Innervation of the trapezius muscle by the intra‐operative measurement of motor action potentials

Abstract

Although the surgical anatomy of the spinal accessory nerve and the cervical plexus has been extensively described, the exact motor innervation of the trapezius has been controversial. Attempts to resolve this question have involved anatomic or electrophysiologic studies in human embryos and animals. Extrapolation of the results to adult humans may not be correct. Accurate identification of muscle innervation is obtainable by intra-operative measurement of motor action potentials produced by direct stimulation of the accessory nerve and the cervical plexus. The study involved 14 patients undergoing supraomohyoid or modified neck dissections. Under direct vision, stimulating electrodes were placed on the identified nerves and motor action potentials, and latencies were recorded by surface electrodes placed over the three portions of the trapezius. In 13 patients, when the accessory nerve was stimulated, motor action potentials were obtained in 13 of 13 in the first portion, 11 of 13 in the second portion, and 10 of 13 in the third portion of the trapezius. In the last patient, the accessory nerve ended in the sternocleidomastoid muscle, and innervation of the trapezius was via C3 as demonstrated by motor action potentials. Responses when the roots of the cervical plexus were stimulated varied. Three patterns were seen: In the first group (seven patients), motor action potentials were distinct from those recorded when the accessory nerve was stimulated. Additionally, latencies were different from those of the accessory nerve. The second group (four patients) had motor action potentials that were similar to those obtained from stimulation of the accessory nerve, although their corresponding latencies were different.(ABSTRACT TRUNCATED AT 250 WORDS)

Trapezius muscle innervation from the spinal accessory nerve and branches of the cervical plexus

“…Some authors 4,20 used histochemical staining to determine which contributions contain motor axons. SOO et al 15 and NORI et al 11 elicited potentials when stimulating the cervical contributions, supporting the histochemical evidence that the trapezius muscle receives contributions from cervical branches in addition to accessory nerve innervation. Williams et al 18 considered the contribution from the cervical plexus to be primarily proprioceptive, not motor.…”

“…Electroneurography can provide insights into how the accessory nerve and the trapezius branches of the cervical plexus specifically contribute to the motor innervation of the three parts of the trapezius muscle. SOO et al 15 and NORI et al 11 used electroneurography to identify the motor innervation of the trapezius muscle without considering the communication between the cervical contributions and the accessory nerve, through which electricity could excite the accessory nerve resulting in a false positive result. To avoid this, the C2-C4 contributions were stimulated before and after the accessory nerve was severed, and the difference in extent of innervation analyzed under the different surgical conditions.…”

Quantitative Anatomy of the Trapezius Muscle in the Human Fetus

“…Like the sternocleidomastoid muscle, the trapezius has double motor innervation by way of the spinal accessory nerve and cervical plexus [2]. Soo et al [17] and Nori et al [18] meticulously identified motor innervation of the trapezius. Their data indicated that the trapezius was innervated by the ventral C2, C3 and C4 spinal nerves; however, this was a variable in each muscle part.…”

Anatomical Study of Accessory Nerve Innervation Relating to Functional Neck Dissection

“…In general, the upper fibers of the trapezius muscle together with the levator scapulae muscle are involved in scapular elevation; the middle fibers are involved in scapular adduction; while the bottom fibers are involved in scapular adduction and lowering. When severing the main trunk of the accessory nerve, while scapular elevation is less likely to be affected, adduction will be slightly affected and lowering will be affected (33,34) . Remmler et al (35) reported that adduction was poor, agreeing with our findings.…”