An anatomic study of the subscapular nerves: A guide for electromyographic analysis of the subscapularis muscle.

Fifty shoulders from 36 human cadavers were examined to identify the nerves innervating the subscapularis muscle and their point of entry into the muscle. Most of the specimens (82%) revealed three independent nerves to the subscapularis, 16% of the specimens demonstrated four nerves, and 2% of the shoulders demonstrated two nerves to the subscapularis. Variability was noted at the level of origin (division or cord) of each primary nerve branch to the muscle. The point of entry of each nerve into the subscapularis was measured from three clinical anatomic landmarks. The entry points were found to closely follow a line running parallel to the vertebral border of the scapula and inferior from the medial surface of the base of the coracoid. Previous electromyogram studies of the subscapularis have used one electrode to study its dynamic function. The anatomic data in this and other series suggest that multiple electrodes may be required for a complete electromyogram study of the subscapularis. The findings of this study facilitate the placement of two intramuscular fine wire electrodes for electromyogrophic analysis, which permits the investigation of the subscapularis muscle as two functional units.