What is the role of electrodiagnostic test in the management of a spinal accessory nerve (SAN) injury?

Updated: Mar 04, 2020
  • Author: Rohan R Walvekar, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Electrodiagnostic tests can be used in the management of SAN injury as follows:

  • To monitor upper trapezius recovery of function

  • To plan a physical therapy course to reduce postoperative morbidity [2]

  • To confirm suspicions of SAN trauma that are related to traction or stretch injury of the nerve

  • To monitor the SAN nerve intraoperatively for identification and preservation [3]

A retrospective study by Kim et al indicated that in a nerve conduction study of the SAN, the best recording site for the upper trapezius “is the midpoint between the C7 spinous process and the acromion,” while the optimal recording site for the middle trapezius is “the junction of middle and lateral thirds of the line between the root of scapular spine and the vertebral spine.” [38]

Some patients with severe SAN injury do not experience the degree of dysfunction that one would expect from their evaluations by EMG. In contrast, patients treated with nerve-sparing neck procedures often present with symptoms and signs suggestive of nerve impairment. These apparently contradictory results can be explained by the influence of several factors, including age, gender, dominant hand, presence of concurrent myopathy or neuropathy, condition of other synergistic shoulder girdle muscles, preoperative or postoperative radiotherapy, and anatomic variations of SAN contributions to trapezius muscle innervation. [15, 39]

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