This is a tutorial on the glenohumeral joint. The glenohumeral joint is, as the name suggests a joint between the head of the humerus and the glenoid cavity of the scapula.
You can see the glenoid cavity of the scapula here. This joint is a synovial ball-and-socket joint and it’s quite an unstable joint because the head of the humerus is relatively large, whereas the glenoid cavity of the scapula is actually quite shallow. it’s very mobile because of this relationship between the shallow glenoid cavity and the large humeral head.
Because of this instability, it’s actually a very mobile joint. at this joint, we have several movements. We’ve got flexion and extension. We’ve got abduction and adduction. We’ve got internal rotation or medial rotation and we’ve also got external rotation. And we’ve also got circumduction, which is a combination of flexion, extension, abduction and adduction. There are a lot of movements at this joint.
I’ve just brought the muscle area in and you could see some of the muscles which surround this joint and actually a bit of stability to it. you’ve got this deltoid muscle here. You’ve got the pectoralis major of the front anteriorly. You’ve got the long head of the biceps, which comes up and goes over the glenohumeral joint and adds a bit of stability there.
At the back, you’ve got the long head of the triceps tendon and you’ve also got the rotator cuff muscles, which are crucial in maintaining stability of this joint. You’ve also got the teres major and the latissimus dorsi muscles.
Apart from the muscles, you’ve got extra-capsular ligaments, which surround the joint. You’ve got bony processes. You’ve got the acromion process and you’ve got the coracoid process.
All these different things adds stability to the glenohumeral joint.
We’ll start off by taking a look at the glenoid cavity. I’ll just remove the humerus. We’re looking laterally now at the right shoulders. we’ll remove the humerus and we’ll take a look at the glenoid cavity.
This is the glenoid cavity of the scapula. It’s not shown on this model, but the margins of this glenoid cavity are surrounded by a fibrocartilaginous collar called the glenoid labrum. This sits around the perimeter, the margins of the glenoid cavity and actually adds a bit of depth to the glenoid cavity.
I’ve just switched over to this diagram here and we’re looking at the same view, a lateral view of the right shoulder. We’ve got the acromion posteriorly and the coracoid process anteriorly. you can see this fibrocartilaginous collar, the glenoid labrum surrounding the glenoid fossa. And you can see superiorly, this is the tendon of the long head of the biceps and it’s been cut. This tendon is actually continuous with the glenoid labrum and it runs over the glenohumeral joint and adds a bit of stability to it.
I’ve just switched back to the model and I’ve isolated the long head of the biceps muscle. You can see this running up on the humerus in between the intertubercular sulcus and it runs over the glenohumeral joint and you can see it attaching to the supraglenoid tubercle. this tendon at its origin is continuous with the glenoid labrum, which I showed you in that previous diagram.
Just like in many other joints, there’s a joint capsule which surrounds the glenohumeral joint. The joint capsule consists of a fibrous and a synovial membrane. The fibrous membrane wraps around the glenohumeral joint. it wraps around the outside of the glenoid labrum and it actually encloses the origin of this tendon.
I’ve just switched back to a diagram. We’ve seen this diagram before. The fibrous membrane of the joint capsule actually encloses the labrum and encloses the origin of the long head of the biceps tendon.
This diagram here just shows the joint capsule itself. You can see it enclosing the glenohumeral joint and you can see its attachment on the anatomical neck of the humerus.
Lining the fibrous membrane, you’ve got the synovial membrane. It’s important to just mention the synovial membrane because the synovial membrane at various points actually protrudes through the fibrous membrane and it forms bursi, which are sort of cushions of fluid lined by synovial membrane which act to reduce friction and to cushion the joint. The bursi are quite important to be aware of because they can get inflamed and cause pain in the shoulder joint.
I’ll just mention a few of these bursi quickly. medially, the synovial membrane protrudes through the fibrous membrane and it forms the subtendinous bursa of the subscapularis or the subscapularis bursa.
I’ll just flick over to the 3D model in a moment, but I’ll just mention this first. You’ve also got a synovial sheath, which wraps around the long head of the biceps tendon as it passes through the intertubercular sulcus between the greater and lesser tubercles of the humerus. You can see this synovial sheath here. This just reduces friction of this tendon.
We’ll just take a look at a couple of those bursi that I mentioned. looking here, we can see the tendon of the subscapularis inserting onto the lesser tubercle of the humerus. I’ll just remove that and you can see the bursa that lies underneath. I’ll just remove this biceps tendon and the coracobrachialis muscle. You can see this bursa – bursi is plural, bursa is singular. You can see this bursa which sat underneath the tendon of the subscapularis muscle. This is the subtendinous bursa of the subscapularis. this is formed by a protrusion of the synovial membrane through the fibrous membrane.
We’ve also got a few other bursi. This big, large bursa here is the subacromial and subdeltoid bursa, which sits obviously under the acromion process and between the deltoid muscle. This is quite important because it can get inflamed because of the very narrow space between the acromion and the head of the humerus.
You’ve also got this bursa which sits on the top of the acromion and lies between the skin and the acromion. You’ve got a small, little bursa which lies underneath the coracoid process. you can see the coracoid process here and the little bursa sits underneath it. And then you’ve got bursi which sit in relation to the rotator cuff muscles. you’ve got a bursa here as well. It’s important to be aware of the subacromial and subdeltoid bursi and the subtendinous bursa of the subscapularis muscle.
Just going back to this diagram again, we’re looking at the joint capsule of the glenohumeral joint. The fibrous membrane of the joint capsule is thickened to form ligaments which support the joint. we’ll take a look at those ligaments now.
There are five ligaments you need to remember. You’ve got three glenohumeral ligaments. You’ve got the transverse humeral ligament and the coracohumeral ligament. the glenohumeral ligaments can be seen here, but they’re not really shown that clearly. They’re not shown as distinct ligaments, but you’ve got a superior, middle and inferior glenohumeral ligament. These attach onto the lesser tubercle and they originate on the margin of the glenoid cavity. you’ve got a superior, middle and inferior glenohumeral ligament.
Next, we’ve got this ligament here, which is the transverse humeral ligament. It attaches from the lesser tubercle to the greater tubercle. This lies over the biceps tendinous. It passes through the intertubercular sulcus.
And lastly we’ve got this ligament called the coracohumeral ligament because it attaches from the coracoid process to the humerus.
Okay! That’s the shoulder joint. just remember the articulating surfaces. It’s a joint synovial ball-and-socket joint between the head of the humerus and the glenoid cavity of the scapula. There’s a joint capsule which surrounds the joint. The synovial membrane protrudes through the fibrous membrane to form bursi and to wrap around the biceps tendon, the long head of the biceps tendon.
You’ve got five ligaments. You’ve got the coracohumeral ligament, the transverse humeral ligament and the three glenohumeral ligaments – superior, middle and inferior.
Stability to the joint is provided by muscles. You’ve got the rotator cuff muscles, pectoralis major, deltoid, long head of the triceps, long head of the biceps, teres major. And you’ve got bony processes. You’ve got the acromion process, the coracoid process and you’ve got extracapsular ligaments providing stability.
You’ve got several movements. You’ve got flexion, extension, abduction, adduction, internal and external rotation and circumduction. quite a lot to learn there actually, but I’ll make another tutorial which will cover the movements of the shoulder joints and the muscles that produce these movements.