MCQ – 88184

Correct Answer � C Explanation

Answer C) Adduction of arm

Spinal part of accessory is placed superficially in the middle of the posterior triangle, so it can be injured accidentally. Injury to sternocleidomastoid muscle does not lead to loss of adduction of the arm.

Spinal accessory nerve supplies trapezius and sternocleidomastoid muscles. 

• Trapezius helps in elevation of scapula, overhead abduction and retraction of scapula.

• Sternocleidomastoid muscle helps in turning the chin to the opposite side, tilt the head towards the shoulder of the same side and when both acting together they draw the head forwards.

The sternocleidomastoid is innervated by the spinal accessory nerve just before entering the posterior triangle. Hence injury of the nerve before posterior triangle, sternocleidomastoid is affected while injury of the nerve in the posterior triangle sternocleidomastoid muscle is spared.