Injury to the accessory nerve results in dysfunction of the trapezius muscle on the affected side, which interferes with normal shoulder function.



(1) stab wound or physical blow to the posterior triangle

(2) excessive stretching of the shoulder, including blunt trauma to the upper extremity

(3) surgery to the posterior triangle (radical neck dissection, lymph node biopsy, removal soft tissue mass, etc.)

(4) extended use of an arm sling

(5) occasionally the palsy may occur spontaneously without a documented preceding event


Physical findings:

(1) paralysis of the trapezius muscle on affected side with muscle wasting.

(2) drooping of the shoulder girdle (shoulder drooping).

(3) downward rotation and protraction of the scapula, with winging of the scapula

(4) inability to shrug the affected shoulder.

(5) active abduction of the shoulder (rotation of arms upwards in the coronal plane starting with the arms at the sides) limited to <= 80 degrees

(6) pain on active abduction of the shoulder

(7) weakness on trying to abduct the shoulder against resistance


Resistive active external rotation test (of Chan and Hems):

(1) The arms are held at the side, with the elbows at 90 degrees.

(2) The patient attempts to externally rotate the shoulder while pushing against the resistance from the examiner's hands.

(3) The medial border of the scapula on the affected side will show increased winging.


Winging on resistive active external rotation is greater than that seen on forward flexion (with the patient pushes off from a wall with the arms extending forward in the sagittal plane at 90 degrees to torso).


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