Attempts to restore abduction of the paralyzed equine arytenoid cartilage. III. Nerve anastomosis.

The purpose of this project was to attempt restoration of abduction of a recently denervated left dorsal cricoarytenoid muscle in the horse by anastomosing the first cervical nerve to the abductor branch of the left recurrent laryngeal nerve. Ten horses were used in the study. In six horses the left recurrent laryngeal nerve was transected and ligated while the ventral branch of the left first cervical nerve was anastomosed to the abductor branch of the left recurrent laryngeal nerve. The remaining four horses also had the left recurrent laryngeal nerve transected and ligated but had no nerve anastomosis performed. Each horse was evaluated preoperatively, and at one week, three and six months after surgery, by endoscopy and determination of upper airway resistance. The endoscopy was performed with the horses breathing room air and while breathing 10% carbon dioxide. All ten horses showed endoscopic signs of complete laryngeal hemiplegia immediately postoperatively. Starting at three months postoperatively clonic movements of the left arytenoid cartilage were observed in four of the six reinnervated horses but not in the sham operated horses. At the sixth postoperative month five reinnervated horses had clonic movements of the left arytenoid cartilage. The comparison of upper airway resistance measurements before surgery and at one week, three and six months after surgery showed no significant differences in either control or experimental horses. Following euthanasia at six months postoperatively, the left and right dorsal crioarytenoid muscles were compared for evidence of reinnervation. No significant difference in weight was noted in the reinnervated horses but the left dorsal cricoarytenoid muscle weighed less than the control horses.