Direct Muscle Neurotization Research Articles

Porcine Acellular Nerve-Derived Hydrogel Improves Outcomes of Direct Muscle Neurotization in Rats.

Background: The ability to reinnervate a muscle in the absence of a viable nerve stump is a challenging clinical scenario. Direct muscle neurotization (DMN) is an approach to overcome this obstacle; however, success depends on the formation of new muscle endplates, a process, which is often limited due to lack of appropriate axonal pathfinding cues. Objective: This study explored the use of a porcine nerve extracellular matrix hydrogel as a neuroinductive interface between nerve and muscle in a rat DMN model. The goal of the study was to establish whether such hydrogel can be used to improve neuromuscular function in this model. Materials and Methods: A common peroneal nerve-to-gastrocnemius model of DMN was developed. Animals were survived for 2 or 8 weeks following DMN with or without the addition of the hydrogel at the site of neurotization. Longitudinal postural thrust, terminal electrophysiology, and muscle weight assessments were performed to qualify and quantify neuromuscular function. Histological assessments were made to qualify the host response at the DMN site, and to quantify neuromuscular junctions (NMJs) and muscle fiber diameter. Results: The hydrogel-treated group showed a 132% increase in postural thrust at 8 weeks compared with that of the DMN alone group. This was accompanied by an 80% increase in the number of NMJs at 2 weeks, and 26% increase in mean muscle fiber diameter at 8 weeks. Conclusions: These results suggest that a nerve-derived hydrogel may improve the neuromuscular outcome following DNM.

Smile Outcomes When Using Masseteric Nerve-based Nerve Transfers versus Direct Muscle Neurotization in Facial Palsy Patients.

In a retrospective cohort study of 20 patients (n = 20), we compared nerve transfer versus DMN over a 6-year period (2016-2021). Outcomes were measured using the validated Sunnybrook score, Ackerman Smile Index, and Terzis scores. Statistical analysis was performed using the Wilcoxon sign rank and Mann-Whitney U tests. Comparing pre- versus postoperative scores after nerve transfers, there was a significant improvement in median overall Sunnybrook score (24 versus 47, P = 0.043), lip elevation (1 versus 2, P = 0.046), open mouth smile (1 versus 3, P = 0.003), and Terzis scores (1 versus 3, P = 0.005), with no difference in resting symmetry (-15 versus -5; P = 0.496). Compared with DMN, there was no difference in median Terzis score improvement from preoperative to postoperative state (2 versus 1, P = 0.838), median smile improvement (2 versus 2, P = 0.838), resting symmetry (10 versus 5, P = 0.144) or overall Sunnybrook score (23 versus 21, P = 1.000). Lip elevation improvement was in favor of nerve transfers (1 versus 0, P = 0.047). This is the first study evaluating nerve transfer neurotization of smile-mimetic muscles and comparing the outcomes with DMN, with masseteric nerve as donor. Nerve transfer leads to improved facial mimetic function, smile excursion and open mouth smiles, as does DMN, with improvement in lip elevation in favor of nerve transfer. Nerve transfer was preferred for more severe smile weakness.

Advances and future directions in the care of patients with facial paralysis

Advances and future directions in the care of patients with facial paralysis

Depressor Reanimation After Facial Nerve Paralysis.

Facial expressions play a fundamental role in interpersonal communication and interaction; consequently, facial palsy has profound effects on the quality of life of patients. Reanimation of lower lip depressors is rarely addressed during facial reanimation but is as important as treating the eye sphincter and the lip levators. Depressors of lower lip are vital for full denture smile and the expression of facial emotions. Static and dynamic techniques are used to reanimate the lower lip depressors. Static techniques provide stationary results either by weakening the contralateral normal side to achieve symmetry using botulinum toxin injection, depressor labi inferioris myectomy and marginal mandibular nerve neurectomy, or by creating static slings and tightening procedures on the affected side. Dynamic techniques provide functional results by reanimating the affected depressor complex using nerve transfers, muscle transfers, and direct muscle neurotization. The purpose of this article is to present an overview of the literature on the applications of these techniques in lower lip reanimation. Furthermore, preoperative evaluation and indications are also discussed.

Sensory protection to enhance functional recovery following proximal nerve injuries: current trends

Proximal nerve injury can lead to devastating functional impairment. Because axonal regeneration is slow, timely reinnervation of denervated muscle does not occur. These denervated muscles atrophy and lose function. Sensory protection is a surgical technique thought to prevent denervated muscle impairment using local sensory nerves to provide trophic support to the muscle until motor nerves can regenerate, and neuromuscular junctions are reestablished. We performed a comprehensive literature search using multiple databases to find primary articles reporting on the outcomes and treatment of sensory protection. This paper reviews the three main approaches to sensory protection: (1) end-to-end neurorrhaphy, (2) end-to-side neurorrhaphy, and (3) direct muscle neurotization. It discusses the evidence supporting each technique and outlines goals for future investigations.

Neurotization to Innervate the Deltoid and Biceps: 3 Cases

To describe our experience using direct muscle neurotization as a treatment adjunct during delayed surgical reconstruction for traumatic denervation injuries. Three patients who had direct muscle neurotization were chosen from a consecutive series of patients undergoing reconstruction for brachial plexus injuries. The cases are presented in detail, including long-term clinical follow-up at 2, 5, and 10 years with accompanying postoperative electrodiagnostic studies. Postoperative motor strength using British Medical Research Council grading and active range of motion were retrospectively extracted from the clinical charts. Direct muscle neurotization was performed into the deltoid in 2 cases and into the biceps in 1 case after delays of up to 10 months from injury. Two patients had recovery of M4 strength, and the other patient had recovery of M3 strength. All 3 patients had evidence on electrodiagnostic studies of at least partial muscle reinnervation after neurotization. Direct muscle neurotization has shown promising results in numerous basic science investigations and a limited number of clinical cases. The current series provides additional clinical and electrodiagnostic evidence that direct muscle neurotization can successfully provide reinnervation, even after lengthy delays from injury to surgical treatment. Microsurgeons should consider direct muscle neurotization as a viable adjunct treatment and part of a comprehensive reconstructive plan, especially for injuries associated with avulsion of the distal nerve stump from its insertion into the muscle.

Direct muscle neurotization after end-to end and end-to-side neurorrhaphy: An experimental study in the rat forelimb model.

The need for the continuous research of new tools for improving motor function recovery after nerve injury is justified by the still often unsatisfactory clinical outcome in these patients. It has been previously shown that the combined use of two reconstructive techniques, namely end-to-side neurorrhaphy and direct muscle neurotization in the rat hindlimb model, can lead to good results in terms of skeletal muscle reinnervation. Here we show that, in the rat forelimb model, the combined use of direct muscle neurotization with either end-to-end or end-to-side neurorrhaphy to reinnervate the denervated flexor digitorum muscles, leads to muscle atrophy prevention over a long postoperative time lapse (10 months). By contrast, very little motor recovery (in case of end-to-end neurorrhaphy) and almost no motor recovery (in case of end-to-side neurorrhaphy) were observed in the grasping activity controlled by flexor digitorum muscles. It can thus be concluded that, at least in the rat, direct muscle neurotization after both end-to-end and end-to-side neurorrhaphy represents a good strategy for preventing denervation-related muscle atrophy but not for regaining the lost motor function.

Peripheral nerve regeneration research: Why is it getting so "cool"?

More than twenty years ago, when I first started working on plasticity and regeneration in the peripheral nervous system, I had the feeling of being part of a little, though lively, scientific community that was rarther isolated in the world of neuroscience which appeared to me as almost only focused on central nervous system. Since then, things have progressively changed very much and, today, interest in the regeneration in the peripheral nervous system, and especially in its main component. i.e. the peripheral nerves (Geuna S, Raimondo S, Ronchi G, et al. Histology of the peripheral nerve and changes occurring during nerve regeneration. Int Rev Neurobiol. 2009;87:27-46.), is sprading tremendouslty among both basic and clinical neuroscientists. Which could be the reasons for this change? I can see, at least, two major factors. First, medicine and surgery have been slowly shifting from a difinition of health as “the absence of disease or infirmity” to a definition of health as “a state of well-being” (WHO. Preamble to the Constitution of the World Health Organization as adopted by the International Health Conference, New York, 19-22 June 1946, and entered into force on 7 April 1948). In other words, more and more attention is being dedicated to the quality of live of the patient. In this view, although peripheral nerve lesions do not usually cause any threat to patients’ live and often the degree of disability is low, nonetheless these types of lesions always affect the quality of live of the patients. Therefore, they have always to be treated! Yet, peripheral nerves are anywhere in the body and thus peripheral nerve regeneration and tissue engeneering touch all branches of medicine and surgery (from neurosurgery to orthopaedics, from plastic surgery to urology, just to make some examples) and thus the potential number of patients that would need to be treated is very high. A second reason that I see as a major determinant of the recent success of peripheral nerve regeneration research is the great recent development of biomaterial sciences that leads to the continuous development of innovative medical devices for reconstructing damaged organs and tissues. For their complex three-dimensional anatomical organization, peripheral nerves represent a perfect target for biomaterial-based tissue engineering and have thus attracted very much the attention of materials scientists and engineers interested not only in the clinical spin off, but also in the potential for large scale industrial spin off generated from basic science results. The collection of papers that have been brought together in this issue of Neural Regeneration Research, aims to give a view on the lively scientific interest on peripheral nerve regeneration research. It includes three review papers as well two research articles. The first review addresses some general emering concepts in peripheral nerve repair that appears to be ready for being translated to the clinics. The other reviews focus on two interesting aspects of peripheral nerve adaptation after injury and regeneration, namely the role of inflammatory cytochines and the sensory reinervation occurring after complex free flap tissue reconstruction. The collection is closed up by two research articles, the first of which addresses the combined use of chitosan membranes and mesenchymal stem cells on nerve regeneration, while the second investigates the potentialities of combining direct muscle neurotization with end-to-end- and end-to-side neurorrhaphy for preventing denervation-related skeletal muscle atrophy. I hope that this collection of papers will be of interest both for experienced nerve researchers, in their efforts for addressing the many challenging scientific questions that still need to be answered in this intriguing research field, and for young scientists and clinicians that are just moving their first steps in this field. I hope that they will create a new and interdisciplinary generation of enthusiastic investigators that will be able to face tomorrow's scientific challenges in peripheral nerve repair and regeneration.

Therapeutic strategies in post-facial paralysis synkinesis in pediatric patients

Synkinetic movements comprise abnormal involuntary contractions of one or more facial muscle groups which follow the desired contraction of another facial muscle group. They are frequently encountered in patients with long standing facial paralysis and seriously affect their psychological status due to the impairment of their facial appearance, function and emotional expressivity. Eleven pediatric patients (2 male and 9 female) presenting with post-facial paralysis synkinesis were included in the study. Mean age was 10.3±4 years and mean denervation time 72.5 months. Patients underwent the following types of treatment: --Cross facial nerve grafting (CFNG) and secondary microcoaptations with botulinum toxin injection which had an improvement of 100% (3 in the 3 grade synkinesis scale) (n=2). --Cross facial nerve grafting (CFNG) and secondary microcoaptations without botulinum toxin injection which had an improvement of 66%(2 in the 3 grade synkinesis scale) (n=5). --CFNG and direct muscle neurotization with (n=2) or without (n=1) botulinum toxin injection where the improvement was 33%. --Contralateral nasalis muscle myectomy was performed in one patient along with CFNG and secondary microcoaptations which resulted in 66% synkinesis improvement. Biofeedback was invariably undertaken by all patients. Postoperative improvement in eye closure and smile was also noted in the respective cases treated for synkinesis ranging from 25 to 50%, with all patients achieving optimum functional return. CFNG with secondary microcoaptations and botulinum toxin injections was found to be a very efficient surgical modality addressing post-facial palsy synkinesis with high improvement in facial function and symmetry. Facial neuromuscular re-education contributes considerably in the treatment.

Outcomes of Mini-Hypoglossal Nerve Transfer and Direct Muscle Neurotization for Restoration of Lower Lip Function in Facial Palsy

Most reconstructions for lower lip palsy focus on paralyzing the contralateral normal lip or providing static support on the affected side. The authors' unit has reported dynamic strategies for lower lip reanimation and use of 40 percent of the hypoglossal nerve (mini-hypoglossal) in facial reanimation. They report their experience with mini-hypoglossal nerve transfer for lower lip palsy. Between 1987 and 2005, 29 patients with unilateral facial palsy had lower lip reanimation with the mini-hypoglossal as the motor donor. Twenty patients had transfer of the mini-hypoglossal to the cervicofacial branch of the facial nerve and nine had direct depressor muscle neurotization. Five patients had a mean denervation time of 14.60 +/- 4.50 months (<2 years), and the rest had a mean denervation time of 10.63 +/- 9.23 years. In late cases, the facial nerve was in-continuity, and preoperative needle electromyographs of depressors showed at least fibrillations. Standardized videos taken preoperatively and at 2 years postoperatively were available for 27 patients and assessed by three independent reviewers. Needle electromyographic results were analyzed. Thirteen patients (48.15 percent) achieved excellent and good results, nine (33.33 percent) had moderate results, and five (18.52 percent) obtained fair results. The difference between the averaged preoperative and postoperative scores was statistically significant, as was the difference in electromyographic outcomes (p < 0.0001, Wilcoxon signed rank test). The nerve transfer and direct neurotization groups had no statistically significant difference in clinical and electromyographic outcomes. Four patients required muscle transfer for further outcome upgrading. Use of the mini-hypoglossal either for nerve transfer or for direct muscle neurotization of lower lip depressors can provide reinnervation and satisfactory clinical function, even for muscles with prolonged partial denervation.

Outcomes of Direct Muscle Neurotization in Pediatric Patients with Facial Paralysis

Multistage reconstructive procedures are often required to try to restore the emotional potential of human expression in cases of facial paralysis. In this study, the senior author's (J.K.T.) experience with the technique of direct nerve to muscle neurotization as a part of multistage facial reanimation procedures is presented. Age, denervation time, etiology of the lesion, previous reconstructive procedures, and types of muscles responsible for animation were analyzed to make evidence-based recommendations on the indications of the technique as well as its role and effectiveness in facial reanimation. Retrospective review of 37 pediatric patients who underwent direct muscle neurotization took place. The patients were divided into three groups, depending on the region that direct neurotization was aiming to augment. Group A involved 28 patients for eye closure and blink, group B included 15 patients for smile, and group C included 19 patients for depressor augmentation. Twenty patients were female and 17 male. Patient age ranged from 1 to 16 years, with a mean age (+/-SD) of 9 +/- 2.8 years. Denervation time ranged from 3 months to 15.25 years, and the mean denervation time was 6.72 years. Electromyographic scoring of the neurotized muscles showed an overall mean improvement of 36 percent for eye closure, 34.25 percent for blink, 37 percent for smile augmentation, and 30 percent for depressor function restoration. Direct muscle neurotization has a valid role in pediatric facial reanimation procedures, as it augments and promotes expressivity.

Comparison of Neurotization Versus Nerve Repair in an Animal Model of Chronically Denervated Muscle

PurposeReinnervation of chronically denervated muscle is clinically unpredictable and poorly understood. Current operative strategies include either direct nerve repair, nerve grafting, nerve transfer, or neurotization. The goal of this study is to compare muscle recovery using microneural repair versus neurotization in a rat model of chronic denervation.MethodsFifty-eight Sprague-Dawley rats had surgical denervation of the tibialis anterior muscle by transecting the common peroneal nerve. After 0, 8, 12, or 22 weeks of denervation, animals were assigned to either a direct repair or a neurotization cohort. An additional 7 animals were used for a sham cohort, and 7 of the 58 were used as controls. After a 12-week recovery period, animals had contractile strength and EMG testing of the tibialis anterior muscle. Peak force and characteristics were compared to the unoperated, contralateral limb. Tibialis anterior muscles were then harvested for mass and histologic evaluation.ResultsSixty-two animals completed testing. Denervated controls demonstrated a significant decrease in muscle mass, contractile strength, and peak motor nerve conduction amplitude compared to sham animals. In all groups, chronicity of denervation adversely affected functional recovery. On average, repair animals performed better than neurotization animals with respect to muscle mass, contractile strength, and peak motor amplitude. Differences in contractile force, however, were significant only at the 0 week denervation group (94% ± 30 vs 50% ± 20, repair vs neurotization). Neurotized muscles processed for histologic analysis demonstrated acetylcholinesterase activity at the nerve-muscle interface, confirming the formation of motor end plates de novo.ConclusionsWe demonstrated that neurotization is capable of reinnervating de novo end plates in chronically denervated muscle. Our data do not support the hypothesis that direct muscle neurotization is superior to nerve repair for functional restoration of chronically denervated muscle. However, as the duration of denervation increases, the difference between outcomes of the neurotization and repair group narrows, suggesting that neurotization may offer a viable surgical alternative in the setting of prolonged denervation.

Concepts of nerve regeneration and repair applied to brachial plexus reconstruction

Brachial plexus injury is a serious condition that usually affects young adults. Progress in brachial plexus repair is intimately related to peripheral nerve surgery, and depends on clinical and experimental studies. We review the rat brachial plexus as an experimental model, together with its behavioral evaluation. Techniques to repair nerves, such as neurolysis, nerve coaptation, nerve grafting, nerve transfer, fascicular transfer, direct muscle neurotization, and end-to-side neurorraphy, are discussed in light of the authors' experimental studies. Intradural repair of the brachial plexus by graft implants into the spinal cord and motor rootlet transfer offer new possibilities in brachial plexus reconstruction. The clinical experience of intradural repair is presented. Surgical planning in root rupture or avulsion is proposed. In total avulsion, the authors are in favor of the reconstruction of thoraco-brachial and abdomino-antebrachial grasping, and on the transfer of the brachialis muscle to the wrist extensors if it is reinnervated. Surgical treatment of painful conditions and new drugs are also discussed.

Early Effect of Gene Therapy on a Direct Muscle Neurotization Model

Direct nerve-to-muscle neurotization has been the subject of both clinical and experimental studies. In this study, the authors report a new animal model to test the regenerative properties of a nerve (musculocutaneous) implanted in a muscle (biceps). They also report the early effects of the application at the implantation site of exogenously administered Brain Derived Nerve Factor (BDNF) and of endogenously produced BDNF, via the administration of an adenoviral construct with a tissue-specific promotor for muscle cells (AdRSV), and containing the BDNF gene. Evaluation included behavioral testing (grooming test), electrical stimulation, Western blot analysis of the distal implanted nerve to determine the presence of locally produced BDNF, and motor end-plate staining of the biceps muscle. At the early time point of 1 week following the musculocutaneous nerve to biceps muscle implantation, there was no increased production of recombinant BDNF at the distal implanted musculocutaneous nerve, as assessed by Western blot analysis. Therefore, there was no significant difference in the behavioral evaluation of the animals at 1 week; the Terzis grooming test showed no statistical difference among groups, but a trend toward better function for the BDNF and the high-dose AdRSV-BDNF groups, compared to the control groups. There was also no difference in the histologic appearance and number of the motor end-plates at the implantation site, compared to the controls. The electrical stimulation of the MC nerve did not produce statistically significant results among the experimental groups. In this direct nerve to muscle neurotization model, the application of AdRSV-BDNF at 3 x 10 (9) pfu/ul did not show enhanced production of BDNF at 1 week.

Direct muscle neurotization after end-to-side neurorrhaphy.

Over the recent years, end-to-side neurorrhaphy has reemerged in the literature for reconstructive nerve surgery. Another technique, in which interest has remained continuous during the last century, is direct nerve implantation into muscle belly, so-called direct muscle neurotization (DMN). In this work, the authors present a new technique to recover muscle innervation through direct nerve implantation into muscle belly, by means of a nerve graft, and sutured with end-to-side neurorrhaphy. They carried out experiments on 20 Wistar rats divided into two groups. In Group 1 (10 rats), on the right side, the peroneal nerve was sutured to the tibial nerve with end-to-side neurorrhaphy. Subsequently, the terminal branches of the same nerve were implanted in the anterior tibial muscle (ATM). On the left side, the peroneal nerve was severed, and the ATM completely denervated. In Group 2 (10 rats), on the right side, the same technique was used as in first group. On the left side, the normal innervation of the ATM was maintained. After 4 months, all muscles and nerves were harvested and evaluations carried out on the morphologic aspect, weight, and histology of the ATM, as well as the histology of the nerves. The authors analyzed the results, which demonstrated good reinnervation of the muscles deprived of any nerve connection.

Direct Muscle Neurotization in Rat Soleus Muscle

-The authors carried out an experimental study using rat soleus muscles to evaluate reinnervation of the denervated muscles by direct muscle neurotization. They also attempted to determine whether there is any difference in the regeneration process between original (tibial) and foreign (peroneal) nerve neurotization. For functional evaluation, they did an electrophysiologic study by analyzing pattern, latency, amplitude, and duration of compound motor action potential. For histochemical studies, both hematoxyline-eosin stain and nicotineamide adenin dehydrogenase stainings were used to identify the morphology and the change of the type of muscle fiber. Combined silver-acetylcholinesterase stain was performed to identify reinnervated motor endplate and axonal sprouting. They confirmed evidence of regeneration of the denervated muscle by direct muscle neurotization. Regenerating muscles showed type groupings of muscle fibers. The newly-formed ectopic motor endplate was connected with axonal sprouting. The giant motor endplate composed of mature axon sprouting and several new ectopic motor endplates, appeared in the neurotization group. There was no significant difference in the regeneration process between original and foreign nerve neurotization.

Direct muscle neurotization in rat soleus muscle.

An experimental study was conducted using rat soleus muscles to characterize reinnervation of the denervated muscles by direct muscle neurotization. Also studied was whether there is any difference in the regeneration process between original (tibial) and foreign (peroneal) nerve neurotization. For functional evaluation, an electrophysiologic study was carried out by analyzing pattern, latency, amplitude, and duration of compound motor action potential. In a histochemical study, both hematoxylin-eosin stain and nicotineamide adenin dehydrogenase stain were used to identify the morphology and the change in the type of muscle fiber. Combined silver-acetylcholinesterase stain was utilized to identify reinnervated motor endplates and axonal sprouting. Evidence of regeneration of the denervated muscle by direct muscle neurotization could be confirmed. Regenerating muscles showed type grouping of muscle fibers. The newly-formed ectopic motor endplate was connected with axonal sprouting. The giant motor endplate composed of mature axon sprouting and several new ectopic motor endplates appeared in the neurotization group. There was no specific difference in the regeneration process between original and foreign nerve neurotization.

Direct Muscle Neurotization Recovers Gastrocnemius Muscle Function

This case report describes a devastating injury in which a distal motor nerve had been avulsed from the muscle belly and was not available for reconstruction. This otherwise irreparable posterior tibial nerve injury was successfully treated by direct neurotization of the muscle belly. The patient did have one small, intact, muscular branch to the medial gastrocnemius muscle; however, electrodiagnostic and clinical examination and recovery pattern suggested the neurotization procedure was responsible for the functional recovery. In the rare situation where no distal nerve is available, and tendon transfers or arthrodesis are inappropriate, direct muscle neurotization can be considered as a salvage technique.

Direct muscle neurotization.

The results of experimental research, as well as of a large clinical series (n = 51) of direct muscle neurotization, have been encouraging enough to warrant extending the indications for the procedure to patients in whom traditional repair by direct nerve suture or nerve graft is impossible, because of the lack of a distal nerve segment, or because of destruction of the neural portion of one or more muscle groups. Prerequisites include a satisfactory volume of muscle with sufficient vascularity and adequate postoperative joint and muscle immobilization.

SECONDARY NERVE RECONSTRUCTION

Presented is a review of nerve grafting, including the indications, technique, and results. Alternative techniques, including vascularized nerve grafts, tubulization, nerve elongation, and direct muscle neurotization are also discussed.