Experimental reinnervation of a strap muscle with a few roots of the phrenic nerve in rabbits

Dual laryngeal reinnervation in bilateral vocal fold paralysis: anatomical pitfalls

BACKGROUND

Bilateral laryngeal reinnervation can be a promising procedure for reanimation of laryngeal muscles, but currently not yet standardized. Besides patient conditions some intraoperative anatomical pitfalls need to be solved.

METHODS

Twelve human head and neck specimens (24 sides) have been studied using microdissection and histological serial sections of the nerves. The surgical anatomy of the dual reinnervation procedure according to JP Marie was investigated notably the branching pattern of the phrenic nerve (PN), the Ansa cervicalis (AC) and the recurrent laryngeal nerve (RLN).

RESULTS

Despite variations of the AC, a prominent inferior common trunk for sterno-hyoid and sterno-thyroid muscles can be used in more than 90% of the specimens. If the AC is missing because of previous surgery, the tiny nerve of the thyro-hyoid muscle can be used preferred. The PN display a double roots pattern from C3 to C4 cervical plexus in 50% of the specimens. A single root pattern can be found and an end-to-lateral neurorraphy can be used. Intra-laryngeal nerves pattern of the RLN display tiny collaterals which cannot be selected for abduction-adduction activity. Direct implantation of the Y-shape great auricular nerve within the posterior crico-arytenoid muscles can be a reliable method leading to challenging mechanical and functional conditions.

CONCLUSION

Several anatomical pitfalls, including intra-operative choices and variants of the donor nerves, but also the challenging intra-laryngeal dissection of the inferior laryngeal nerve need to be solved. A successful laryngeal reinnervation still needs further studies for a simplified procedure.

A Review of Treatment of Bilateral Vocal Fold Movement Impairment

Purpose of Review

Bilateral vocal fold immobility is a challenging life-threatening problem involving multiple treatment options and nuanced clinical decision making. We aim to provide relevant background on the etiology, diagnosis, and management of bilateral vocal fold movement impairment (BVFMI).

Recent Findings

Over the last 20 years, the management of bilateral vocal fold immobility has advanced significantly with the addition of multiple endoscopic approaches as well as procedures with the goal of returning dynamic function to the larynx, among them: selective reinnervation. Chemodenervation has also demonstrated promising results as a temporizing procedure in appropriately selected patients with BVFMI.

Summary

Tracheostomy remains the mainstay of emergent treatment for airway obstruction secondary to bilateral vocal fold immobility. However, recent advances in endoscopic approaches allow for avoidance of tracheostomy in many patients. Developments in dynamic procedures with the aim of restoring laryngeal function allow for adequate airway management while maintaining voice quality and limiting aspiration risk.

Olfactory Ecto-Mesenchymal Stem Cells in Laryngeal Nerve Regeneration in Rats

Selective intralaryngeal reinnervation has been shown to be effective in experimental models. This consists of independently reinnerving the adductor and abductor of laryngeal muscles of the larynx, in order to prevent any misalignment of the axonal regrowth, improve the functional recovery and tend toward reduction of synkinesis. The surgical technique remains complex. Current research focuses on simplifying and improving this technique. Olfactory ectomesenchymal stem cells (OEMSC) represent an interesting candidate for cell therapy and could be obtained from olfactory mucosa. Recent reports suggest a neuroregenerative potential in various animal models of central and peripheral nervous systems injuries. The aim of this study was dual: to develop a simple surgical model of selective reinnervation applicable in humans and to evaluate the relevance of OEMSC-based cell therapy for improving axonal guidance. Eight Fisher syngeneic rats were used to carry out the OEMSCs culture. Thirty-four Fisher syngeneic rats were operated on, divided into three groups depending on the transplanting. For all the rats, we have performed a side to end anastomosis of the vagal nerve with the inferior laryngeal nerve by interposition of a nerve graft from the left femoral nerve. Then, the first group didn't have any injection, the second group has an injection of thrombin and the third group has an injection of one million EOMSCs. Three months after surgery, laryngeal muscle activity was evaluated by videolaryngoscopy and electromyography recordings. In order to illustrate the quality of axonal regrowth, a fluorescent tracer was injected into the right posterior crico-arytenoid muscle (PCA) to reveal the cellular bodies of the motoneurons responsible for reinnervation of the PCA in the central nervous system. In our study, no improvement was found during the videolaryngological functional evaluation or with regard to the electrical activity of the PCA muscle. The cells colabelled in retrograde tracing were numerous in all groups, reflecting abnormal axonal regeneration. The interposition of a nerve graft, as side to end anastomosis between the vagus nerve and the inferior laryngeal nerve, filled with OEMSCs, does not provide better reinnervation of a hemilarynx.

Dual innervation may occur in a partially denervated muscle

INTRODUCTION

With a view to simplifying surgical techniques for selective laryngeal reinnervation, we addressed the question of whether it is feasible to receive additional innervation by a partially denervated muscle using an infrahyoid muscle model.

METHODS

In 90 rats (6 groups of 15), phrenic nerve transfer was used to reinnervate the sternothyroid muscle. In some cases, residual innervation by the original nerve was present. Three months later we performed electromyographic studies, contraction strength measurements, histologic assessment, and retrograde labeling.

RESULTS

Muscles reinnervated by the phrenic nerve had a greater "dual-response" rate (in terms of nerve latency, contraction strength, and retrograde labeling) than muscles in the control groups.

DISCUSSION

The phrenic nerve can impart its inspiratory properties to an initially denervated strap muscle-even when residual innervation is present. The preservation of contractile potential confirmed the feasibility of dual innervation in a previously injured muscle. Muscle Nerve 59:108-115, 2019.

Role of reinnervation in the management of recurrent laryngeal nerve injury: current state and advances

PURPOSE OF REVIEW

To present the current state of knowledge concerning different laryngeal reinnervation procedures for unilateral and bilateral vocal palsy.

RECENT FINDINGS

Recent reports show positive outcomes on both unilateral and bilateral reinnervations. The phrenic nerve is the most commonly used donor for bilateral vocal palsy, but use of the superior laryngeal nerve has also been suggested.

SUMMARY

Reinnervation of the larynx is a complex undertaking that can be performed by ENT surgeons with skills in microsurgery. Advances in this this field represent a paradigm shift in laryngeal rehabilitation and a prerequisite for laryngeal transplantation. Advances in basic understanding of nerve regeneration and in particular the need to surgically manage competitive reinnervation make the results of laryngeal reinnervation more predictable.

Reinnervation of denervated muscle by implantation of nerve-muscle-endplate band graft to the native motor zone of the target muscle

INTRODUCTION

Motor endplate reinnervation is critical for restoring motor function of the denervated muscle. We developed a novel surgical technique called nerve-muscle-endplate band grafting (NMEG) for muscle reinnervation.

METHODS

Experimentally denervated sternomastoid muscle in the rat was reinnervated by transferring a NMEG from the ipsilateral sternohyoid muscle to the native motor zone (NMZ) of the target muscle. A NMEG pedicle contained a block of muscle (~ 6 × 6 × 3 mm), a nerve branch with axon terminals, and a motor endplate band with numerous neuromuscular junctions. At 3 months after surgery, maximal tetanic muscle force measurement, muscle mass and myofiber morphology, motoneurons, regenerated axons, and axon-endplate connections of the muscles were analyzed.

RESULTS

The mean force of the reinnervated muscles was 82% of the contralateral controls. The average weight of the treated muscles was 89% of the controls. The reinnervated muscles exhibited extensive axonal regeneration. Specifically, the mean count of the regenerated axons in the reinnervated muscles reached up to 76.8% of the controls. The majority (80%) of the denervated endplates in the target muscle regained motor innervation.

CONCLUSIONS

The NMZ of the denervated muscle is an ideal site for NMEG implantation and for the development of new microsurgical and therapeutic strategies to achieve sufficient axonal regeneration, rapid endplate reinnervation, and optimal functional recovery. NMEG-NMZ technique may become a useful tool in the treatment of muscle paralysis caused by peripheral nerve injuries in certain clinical situations.

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

BACKGROUND

This study was designed to determine the correlation between functional recovery and the extent of axonal regeneration after muscle reinnervation with our recently developed nerve-muscle-endplate band grafting (NMEG) technique in a rat model.

MATERIALS AND METHODS

The right experimentally paralyzed sternomastoid (SM) muscle by nerve transection was immediately reinnervated with an NMEG pedicle harvested from a neighboring sternohyoid muscle. The NMEG pedicle contained a muscle block (6 × 6 × 3 mm), a donor nerve branch with nerve terminals, and a motor endplate band. Three months after surgery, the tetanic force of the SM muscle was measured and the regenerated axons in the muscle were detected using neurofilament immunohistochemistry.

RESULTS

The results showed that the maximal tetanic force (a measure of muscle functional recovery) of the NMEG-reinnervated SM muscle reached up to 66.0% of the normal control. The wet weight of the reinnervated SM muscle (a measure of muscle mass recovery) was 87.2% of the control. The area fraction of the regenerating axons visualized with neurofilament staining within the NMEG-reinnervated SM muscle (a measure of muscle reinnervation) was 42.3%. A positive correlation was revealed between the extent of muscle reinnervation and maximal muscle force.

CONCLUSIONS

Our newly developed NMEG technique results in satisfactory functional outcomes and nerve regeneration. Further improvement in the functional recovery after NMEG reinnervation could be achieved by refining the surgical procedure and creating an ideal environment that favors axon-endplate connections and accelerates axonal growth and sprouting.

Comparison of muscle force after immediate and delayed reinnervation using nerve-muscle-endplate band grafting

BACKGROUND

Because of poor functional outcomes of currently used reinnervation methods, we developed novel treatment strategy for the restoration of paralyzed muscles-the nerve-muscle-endplate band grafting (NMEG) technique. The graft was obtained from the sternohyoid muscle (donor) and implanted into the ipsilateral paralyzed sternomastoid (SM) muscle (recipient).

METHODS

Rats were subjected to immediate or delayed (1 or 3 mo) reinnervation of the experimentally paralyzed SM muscles using the NMEG technique or the conventionally used nerve end-to-end anastomosis. The SM muscle at the opposite side served as a normal control.

RESULTS

NMEG produced better recovery of muscle force as compared with end-to-end anastomosis. A larger force produced by NMEG was most evident for small stimulation currents.

CONCLUSIONS

The NMEG technique holds great potential for successful muscle reinnervation. We hypothesize that even better muscle reinnervation and functional recovery could be achieved with further improvement of the environment that favors axon-end plate connections and accelerates axonal growth and sprouting.

Force recovery and axonal regeneration of the sternomastoid muscle reinnervated with the end-to-end nerve anastomosis

BACKGROUND

End-to-end nerve anastomosis (EEA) is a commonly used nerve repair technique. However, this method generally results in poor functional recovery. This study was designed to determine the correlation of functional recovery to the extent of axonal reinnervation after EEA procedure in a rat model.

MATERIALS AND METHODS

Seven adult rats were subjected to the immediate reinnervation of an experimentally paralyzed sternomastoid (SM) muscle. The SM nerve was transected and immediately repaired with EEA. The SM muscle at the opposite side, without nerve transection, served as a control. Three months after EEA nerve repair, the muscle force of the SM muscle was measured and the regenerated axons in the muscle were detected using neurofilament immunohistochemistry.

RESULTS

Three months after surgery, the reinnervated SM muscle produced limited anatomical and functional recovery (calculated as the percentage of the control). Specifically, the wet weight of the operated SM muscle (a measure of muscle mass recovery) was 78.0% of the control. The maximal tetanic force (a measure of muscle functional recovery) was 56.7% of the control. The area fraction of the neurofilament stained intramuscular axons (a measure of axonal regeneration and muscle reinnervation) was measured to be only 13.4% of the control. A positive correlation was revealed between the extent of muscle reinnervation and maximal muscle force.

CONCLUSIONS

The EEA reinnervated SM muscle in the rat yielded unsatisfactory muscle force recovery as a result of mild to moderate nerve regeneration. Further work is needed to improve the surgical procedure, enhance axonal regeneration, and/or develop novel treatment strategies for better functional recovery.

Olfactory ensheathing cells in a rat model of laryngeal reinnervation

OBJECTIVES

Olfactory ensheathing cells have been used successfully for recovery of nervous system lesions. The aim of our study was to determine whether olfactory ensheathing cells from the olfactory bulb or olfactory mucosa were able to improve functional recovery in a laryngeal reinnervation animal model.

METHODS

Fifty-nine rats were divided into 6 groups. A group without nerve section (group 1; n=10) and a group without anastomosis (group 2; n=11) served as controls. Right vagus nerve section and immediate anastomosis (nonselective reinnervation) was performed in 4 other groups, as follows. In group 3 (n=10), there was selective reinnervation without any addition of substance; groups 4 (n=10), 5 (n=10), and 6 (n=8) received, on the section and anastomosis site, and at the same time, cultivated olfactory bulb, cultivated olfactory mucosa, and noncultivated olfactory mucosa from inbred rats, respectively. Three months later, videolaryngoscopy with vocal fold movement measurements, electromyography, and histologic examination were performed.

RESULTS

The best right vocal fold angular movement (3.05 degrees +/- 1.14 degrees) was observed in group 5 with cultivated olfactory mucosa, versus group 3 (-0.28 degrees +/- 1.51 degrees; p = 0.06). The relative angular vocal fold movement was better in group 5 (p = 0.05). The mobility score was 0.6 +/- 0.27 for group 3 and 1.4 +/- 0.31 for group 5 (p = 0.07). Less synkinesis was observed in the reinnervated groups with cell addition, particularly with noncultivated olfactory mucosa (group 6; p = 0.05).

CONCLUSIONS

Olfactory ensheathing cells obtained from olfactory mucosa cultures seem to improve functional laryngeal reinnervation in a rat model of nonselective vagus nerve section and anastomosis.

Locations of the motor endplate band and motoneurons innervating the sternomastoid muscle in the rat

Sternocleidomastoid (SCM) is a long muscle with two bellies, sternomastoid (SM) and cleidomastoid (CM) in the lateral side of the neck. It has been widely used as muscle and myocutaneous flap for reconstruction of oral cavity and facial defects and as a candidate for reinnervation studies. Therefore, exact neuroanatomy of the SCM is critical for guiding reinnervation procedures. In this study, SM in rats were investigated to document banding pattern of motor endplates (MEPs) using whole-mount acetylcholinesterase (AChE) staining and to determine locations of the motoneurons innervating the muscle using retrograde horseradish peroxidase (HRP) tracing technique. The results showed that the MEPs in the SM and CM were organized into a single band which was located in the middle portion of the muscle. After HRP injections into the MEP band of the SM, ipsilaterally labeled motoneurons were identified in the caudal medulla oblongata (MO), C1, and C2. The SM motoneurons were found to form a single column in lower MO and dorsomedial (DM) nucleus in C1. In contrast, the labeled SM motoneurons in C2 formed either one (DM nucleus), two [DM and ventrolateral (VL) nuclei], or three [DM, VL, and ventromedial (VM)] columns. These findings are important not only for understanding the neural control of the muscle but also for evaluating the success rate of a given reinnervation procedure when the SM is chosen as a target muscle.

Diaphragmatic effects of selective resection of the upper phrenic nerve root in dogs

The aim of this study was to evaluate the effects on the diaphragm of upper phrenic nerve root resections in dogs. During laryngeal reinnervation, selective resections of the upper phrenic nerve root (C5) were performed unilaterally (right side, n=7; Group A) and bilaterally (n=6; Group B) and compared to non denervated animals (n=5). After 8 months, a diaphragmatic evaluation was performed: X-ray, EMG, transdiaphragmatic pressure (Pdi) after ipsi- and bilateral tetanic stimulation of the phrenic nerves and a bilateral histological study of five hemidiaphragmatic regions. EMG alterations were significantly more severe in Group B than in Group A, for the left (p<0.05) and right hemidiaphragms (p<0.01). No differences in the X-rays were noted between the three groups. The Pdi of the three groups after occlusion and phrenic nerve stimulations (unilateral and bilateral) were not statistically different. Histological data demonstrated that there were no differences in fibre irregularity, predominant fibre type or fibrosis between the three groups. Macroscopic and microscopic atrophy, which was mainly present on the anterior regions of the hemidiaphragms, was significantly higher in Group B than in Group A and undenervated dogs (p<0.05). In conclusion, resection of the upper phrenic nerve root of one phrenic nerve (right side) have limited effect on the diaphragm in dogs. However, resection of the upper phrenic nerve root on both sides resulted in a significant effect on the EMGs and histology of the entire diaphragm without any significant consequences on transdiaphragmatic pressure.

Restoration of diaphragmatic function after diaphragm reinnervation by inferior laryngeal nerve; experimental study in rabbits

OBJECTIVES

To assess the possibilities of reinnervation in a paralyzed hemidiaphragm via an anastomosis between phrenic nerve and inferior laryngeal nerve in rabbits. Reinnervation of a paralyzed diaphragm could be an alternative to treat patients with ventilatory insufficiency due to upper cervical spine injuries.

MATERIAL AND METHOD

Rabbits were divided into five groups of seven rabbits each. Groups I and II were respectively the healthy and the denervated control groups. The 3 other groups were all reinnervated using three different surgical procedures. In groups III and IV, phrenic nerve was respectively anastomosed with the abductor branch of the inferior laryngeal nerve and with the trunk of the inferior laryngeal nerve. In group V, the fifth and fourth cervical roots were respectively anastomosed with the abductor branch of the inferior laryngeal nerve and with the nerve of the sternothyroid muscle (originating from the hypoglossal nerve). Animals were evaluated 4 months later using electromyography, transdiaphragmatic pressure measurements, sonomicrometry and histological examination.

RESULTS

A poor inspiratory activity was found in quiet breathing in the reinnervated groups, with an increasing pattern of activity during effort. In the reinnervated groups, transdiaphragmatic pressure measurements and sonomicrometry were higher in group III with no significant difference with groups IV and V.

CONCLUSION

Inspiratory contractility of an hemidiaphragm could be restored with immediate anastomosis after phrenic nerve section between phrenic nerve and inferior laryngeal nerve.

Laryngeal reinnervation

Laryngeal reinnervation refers to any of a number of surgical procedures intended to restore neural connections to the larynx, which have usually been lost from some type of trauma (eg, surgical). The nerve function(s) to be restored may be those of the recurrent laryngeal nerve or its subdivisions, those of the superior laryngeal nerve, or both, and they may be motor or sensory. Several different donor nerves are available and have been described. The technique used may be direct end-to-end anastomosis (neurorrhaphy), direct implantation of a nerve ending into a muscle, the nerve-muscle pedicle technique, or muscle-nerve-muscle methods. These nerves and techniques may be combined in many ways. A number of new techniques have been reported in animal studies; however, the animal studies do not always predict the results of analogous surgeries in human patients. The historical and current perspectives on these techniques are discussed in this article.