All the muscles of the larynx except the cricothyroid are supplied by the recurrent laryngeal branch of the vagus (X). Injury to one nerve usually leaves the ipsilateral vocal cord paralyzed in moderate adduction. Bilateral injury may result in airway compromise leading to reintubation and possibly tracheostomy. The motor branch of the superior laryngeal nerve innervates the cricothyroid muscle, which rotates the cricoid cartilage relative to the thyroid cartilage, tensing the vocal cords. Loss of this function results in compromised timbre, endurance and high range of the voice. Staying away from the lateral wall of the larynx when isolating the superior pole vessels helps protect the nerve.
The recurrent laryngeal nerve on the right is rarely non-recurrent, descending directly to the cricopharyngeal angle from above. This occurs when the right subclavian artery arises anomalously as the fourth branch of the arch and runs behind esophagus or between esophagus and trachea to reach the arm. The absence of the vessel in its normal location leads to failure of the nerve on the right to loop in embryologic life. The aberrant position of the artery can cause difficulty swallowing (dysphagia lusoria).
At its termination, the recurrent nerve most often (80%) lies posterior to the inferior thyroid artery or between its branches, about half the time in the tracheoesophageal (TE) groove or slightly anterior (44%).