04/03/2026
The Shoulder Joint - The Big Picture
The shoulder is not just one joint
It’s a system of 4 joints working together
1️⃣ The main Ball & Socket
Glenohumeral Joint
* Ball = top of the humerus (arm bone)
* Socket = shallow part of the shoulder blade
* Very mobile
* Not very stably
Because the socket is shallow, the shoulder trades stability for mobility
2️⃣ The shoulder Blade Joint
Scapulothoracic Joint
This is NOT a true joint, hence one that is often forgotten ~ but functionally it’s HUGE
It’s how the shoulder blade glides on
The rib cage
This is extremely important
If the shoulder bade doesn’t move well ~> the arm cannot move well
3️⃣ & 4️⃣ The Collarbone Joint
Acromioclavicular joint
~ clavicle meets acromion
~ fine tuning + force transfer
Sternoclavicular joint
~ clavicle meets sternum
~ this is the only true bony attachment of the arm to the trunk
~ very important for load transfer
These connect the collarbone to the:
* the shoulder blade
* The sternum
Key concept : Shoulder Rhythm
When you life your arm overhead :
• First ~ 30• = mostly your arm bone
• After that = arm + shoulder blade working together
This is called Scapulohumeral rhythm
If the shoulder blade doesn’t upwardly rotate properly -> you get :
* impingement
* Compensation
* Neck tightness
* Lat Dominance
* Rotator cuff strain
Simple Stability idea :
The shoulder depends on :
* Muscles for stability (not bone structure)
* Proper rib cage position
* Proper breathing
Which is why the neck, thoracic, diaphragm, glutes and even the big toe matter.
Everything is connected through tension and force transfer