Movements

The glenoid fossa is shallow and contains the glenoid labrum which deepens it and aids in stability. With 120 degrees of unassisted flexion, the glenohumeral joint is the most mobile joint in the body.

Scapulohumeral rhythm helps to achieve further range of movement.

The rotator cuff muscles of the shoulder produce a high tensile force, and help to pull the head of the humerus into the glenoid fossa.

Movements of the shoulder joint
Movement	Muscles	Origin	Insertion
Flexion	Anterior fibers of deltoid	Clavicle	Middle of lateral surface of shaft of humerus
	Clavicular part of pectoralis major	Clavicle	Lateral lip of bicipital groove of humerus
	Long head of biceps brachii	Supraglenoid tubercle of scapula	Tuberosity of radius, Deep fascia of forearm
	Short head of biceps brachii	Coracoid process of scapula	Tuberosity of radius, Deep fascia of forearm
	Coracobrachialis	Coracoid process	Medial aspect of shaft of humerus
Extension	Posterior fibers of deltoid	Spine of scapula	Middle of lateral surface of shaft of humerus
	Latissimus dorsi	Iliac crest, lumbar fascia, spines of lower six thoracic vertebrae, lower 3-4 ribs, inferior angle of scapula	Floor of bicipital groove of humerus
	Teres major	Lateral border of scapula	Medial lip of bicipital groove of humerus
Abduction	Middle fibers of deltoid	Acromion process of scapula	Middle of lateral surface of shaft of humerus
Abduction	Supraspinatus	Supraspinous fossa of scapula	Greater tuberosity of humerus
Adduction	Sternal part of pectoralis major	Sternum, upper six costal cartilages	Lateral lip of bicipital groove of humerus
	Latissimus dorsi	Iliac crest, lumbar fascia, spines of lower six thoracic vertebrae, lower 3-4 ribs, inferior angle of scapula	Floor of bicipital groove of humerus
	Teres major	Lower third of lateral border of scapula	Medial lip of bicipital groove of humerus
	Teres minor	Upper two thirds of lateral border of scapula	Greater tuberosity of humeruis
Lateral rotation	Infraspinatus	Infraspinous fossa of scapula	Greater tuberosity of humerus
	Teres minor	Upper two thirds of lateral border of scapula	Greater tuberosity of humerus
	Posterior fibers of deltoid	Spine of scapula	Middle of lateral surface of shaft of humerus
Medial rotation	Subscapularis	Subscapular fossa	Lesser tuberosity of humerus
	Latissimus dorsi	Iliac crest, lumbar fascia, spines of lower 3-4 ribs, inferior angle of scapula	Floor of bicipital groove of humerus
	Teres major	Lower third of lateral border of scapula	Medial lip of bicipital groove of humerus
	Anterior fibers of deltoid	Clavicle	Middle of lateral surface of shaft of humerus

Capsule

The glenohumeral joint has a loose capsule that is lax inferiorly and therefore is at risk of dislocation inferiorly. The long head of the biceps brachii muscle travels inside the capsule to attach to the supraglenoid tubercle of the scapula.

Because the tendon is inside the capsule, it requires a synovial tendon sheath to minimize friction.

A number of bursae in the capsule aid mobility. Namely, they are the subdeltoid bursa (between the joint capsule and deltoid muscle), subcoracoid bursa (between joint capsule and coracoid process of scapula), coracobrachial bursa (between subscapularis muscle and tendon of coracobrachialis muscle), subacromial bursa (between joint capsule and acromion of scapula) and the subscapular bursa (between joint capsule and tendon of subscapularis muscle, also known as subtendinous bursa of subscapularis muscle). The bursa are formed by the synovial membrane of the joint capsule. An inferior pouching of the joint capsule between teres minor and subscapularis is known as the axillary recess.

It is important to note that the shoulder joint is a muscle dependent joint as it lacks strong ligaments.

Ligaments

Superior, middle and inferior glenohumeral ligaments
Coracohumeral ligament
Transverse humeral ligament

Pathology

The capsule can become inflamed and stiff, with abnormal bands of tissue (adhesions) growing between the joint surfaces, causing pain and restricting movement of the shoulder, a condition known as frozen shoulder or adhesive capsulitis.