If the axillary nerve is damaged, which muscle would be most directly affected?

• A. Latissimus dorsi
• B. Deltoid
• C. Pectoralis major
• D. Teres major

Answer: (B)

Damage to the axillary nerve most directly affects muscles it innervates: the deltoid and teres minor. Among the options, the deltoid is the muscle supplied by the axillary nerve, so it would be the most directly impacted. When the nerve is injured, the deltoid loses function, leading to weakness in shoulder abduction beyond the initial 15 degrees (since that first phase is mainly from the supraspinatus). The other muscles listed—latissimus dorsi, pectoralis major, and teres major—receive their nerves from different branches (thoracodorsal for latissimus dorsi, pectoral nerves for pectoralis major, lower subscapular nerve for teres major), so they are not as directly affected by axillary nerve damage.