Can damage to the 11th cranial nerve cause sustained muscle contraction of the trapezius? if so, how can it be treated and what is most effective?

Nerve injury: Damage to the spinal accessory nerve (cranial nerve 11) will cause atrophy and fasciculations and not sustained muscle contraction of the sternocleidomastoid and the trapezius muscles. The treatment consists of an interposition nerve graft that takes 3-12 months to regenerate. If this is not successful, then muscle and tendon transfers are used to stabilize and reduce pain in the scapula.

Rare: Isolated CN injury is rare. Weakness of head turn to resistance or shoulder shrug weakness is seen. Spasm is usually not due to accessory nerve lesion.