Postoperative examination revealed that the medial border and inferior angle of the left scapula became unusually prominent (projected posteriorly) when the arm was carried forward in the sagittal plane, especially if the patient pushed with outstretched arm against heavy resistance (e.g., a wall). What muscle must have been denervated during the axillary dissection?

Serratus Anterior, innervated by the long thoracic nerve, draws the scapula forward. If it is denervated, there is no muscle to oppose the motion of the trapezius which is elevating and retracting the scapula. The medial border of the scapula falls away from the posterior chest wall and begins to look like an angel's wing. This is termed a "winged scapula." A winged scapula commonly occurs after an injury to the long thoracic nerve, which runs on the superficial surface of serratus anterior and is paicularly vulnerable to trauma. The long thoracic nerve contains contributions from C5, 6, and 7, so remember the saying "C5, 6, and 7 keep the wings from heaven."