A functional evaluation of ansa cervicalis nerve transfer for unilateral vocal cord paralysis: Future directions for laryngeal reinnervation

Abstract

There are a variety of methods for treating unilateral vocal cord paralysis, but to date there are few objective studies that evaluate the functional results of nerve transfer from the ansa cervicalis. Six dogs underwent unilateral recurrent laryngeal nerve section with immediate reanastamosis to the sternothyroid branch of the ansa cervicalis. After 5 to 6 months, measurements of vocal efficiency and acoustic parameters, videolaryngoscopy, videostroboscopy, and evoked electromyography were performed. Identical measurements were made in eight control dogs during normal electrically induced phonation and a simulated unilateral recurrent laryngeal nerve paralysis. Histologic analysis of both vocalis muscles, recurrent laryngeal nerves, ansa cervicalis, and the ansa-recurrent laryngeal nerve anastamosis site was performed. Evidence of reinnervation was found in all of the animals that underwent nerve transfer. The vocal efficiency and acoustic quality after ansa cervicalis nerve transfer were dependent on the degree of electrical stimulation from the transferred nerve to the reinnervated cord during phonation. In the absence of electrical stimulation to the nerve transfer, physiologic vocal cord motion could not be elicited from the reinnervated cord.

Nerve-Muscle-Endplate Band Grafting

“…Partial reinnervation and poor functional recovery after microsuture repair of the injured peripheral nerves are most likely related to mechanical trauma, tension or infection of the anastomosis, devascularization of the nerves after dissection, neuroma formation, scaring, misdirected axonal growth at the repair site, and the loss of nerve fiber population that prevents axons reaching their target organs. 78 Usually, a small number of regenerating axons could pass through the repair site. Thus, few axons make functional connections which are not enough for activating a paralyzed muscle.…”

Muscle reinnervation with nerve-muscle-endplate band grafting technique: correlation between force recovery and axonal regeneration

“…However, only about 50% of patients regain useful function [8,9]. Factors behind poor functional recovery include tension of the anastomosis, neuroma formation, scaring, and loss of the nerve fiber population [10]. Studies have shown that in EEA fewer nerve fibers could pass through the coaptation site and reach the target organ [11].…”

Ansa to recurrent laryngeal neurorrhaphy in the setting of laryngeal nerve sacrifice: a cadaveric study to evaluate a reconstructive option

“…The AC-to-RLN anastomosis has been described as an excellent reconstructive option. Though this option does not result in volitional movement, abduction or adduction of the reinnervated fold, it does result in excellent medialization of the paralyzed fold, corrects arytenoid malposition, and prevents progressive loss of thyroarytenoid muscle bulk [2]. A unique advantage of the approach is that it restores vocal tone without affecting mucosal wave properties.…”

“…Regardless of the etiology, vocal fold paralysis from RLN injury leads to incomplete glottic closure, resulting in dysphonia, vocal fatigue, aspiration, and a significant decrease in quality of life. Management of unilateral vocal fold paralysis can be accomplished in a variety of ways -including thyroplasty, vocal fold injections, arytenoid adductions, or laryngeal reinnervation [2]. Laryngeal reinnervation refers to any method that seeks to reconstitute neural pathways to the vocal fold.…”