What causes abnormal needle EMG in Latissimus dorsi muscles (on the sides- no electrical activity), upper arms/body weakness and scapular winging?

Injury 2 the long-- --thoracic nerve of Bell. It inervates(sp) the serratus anterior which stabilizes the scapula.This wwould cause scapular winging, & poor function of the arm, ,as the function depends on a stable scapula. .