The dynamic interaction of bones, joints, muscles, and ligaments establishes the foundation for the unique functions of the human shoulder. The bones which provide the framework for the shoulder girdle are the humerus, scapula, and clavicle. The shoulder girdle consists of three joints and one articulation: sternoclavicular joint, acromioclavicular joint, glenohumeral joint (shoulder joint), and scapulothoracic articulation. The muscles and ligaments of the shoulder allow and restrict movement along with providing active and passive stabilization of the shoulder. Biomechanically, the shoulder has three degrees of freedom and the muscles act at the shoulder to permit particularly free motion: flexion, extension, abduction, adduction, circumduction, internal rotation, and external rotation. Static stability of shoulder is provided by the labrum, capsule, and glenohumeral ligament while dynamic stability is provided by the rotator cuff, long head of the biceps tendon, and periscapular muscles [7
The brachial plexus supplies all the motor and most of sensory functions of the shoulder, except the cephalad cutaneous areas of the shoulder, which are innervated by the supraclavicular nerves, originating from the superficial cervical plexus (C3-C4) [1
]. Effective control of postoperative shoulder pain generally requires local anesthetic blockade of the nerve supply to the synovium, capsule, articular surfaces, periosteum, ligaments, and muscles of the shoulder [1
]. The terminal branches of the brachial plexus that supply the majority of the shoulder innervation are the suprascapular and axillary nerves (Figures and ).
Figure 1 Anterior innervation of the shoulder joint. The suprascapular nerve and axillary nerve are the primary nerves supplying the capsule and the glenohumeral joint (Borgeat and Ekatodramis ). (Reprinted with permission from Elsevier.)
Figure 2 Posterior innervation of the shoulder joint. The suprascapular nerve and axillary nerve are the primary nerves supplying this region (Borgeat and Ekatodramis ). (Reprinted with permission from Elsevier.)
The suprascapular nerve supplies sensory innervation to the subacromial bursa, acromioclavicular joint, coracoclavicular ligament, and 70% of the shoulder joint capsule [8
]. This nerve arises from the superior trunk of the brachial plexus, C5-C6 and possibly C4. The suprascapular nerve descends posteriorly, passing through the scapular notch, innervating the supraspinatus and infraspinatus muscles. It provides sensation for the posterior shoulder capsule, acromioclavicular joint, subacromial bursa, and coracoclavicular ligament.
The axillary nerve originates from C5-C6 nerve roots, with occasional contribution from C4. It is derived from the posterior cord of the brachial plexus. The axillary nerve crosses the anteroinferior aspect of the subscapularis muscle where it crosses posteriorly through the quadrilateral space and divides into two trunks. The anterior trunk supplies the motor innervation to the anterior and middle deltoid muscle. The posterior trunk gives off a branch to the teres minor muscle and the posterior deltoid muscle before terminating as the superior lateral brachial cutaneous nerve, which supplies the cutaneous innervation to the skin overlying the deltoid muscle.