Experimental studies for correction of superior laryngeal paralysis by fusion of the thyroid to cricoid cartilages.

Contraction of the cricothyroideus muscles (CTMs), innervated by the superior laryngeal nerves (SLNs), modulates the voice by tilting the thyroid cartilage anteriorly onto the top of the cricoid and tensing the vocal cords. Either unilateral or bilateral paralysis of the SLNs is disabling for individuals with above-average voice demands. Some patients never compensate for this paralysis; there is no surgical procedure recognized to correct it. This study tested the hypothesis that surgical fusion of the thyroid and cricoid cartilages anteriorly can correct the problems of SLN injury by duplicating the mechanical tilt of the thyroid onto the cricoid cartilage normally produced by the CTMs. The SLNs were cut in 12 dogs. In six the cricoid and thyroid cartilages were fused anteriorly. Vocal cord and airway function was assessed preoperatively, immediately postoperatively, and 6 to 10 weeks after surgery. Following surgery there was no airway compromise and there appeared to be a more satisfactory compensation for the SLN paralysis in the fused larynges as compared with the unfused controls as determined by cinelaryngoscopic analysis.