After undergoing modified radical mastectomy for cancer of the right breast, a 52-year-old female teacher becomes aware that the medial end of her scapula becomes prominent in protraction movements at the shoulder. She also complains of some weakness in complete abduction of the same shoulder. What nerve was injured?

Axillary dissection during modified radical mastectomy requires exposing the long thoracic and thoracodorsal nerves. Injury to the long thoracic nerve that supplies the serratus anterior muscle causes "winging of the scapula". The intercostobrachial nerve supplies sensory innervation to the skin in the axilla and proximal upper extremity. The medial and ulnar nerves are outside of the usually axillary dissection field.