Thyroarytenoid muscle maintains normal contractile force in chronic vocal fold immobility

Denervation of skeletal muscle typically results in irreversible denervation atrophy over time. This finding has generated controversy as to the efficacy of reinnervation procedures for chronic vocal fold immobility related to recurrent laryngeal nerve injury.

To test the hypothesis that chronic vocal fold immobility after recurrent laryngeal nerve injury does not result in diminished maximal isometric force generation in the thyroarytenoid muscle.

Adult random-bred cats underwent either unilateral laryngeal denervation (n = 6) or sham surgery (n = 6). After 6 months, videolaryngoscopy was performed followed by in vitro measurement of maximal isometric tetanic force produced by the thyroarytenoid muscle.

All animals in the denervation group showed right vocal fold paralysis after the initial denervation operation; none of these animals had return of appropriately phased movement with respiration. Four had intermittent disorganized twitching movements. One had these movements plus an occasional weak adduction, and one had no movement. Normal vocal fold mobility was observed in 6 of 6 animals undergoing sham surgery. The maximal isometric tetanic force measured from the thyroarytenoid muscle in the sham group was 438 mN (+/-92 mN standard deviation [SD]). The maximal isometric tetanic force measured from the thyroarytenoid muscle in the chronically immobile group was 405 mN (+/-107 mN SD). Differences were not statistically significant.

Maximal isometric force in the thyroarytenoid muscle is not diminished in chronic vocal fold immobility after recurrent laryngeal nerve injury. We conclude that the possibility for restoration of contractile force to the chronically immobile thyroarytenoid muscle exists. This finding supports the pursuit of reinnervation procedures in the treatment of chronic vocal fold immobility.