- articulation: ball and socket joint between the head of the humerus and the glenoid
- joint: shoulder
- ligaments: glenohumeral, coracohumeral and transverse humeral ligaments
- movements: arm flexion, extension, adduction, abduction, and internal and external rotation
- blood supply: anterior and posterior humeral circumflex, and subscapular arteries
- innervation: suprascapular, subscapular, axillary and lateral pectoral nerves
Due to the relatively small contact area between the two joint surfaces, it is the most mobile joint in the body. The glenoid labrum adds depth to the glenoid fossa that otherwise would have been a shallow socket. The stability of the joint is increased by the coracoacromial arch, the fusion of tendons of scapular muscles with the joint capsule and the muscles attaching the humerus to the pectoral girdle.
The number of muscles involved in movement around the shoulder is vast and a large proportion of them act at the glenohumeral joint. See movements of the arm.
The four rotator cuff muscles act to stabilize the joint.
- produced by the deltoid assisted by the supraspinatus
- produced by the short scapular muscles (except supraspinatus) when the deltoid relaxes. Assisted by the pectoralis major and latissimus dorsi
- clavicular head of the pectoralis major and the anterior fibers of the deltoid, assisted by the coracobrachialis and biceps
- latissimus dorsi, posterior fibers of the deltoid and the long head of the triceps
- lateral rotation: infraspinatus and teres minor
- medial rotation: subscapularis and teres major
The joint capsule extends from the margin of the glenoid fossa (beyond the supraglenoid fossa) to the anatomical neck of the humerus, incorporating the insertion of the long head of biceps brachii tendon, but extending inferomedially to include the surgical neck. It is reinforced by the rotator cuff, except inferiorly, where it is at its weakest .
The synovial membrane is attached around the glenoid labrum and lines the capsule. It is attached to the articular margin of the head of the humerus and covers the bare area of the surgical neck that lies within the capsule at the upper end of the shaft. It invests the long head of the biceps in a tubular sleeve that is reflected back along the tendon to the transverse ligament and adjoining floor of the intertubercular groove. It herniates through the anterior aspect of the capsule to communicate with the subscapularis bursa. Sometimes it communicates with the infraspinatus bursa posteriorly.
There are many bursae associated with the shoulder but two, in particular, have clinical significance :
- subacromial bursa
- subscapular bursa: between subscapularis tendon and glenoid neck; communicates with the joint cavity via the foramen of Weitbrecht (between the superior and middle glenohumeral ligament)
- transverse humeral ligament
- continuation of the coracohumeral ligament
- small broad ligament that extends between the lesser and greater tuberosities superior to the epiphyseal line, enclosing the long head of biceps brachii tendon and its sheath in the bicipital groove
- forms a tunnel thus preventing it from subluxating out of the groove during shoulder movement
- some deep fibers of the subscapularis tendon attachment to the lesser tuberosity may contribute
- glenohumeral ligaments
- superior glenohumeral ligament
- middle glenohumeral ligament
- inferior glenohumeral ligament
- coracohumeral ligaments
- from the undersurface of the coracoid process, laterally across the capsule to which it becomes attached at the margin of the greater tuberosity and along the transverse ligament
- coracoacromial ligament
- strong flat triangular band
- from the medial border of the acromion, in front of the acromioclavicular articulation, it fans out to the lateral border of the coracoid process
- serves to increase the surface upon which the head of the humerus may be supported
Glenohumeral joint stabilizers are divided into:
- static or anatomical: articular surface, labrum, glenohumeral ligaments, glenohumeral joint capsule, coracoacromial arch, negative adhesive forces
- dynamic or functional: rotator cuff, long head of biceps tendon