Shoulder Anatomy: Clavicle, Scapula and Humerus, these bones make 5 articulations-Sternoclavicular, Acromioclavicular, Glenohumeral, Scapulothoracic, Subacromial space.
The Glenohumeral joint has greater range of motion than any other joint. The end of the scapula called the glenoid meets the head of the humerus to form a flenohumeral cavity that acts as a flexible ball and socket joint. The joint cavity is cushioned by articular cartilage covering the head of the humerus and of the glenoid. The joint is stabilised by a ring of fibrous cartilage surrounding the glenoid called the labrum. There are at least 30 muscles that provide support for the shoulder complex.

Ligaments….are the main source of stability for the shoulder, they help hold the shoulder in place and keep it from dislocating. These ligaments of the shoulder complex are:

Rotator cuff: Comprises as agroup of 4 (four) tendons, Supraspinatus, Infraspinatus, Teres minor, Subscapularis, they connect to the humerus-greater tuberosity. The rotator cuff muscles are important in shoulder movements and in maintaining glenohumeral joint (shoulder joint) stability. These muscles arise from the scapula and connect to the head of the humerus forming a cuff at the shoulder joint. They hold the head of the humerus in the small and shallow glenoid fossa of the scapula.

During abduction of the arm, the rotator cuff compresses the glenohumeral joint, a term known as concavity compression, in order to allow the large deltoid muscle to further elevate the arm. In other words, without the rotator cuff, the humeral head would ride up partially out of the glenoid fossa, lessening the efficiency of the deltoid muscle. The anterior and posterior directions of the glenoid fossa are more susceptible to shear force perturbations as the glenoid fossa is not as deep relative to the superior and inferior directions. The rotator cuff’s contributions to concavity compression and stability vary according to their stiffness and the direction of the force they apply upon the joint.
During abduction of the arm, the rotator cuff compresses the glenohumeral joint, a term known as concavity compression, in order to allow the large deltoid muscle to further elevate the arm. In other words, without the rotator cuff, the humeral head would ride up partially out of the glenoid fossa, lessening the efficiency of the deltoid muscle. The anterior and posterior directions of the glenoid fossa are more susceptible to shear force perturbations as the glenoid fossa is not as deep relative to the superior and inferior directions. The rotator cuff’s contributions to concavity compression and stability vary according to their stiffness and the direction of the force they apply upon the joint.