Intraoperative electromyography for identification of the trapezius muscle innervation: clinical proof of a new anatomical concept.

OBJECTIVE/HYPOTHESIS: There is still considerable controversy among surgeons on trapezius muscle innervation. In addition, the rate of unexpected postoperative trapezius pareses is unacceptably high. Recent anatomical findings might answer most of the questions. The objective of the present study was to clinically prove the recent anatomical findings, especially the concept of the innervation of the descending part of the trapezius muscle. STUDY
DESIGN: Intraoperative electromyography of the spinal accessory nerve and its branches in the posterior triangle of the neck.
SETTING: Intraoperative electromyography was performed during 17 modified radical neck dissections on 14 patients of both sexes ranging in age from 44 to 68 years (mean age, 56 y). Potentials were registered through pairs of needle electrodes placed in each of the three parts of the trapezius muscle. Intraoperatively, the spinal accessory nerve and its fine cranial branch passing toward the descending part of the muscle were identified and stimulated in the posterior triangle of the neck.RESULTS Stimulation of the fine cranial branch of the spinal accessory nerve led to a clearly visible and recordable contraction in the descending part of the trapezius muscle in all patients. Stimulation of the main trunk of the spinal accessory nerve in the posterior triangle of the neck distal to the above-mentioned branching led to a clearly visible and recordable contraction in the transverse and ascending parts of the muscle.
CONCLUSIONS: The results strongly support recent anatomical findings showing that, functionally, the most important descending part of the trapezius muscle is innervated by a fine single branch arising from the spinal accessory nerve in the posterior triangle of the neck. This may help to prevent more patients undergoing modified radical neck dissections from shoulder-arm syndrome.