinatus as well. And there are the four muscles that form this rotator cuff supraspinatus, infraspinatus, teres minor, and subscapularis and they form this cuff around the humerus around the head of the humerus. Teres major here doesn't because that attaches to the shaft of the humerus lower down, it doesn't actually form this rotator cuff. Here we can see teres major running from the lateral border of the scapula here and into the inferior angle and passing towards the shaft of the humerus. Specifically attaches to the intertubercular groove, the medial lip of the intertubercular groove and here we can see it's innervated via the lower subscapular nerve. It adducts and medially rotates the shoulder joint.

07:56 So teres major is an adductor where deltoid and supraspinatus were an abductor. Teres major helps to adduct and also medially rotate the shoulder joint. Subscapularis is coming from the subscapular fossa. It is running to the lesser tubercle, so where the other three rotator cuff muscles are running to the greater tubercle, this runs to the lesser tubercle of the humerus.

08:24 Innervated via upper and lower subscapular nerves. It is important in medially rotating and adducting the shoulder joint. So, we have adduction and medial rotation. It works with teres major but it also helps to hold the head of the humerus in the glenoid cavity.

08:46 And this feature here holding the head of the humerus in the glenoid cavity mean it is the part of the rotator cuff. And here we can see those rotator cuff muscles in their kind of anatomical orientation. We can see here we have got the shoulder joint, we can see its anterior view on the right hand side. So the chest wall has been removed.

09:11 Here we can see the anterior surface of the scapula, we have subscapularis muscle. Subscapularis muscle passing towards the lesser tubercle. Here coming from the posterior surface of the scapula, we can see teres major, see it here. But we see it is running to the medial lip of the intertubercular groove, alongside latissimus dorsi here. They share a similar insertion. But because teres major is not passing towards the head of the humerus, it’s not a rotator cuff muscle. Here we can see the subscapularis, this. On this posterior surface, we can see we have supraspinatus. We can see that just here. We can see the various parts of deltoid have been cut, have been reflected. So we can see deep to deltoid where we then have supraspinatus, infraspinatus, and teres minor and these are running towards the greater tubercle. Remember the greater tubercle having those three facets superior, here we can make out the middle, here we can make out the inferior. Remember supraspinatus pass to the superior facet, infraspinatus pass to the middle facet and teres minor pass to the inferior facet.

10:38 So we can see these on this posterior view. We can see the muscles originating from the scapula and forming this cuff around the head of the humerus. So all of these muscles, except supraspinatus, are rotators of the humerus. All of these except supraspinatus, are rotators.

10:58 But supraspinatus still runs in the direction that forms this cuff around the head of the humerus, so acting as a rotator cuff. Very important to remember that supraspinatus just abducts. Tendons of these four muscles blend with the joint capsule and form a musculotendinous sheath and this surrounds the glenohumeral joint. Tendons blend with the joint capsule, we can see this tendons here, and they help to protect and stabilize the joint. It's the tonic contractions or these baseline contractions of these muscles that hold the relatively large humeral head against the shallow glenoid cavity. So the shallow glenoid cavity and the large humeral head is held in position via these rotator cuff muscles. So in this lecture we have looked at the anterior and posterior axio-appendicular muscles. The anterior ones, pectoralis major and minor, subclavius and serratus anterior. And then posterior muscles split into those two groups, superficial and deep. Trapezius and latissimus dorsi in the superficial. Levator scapulae and rhomboid major and minor in the deep. We then looked at the deltoid, supraspinatus, infraspinatus, teres major and minor, and subscapularis muscles that form the scapulohumeral muscles. Specifically mentioning the rotator cuff which is supraspinatus, infraspinatus, teres minor and subscapularis. We then looked at their origins, their insertions and their movements.