Okay, so this is a tutorial on the glenohumeral joint. So the glenohumeral joint is (as the
name suggests) the joint between the head of the humerus and the glenoid cavity of the
scapula. So you can see the glenoid cavity of the scapula here.
This joint is a synovial ball-and-socket joint. 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. So it's very mobile because of this relationship between the shallow glenoid
cavity and the large humeral head.
So 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. We've also
got circumduction, which is a combination of flexion, extension, abduction and adduction.
So there's a lot of movements at this joint.
So I just brought the muscle area in and you can see some of the muscles which surrounds
this joint and actually add a bit of stability to it. So we've got this deltoid muscle here.
You've got the pectoralis major at the front (anteriorly).
You've got the long head of the biceps, which comes up and goes over the glenohumeral joint
and that's a bit of stability there.
At the back, you've got the long head of the triceps tendon and you've obviously got the
rotator cuff muscles, which is crucial in maintaining the stability of this joint. You've
also got the teres major and the latissimus dorsi muscles.
So apart from the muscles, we've got extra capsular ligaments, which surround the joint
and you've got bony processes. So you've got the acromion process and you've got the coracoid
process. So all these different things adds stability to the glenohumeral joint.
We'll start off by taking a look at the glenoid cavity. So I'll just remove the humerus. We're
looking laterally now at the right shoulder. So 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 in this model, but the margins
of this glenoid cavity 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.
So 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.
You can see superiorly, this is the tendon of the long head of the biceps. It's been
cut. So this tendon is actually continuous with the glenoid labrum. It lands over the
glenohumeral joint and adds a bit of stability to it.
So 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. You can see it attaching to the supraglenoid tubercle.
So this tendon at this origin is continuous with the glenoid labrum, which I've showed
you in that previous diagram.
So 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 head of the origin of this tendon.
So 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.
So this diagram here just shows the joint capsule itself. So you can see it enclosing
the glenohumeral joint and you can see its attachment on the anatomical neck of the humerus.
So 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 bursae which are and sort of cushions
of fluid lined by synovial membrane, which act to reduce friction and to cushion the
joint.
The bursae 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 bursae quickly.
Medially, the synovial membrane protrudes to 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 for 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. So you can see this synovial sheath here. This just reduces friction of
this tendon.
So we'll just take a look at a couple of those bursae that I've mentioned.
Looking here, we can see the tendon of the subscapularis inserting into 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 -- 'bursae' is plural, 'bursa' is singular -- so you can see this bursa which sat underneath
the tendon of the subscapularis muscle. So 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 bursae. This big, large bursa here is the subacromial and subdeltoid
bursa, which sits obviously under the acromnion 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 top of the acromion and lies between the skin
and the acromion.
You've got small little bursa, which lies underneath the coracoid process. So you can
see the coracoid process here and the little bursa sits underneath it.
And then you've got bursae which sit in relation to the rotator cuff muscles. So we've got
a bursa here as well.
It's important to be aware of the subacromial and subdeltoid bursae and the subtendinous
bursa of the subscapularis muscle.
Just going back to this diagram again, so looking at joint capsule of the glenohumeral
joint, the fibrous membrane of the joint capsule is thickened to form ligaments which support
the joint. So 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.
So the glenohumeral ligament can be seen here, but they're not really shown 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. So you've got a superior, middle and inferior glenohumeral ligament.
Next, we've got this ligament here, which is the transverse humeral ligament. This attaches
from the lesser tubercle to the greater tubercle. This lies over the biceps tendons. 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! So that's the shoulder joint. Just remember the articulating surfaces. There's a joint,
a 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 to the fibrous membrane to form bursae and to wrap around the biceps tendon,
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 extra capsular ligaments providing stability.
You've got several movements. You've got flexion, extension, abduction, adduction, internal
and external rotation and circumduction.
It's quite a lot to learn there actually, but I'll make another tutorial, which will cover
the movements that the shoulder joint and the muscles that produce these movements.