What’s Inside Our Shoulder?


Our shoulder joint is known as the Glenohumeral joint and is traditionally referred to as a ball and socket joint as the rounded head of the humerus (the upper arm bone) slots into the cavity of our scapula (shoulder blade) seen in the image here.

The head of the humerus is able to pivot in all directions by two structures: synovial fluid and a fibrocartilage structure called the labrum. The labrum is a smooth structure that allows movements between to bone structures while the synovial fluid reduces any friction during movement.


Structures within the joint

Muscles and tendons


When talking about the muscles of the shoulder complex we usually refer to the 4 rotator cuff muscles which stem off the shoulder blade and attach on the humerus.

These muscles are:

Supraspinatus: This is responsible for shoulder abduction and the origin (the muscles fixed attachment) of the supraspinatus is at the supraspinatus fossa of the scapula where the insertion (bony attachment that moves with contraction) is at the greater tubercle of the humerus.

Infraspinatus: Responsible for external rotation of the shoulder and originates at the infraspinatus fossa of the scapula and inserts into the greater tubercle of the humerus.

Teres Minor: Responsible for external rotation and assists in adduction. The origin is the lateral border of the scapula and inserts into the greater tubercle of the humerus.

Subscapularis: Responsible for internal rotation of the shoulder and originates at the subscapularis fossa of the scapula and inserts into the lesser tubercle of the humerus.

The shoulder complex also has a meaty muscle that caps over the top of the joint known as the deltoid. The Deltoid is responsible for shoulder flexion, abduction and internal rotation. The deltoid has two heads that attach at the lateral aspect of the clavicle (anterior head) and the acromion process at the end of the spine of the scapula (middle head) and inserts into the deltoid tuberosity of the humerus.




Superior glenohumeral ligament
Middle glenohumeral ligament
Inferior glenohumeral ligament
Coracohumeral ligament
Transverse humeral ligament
Coraco-acromial ligament

Blood Supply:

The shoulder complex receives blood supply from four arteries:
Anterior circumflex humeral artery
Posterior circumflex humeral artery
Suprascapular artery
Scapular circumflex artery

Nerve Innovation:

The nerves that supply the joint are found in the bundle of nerves that stem off the back of the neck and travel over the first rib, under the collarbone and into the armpit. Specifically these nerves are:
Suprascapular nerve
Axillary nerve
Lateral pectoral nerve



The glenohumeral joint capsule forms between the neck of the humerus and the glenoid fossa (where the labrum attaches against). The front of the capsule is reinforced by the three glenohumeral ligaments mentioned above and the rotator cuff muscles support the joint both posteriorly and superiorly while also assisting anteriorly.


A Bursa is a synovial fluid filled sack located at joint sites to allow for muscle tendons (attachment sites for muscles) to slide over with no bony rubbing or friction. There are five bursae in the shoulder complex: subacromial-subdeltoid bursa, supra-acromial bursa, subscapular bursa, coracoclavicular bursa and the subcoracoid bursa.


Common shoulder injuries seen at the clinic:

These include general overuse injuries leading to inflammation and wear & tear, traumatic injuries, postural deformities, shoulder instability and arthritis.

Overuse injuries:
Specifically in the gym caused from repetitive movements can lead to inflammation of the muscle tendons or the surrounding structures and unless treated correctly, can lead to wearing of the tendon.

Such as Falling on out-stretched hands (FOOSH injuries), dropping a weight that is supported by one of the shoulders or direct trauma. This can lead to muscle tears of the rotator cuff group, ligament sprains, labral tears or bone fractures.

Postural deformities:
We see a lot of desk sitters with an excessive upper back hunch/ kyphosis that encloses the space in the shoulder joint especially on shoulder abduction/ laterally raising one arm causing jamming within the shoulder joint together with muscle tightness and muscle imbalances caused from poor posture.

Shoulder instability
Weak shoulders allows for excessive movement within the joint from poor rotator cuff muscle strength and loose ligaments. This usually occurs after a fall causing a ligament sprain where the ligaments never go back to their original length and stay laxed, together with weakened shoulder muscles, the person will present with pain, deformed shoulder joint on appearance and reduced range of movement.


Osteoarthritis will affect the smooth cartilaginous structure (the labrum) between the ball and socket causing the degeneration resulting in bone on bone during certain movements. This traditionally affects people over the age of 50 and a treatment program will be prescribed for pain management that may result in surgery.


Strengthening the shoulder joint

To strengthen the shoulder joint we strengthen both the rotator cuff muscles and the shoulder joint in general.
To strengthen the rotator cuff we work on 3 pain movements: external rotation, shoulder blade retraction and internal rotation. These movements are in the image below with the photos on the left column being our starting position and the photo on the right being our finishing position.

To strengthen external rotation we start with our elbow tucked in to our torso and we pull the theraband across our body as if we are opening a newspaper.

To strengthen shoulder retraction we bring the theraband around our back and cross it over from our front and pulling both arms out keeping your elbows tucked in. You should feel a squeeze between the shoulder blades and holding the contraction at end range.

To strengthen internal rotation we start with our elbow tucked in to our torso and we pull the theraband towards our body as if we are closing a newspaper.


For general shoulder strengthening we get a swiss ball and stand far enough back from the wall that our arm is straight out infront of us holding the ball against the wall. From here we do circular movements both clockwise and anticlockwise, then move the ball higher, lower, to the left and to the right from our initial starting position so the ball is further away from our midpoint and repeat the circular movements.



Kyle Michelle


This article has been prepared by Kyle Michelle.  If you have any questions for Kyle or would like to know more about the glenohumeral joint, please leave your comments below.