Which nerve innervates the trapezius and what is a common injury sign?

Which nerve innervates the trapezius and what is a common injury sign?

• A. Dorsal scapular nerve; scapular tipping
• B. Axillary nerve; loss of abduction
• C. Spinal accessory nerve; shoulder droop and scapular winging
• D. Long thoracic nerve; winged scapula

Answer: (C)

The nerve that supplies the trapezius is the spinal accessory nerve (cranial nerve XI). The trapezius stabilizes and moves the scapula: its upper fibers elevate the shoulder, the middle fibers retract, and the lower fibers depress and upwardly rotate the scapula to allow arm elevation. When the spinal accessory nerve is injured, the trapezius can’t hold the scapula in place or help with upward rotation, so the shoulder sags (droop) and the scapula may wing as it loses posterior stabilization, especially during arm lifting. This sign set—shoulder droop with scapular winging—is characteristic of trapezius dysfunction due to spinal accessory nerve injury. The other nerves listed don’t innervate the trapezius, so their injury would produce different patterns (for example, deltoid weakness with loss of abduction, serratus anterior weakness with classic winging, or rhomboid weakness with reduced scapular retraction).

The nerve that supplies the trapezius is the spinal accessory nerve (cranial nerve XI). The trapezius stabilizes and moves the scapula: its upper fibers elevate the shoulder, the middle fibers retract, and the lower fibers depress and upwardly rotate the scapula to allow arm elevation. When the spinal accessory nerve is injured, the trapezius can’t hold the scapula in place or help with upward rotation, so the shoulder sags (droop) and the scapula may wing as it loses posterior stabilization, especially during arm lifting.

This sign set—shoulder droop with scapular winging—is characteristic of trapezius dysfunction due to spinal accessory nerve injury. The other nerves listed don’t innervate the trapezius, so their injury would produce different patterns (for example, deltoid weakness with loss of abduction, serratus anterior weakness with classic winging, or rhomboid weakness with reduced scapular retraction).