The structure of the shoulder

[Josephine]

In order to understand the various conditions and injuries that can occur in a shoulder, it's useful to first understand how the shoulder is constructed. This will be done under these headings:

1. bones
2. muscles
3. ligaments

The bones that are involved in the make up of the shoulder joint are

1. the humerus
2. the scapula (shoulder blade)
3. the clavicle (collar bone)
4. glenoid (socket)

Where these bones meet are also important features

1. acromioclavicular joint
2. coracoclavicular ligament
3. coracoacromial ligament

Although technically a ball and socket joint, it is a very shallow joint, quite unlike the hip where the ball is held securely by an encompassing ring of bone in the form of the acetabulum (cup or socket). Instead, the glenoid is just a shallow dish that the humeral head rests against. The sole responsibility for the containment of the joint rests in the circle of muscles called the ROTATOR CUFF. The term ‘rotator cuff’ refers to the muscles and tendons that keep the ball humerus in the shoulder socket.

These muscles grip the humeral head like so

The muscles concerned are

1. supraspinatous
2. subscapularis
3. teres minor
4. long head of biceps tendon

1. supraspinatous tendon
2. subscapularis tendon
3. joint capsule
4. teres minor tendon
5. infraspinatous tendon

Explanatory note:

a tendon attaches a muscle to bone (or some other structure such as the eyeball)
a ligament is an attachment between two bones​