As already mentioned, the cervical plexus has important connections to the spinal accessory nerve. A branch from the second cervical nerve typically joins the spinal accessory nerve before it enters the sternocleidomastoid muscle. Also, branches from the second, third, and fourth cervical nerves join the spinal accessory nerve (Fig. 5-22). Although the branches connecting the cervical plexus with the spinal accessory nerve are believed to be sensory, surgical evidence suggests that their preservation results in better shoulder function.
A thorough knowledge of the anatomy of the cervical plexus is necessary to preserve the connecting branches with the spinal accessory nerve. The cervical plexus is formed by the ventral rami of the second, third, and fourth cervical nerves, and also sometimes with a contribution from the first (Fig. 2-20). This neural network has two types of branches, superficial or cutaneous, and deep. The superficial branches arise from a series of loops between the second, third, and fourth cervical nerves. The most constant are the lesser occipital, the great auricular, the transverse cervical, and the supraclavicular nerves. Most of these sensory branches will be transected during the operation.
On the other hand, the deep branches are largely motor, except for the contribution to the sternocleidomastoid and trapezius muscles, where controversy still remains. The deep branches include the ansa hypoglossi, or ansa cervicalis (Fig. 5-23), the phrenic nerve (Fig. 5-21), and the branches to the trapezius muscle (Fig. 5-22). Except for the ansa cervicalis, whose traject is different, the deep branches of the cervical plexus should be preserved by keeping the dissection superficial to their course. The anterior cervical nerves should be sectioned distal to the point where the deep branches leave the main root (Fig. 4-42). The motor supply to the levator scapulae muscle can also be preserved by staying superficial to the deep layer of the cervical fascia at the level of the midportion of the levator scapulae. This is where the neurovascular supply enters the muscle.
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