The shoulder is a complex articulation that joins the scapulothoracic joint to the superior member. It is formed by four separate joints and a muscle group.

The joints are:
— The glenohumeral joint, attaching the humeral head to the glenoid fossa;
— The acromioclavicular join, attaching the clavicle to the acromion;
— The sternoclavicular joint located between the clavicle and the sternum;
— The connections between the scapula and the cervical and thoracic spine muscles.

The superficial muscles responsible for shoulder movements are:
— Pectoralis major, that pulls the arm forward;
— Trapezius, that elevates the shoulder;
— Deltoid, that raises the arm laterally;
— Latissimus dorsi that pulls the arm down.

The deltoid, together with a set of smaller muscles, covers the humeral head, form the prominence of the shoulder joint and help prevent joint dislocations.

The pectoralis major forms the anterior of the axilla while the posterior part is formed by the latissimus dorsi and the teres major muscle. The axillary vessels and the brachial plexus network of nerves go through this region.

The glenoid labrum is a fibrocartilaginous structure, similar to a meniscus, which increases the contact with the humeral head, thus stabilizing the joint.

The Rotator Cuff is a four-muscle set:
— supraspinatus;
— infraspinatus;
— teres minor;
— subscapularis.

These muscles are smaller when compared to the pectoralis major and the deltoid muscles, but they are essential for shoulder and scapulothoracic joint movements.

The Rotator Cuff is a convergence of tendons around the humeral head. The tendons of the four muscles join with the articular capsule of the glenohumeral joint.

Their main functions are:
— to centre and lower the humeral head;
— to enhance the rotations of the glenohumeral joint ;
— to stabilise the glenohumeral joint;
—  to provide a closed compartment, which is important to assure the nutritional needs of the joints.