Unilateral vocal fold paralysis (UVFP) is characterized by various degrees of pathological motion impairment caused by a nervous system disorder and is an important clinical entity in otolaryngology. The extent of regeneration of nerve fibers after damage varies among patients. Significant misdirected regeneration occurs in some cases, while only slight synkinesis occurs in others. This variation is a major cause of the considerable inconsistencies in the vibratory patterns of the vocal folds among patients with UVFP. In patients with UVFP, negative effects on vocal fold vibration are caused by an off-midline position of the affected vocal fold, decreased stiffness and tension, reduced thickness of the vocal fold, atrophic changes of the thyroarytenoid (TA) muscle, and synkinetic movement of the vocal fold on the affected side. Conventional phonosurgery aims to correct glottal insufficiency by locating the affected vocal fold at the midline and to augment its mass. However, some patients do not recover their “normal” voice after surgery [1, 2]. Chapter 1 stressed that a normal voice can be attained by moving the immobile vocal fold to a median location and ensuring symmetrical bulk and tension of the unaffected vocal fold. Because conventional phonosurgical procedures aim to offer “static” adjustment of these features, the TA muscle does not function as the “body” of the immobile vocal fold and provides little contribution to voice production and tuning. Therefore, in addition to median location of the affected vocal fold, reacquisition of TA muscle tonus by reinnervation is important to recover the patients’ own preinjury voice with a dynamic mucosal wave.

Modern imaging techniques such as computed tomography, magnetic resonance imaging, and ultrasonography have advanced during the last four decades and now facilitate the establishment of the various causes of vocal fold paralysis. This has improved the surgical treatment of patients with previously inoperable life-threatening diseases. However, UVFP sometimes persists or even appears as a complication following surgery, resulting in breathy dysphonia and/or swallowing difficulties that affect patients’ postoperative quality of life [3–6] despite the primary disease having been addressed. Thus, phonosurgical treatment for paralytic dysphonia is important to improve patients’ quality of life after treatment of the primary disease. However, as shown in Chap. 2, conventional phonosurgery does not always help to recover the patient’s own preinjury voice, although the voice quality usually improves to some extent after surgery. Static correction of the glottal configuration with respect to glottal closure and augmentation of the vocal fold is often insufficient to restore the vocal fold thickness, stiffness, and mass that are normally produced by TA muscle contraction.

Immediate reconstruction of the recurrent laryngeal nerve (RLN) at the time of tumor extirpation is reportedly effective in restoring vocal function after surgery [7–10]. However, when a patient seeks treatment for breathy dysphonia after the occurrence of UVFP, conventional static procedures are usually chosen. Although such procedures result in improvement of vocal function after surgery, they do not restore the normal preparalysis voice. In such persistent cases, especially those after neck surgeries, locating the peripheral stump of the RLN is not feasible; thus, nerve transfer and nerve interposition techniques cannot be applied to TA muscle reinnervation. Nerve–muscle pedicle (NMP) flap implantation may be a promising technique to facilitate reinnervation of a denervated muscle, even when the peripheral stump of the RLN is not located. However, since Tucker et al. [11–15] and May and Beery [16] reported improvement in patients’ voices after the NMP procedure, no authors have reported favorable vocal function after this procedure. This paucity of data may be ascribed to the lack of consistent effects of the NMP method that has been reported in animal experiments. The author and his colleagues performed basic experiments using a UVFP animal model and revealed that NMP flap implantation to the denervated rat TA muscle facilitated recovery of the bulk of the muscle size and individual muscle fibers, neuromuscular junctions, and function as reflected on evoked electromyographic test results. Based on our results, the NMP technique has been refined and successfully applied clinically with excellent results [17, 18].

The author has performed refined NMP flap implantation combined with arytenoid adduction on more than 80 patients. Because of their favorable vocal outcomes, the number of patients who seek treatment for paralytic dysphonia at the author’s institution is increasing. However, several issues remain to be resolved.