Brief electrical stimulation after facial nerve transection and neurorrhaphy: a randomized prospective animal study

Effects of Electrical Stimulation on Facial Paralysis Recovery after Facial Nerve Injury: A Review on Preclinical and Clinical Studies

Various methods have been used to improve function and manage facial nerve injury. Although electrical stimulation therapy is frequently used to treat facial paralysis, its effects have been found to vary and no clear standards have been developed. The current review describes the results of preclinical and clinical studies evaluating the effectiveness of electrical stimulation therapy in promoting the recovery of a peripheral facial nerve injury. Evidence is presented showing the efficacy of electrical stimulation in promoting nerve regeneration after peripheral nerve injuries in both animal models and human patients. The ability of electrical stimulation to promote the recovery of facial paralysis was found to depend on the type of injury (compression or transection), the species of animal tested, the type of disease, the frequency and method of electrical stimulation, and the duration of the follow-up. Electrical stimulation, however, can also have potential negative outcomes, such as reinforcing synkinesis, including mistargeted axonal regrowth via inappropriate routes; excessive collateral axonal branching at the lesion site; and multiple innervations at neuromuscular junctions. Because of the inconsistencies among studies and the low quality of evidence, electrical stimulation therapy is not currently regarded as a primary treatment of facial paralysis in patients. However, understanding the effects of electrical stimulation, as determined in preclinical and clinical studies, is important for the potential validity of future research on electrical stimulation.

Facial nerve repair utilizing intraoperative repair strategies

OBJECTIVES

To determine whether functional and anatomical outcomes following suture neurorrhaphy are improved by the addition of electrical stimulation with or without the addition of polyethylene glycol (PEG).

METHODS

In a rat model of facial nerve injury, complete facial nerve transection and repair was performed via (a) suture neurorrhaphy alone, (b) neurorrhaphy with the addition of brief (30 minutes) intraoperative electrical stimulation, or (c) neurorrhaphy with the addition electrical stimulation and PEG. Functional recovery was assessed weekly for 16 weeks. At 16 weeks postoperatively, motoneuron survival, amount of regrowth, and specificity of regrowth were assessed by branch labeling and tissue analysis.

RESULTS

The addition of brief intraoperative electrical stimulation improved all functional outcomes compared to suturing alone. The addition of PEG to electrical stimulation impaired this benefit. Motoneuron survival, amount of regrowth, and specificity of regrowth were unaltered at 16 weeks postoperative in all treatment groups.

CONCLUSION

The addition of brief intraoperative electrical stimulation to neurorrhaphy in this rodent model shows promising neurological benefit in the surgical repair of facial nerve injury.

LEVEL OF EVIDENCE

Animal study.

Conductive conduit small gap tubulization for peripheral nerve repair

Despite advances in surgical techniques, functional recovery following epineurial neurorrhaphy of transected peripheral nerves often remains quite unsatisfactory. Small gap tubulisation is a promising approach that has shown potential to traditional epineurial neurorrhaphy in the treatment of peripheral nerve injury. Thus, the goal of this study is to evaluate sciatic nerve regeneration after nerve transection, followed by small gap tubulization using a reduced graphene oxide-based conductive conduit. In vitro, the electrically conductive conduit could promote Schwann cell proliferation through PI3K/Akt signaling pathway activation. In vivo, the results of electrophysiological and walking track analysis suggest that the electrically conductive conduit could promote sensory and motor nerve regeneration and functional recovery, which is based on the mechanisms of selective regeneration and multiple-bud regeneration. These promising results illustrate electrically conductive conduit small gap tubulization as an alternative approach for transected peripheral nerve repair.

rGO-based conductive nerve conduit as a scaffold to bridge peripheral nerve transected injury and 2 mm gap provides a suitable microenvironment for axons selective regeneration.

Advances in electrical and magnetic stimulation on nerve regeneration

Central and peripheral nerve injuries pose a great threat to people. Complications such as inflammation, muscle atrophy, traumatic neuromas and delayed reinnervation can bring huge challenges to clinical practices and barriers to complete nerve regrowth. Physical interventions such as electrical and magnetic stimulation show satisfactory results with varying parameters for acute and chronic nerve damages. The biological basis of electrical and magnetic stimulation mainly relies on protein synthesis, ion channel regulation and growth factor secretion. This review focuses on the various paradigms used in different models of electrical and magnetic stimulation and their regenerative potentials and underlying mechanisms in nerve injuries. The combination of physical stimulation and conductive biomaterial scaffolds displays an infinite potentiality in translational application in nerve regeneration.

Adipose-derived stem cells delay muscle atrophy after peripheral nerve injury in the rodent model

INTRODUCTION

Injuries to peripheral nerves cause distal muscle atrophy. The effects of adipose-derived stem cell (ASC) injections into a muscle after injury were examined.

METHODS

A 1.5 cm defect in the rat sciatic nerve was created, resulting in gastrocnemius muscle atrophy. The nerve defect was repaired with autograft; DiR-labeled ASCs were injected into the gastrocnemius immediately postoperatively. Quantitation of gross musculature and muscle fiber area, cell survival, fibrosis, lipid deposition, inflammation, and reconstructive responses were investigated.

RESULTS

ASCs were identified in the muscle at 6 weeks, where injections showed increased muscle mass percentage retained, larger average fiber area, and less overall lipid content accumulated throughout the musculature. Muscles having received ASCs showed increased presence of interlukin-10 and Ki67, and decreased inducible nitric oxide synthase (iNOS).

DISCUSSION

This investigation is suggestive that an ASC injection into denervated muscle post-operatively is able to delay the onset of atrophy. Muscle Nerve 59:603-603, 2019.

Bridging larger gaps in peripheral nerves using neural prosthetics and physical therapeutic agents

Peripheral nerve injuries are relatively common and can be caused by a variety of traumatic events such as motor vehicle accidents. They can lead to long-term disability, pain, and financial burden, and contribute to poor quality of life. In this review, we systematically analyze the contemporary literature on peripheral nerve gap management using nerve prostheses in conjunction with physical therapeutic agents. The use of nerve prostheses to assist nerve regeneration across large gaps (> 30 mm) has revolutionized neural surgery. The materials used for nerve prostheses have been greatly refined, making them suitable for repairing large nerve gaps. However, research on peripheral nerve gap management using nerve prostheses reports inconsistent functional outcomes, especially when prostheses are integrated with physical therapeutic agents, and thus warrants careful investigation. This review explores the effectiveness of nerve prostheses for bridging large nerve gaps and then addresses their use in combination with physical therapeutic agents.

Hypoglossal-facial 'side'-to-side Neurorrhaphy Combined with Electrical Myostimulation for Facial Palsy in Rats

Introduction This study investigated the effect of combining hypoglossal-facial nerve “side”-to-side neurorrhaphy and electrical myostimulation in a rat model of facial palsy.

Methods Rats with facial nerve crush injury were subjected to control condition, monotherapy of either neurorrhaphy or electrical myostimulation, or bitherapy of the two treatments. After 1, 3, and 6 months, rats were performed the facial symmetry evaluation, electrophysiological examination and the retrograde labeling of motor neurons.

Results As early as 3 months after injury, face symmetry significantly improved in rats of the bitherapy group. At 3 or 6 months after injury, either the parameters of electrophysiological examination or the number of labeled motor neurons were significantly increased in the bitherapy group than in any other group.

Discussion The combination of neurorrhaphy and electrical myostimulation effectively promoted the functional recovery after facial nerve crush injury.

Electrical stimulation promotes regeneration and re-myelination of axons of injured facial nerve in rats

Objective To investigate the effects of electrical stimulation (ES) on the nerve regeneration and functional recovery of facial expression muscles in facial nerve defect rats. Methods Sixty rats were surgically introduced with a 1-cm defect on the right facial nerves and evenly divided into the Surgery group (Group A, the main trunk of the right facial nerve was surgically cut-off with a 1.0 cm at the foramina stylomastoideum) and the Surgery + ES group (Group B). Twenty normal rats were as normal control group (without receiving surgery or ES). For rats in group B, the orbicularis oris muscle of the right paralyzed face was stimulated with an electrical pulse of 3 V, 20 Hz and 0.3 mA for 1 h each day. The effects of ES on the facial muscle movement, compound muscle action potentials (CMAPs), histological structure, and the expression levels of S100B and NF200 proteins were comparatively studied. Results In group A, facial paralysis scores were slightly improved from day 1 to 28; the facial nerve trunks had swelled and malformed till day 14; and CMAPs could be induced in fewer animals and were abnormal, resulting in a slow recovery of the facial muscle movement. In group B, facial paralysis scores were improved from 4 to 2.6 during the 4 weeks; more rats showed a higher amplitude and shorter latency of CMAPs from day 14 to 28 after surgery; and increased axons and the expression of S100B and NF200 proteins and gradually decreased swelling in the injured facial nerve. Conclusion ES promotes outgrowth and myelination of axons and a partial functional recovery of facial muscles in injured facial nerve rats.

Brief electrical stimulation and synkinesis after facial nerve crush injury: a randomized prospective animal study

BACKGROUND

Recent studies have examined the effects of brief electrical stimulation (BES) on nerve regeneration, with some suggesting that BES accelerates facial nerve recovery. However, the facial nerve outcome measurement in these studies has not been precise or accurate. Furthermore, no previous studies have been able to demonstrate the effect of BES on synkinesis. The objective of this study is to examine the effect of brief electrical stimulation (BES) on facial nerve function and synkinesis in a rat model.

METHODS

Four groups of six rats underwent a facial nerve injury procedure. Group 1 and 2 underwent a crush injury at the main trunk of the nerve, with group 2 additionally receiving BES for 1 h. Group 3 and 4 underwent a transection injury at the main trunk, with group 4 additionally receiving BES for 1 h. A laser curtain model was used to measure amplitude of whisking at 2, 4, and 6 weeks. Fluorogold and fluororuby neurotracers were additionally injected into each facial nerve to measure synkinesis. Buccal and marginal mandibular branches of the facial nerve were each injected with different neurotracers at 3 months following injury. Based on facial nucleus motoneuron labelling of untreated rats, comparison was made to post-treatment animals to deduce whether synkinesis had taken place. All animals underwent trans-cardiac perfusion with subsequent neural tissue sectioning.

RESULTS

At week two, the amplitude observed for group 1 and 2 was 14.4 and 24.0 degrees, respectively (p = 0.0004). Group 4 also demonstrated improved whisking compared to group 3. Fluorescent neuroimaging labelling appear to confirm improved pathway specific regeneration with BES following facial nerve injury.

CONCLUSIONS

This is the first study to use an implantable stimulator for serial BES following a crush injury in a validated animal model. Results suggest performing BES after facial nerve injury is associated with accelerated facial nerve function and improved facial nerve specific pathway regeneration in a rat model.