• Distal articular surfaces

The humeral head the distal articular surface of glenohumeral joint and has an articular surface area larger than glenoid articular surfaces, forming one – third to one – half of a sphere.In anatomical position , the head faces medially , superiorly and posteriorly with regard to shaft of the humerus and the humeral condyles .

ANGLE OF INCLINATION : It is formed by an axis through the humeral head and neck in relation to a longitudinal axis though the shaft of the humerus and is normally between 130 to 150 degree .

ANGLE OF TORSION: It is formed by an axis through the humeral head and neck in relation to an axis through the humeral condyles .but is approximately 30 degree posteriorly

        Glenohumeral accessory structures

       Glenoid labrum

This accessory structure surrounds and is attached to periphery of the glenoid fossa, enhancing the depth or concavity of fossa by approximately 50%. It prevent the translation of humeral head and protect the outer ridges of body margin.It also dissipate the joint contact force.

       Glenohumeral joint Capsule

The capsule of  glenohumeral joint cover the joint in all direction .It is weak , loose, large .

          Glenohumeral Ligaments

1. Superior glenohumeral ligament aries from superior glenoid labrum and attaches to the anterior aspect mid of humerus of glenohumeral joint .

Function: It help to prevent anterior and inferior translation of the humeral head

1. Inferior glenohumeral ligament aries from Anterior glenoid labrum and attaches to anterior aspect of humerus .

Function: It help in rotatary stability (medial and lateral rotation)

• Middle glenohumeral ligament aries from inferior glenoid labrum and attaches to humerus

Function: It prevent inferior translation of humeral head .

1. Coracohumeral ligament is a extra capsular ligament which provide stability during lateral rotation.

           Glenohumeral Kinematics

The glenohumeral joint is usually described as having three rotatory degree of freedom .

• Flexion and extension

It occur about a coronal axis passing through the center of the humeral head.The glenohumeral joint is often considered to have 120 degree of flexion and 50degree of extension .

• Medial and lateral rotation

It occur about a long axis parallel to the shaft of the humerus and passing though the center of the humeral head. The ranges of Medial and lateral rotation varies with position

• Abduction and Adduction

Abduction and Adduction of the glenohumeral joint occurs around an A-P axis passing through the humeral head center. ROM of abduction is from 90to 120 degree

• Intra-Articular glenohumeral motion

Full ROM of the glenohumeral joint is, to a reasonable degree, a function of the intra – articular movement of the incongruent articular surfaces .

Static stabilization

The glenohumeral joint is a incongruenet joint so the bony geometry alone cannot maintain joint stability with the arm relaxed at the side ,requiring the contribution of other mechanisms.To maintain the equilibrium,a caudally directed forces is needed and could be supplied by active contraction or passive tension of muscle, such as the deltoid ,supraspinatus ,or thr long heads of the biceps brachii and triceps brachii.

The rotator interval capsule( superior capsule , superior glenohumeral ligament, and coracohumeral ligament ) is the structure that are taut when arm is at the side posses both magnitude and orientation for this stabilization function .The resultant vector formed from the gravity and rotator interval capsule vector created a force that compresses the humeral head into lower portion of the glenoid fossa and prevent the inferior humeral head translation.

Dynamic stabilization

1. The deltoid and glenohumeral stabilization

It is generally accepted that the deltoid muscle is a prime mover for glenohumeral abduction. The anterior deltoid is also considered the prime mover in glenohumeral joint flexion .Both abduction and flexion are elevation activities with many biomechanical similaties. However, examination of the resultant line action of the deloid muscle in abduction can used to highlight the stabilization needs of the glenohumeral joint in elevation activities.

The action line of all three segment of the deltoid. The resultant pull of three deltoid segment resolves into a very large translator component and small rotary components so that an isolated constraction of deltoid would cause the deltoid to produce more superior translation than rotation of the humerus.

2. The Rotator cuff glenohumeral stabilization

Rotator cuff ( supraspinatus ,Infraspinatus , teres minor and Subscapularis muscle )it contribute to dynamic stabilization of the glenohumeral joint.The force of the Infraspinatus, teres minor,or Subscapularis muscles taken together resolves into its components such that perpendicular force component not only tends to cause atleast some rotation of humerus given its orientation to the long axis of the bone, but it also compresses the head into glenoid fossa.

3. The Supraspinatus and glenohumeral stabilization

Although the supraspinatus muscle is part of the rotator cuff muscles , has a superior translaory component, rather than inferior component found in the other muscles of cuff . Given its line of pull, the supraspinatus cannot contribute to offsetting the upward dislocating action of the deltoid. 

The supraspinatus is still an effective stabilizer of the glenohumeral joint, however , because of its contribution to joint compression. Because the more superior location of the supraspinatus results in a line of action that lies farther from glenohumeral joint axis thn the action lines of the other rotator cuff muscles, the larger supraspinatus moments arm is capable of independently producing a full or nearly full range of glenohumeral joint abduction while simultaneously stabilizing the joint . Gravity acts as a stabilizing synergist to the supraspinatus by offsetting thee small upward translator pull of the muscle.

4. The Long head of the Biceps brachii and glenohumeral stabilization

The long head of the biceps brachii runs superiorly from the anterior shaft of the humerus through the bicipital grove between the greater and lesser tubercles to attach to the supraglenoid tubercle and superior labrum . The biceps muscle  is capable of contributing to the force of flexion and can if the humerus is lateral rotated , contribute.