Description

This video is about the shoulder joint.
In this video, we break down all the anatomical structures that make and support the shoulder joint (bones, ligaments, bursae, rotator cuff muscles).

Structures involved in the shoulder joint:
Bones and Articular Surfaces:
• Scapula – Flat, triangular bone forming the posterior base of the shoulder joint.
• Humerus – Long bone of the upper arm; the head articulates with the glenoid cavity.
• Clavicle – Acts as a strut between the sternum and scapula.
• Glenoid cavity (Cavitas glenoidalis) – Shallow socket on the scapula that receives the head of the humerus.
• Head of humerus (Caput humeri) – Ball-shaped proximal end of the humerus that articulates with the scapula.
• Anatomical neck of humerus – Narrowing just below the humeral head; attachment site for the joint capsule.
• Intertubercular groove (Sulcus intertubercularis) – Groove between the tubercles of the humerus for the biceps tendon.

Labrum and Capsule:
• Glenoid labrum (Labrum glenoidale) – Fibrocartilaginous rim that deepens the glenoid cavity for stability.
• Articular capsule (Capsula articularis) – Encloses the joint and blends with periosteum.
• Synovial membrane – Inner lining of the joint capsule that produces synovial fluid.
• Fibrous capsule – Outer layer providing mechanical support.
• Axillary recess – Inferior fold of the capsule allowing arm abduction.

Glenohumeral Ligaments:
• Superior glenohumeral ligament – Stabilizes the joint when the arm is at rest.
• Middle glenohumeral ligament – Stabilizes during mid-range abduction and rotation.
• Inferior glenohumeral ligament – Strongest, prevents anterior dislocation in abducted/externally rotated arm (ABER position).
• Coracohumeral ligament – Supports the superior capsule, limits external rotation.
• Transverse humeral ligament – Covers the bicipital groove and holds the biceps tendon in place.

Coracoacromial Arch & Ligaments:
• Coracoacromial ligament – Connects the coracoid process to the acromion, forming a superior arch.
• Coracoacromial arch – Prevents upward displacement of the humeral head.
• Acromioclavicular joint – Between clavicle and acromion; involved in arm elevation.
• Coracoclavicular ligament – Anchors clavicle to scapula, indirect shoulder stabilizer.

Rotator Cuff Muscles (Mnemonics SITS):
• Supraspinatus – Initiates abduction; commonly involved in impingement.
• Infraspinatus – External rotator, active in deceleration during throwing.
• Teres minor – Assists with external rotation and stabilization.
• Subscapularis – Primary internal rotator and anterior stabilizer.

Other Muscles Mentioned:
• Deltoid – Abducts the arm after supraspinatus initiates the movement.
• Teres major – Assists with internal rotation and adduction.
• Biceps brachii (long head) – Originates from supraglenoid tubercle; involved in shoulder stabilization.

Tendons and Sheaths:
• Long head of biceps tendon – Intracapsular, extrasynovial tendon that stabilizes the joint and is prone to tendinitis.
• Intertubercular tendon sheath – Encloses the long head of biceps in the bicipital groove.

Bursae of the Shoulder:
• Subacromial bursa – Between acromion and supraspinatus tendon; inflamed in impingement.
• Subdeltoid bursa – Cushions the deltoid muscle over the joint capsule.
• Subtendinous bursa of teres major – Reduces friction under teres major.
• Coracobrachial bursa – Lies beneath coracobrachialis muscle.
• Coracoclavicular bursa – Found between coracoid process and clavicle.
• Subcutaneous acromial bursa – Superficial, aids with overhead arm motion.

Clinical Conditions Discussed:
• Shoulder dislocation (especially anterior in ABER position)
• SLAP tear (Superior Labrum Anterior Posterior lesion)
• Rotator cuff tear (especially supraspinatus tendon)
• Subacromial impingement syndrome
• Frozen shoulder (Adhesive capsulitis)
• Biceps tendinitis and instability
• Shoulder pain during overhead activity
• Weakness and limited range of motion due to cuff dysfunction

Sources:
• Kozlowski, T. (2017). Memorix Anatomy, 2nd ed.
• Standring, S. (2020). Gray’s Anatomy, 42nd edition
• Tubbs RS, Shoja MM, Loukas M. (2016). Bergman’s Encyclopedia of Human Anatomic Variation
• White TD, Folkens PA. (2005). The Human Bone Manual

Programs used: Complete Anatomy, Biorender, PowerPoint

Transcript

Introduction & Content
0:00
Your shoulder can throw a baseball, do a handstand, or reach behind your back—all
0:05
thanks to the most flexible synovial joint in your body: the shoulder joint.
0:10
What makes it even more interesting is that this incredible range of motion depends on a small
0:15
group of muscles called the rotator cuff muscles. They hold the joint in place… and they’re also
0:21
one of the most common sources of shoulder pain. In this video, we’ll break down the anatomy of the
0:26
shoulder joint to understand what gives it such a wide range of motion. And then we’ll look at its
0:31
support structures, like the rotator cuff muscles, how they function, and understand the function of
0:36
those small pillow structures called bursae. What’s up everyone, my name is Taim. I’m a
0:41
medical doctor, and I make animated medical lectures to make different topics in medicine
0:45
visually easier to understand. If you’d like a PDF version or a quiz of this presentation, you can
0:49
find it on my website, along with organized video lectures to help with your studies.
Shoulder Joint Components
0:53
Alright, let’s get started. The Shoulder joint. Also known as, glenohumeral
0:59
joint. It’s the most mobile joint in the human body, and arguably also the most vulnerable.
1:05
Let’s strip away all the soft tissue for now and build it up layer by layer so you can really see
1:10
how this articulation is constructed. The bones we can see here are the humerus, scapula, and the
1:16
clavicle. The shoulder joint is an articulation between the glenoid cavity of the scapula and
1:21
the head of the humerus. The glenoid cavity is a shallow deep surface, while the rounded head of
1:27
the humerus is like a ball that is faced towards it. But here’s the issue, the humeral head is much
1:33
larger than the glenoid cavity. This is great for range of motion, but not so great for stability.
1:38
To fix that, the joint has a fibrocartilaginous ring called the glenoid labrum. This structure
1:45
deepens the glenoid cavity slightly, increasing the articular surface area by about 50%. This is
1:51
a really important stabilizer that helps hold the humeral head in place, especially during
1:56
sudden or forceful movements. Sitting right external to it,
2:00
we have the synovial membrane. This is the inner layer of the joint capsule, and what it does is
2:06
that it produces something called synovial fluid. Synovial fluid is a viscous lubricant
2:12
that reduces friction and nourishes the articular cartilage. Think of it as the oil in the engine.
2:18
Externally to this synovial membrane, we can see some ligaments that reinforce the capsule. The
2:24
upper one is called superior glenohumeral ligament, which runs from the superior
2:29
aspect of the glenoid to the humerus, providing stability when the arm is at rest or in adduction.
2:35
We can see the middle glenohumeral ligament, that acts like a seatbelt during mid-range abduction
2:40
and external rotation. This is sometimes absent in some people. Then we can see the inferior
2:47
glenohumeral ligament, which is the strongest and most important stabilizer in the abducted
2:52
and externally rotated position. It acts as a hammock underneath the humeral head and is the
2:58
main structure preventing anterior dislocation. If you’ve ever heard of the “ABER” position,
3:03
this is a position where the arm is in abduction and external rotation. This is where
3:08
shoulder dislocations most often happen, and this ligament is just basically what tries to stop it.
3:15
Next, we add the coracohumeral ligament. This originates from the lateral border
3:20
of the coracoid process and blends with the superior capsule and supraspinatus tendon.
3:26
It provides superior stability and also plays a role in limiting external rotation.
3:32
Now, we bring in two additional ligaments that, while not part of the glenohumeral capsule per se,
3:38
are still important to shoulder function. The transverse humeral ligament as you see here, goes
3:44
over the intertubercular groove of the humerus and holds the long head of the biceps tendon in place
3:49
as it exits the joint capsule, i’ll show you in a minute, but without it, the tendon could dislocate
3:55
medially, which is a rare but it do happen. Then there’s the coracoacromial ligament, which forms
4:01
the coracoacromial arch. This structure doesn’t directly stabilize the glenohumeral joint, but
4:06
it acts like a ceiling that prevents the humeral head from displacing superiorly. It’s part of the
4:12
subacromial space, and when things get tight in that area, you get subacromial impingement
4:18
syndrome due to compression of structures like the supraspinatus tendon or the subacromial bursa.
4:24
Alright let’s keep building on this, by adding a layer on top of them, and this layer is called
4:29
the fibrous layer of the articular capsule. This is the tough, external layer that encloses the
4:35
joint and attaches from the anatomical neck of the humerus to the margins of the glenoid cavity,
4:40
blending with the periosteum. It provides tensile strength and mechanical support, resisting
4:46
dislocation and anchoring the joint in space. One interesting thing is, there’s something
4:52
called the axillary recess. This is a pouch-like extension of the capsule that sits inferiorly, and
4:59
what it does is that it allows the humeral head to glide downward when the arm is abducted. It slacks
5:05
the system off a little bit which is normal. Interestingly, In adhesive capsulitis, or what we
5:10
call frozen shoulder, this recess becomes fibrotic and contracted, severely restricting motion.
5:17
So what you’re looking at now, with all its supporting structures in place,
5:21
is the glenohumeral joint. A very mobile joint. On top of all of these supporting structures,
Rotator Cuff Muscles
5:27
the joint also has some dynamic stabilizers, called the rotator cuff muscles. These are
5:33
four muscles that originate from the scapula and insert onto the humerus,
5:37
enveloping the glenohumeral joint like a cuff, hence the name. They provide dynamic stabilization
5:44
by compressing the humeral head into the glenoid during movement. Let’s go through them one by one.
5:50
First we can see the subscapularis. This is the only rotator cuff muscle located on the anterior
5:56
surface of the scapula. It originates from the subscapular fossa and inserts into the lesser
6:01
tubercle of the humerus. It’s the primary internal rotator of the humerus and also
6:06
helps resist anterior dislocation by reinforcing the front of the joint capsule. You can see how
6:13
it spans from the costal side of the scapula and tucks neatly under the coracoid process.
6:19
Now let’s rotate to the posterior view to see the other three. Here’s the teres minor, a small,
6:26
narrow muscle that originates from the lateral border of the scapula and inserts on the greater
6:31
tubercle of the humerus. Its function is external rotation and slight adduction of the arm, and it’s
6:37
most active during fine-tuned shoulder control. Superior to it, we find the infraspinatus,
6:43
which arises from the infraspinous fossa of the scapula. This muscle is a major external rotator
6:49
and is especially important in decelerating the arm during overhead throwing motions,
6:54
so it gets a lot of strain in athletes like pitchers and tennis players. The last one
7:00
is at the top, called the supraspinatus, originating from the supraspinous fossa.
7:05
It passes under the acromion and inserts on the greater tubercle of the humerus. Functionally,
7:10
it initiates abduction of the arm, the first 15 degrees, before the deltoid takes over.
7:16
It also plays a role in stabilizing the humeral head during shoulder elevation.
7:21
These four, subscapularis, infraspinatus, teres minor, and supraspinatus—are collectively called
7:27
the rotator cuff muscles, or sometimes referred to by the mnemonic SITS, each letter corresponds to
7:33
a muscle. Only these four are called rotator cuff muscles because they all share the common feature
7:39
of inserting around the joint capsule and actively contributing to joint stabilization during motion.
7:46
Other shoulder muscles like deltoid or teres major move the shoulder
7:50
but don’t reinforce the capsule itself. Clinically, the rotator cuff is extremely
7:55
important because it’s one of the most common sources of shoulder pathology. The supraspinatus
8:00
is the most frequently injured—particularly in rotator cuff tears—often due to impingement under
8:06
the acromion or age-related tendon degeneration. In general partial or full-thickness tears in
8:12
any of the rotator cuff muscles can lead to shoulder pain, weakness, and limited motion,
8:16
especially in elevation and rotation. So, that was the rotator cuff. The shoulder joint
Bursae of the Shoulder
8:22
actually has another supporting system, these are small friction-reducing pillows we refer to
8:29
as bursae. Think of these as synovial-fluid filled cushions that reduce friction between soft tissues
8:35
and bone during movement. First, we have the subdeltoid bursa, which sits between the deltoid
8:41
muscle and the joint capsule. Closely related is the subacromial bursa, located between the
8:47
acromion and the supraspinatus tendon. These two bursae often communicate and are commonly involved
8:53
in impingement syndromes. Next is the subtendinous bursa of the teres major, which reduces friction
8:59
as the muscle glides over the humerus. The coracobrachial bursa cushions the
9:04
coracobrachialis muscle, and the coracoclavicular bursa lies between the coracoid process and
9:09
clavicle, often inflamed in repetitive overhead activity. Then we can see the
9:15
subcutaneous acromial bursa, just under the skin and superficial to the acromion,
9:20
it helps with skin movement during overhead elevation or load-bearing activities.
9:25
Alright, that was the bursae. Last important thing I wanna mention here is, if we look at the deeper
9:30
anterior aspect again, we got something called the intertubercular tendon sheath. This sheath
9:36
encases the long head of the biceps tendon as it runs through the intertubercular groove. Remember
9:42
the transverse humeral ligament we talked about earlier? This ligament spans across
9:46
the groove to hold the sheath and tendon in place, preventing medial displacement.
9:51
And so here’s how this looks like, you can see the tendon of the long head of
9:55
the biceps brachii itself. It originates from the supraglenoid tubercle and labrum,
10:00
passes within the shoulder joint itself, and then exits through the bicipital groove. It’s
10:05
technically intracapsular but extrasynovial, which makes it susceptible to inflammation especially if
10:11
you move your shoulder a lot in repetitive motion. And with that, we’ve now covered all the static
Outro & Next Topic
10:17
and dynamic components that make up the shoulder joint, capsular structures, ligaments, muscles,
10:22
bursae, and tendons. It’s a very delicate system. In the next video, we’ll continue our skeletal
10:28
system series by covering the humerus itself, its anatomical landmarks,
10:32
muscle attachments, and how it fits into both proximal and distal articulations.
10:37
Click the next video, and I’ll see you there. If you want a handmade PDF version of this
10:40
lecture, take a quiz to test your knowledge, or access an organized list of all my videos,
10:45
you can find everything on my website. Thanks for watching! See you in the next one.