Optimal Trapezius Electrophysiological Recording Site.

BACKGROUND: Various active recording electrode positions for the trapezius motor nerve conduction study have been suggested.

OBJECTIVE: To determine the optimal recording site of the trapezius muscles in a spinal accessory nerve conduction study.

DESIGN: Retrospective descriptive study.

SETTING: Department of physical medicine and rehabilitation in a tertiary clinic center.

PARTICIPANTS: Thirty-four patients between 33 and 82 years of age with preoperative head and neck cancer (68 upper and middle trapezius muscles).

INTERVENTIONS: Analysis of compound muscle action potentials (CMAPs) of upper and middle trapezius.

MAIN OUTCOME MEASUREMENTS: CMAP latency and amplitudes were obtained at five and four recording points with constant intervals on the horizontal line of the upper and middle trapezius, respectively.

RESULTS: The maximum CMAP amplitude of the upper trapezius was (mean ± SD) 8.5 ± 1.4 mV with the recording at the midpoint between the C7 spinous process and the lateral margin of the acromion. The maximum CMAP amplitude of the middle trapezius was 4.2 ± 1.4 mV, recorded on the horizontal line at the junction of the middle and lateral thirds between the root of the scapular spine and the vertebral spinous process.

CONCLUSION: The optimal recording site in motor nerve conduction study of the trapezius is the midpoint between the C7 spinous process and the acromion for the upper trapezius, and the junction of middle and lateral thirds of the line between the root of scapular spine and the vertebral spine for the middle trapezius.