The main goal of this step of the operation is to locate the nerve at the entrance of the sternocleidomastoid muscle. The dissection of the entire course of the nerve between the sternocleidomastoid muscle and the internal jugular vein will be performed in a later step of the procedure.
The spinal accessory nerve enters the sternocleidomastoid muscle approximately at the junction of the upper and middle third of the muscle. The transverse process of the atlas serves as a useful anatomical landmark (Fig. 4-16).
Adequate exposure of the area requires posterior retraction of the sternocleidomastoid muscle. The small vessels that usually go along with the nerve are carefully cauterized and the nerve is examined for divisions that may appear before it enters the muscle. All nerve branches must be preserved to obtain the best shoulder function. Sometimes a branch from the second cervical nerve can be seen joining the spinal accessory nerve before its entrance into the sternocleidomastoid muscle. Although most anatomy books consider this and other branches from the cervical plexus to be mainly sensory, it is our experience that preservation of these branches helps to prevent shoulder dysfunction after the operation.
Once the nerve is identified, wet surgical sponges are introduced between the muscle and the fascia, avoiding excessive pressure and stretching maneuvers that may lead to spinal accessory nerve damage. The dissection now continues along the upper border of the surgical field.
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