The shoulder is a complex joint made up of bones, ligaments, muscles and tendons. It connects the arm to the torso and allows a wide variety of arm movements.

Bones :

The shoulder is made up of 3 bones:

  • The collarbone : this is the bone that forms the anterior part of the shoulder girdle. it is articulated on the shoulder.
  • The scapula (or scapula): is a triangular bone located in the upper part of the back which is articulated with the arm and serves mainly as site of muscular attachment.
  • The humerus which is the long bone of the arm.

These bones are linked together and form 2 joints. The main joint is the glenohumeral (GH) joint called the shoulder joint. It is a spheroid type ball joint. It joins the upper end of the humerus to the scapula . It is the most mobile joint in the body and is therefore subject to many phenomena of dislocation or inflammation. This articulation allows the movement of the arm in a circular rotation.

The labrum is a piece of cartilage that protects the head of the humerus and the glenoid. This cartilage plays a role in stabilizing the joint.

The second joint is the acromioclavicular (AC) joint . It is formed by the collarbone and the scapula. They connect together in the acromion which is at the tip of the shoulder.

The ligaments:

They constitute a powerful connective tissue which unites the bones and prevents them from separating. There are three groups of ligaments:

  • Coracoclavicular ligaments ( LCC ): composed of the conoid and trapezoidal ligaments. They attach the collarbone to the scapula in its part called the coracoid process .
  • The glenohumeral ligaments ( LGH ): are a group of 3 ligaments that attach the head of the humerus to the scapula in its glenoid cavity . They are: the upper glenohumeral ligament (LGHS), the middle glenohumeral ligament (LGHM) and the lower glenohumeral ligament (LGHI).
  • The coracohumeral ligaments ( CHL ): These ligaments attach the humerus to the scapula in its coracoid process . Its role is not fully understood.

Muscles :

The shoulder joint is surrounded by a group of 4 muscles that form the rotator cuff and attach the humerus to the scapula . These are: the supraspinatus muscle , the infraspinatus muscle , the small round muscle and the subscapular muscle . The rotator cuff muscles stabilize the shoulder joint ( glenohumeral ) and assist in the rotation of the arm.


The tendons of the shoulder joint consist of 4 tendons of the muscles of the cuff: supraspinatus; infraspinatus; small circle ; subscapular. Another long bicep tendon that slides between these tendons in a groove.

The synovial membrane:

The shoulder joint is enclosed in a capsule called the synovial membrane. It is an envelope of soft tissue that surrounds the glenohumeral joint and attaches to the scapula, humerus and head of the biceps. It is bordered by a thin, smooth synovial membrane. The synovial membrane secretes a liquid that helps lubricate the joint.