In a shoulder injury, which injury requires checking the deltoid sensation to assess axillary nerve function?

• A. AC joint separation
• B. Rotator cuff tear
• C. Shoulder dislocation
• D. Humeral head fracture

Answer: (C)

The key idea is that the axillary nerve supplies the deltoid muscle and provides sensation over the lateral shoulder. It runs close to the surgical neck of the humerus, where it can be injured by shoulder dislocations. When a dislocation occurs, traction or compression can damage the axillary nerve, leading to weakness of deltoid (and thus reduced arm abduction beyond the initial 15 degrees) and sensory loss over the lateral (regimental badge) area of the shoulder. Therefore, in a shoulder injury, checking deltoid sensation is a focused way to assess axillary nerve function.

Other injuries listed are less likely to involve the axillary nerve in a way that requires this specific check: AC joint separation and rotator cuff tears typically affect stabilizing structures or tendons, not the axillary nerve, and while a humeral neck fracture can injure the axillary nerve, the prompt most strongly points to dislocation as the scenario that necessitates assessing deltoid sensation.