Accessory Nerve Injury Workup

Updated: Jan 24, 2022
  • Author: Rohan R Walvekar, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Imaging Studies

High-resolution ultrasonography (HRUS) allows visualization of the normal SAN, as well as changes after accessory nerve injury. The SAN appears as a singular small (approximately 1 cm in diameter on ultrasound), hypoechoic tubular structure in the transverse plane and as a hypoechoic linear structure in the longitudinal plane. It is best identified in the posterior cervical triangle. In addition, HRUS is able to demonstrate hyperechoic and atrophic changes in the trapezius muscle, granuloma formation, and scar entrapment of the SAN in the region of the injury and the normal course of the nerve beyond. However, the actual transection of the SAN is not readily visualized by HRUS. [9]

A retrospective study by Powell et al indicated that, preoperatively, SAN injuries can more accurately be characterized by ultrasonography than by magnetic resonance imaging (MRI). SAN injuries in the study, most of which were iatrogenic, were surgically confirmed as stump neuromas and incomplete nerve injuries. The investigators determined that 95% of the preoperative ultrasonography reports, versus 24% of those derived from MRI, agreed with the surgical diagnosis. [39]  However, ultrasonography is operator dependent, so when ultrasonographic results are in doubt, MRI should still be considered.


Other Tests

Electrodiagnostic tests

Electrodiagnostic tests are most sensitive for the detection of nerve conduction impairment. [2]

Nerve conduction studies reveal prolonged latencies in nerve injury, while electromyography (EMG) may reveal signs of denervation or reinnervation, depending on the timing of the study. [20]

Electrophysiologic integrity of the SAN does not correlate well with the clinical symptoms and outcome measures for shoulder dysfunction. [3]

However, EMG has shown a positive correlation with range-of-motion (ROM) tests, particularly active shoulder abduction with contralateral head rotation as a test of strength. Consequently, this physical examination maneuver serves as a reliable and cost-effective tool for evaluating the degree of upper trapezius denervation.

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.” [40]

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, 41]

Clinical evaluation of shoulder function

Clinical evalution of shoulder function includes the following:

  • ROM assessment by goniometry to evaluate flexion and abduction of the shoulder joint
  • Manual measure of muscle strength in the motions of elevation, flexion, and abduction [4]

The constant shoulder scale is as follows:

  • This weighted test takes 10 minutes to perform and combines patient symptom scores (35%) and objective measures of active shoulder function (65%) and is a validated clinical assessment with established accuracy across many diseases that affect the shoulder.

  • Scores range from 0-100, with higher scores indicating better shoulder function. [42]

The disease-specific quality-of-life (QOL) questionnaires are sensitive tools to evaluate shoulder function. Some more common questionnaires that have been validated for shoulder specific evaluations include the following:

  • The University of Washington QOL scale – shoulder domain

  • The neck dissection impairment index

  • The shoulder disability questionnaire (SDQ) [43]

Intraoperative diagnosis is intuitive. A provoked movement of the shoulder in response to cautery or dissection must be carefully reviewed. Clinically examining the patient’s motor function postoperatively is best; in addition, widely explore the area during surgery to rule out an inadvertent injury. [14]