Laryngeal Adductor Function in Experimental Models of Recurrent Laryngeal Nerve Injury

Objectives/Hypothesis: Most patients with unilateral vocal fold paralysis experience some degree of spontaneous reinnervation, which depends upon the type and severity of recurrent laryngeal nerve (RLN) injury. After partial recovery, the paretic vocal fold may or may not adduct adequately to allow glottic closure, which in turn affects phonatory and swallowing outcomes. This process was studied in a series of canine laryngeal nerve injury models. Study Design: Animal (canine) experiments. Methods: Maximum stimulable laryngeal adductor pressure (LAP) was measured pretreatment (baseline) and at 6 months following experimental RLN injuries (total n=59). The nine study groups were designed to simulate a range of severities of RLN injury. Results: The greatest LAP recovery, at 108% of original baseline, was seen in a 50% transection model; the least recovery was seen when the RLN underwent complete transection with repair, at 56% with precise alignment and 50% with alignment reversed. Intermediate models (partial RLN injuries) gave intermediate results. Crush models recovered 105% of LAP, whereas a half-transection, half-crush injury recovered 72%, and cautery injuries recovered 61%. Controls (complete transection without repair) had no measurable recovery. Conclusions: The injured RLN has a strong tendency to recover. Restoration of adductor strength, as determined by the LAP, was predictably related to the severity of RLN injury. The model RLN injuries studied provide a range of expected outcomes that can be used for future experiments exploring interventions that may improve postinjury adductor function.