Which nerve innervates the deltoid and teres minor and enables shoulder abduction and external rotation, with sensory coverage over the lateral shoulder?

Which nerve innervates the deltoid and teres minor and enables shoulder abduction and external rotation, with sensory coverage over the lateral shoulder?

• A. Axillary nerve
• B. Musculocutaneous nerve
• C. Radial nerve
• D. Median nerve

Answer: (A)

The axillary nerve is responsible here. It comes from the posterior cord and carries fibers from C5–C6. It innervates both the deltoid and the teres minor, so it enables shoulder abduction (primarily beyond the initial 15 degrees provided by the supraspinatus) and external rotation (a key action of teres minor). It also provides sensation to the lateral aspect of the shoulder through the superior lateral cutaneous nerve of the arm, often described as the regimental badge area. The other nerves listed don’t supply both deltoid and teres minor or the lateral shoulder skin: the musculocutaneous nerve mainly handles forearm flexors and lateral forearm sensation; the radial nerve covers posterior arm/forearm and dorsum of the hand; the median nerve supplies most forearm flexors and palmar sensation.

The axillary nerve is responsible here. It comes from the posterior cord and carries fibers from C5–C6. It innervates both the deltoid and the teres minor, so it enables shoulder abduction (primarily beyond the initial 15 degrees provided by the supraspinatus) and external rotation (a key action of teres minor). It also provides sensation to the lateral aspect of the shoulder through the superior lateral cutaneous nerve of the arm, often described as the regimental badge area. The other nerves listed don’t supply both deltoid and teres minor or the lateral shoulder skin: the musculocutaneous nerve mainly handles forearm flexors and lateral forearm sensation; the radial nerve covers posterior arm/forearm and dorsum of the hand; the median nerve supplies most forearm flexors and palmar sensation.