Thyroarytenoid muscle maintains normal contractile force in chronic vocal fold immobility

Background. Denervation of skeletal muscle typically results in irreversibl e denervation atrophy over time. This finding has generated controversy as to the efficacy of reinnervation procedures for chronic vocal fold immobili ty related to recurrent laryngeal nerve injury. Objective: To test the hypo thesis that chronic vocal fold immobility after recurrent laryngeal nerve i njury does not result in diminished maximal isometric force generation in t he thyroarytenoid muscle. Study Design: Adult random-bred cats underwent ei ther unilateral laryngeal denervation (n = 6) or sham surgery (n = 6). Afte r 6 months, videolaryngoscopy was performed followed by in vitro measuremen t of maximal isometric tetanic force produced by the thyroarytenoid muscle. Results: All animals in the denervation group showed right vocal fold para lysis after the initial denervation operation; none of these animals had re turn of appropriately phased movement with respiration. Four had intermitte nt disorganized twitching movements. One had these movements plus an occasi onal weak adduction, and one had no movement. Normal vocal fold mobility wa s observed in 6 of 6 animals undergoing sham surgery. The maximal isometric tetanic force measured from the thyroarytenoid muscle in the sham group wa s 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 signif icant. Conclusion: Maximal isometric force in the thyroarytenoid muscle is not diminished in chronic vocal fold immobility after recurrent laryngeal n erve injury. We conclude that the possibility for restoration of contractil e force to the chronically immobile thyroarytenoid muscle exists. This find ing supports the pursuit of reinnervation procedures in the treatment of ch ronic vocal fold immobility.