Accessory Nerve Block
The accessory nerve (i.e., cranial nerve XI) is occasionally blocked
to supplement the interscalene brachial plexus approach for shoulder procedures.
Blockade of the accessory nerve results in motor paralysis of the trapezius muscle,
ensuring lack of patient movement during the surgical procedure. The nerve traverses
the posterior triangle of the neck (bordered by the posterior border of the sternocleidomastoid
muscle, middle third of the clavicle, and anterior border of the trapezius muscle)
in a very superficial
position after emerging from the substance of the sternocleidomastoid muscle at the
junction of the superior and middle thirds of that muscle's posterior border. It
can easily be blocked at that site by an injection of 6 to 10 mL of local anesthetic.
This nerve is often unintentionally anesthetized when a superficial cervical plexus
block is performed.
