Innervation Motor deltoid teres minor Sensory superficial lateral cutaneous nerve of arm lateral shoulder sensation Origin Originates from the brachial plexus middle trunk, posterior division, posterior cord Carries fibers from C5 and C6 Course Comes off posterior cord behind the axillary artery, anterior to the subscapularis muscle Travels through the quadrangular space runs here with the posterior circumflex humeral artery and vein Gives off an anterior, posterior, and articular terminal branch Terminal branches anterior branch wraps around the surgical neck of the humerus on the undersurface of the deltoid supplies the anterior deltoid muscle traditional "safe zone" from lateral acromion is 5 cm axillary nerve has been shown to run 3-5 cm from the acromion in 20% of patients damage to nerve with a muscle split here will denervate the anterior deltoid terminates in small cutaneous branches for the anterior/anterolateral skin posterior branch supplies the teres minor and posterior deltoid muscles pierces the deep fascia and terminates as the superior lateral cutaneous nerve of the arm articular branch enters the shoulder joint inferior to the subscapularis