Neuroanatomy USMLE Step 1 Practice Question

A 22-year-old male football player sustains an anterior shoulder dislocation during a tackle. On examination, blood pressure is 128/82 mmHg, heart rate 96/min, and temperature 37.2°C. He reports severe shoulder pain and demonstrates impaired cutaneous sensation over the lower half of the deltoid muscle. X-ray confirms anterior humeral head displacement. Strength testing of shoulder abduction remains intact. These findings suggest injury to which of the following nerves?