Peripheral nerve injury and repair

Timing and Predictors of Upper Extremity Peripheral Nerve Reconstruction

Primary neurorrhaphy is the preferred reconstruction modality over nerve grafting, especially for motor nerves. The main limitation to primary repair is often dictated by tension secondary to increased nerve defect length. A retrospective review was conducted on sharp transections of mixed motor and purely sensory nerves in the upper extremity to assess factors influencing defect length. Two groups of either primary repair or nerve graft/conduit were created for comparison. Overall, 71 injured mixed motor nerves and 224 injured sensory nerves were included in the analysis. There were no significant differences in patient demographics between the groups. The primary repair group had a significantly shorter time interval between injury and surgical fixation when compared to the conduit/graft group. Conduit or graft technique was associated with a significantly larger tissue gap after preparation of the nerve ends. Our data suggest that the optimal time for primary repair is within 3 days after injury for mixed nerves and within 7 days for purely sensory nerves. A total of 167 nerve reconstructions were included in a random forest plot, which demonstrated nerve defect size to be influenced by days from injury, type of nerve injured, age, and hypertension. A publicly available 4-feature calculator, nerve evaluation and retraction variability estimator-NERVE, was developed from the forest plot to predict a patient's nerve deficit of ± 3.78 mm on an average, R2=0.89. This calculator could aid surgeons with surgical planning by estimating the potential need of grafts or conduits for reconstruction.

Evaluating motor unit properties after nerve transfer surgery

Nerve transfer surgery (NTS) shows promise in restoring movement to muscles paralyzed by spinal cord (SCI) and peripheral nerve injury (PNI). Yet, motor outcomes vary, and the neurophysiological factors influencing responders and non-responders remain unclear. As the fundamental goal of NTS is to reinnervate paralyzed muscles by creating new motor units (MUs), we examined MU properties after NTS for individuals with SCI and PNI. Nine participants (3 SCI, 6 PNI, 50.3 ± 13.9 years) >18 months post-NTS were evaluated and compared to either age-matched controls (SCI) or the contralateral limb (PNI). We used a sophisticated, signal processing software known as Decomposition-Based Quantitative Electromyography (DQEMG) and near-fiber EMG to examine MU characteristics sampled from needle electromyography signals recorded during low-intensity contractions. The NTS muscle MU potentials (MUP) were larger, and near-fiber MUPs (NFM) were more temporal dispersed than controls. Measures of neuromuscular junction instability were greater in NTS muscles compared to controls (p < 0.05). Firing rates of MU, and MUP phases and turns were not different between groups (p > 0.05). Overall, these data suggest the quality of reinnervation post-surgery requires further investigation as a potential mediator of motor outcome and the required time for successful reinnervation may be longer than currently predicted.

ARA290, an alternative of erythropoietin, inhibits activation of NLRP3 inflammasome in schwann cells after sciatic nerve injury

The challenge of repairing peripheral nerve injury is a critical issue that needs to be addressed urgently. Previous research has shown that erythropoietin (EPO) and its prolonged peptides exhibit beneficial effects in neurological disorders. In our study, we demonstrated that both EPO and pyroglutamic acid helix B surface peptide (pHBSP, also known as ARA290) inhibit the early inflammatory response and promote functional recovery after sciatic nerve crush injury in rat models. Our experimental results demonstrate that significant inflammatory response occurred in Schwann cells after sciatic nerve injury, and that the activation of NLRP3 inflammasome in Schwann cells is inhibited after EPO and ARA290 treatment. Our study further demonstrated that EPO and ARA290 inhibit the activation of NLRP3 inflammasome in Schwann cells by inhibiting NF-κB phosphorylation and reducing reactive oxygen species (ROS) production. In summary, EPO and ARA290 promote repair and regeneration by inhibiting the activation of NLRP3 inflammasome after sciatic nerve injury.

Imaging of Peripheral Nerves: AJR Expert Panel Narrative Review

Peripheral nerve imaging provides information that can be critical to the diagnosis, staging, and management of peripheral neuropathies. MRI and ultrasound are the imaging modalities of choice for clinical evaluation of the peripheral nerves given their high soft-tissue contrast and high resolution, respectively. This AJR Expert Panel Narrative Review describes MRI- and ultrasound-based techniques for peripheral nerve imaging; highlights considerations for imaging in the settings of trauma, entrapment syndromes, diffuse inflammatory neuropathies, and tumor; and discusses image-guided nerve interventions, focusing on nerve blocks and ablation.

Traumatic Versus Nontraumatic Hand Digit Amputations: Neuroma Risk, Prevention Success, and Predictive Factors

PURPOSE

Digital amputations can occur following trauma for a variety of reasons. The objective of the study was to evaluate the difference in neuroma rates between elective and emergent digital amputations and the factors contributing to persistent pain following amputation.

METHODS

A retrospective review of 907 patients treated with digital amputation from 2015 to 2023 met inclusion criteria. Demographic data, comorbidities, body mass index, workers' compensation cases, surgical data, digit (zone) injuries, and indications for surgery were noted. A total of 1,171 amputations were included.

RESULTS

At a median duration of follow-up of 2.6 months (interquartile range, 1.8-6.7), individuals who received elective procedures (n = 401) exhibited a neuroma rate of 4%, whereas those who underwent emergent surgeries (n = 506) had a neuroma rate of 3.2%. Patients were predominantly male (74%) with an average age of 52 years. Comorbidities were more frequent in patients who underwent elective surgeries. One hundred eleven patients had severe stump pain affecting their day-to-day lives, of which 32 (female, 28%) were diagnosed with a neuroma (mean follow-up: 18 months). In neuroma cases, 18 were treated with revision amputations, and 11 had nonsurgical treatments for their neuropathic symptoms. Other factors associated with pain following amputation included: proximal amputations (zones 4 and 5), middle finger amputations, alcohol abuse, tumors, rheumatoid arthritis, blast injury, crush injury, and multiple amputations in revision surgery.

CONCLUSIONS

In this single institutional retrospective study, elective and emergent surgeries had comparable symptomatic neuroma rates. Factors predictive of pain following amputation included more proximal amputations, pre-existing alcohol use, inflammatory arthritis or vasculitis, and blast mechanism. These factors may be selected for patients best suited for prophylactic targeted muscle reinnervation or regenerative peripheral nerve interface surgeries at the time of amputation.

TYPE OF STUDY/LEVEL OF EVIDENCE

Prognostic IV.

Mechanism and Application of Chinese Herb Medicine in Treatment of Peripheral Nerve Injury

Peripheral nerve injury (PNI) encompasses damage to nerves located outside the central nervous system, adversely affecting both motor and sensory functions. Although peripheral nerves possess an intrinsic capacity for self-repair, severe injuries frequently result in significant tissue loss and erroneous axonal junctions, thereby impeding complete recovery and potentially causing neuropathic pain. Various therapeutic strategies, including surgical interventions, biomaterials, and pharmacological agents, have been developed to enhance nerve repair processes. While preclinical studies in animal models have demonstrated the efficacy of certain pharmacological agents in promoting nerve regeneration and mitigating inflammation, only a limited number of these agents have been translated into clinical practice to expedite nerve regeneration. Chinese herb medicine (CHM) possesses a longstanding history in the treatment of various ailments and demonstrates potential efficacy in addressing PNI through its distinctive, cost-effective, and multifaceted methodologies. This review critically examines the advancements in the application of CHM for PNI treatment and nerve regeneration. In particular, we have summarized the most commonly employed and rigorously investigated CHM prescriptions, individual herbs, and natural products, elucidating their respective functions and underlying mechanisms in the context of PNI treatment. Furthermore, we have deliberated on the prospective development of CHM in both clinical practice and fundamental research.

Delayed Repair of Recurrent Motor Branch Injury after Carpal Tunnel Release

Iatrogenic injury to the recurrent motor branch of the median nerve is an uncommon but severe complication following carpal tunnel release. Surgeons should be aware of the anatomical variations of this branch, particularly with the advent of smaller incisions and endoscopic techniques. Here, we present the case of a 60-year-old woman whose recurrent motor branch injury was not identified until 2 years following her index procedure. She underwent a successful primary repair 25 months after her initial injury, with notable improvements in thumb function, strength, and return of thenar muscle bulk beginning 2 months after surgery and continuing through last follow-up at 7 months. Our patient's outcome suggests that repair of a severed recurrent motor branch remains a viable option 2 years after initial injury and that functional improvement and thenar muscle reinnervation can occur even after considerable time has elapsed.

Pain without presence: a narrative review of the pathophysiological landscape of phantom limb pain

Phantom limb pain (PLP) is defined as the perception of pain in a limb that has been amputated. In the United States, approximately 30,000-40,000 amputations are performed annually with an estimated 2.3 million people living with amputations. The prevalence of PLP among amputees is approximately 64%. Over the years, various theories regarding the etiology of PLP have been proposed, with some gaining more prominence than others. Yet, there is a lack of consensus on PLP mechanisms as the current literature exploring the pathophysiology of PLP is multifactorial, involving complex interactions between the central and peripheral nervous systems, psychosocial factors, and genetic influences. This review seeks to enhance the understanding of PLP by exploring its multifaceted pathophysiology, including genetic predispositions. We highlight historical aspects of pain theories and PLP, examining how these theories have expanded to include psychosocial dimensions associated with chronic pain in amputees. Additionally, we present significant findings from both human and animal studies focused on neuroaxial systems and recent advances in molecular research to further elucidate the complex and multifactorial nature of PLP. Ultimately, we hope that the integration of current theoretical frameworks and findings will lay a more robust foundation for future research on PLP.

Angiogenesis-promoting effect of SKP-SC-EVs-derived miRNA-30a-5p in peripheral nerve regeneration by targeting LIF and ANGPT2

Ischemia and hypoxia caused by vascular injury intensify nerve damage. Skin precursor-derived Schwann cells have demonstrated an accelerated in vivo prevascularization of tissue-engineered nerves. Furthermore, extracellular vesicles from skin precursor-derived Schwann cells (SKP-SC-EVs) show the potential in aiding peripheral nerve regeneration. Nonetheless, the capacity of SKP-SC-EVs to facilitate nerve repair via angiogenesis remains uncertain. This study observed that SKP-SC-EVs significantly enhanced angiogenesis, evidenced by increased transparency of the tissue-engineered nerve graft and ultrasonic blood flow imaging. In vitro experiments confirmed that SKP-SC-EVs promote the proliferation, migration, and tube formation of human umbilical vein endothelial cells, a standard model for assessing angiogenic potential. Additionally, a comprehensive miRNA expression profile of SKP-SC-EVs was performed, leading to the identification of potential candidates through functional experiments. Among these, miR-30a-5p emerged as a significant candidate, demonstrating remarkable proangiogenic effects both in vivo and in vitro, akin to the effects of SKP-SC-EVs. Furthermore, luciferase reporter assay and functional experiments revealed that miR-30a-5p in SKP-SC-EVs promotes angiogenesis by targeting ANGPT2 and LIF without sufficient VEGFa. Thus, the enrichment of miR-30a-5p in SKP-SC-EVs indicates its pivotal role as a regulator of angiogenesis, presenting a promising avenue for cell-free treatment of peripheral nerve injury.

Biomechanical modelling infers that collagen content within peripheral nerves is a greater indicator of axial Young's modulus than structure

The mechanical behaviour of peripheral nerves is known to vary between different nerves and nerve regions. As the field of nerve tissue engineering advances, it is vital that we understand the range of mechanical regimes future nerve implants must match to prevent failure. Data on the mechanical behaviour of human peripheral nerves are difficult to obtain due to the need to conduct mechanical testing shortly after removal from the body. In this work, we adapt a 3D multiscale biomechanical model, developed using asymptotic homogenisation, to mimic the micro- and macroscale structure of a peripheral nerve. This model is then parameterised using experimental data from rat peripheral nerves and used to investigate the effect of varying the collagen content, the fibril radius and number density, and the macroscale cross-sectional geometry of the peripheral nerve on the effective axial Young's moduli of the whole nerve. Our results indicate that the total amount of collagen within a cross section has a greater effect on the axial Young's moduli compared to other measures of structure. This suggests that the amount of collagen in a cross section of a peripheral nerve, which can be measured through histological and imaging techniques, is one of the key metrics that should be recorded in the future experimental studies on the biomechanical properties of peripheral nerves.

Peripheral nerve regeneration using a bioresorbable silk fibroin-based artificial nerve conduit fabricated via a novel freeze-thaw process

While silk fibroin (SF) obtained from silkworm cocoons is expected to become a next-generation natural polymer, a fabrication method for SF-based artificial nerve conduits (SFCs) has not yet been established. Here, we report a bioresorbable SFC, fabricated using a novel freeze-thaw process, which ensures biosafety by avoiding any harmful chemical additives. The SFC demonstrated favorable biocompatibility (high hydrophilicity and porosity with a water content of > 90%), structural stability (stiffness, toughness, and elasticity), and biodegradability, making it an ideal candidate for nerve regeneration. We evaluated the nerve-regenerative effects of the SFC in a rat sciatic-nerve-defect model, including its motor and sensory function recovery as well as histological regeneration. We found that SFC transplantation significantly promoted functional recovery and nerve regeneration compared to silicone tubes and was almost equally effective as autologous nerve transplantation. Histological analyses indicated that vascularization and M2 macrophage recruitment were pronounced inside the SFC. These results suggest that the unique properties of the SFC further enhanced the peripheral nerve regeneration mechanism. As no SFC has been applied in clinical practice, the SFC reported herein may be a promising candidate for repairing extensive peripheral nerve defects.

Application of Mesenchymal Stem Cell-Derived Schwann Cell-like Cells Spared Neuromuscular Junctions and Enhanced Functional Recovery After Peripheral Nerve Injury

In general, the nerve cells of the peripheral nervous system regenerate normally within a certain period after the physical damage of their axon. However, when peripheral nerves are transected by trauma or tissue extraction for cancer treatment, spontaneous nerve regeneration cannot occur. Therefore, it is necessary to perform microsurgery to connect the transected nerve directly or insert a nerve conduit to connect it. In this study, we applied human tonsillar mesenchymal stem cell (TMSC)-derived Schwann cell-like cells (TMSC-SCs) to facilitate nerve regeneration and prevent muscle atrophy after neurorrhaphy. The TMSC-SCs were manufactured in a good manufacturing practice facility and termed neuronal regeneration-promoting cells (NRPCs). A rat model of peripheral nerve injury (PNI) was generated and a mixture of NRPCs and fibrin glue was transplanted into the injured nerve after neurorrhaphy. The application of NRPCs and fibrin glue led to the efficient induction of sciatic nerve regeneration, with the sparing of gastrocnemius muscles and neuromuscular junctions. This sparing effect of NRPCs toward neuromuscular junctions might prevent muscle atrophy after neurorrhaphy. These results suggest that a mixture of NRPCs and fibrin glue may be a therapeutic candidate to enable peripheral nerve and muscle regeneration in the context of neurorrhaphy in patients with PNI.

A New Concept in Peripheral Nerve Repair: Incorporating the Tunica Adventitia

BACKGROUND

 Pedicled, prefabricated, and free nerve flaps have several drawbacks, such as requiring microsurgical anastomosis, the need for secondary operations and the risk of developing thrombosis. In this study, we aimed to vascularize the repaired nerve in a single session by establishing a connection between the epineurium of the repaired median nerve and the tunica adventitia of the brachial artery.

METHODS

 The technique was performed on the median nerves of a total of 42 rats over 13 weeks. While group 1 didn't receive any intervention, the following three groups (2, 3, and 4) received classic treatments (coaptation, graft, and vein conduit). In addition to classic treatments, the other three groups (5, 6, and 7) were vascularized by attaching the adventitia of the brachial artery to the repaired nerves. Nerve regeneration was evaluated using functional tests, immunohistochemical analysis, and electron microscope.

RESULTS

 The vascularized groups (5, 6, and 7) showed earlier functional recovery (p < 0.05). Vascularization reduced inflammation in the coaptation group, reduced fibrosis and degeneration in the nerve graft group, and reduced fibrosis, degeneration and disorganization while increased the number of passing fibers and myelination in the vein conduit group (p < 0.05). Vascularization provided superior ultrastructural findings. Microscopic analysis revealed a novel finding of "zone of neurovascular interaction" between the adventitia and the regenerating nerve.

CONCLUSION

 Vascularizing the repaired nerves with this new technique provided faster functional and better histological healing. Unlike classic vascularization techniques, this method does not require microsurgical anastomosis, does not carry the risk of thrombosis, and does not necessitate secondary operations. The "zone of neurovascular interaction" identified in this study revealed regenerating axon clusters alongside newly developed blood vessels. This important finding highlights a potential role of the tunica adventitia in nerve regeneration.

One Size Does Not Fit All: Prediction of Nerve Length in Implant-based Nipple-Areola Complex Neurotization

BACKGROUND

 Breast reconstruction with sensory restoration is gaining recognition as an important goal. Successful reinnervation has been shown in autologous reconstruction but not widely studied in implant-based reconstruction (IBR). This article describes our technique for nipple-areola complex (NAC) neurotization to predict maximal nerve length. We also propose a novel equation that can be utilized preoperatively to estimate the total nerve length required for NAC neurotization.

METHODS

 This is a retrospective study of patients who underwent nerve reconstruction with IBR between April 2021 and May 2022. An equation based on the arc length of a circle was utilized to predict the total nerve length required. Postoperative assessment of sensation was performed at 3, 6, and 12 months using Semmes-Weinstein monofilament testing in all four breast quadrants and the NAC. Patients completed the Breast-Q Sensation Module preoperatively and at 3, 6, and 12 months.

RESULTS

 NAC neurotization was performed in 58 patients undergoing IBR. The average length of intercostal nerve (ICN) harvested was 5.3 cm for staged reconstructions and 5.6 cm for direct-to-implant reconstruction. The average total nerve length (allograft + mobilized ICN) was 12.3 cm. On average, 6.9 cm of nerve allograft was used. The mean difference between total nerve length and predicted nerve length was 0.47 cm (range -3.5 to 4.6 cm). There was a significant improvement in sensory monofilament values measured in all four breast quadrants and the NAC between 3 to 6 and 6 to 12 months postoperatively.

CONCLUSION

 A thorough understanding of sensory anatomy and precise surgical techniques are essential to perform NAC neurotization successfully. Our early results suggest the positive impact of breast sensation on patient quality of life.

Insights Into the Epidemiology of Peripheral Nerve Injuries in the United States: Systematic Review

BACKGROUND

Peripheral nerve injuries (PNI) range from mild neurapraxia to severe transection, leading to significant morbidity. Despite their impact, the societal implications of PNI in the United States are not well understood. This study aims to systematically review the literature on PNI epidemiology in the United States. We hypothesize that this review will reveal significant gaps in the understanding of PNI incidence, demographics, and economic impact.

METHODS

Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, we queried the literature for studies on PNI that reported at least one of the following: incidence rates, demographics, affected nerve distribution, injury mechanisms, surgical intervention rates, and associated direct costs. Exclusion criteria included non-English publications, abstracts, conference proceedings, reviews, or editorials, studies published before 2000, non-US studies, or studies focusing solely on digital nerves or plexus injuries.

RESULTS

Fifteen studies met the inclusion criteria. Data indicate a higher incidence of upper extremity nerve injuries compared with lower extremity injuries. The literature lacks comprehensive reporting on surgical intervention rates, with no recent data since 2013. There is a notable absence of nationwide epidemiological data on PNI mechanisms and recent cost data, with most information over a decade old and primarily focused on inpatient costs, neglecting outpatient visits, physical therapy, and medication expenses.

CONCLUSION

The epidemiological data on PNI are limited and outdated, highlighting the need for further research. Future studies should focus on recent trends in PNI incidence, injury mechanisms, and financial burden, including comprehensive reporting on surgical interventions, to inform strategies aimed at improving patient outcomes and health care resource allocation.

Psychology of nerve injury, repair, and recovery: a systematic review

Background

Peripheral nerve injuries (PNIs) are associated with significant physical and psychological challenges, impacting both functional recovery and quality of life. Despite the physical focus of traditional treatments, psychological factors play a crucial role in the outcomes of PNI repair and recovery.

Objectives

This systematic review aims to evaluate the impact of psychological and social factors on the repair and recovery of peripheral nerve injuries.

Methods

A comprehensive literature search was conducted in PubMed/Medline, EMBASE, and Cochrane databases, covering studies from January 1985 to December 2022. A total of 36,190 records were identified, and after screening with Rayyan AI and applying inclusion criteria, 111 articles were selected for review.

Results

The review highlights that pre-existing psychological conditions, as well as psychological responses to the injury and treatment, significantly influence recovery outcomes in PNI patients. Psychological interventions, when integrated into standard care, may improve functional recovery and quality of life.

Conclusions

Psychosocial factors are critical in the management of PNIs and should be incorporated into treatment algorithms to enhance patient outcomes. Future research should focus on developing and integrating psychological support strategies in PNI treatment protocols.

Early aggressive constriction resection for hourglass-like constriction of peripheral nerve in the upper extremity: a retrospective study

OBJECTIVES

The hourglass like constriction (HGC) of peripheral nerves is a characteristic pathological manifestation of Neuralgic Amyotrophy. Once identified, early surgical intervention is essential. However, the method of surgery is controversial, particularly regarding whether HGC needs to be excised. This study aims to explore the efficacy of early aggressive resection of HGC in the upper limb nerves.

MATERIALS AND METHODS

This retrospective study focuses on 13 nerves of spontaneous upper limb paralysis treated at our hospital from June 2019 to July 2023, in which HGC was identified during surgery. During surgery, epineurectomy and interfascicular neurolysis were performed on the constricted areas. Post-neurolysis, constriction excision was carried out if any of the following conditions were met: (1) A single constriction with constriction ≥75%. (2) Constriction combined with torsion. (3) The presence of ≥2 constrictions. Regular face-to-face follow-ups were conducted postoperatively.

RESULTS

Four cases with a single constriction of less than 75% underwent epineurotomy and interfascicular neurolysis; eight underwent constriction excision, of which four cases with a single constriction and associated torsion had direct end-to-end suturing after excision, and four had more than two constrictions treated with autologous sural nerve grafts. Postoperative follow-ups showed good recovery in all but one case, which had unique pathological features and had underwent only epineurectomy, showing moderate recovery.

CONCLUSIONS

For early surgical treatment of HGCs in peripheral nerves of the upper limbs, if severe constriction, constriction combined with torsion, or the presence of more than two constrictions are identified during surgery, aggressive constriction resection may be a better option.

Epidemiology and regional variance of traumatic peripheral nerve injuries in Sweden: A 15-year observational study

INTRODUCTION

Traumatic peripheral nerve injuries pose significant challenges to healthcare systems and individuals, affecting sensory function, causing neuropathic pain, and impairing quality of life. Despite their impact, comprehensive studies on the epidemiology and regional variance of these injuries are scarce. Understanding the incidence, trends, and anatomical distribution of such injuries is essential for targeted interventions and resource allocation.

METHODS

This observational study utilized register-based data from the Swedish National Patient Register covering the period from 2008 to 2022. Incidence rates, trends, and anatomical distribution of traumatic peripheral nerve injuries were analyzed using descriptive statistics, Poisson regression modeling, and regional comparisons.

RESULTS

Higher incidences of peripheral nerve injuries were observed among men compared to women across all age groups. The hand and wrist were the most commonly affected sites. Regional variations in incidence rates were evident, with some regions consistently exhibiting higher rates compared to others. Notably, a decreasing trend in injuries was observed over the study period.

CONCLUSION

This study underscores the importance of targeted interventions and preventive strategies, considering sex, age, and regional disparities. Further research incorporating individual patient-level data is warranted to enhance our understanding and inform tailored interventions to reduce the burden of these injuries.

Targeted muscle reinnervation in upper extremity amputations

PURPOSE

Targeted muscle reinnervation (TMR) is a relatively recent surgical innovation that involves the coaptation of major peripheral nerves to a recipient motor branch that innervates an expendable muscle target. The original indication for TMR was augmentation and optimization of myoelectric signals in the amputated limb for use of myoelectric prosthetics. Incidentally, surgeons and patients discovered that the technique also could treat and prevent phantom and residual limb pain. TMR is performed at the time of amputation or delayed any time after the amputation, and TMR can also be performed at any level of amputation. In the upper extremity, studies have detailed the various techniques and coaptations possible at each amputation level to create intuitive myoelectric signals and treat neurogenic pain. Treatment of peripheral nerves in the amputee with TMR should be a consideration for all patients with major upper extremity amputations, especially at large institutions able to support multidisciplinary limb salvage teams. This review article summarizes the current literature and authors' techniques and recommendations surrounding TMR in the upper extremity amputee including techniques relevant to each level of upper extremity amputation.

An analysis of differential gene expression in peripheral nerve and muscle utilizing RNA sequencing after polyethylene glycol nerve fusion in a rat sciatic nerve injury model

Application of polyethylene glycol (PEG) to a peripheral nerve injury at the time of primary neurorrhaphy is thought to prevent Wallerian degeneration via direct axolemma fusion. The molecular mechanisms of nerve fusion and recovery are unclear. Our study tested the hypothesis that PEG alters gene expression in neural and muscular environments as part of its restorative properties. Lewis rats underwent unilateral sciatic nerve transection with immediate primary repair. Subjects were randomly assigned to receive either PEG treatment or standard repair at the time of neurorrhaphy. Samples of sciatic nerve distal to the injury and tibialis muscle at the site of innervation were harvested at 24 hours and 4 weeks postoperatively. Total RNA sequencing and subsequent bioinformatics analyses were used to identify significant differences in differentially expressed genes (DEGs) and their related biological pathways (p<0.05) in PEG-treated subjects compared to non-PEG controls. No significant DEGs were identified in PEG-treated sciatic nerve compared to controls after 24 hours, but 1,480 DEGs were identified in PEG-treated tibialis compared to controls. At 4 weeks, 918 DEGs were identified in PEG-treated sciatic nerve, whereas only 3 DEGs remained in PEG-treated tibialis compared to controls. DEGs in sciatic were mostly upregulated (79%) and enriched in pathways present during nervous system development and growth, whereas DEGs in muscle were mostly downregulated (77%) and related to inflammation and tissue repair. Our findings indicate that PEG application during primary neurorrhaphy leads to significant differential gene regulation in the neural and muscular environment that is associated with improved functional recovery in animals treated with PEG compared to sham non-PEG controls. A detailed understanding of key molecules underlying PEG function in recovery after peripheral nerve repair may facilitate amplification of PEG effects through systemic or focal treatments at the time of neurotmesis.

Cutting-Edge Approaches for Nerve Debridement Prior to Repair

Peripheral nerve injuries can be devastating. Although neuropraxic and some axonotmesis injuries will recover spontaneously, nerve repair or reconstruction is required to restore function in high-grade axonotmesis or neurotmesis injuries. The first step of nerve repair or reconstruction is adequate nerve debridement with removal of necrotic and fibrous tissues. Debridement decreases neuroma formation at the repair site and produces an optimal surface for axonal regeneration. This article discusses nerve debridement, including the goals of debridement, debridement techniques, and signs of adequate nerve debridement before repair.

Study on the Role and Mechanism of Exosomes Derived from Dental Pulp Stem Cells in Promoting Regeneration of Myelin Sheath in Rats with Sciatic Nerve Injury

The prognosis of peripheral nerve injury (PNI) is usually poor, and currently, there is no effective treatment for PNI. Studies have shown that exosomes derived from mesenchymal stem cells could promote nerve regeneration by optimizing the function of endogenous Schwann cells (SCs), while the mechanism is unclear. Autophagy, a highly conserved intracellular catabolic process responsible for maintaining cellular homeostasis, has been proved to be involved in the regulation of nerve repair after injury. We explored the effect of exosomes derived from dental pulp stem cells (DPSC-Exos) on the regeneration of myelin sheath in rats with sciatic nerve injury (SNI). In vitro and in vivo experiments were performed to clarify whether the effect of DPSC-Exos is associated with autophagy of SCs and to reveal the mechanism at the molecular level. Our results showed that the SCs of SNI rats exhibited the obvious autophagic characteristics, and the increase of P53 expression was an internal factor of autophagy. Our mechanism research indicated that DPSC-Exos could deliver miR-122-5p from DPSCs into SCs and suppressed the rapamycin (RAPA)-induced autophagy in SCs by inhibiting P53 expression. Rescue experiments showed that both the use of GW4869 and overexpression of exogenous P53 in SCs could reverse the inhibitory effect of DPSCs on the autophagy in SCs from co-culture system. In short, our study indicated that DPSC-Exos could promote the regeneration of the myelin sheath through suppressing the autophagy in SCs caused by PNI via miR-122-5p/P53 pathway; this provides researchers with another option for precise repair of PNI.

Therapeutic roles of coenzyme Q10 in peripheral nerve injury-induced neurosensory disturbances: Mechanistic insights from injury to recovery

Peripheral nerve injuries (PNIs) are prevalent conditions mainly resulting from systemic causes, including autoimmune diseases and diabetes mellitus, or local causes, for example, chemical injury and perioperative nerve injury, which can cause a varying level of neurosensory disturbances (NSDs). Coenzyme Q10 (CoQ10) is an essential regulator of mitochondrial respiration and oxidative metabolism. Here, we review the pathophysiology of NSDs caused by PNIs, the current understanding of CoQ10's bioactivities, and its potential therapeutic roles in nerve regeneration, based on evidence from experimental and clinical studies involving CoQ10 supplementation. In summary, CoQ10 supplementation shows promise as a neuroprotective agent, potentially enhancing treatment efficacy for NSDs by reducing oxidative stress and inflammation. Future studies should focus on well-designed clinical trials with large sample sizes, using CoQ10 formulations with proven bioavailability and varying treatment duration, to further elucidate its neuroprotective effects and to optimize nerve regeneration in PNIs-induced NSDs.

Neutral Red Labeling: A Novel Vital Staining Method for Investigating Central and Peripheral Nervous System Lesions

Multiple sclerosis, neuromyelitis optica, Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy are representative demyelinating diseases of the central and peripheral nervous system. Remyelination by myelin forming cells is important for functional recovery from the neurological deficits caused in the demyelinating diseases. Lysophosphatidylcholine-induced demyelination in mice is commonly used to identify and study the molecular pathways of demyelination and remyelination. However, detection of focally demyelinated lesions is difficult and usually requires sectioning of demyelinated lesions in tissues for microscopic analysis. In this review, we describe the development and application of a novel vital staining method for labeling demyelinated lesions using intraperitoneal injection of neutral red (NR) dye. NR labeling reduces the time and effort required to search for demyelinated lesions in tissues, and facilitates electron microscopic analysis of myelin structures. NR labeling also has the potential to contribute to the elucidation of pathologies in the central and peripheral nervous system and assist with identification of drug candidates that promote remyelination.

Research advancements on nerve guide conduits for nerve injury repair

Peripheral nerve injury (PNI) is one of the most serious causes of disability and loss of work capacity of younger individuals. Although PNS has a certain degree of regeneration, there are still challenges like disordered growth, neuroma formation, and incomplete regeneration. Regarding the management of PNI, conventional methods such as surgery, pharmacotherapy, and rehabilitative therapy. Treatment strategies vary depending on the severity of the injury. While for the long nerve defect, autologous nerve grafting is commonly recognized as the preferred surgical approach. Nevertheless, due to lack of donor sources, neurological deficits and the low regeneration efficiency of grafted nerves, nerve guide conduits (NGCs) are recognized as a future promising technology in recent years. This review provides a comprehensive overview of current treatments for PNI, and discusses NGCs from different perspectives, such as material, design, fabrication process, and composite function.

Extracellular vesicle therapy in neurological disorders

Extracellular vesicles (EVs) are vital for cell-to-cell communication, transferring proteins, lipids, and nucleic acids in various physiological and pathological processes. They play crucial roles in immune modulation and tissue regeneration but are also involved in pathogenic conditions like inflammation and degenerative disorders. EVs have heterogeneous populations and cargo, with numerous subpopulations currently under investigations. EV therapy shows promise in stimulating tissue repair and serving as a drug delivery vehicle, offering advantages over cell therapy, such as ease of engineering and minimal risk of tumorigenesis. However, challenges remain, including inconsistent nomenclature, complex characterization, and underdeveloped large-scale production protocols. This review highlights the recent advances and significance of EVs heterogeneity, emphasizing the need for a better understanding of their roles in disease pathologies to develop tailored EV therapies for clinical applications in neurological disorders.

A tacrolimus-eluting nerve guidance conduit enhances regeneration in a critical-sized peripheral nerve injury rat model

Critical-sized peripheral nerve injuries pose a significant clinical challenge and lead to functional loss and disability. Current regeneration strategies, including autografts, synthetic nerve conduits, and biologic treatments, encounter challenges such as limited availability, donor site morbidity, suboptimal recovery, potential immune responses, and sustained stability and bioactivity. An obstacle in peripheral nerve regeneration is the immune response that can lead to inflammation and scarring that impede the regenerative process. Addressing both the immunological and regenerative needs is crucial for successful nerve recovery. Here, we introduce a novel biodegradable tacrolimus-eluting nerve guidance conduit engineered from a blend of poly (L-lactide-co-caprolactone) to facilitate peripheral nerve regeneration and report the testing of this conduit in 15-mm critical-sized gaps in the sciatic nerve of rats. The conduit's diffusion holes enable the local release of tacrolimus, a potent immunosuppressant with neuro-regenerative properties, directly into the injury site. A series of in vitro experiments were conducted to assess the ability of the conduit to maintain a controlled tacrolimus release profile that could promote neurite outgrowth. Subsequent in vivo assessments in rat models of sciatic nerve injury revealed significant enhancements in nerve regeneration, as evidenced by improved axonal growth and functional recovery compared to controls using placebo conduits. These findings indicate the synergistic effects of combining a biodegradable conduit with localized, sustained delivery of tacrolimus, suggesting a promising approach for treating peripheral nerve injuries. Further optimization of the design and long-term efficacy studies and clinical trials are needed before the potential for clinical translation in humans can be considered.

Aetiologies of iatrogenic occipital nerve injury and outcomes following treatment with nerve decompression surgery

INTRODUCTION

This study analyzed the etiologies and treatment of iatrogenic occipital nerve injuries.

METHODS

Patients with occipital neuralgia (ON) who were screened for occipital nerve decompression surgery were prospectively enrolled. Patients with iatrogenic occipital nerve injuries who underwent nerve decompression surgery were identified. Data included surgical history, pain characteristics, and surgical technique. Outcomes included pain frequency (days/month), duration (h/day), intensity (0-10), migraine headache index (MHI), and patient-reported percent-resolution of pain.

RESULTS

Among the 416 patients with ON, who were screened for occipital nerve decompression surgery, 12 (2.9%) cases of iatrogenic occipital nerve injury were identified and underwent surgical treatment. Preoperative headache frequency was 30 (±0.0) days/month, duration was 19.4 (±6.9) h, and intensity was 9.2 (±0.9). Neuroma excision was performed in 5 cases followed by targeted muscle reinnervation in 3, nerve cap in 1, and muscle burial in 1. In patients without neuromas, greater occipital nerve decompression and/or lesser occipital nerve neurectomy were performed. At the median follow-up of 12 months (IQR 12-12 months), mean pain frequency was 4.0 (±6.6) pain days/month (p < 0.0001), duration was 6.3 (±8.9) h (p < 0.01), and intensity was 4.4 (±2.8) (p < 0.001). Median patient-reported resolution of pain was 85% (56.3%-97.5%) and success rate was (≥50% MHI improvement) 91.7%.

CONCLUSIONS

Iatrogenic occipital nerve injuries can be caused by various surgical interventions, including craniotomies, cervical spine interventions, and scalp tumor resections. The associated pain can be severe and chronic. Iatrogenic ON should be considered in the differential diagnosis of post-operative headaches and can be treated with nerve decompression surgery or neuroma excision with reconstruction of the free nerve end.

Scaffold design considerations for peripheral nerve regeneration

Peripheral nerve injury (PNI) represents a serious clinical and public health problem due to its high incurrence and poor spontaneous recovery. Compared to autograft, which is still the best current practice for long-gap peripheral nerve defects in clinics, the use of polymer-based biodegradable nerve guidance conduits (NGCs) has been gaining momentum as an alternative to guide the repair of severe PNI without the need of secondary surgery and donor nerve tissue. However, simple hollow cylindrical tubes can barely outperform autograft in terms of the regenerative efficiency especially in critical sized PNI. With the rapid development of tissue engineering technology and materials science, various functionalized NGCs have emerged to enhance nerve regeneration over the past decades. From the aspect of scaffold design considerations, with a specific focus on biodegradable polymers, this review aims to summarize the recent advances in NGCs by addressing the onerous demands of biomaterial selections, structural designs, and manufacturing techniques that contributes to the biocompatibility, degradation rate, mechanical properties, drug encapsulation and release efficiency, immunomodulation, angiogenesis, and the overall nerve regeneration potential of NGCs. In addition, several commercially available NGCs along with their regulation pathways and clinical applications are compared and discussed. Lastly, we discuss the current challenges and future directions attempting to provide inspiration for the future design of ideal NGCs that can completely cure long-gap peripheral nerve defects.

Intravenous administration of recombinant Phα1β: Antinociceptive properties and morphine tolerance reversal in a cancer-associated pain model

Cancer-related pain is considered one of the most prevalent symptoms for those affected by cancer, significantly influencing quality of life and treatment outcomes. Morphine is currently employed for analgesic treatment in this case, however, chronic use of this opioid is limited by the development of analgesic tolerance and adverse effects, such as digestive and neurological disorders. Alternative therapies, such as ion channel blockade, are explored. The toxin Phα1β has demonstrated efficacy in blocking calcium channels, making it a potential candidate for alleviating cancer-related pain. This study aims to assess the antinociceptive effects resulting from intravenous administration of the recombinant form of Phα1β (r-Phα1β) in an experimental model of cancer-related pain in mice, tolerant or not to morphine. The model of cancer-induced pain was used to evaluate these effects, with the injection of B16F10 cells, followed by the administration of the r-Phα1β, and evaluation of the mechanical threshold by the von Frey test. Also, adverse effects were assessed using a score scale, the rotarod, and open field tests. Results indicate that the administration of r-Phα1β provoked antinociception in animals with cancer-induced mechanical hyperalgesia, with or without morphine tolerance. Previous administration of r-Phα1β was able to recover the analgesic activity of morphine in animals tolerant to this opioid. r-Phα1β was proved safe for these parameters, as no adverse effects related to motor and behavioral activity were observed following intravenous administration. This study suggests that the concomitant use of morphine and r-Phα1β could be a viable strategy for pain modulation in cancer patients.

Increasing Awareness of Complications of Nerve Injury Following Shoulder Surgery: Preventing Delays in Referral and Treatment

BACKGROUND

Nerve injuries remain a challenging complication after shoulder surgery. While most resolve spontaneously, some require surgical intervention. This study describes the characteristics of patients sustaining nerve injuries following shoulder surgery, evaluates referral patterns to nerve surgeons, and characterizes nerve surgeries performed and their outcomes. Increased awareness of these injuries allows patients and providers to be better informed regarding the appropriate management when these complications occur.

METHODS

A retrospective review of referrals with nerve injuries following shoulder surgery between 2007 and 2015 was performed. The final analysis included 65 patients. Data reviewed included demographics, procedure and anesthesia type, and diagnosis of nerve injury. Time to referral to nerve surgeon and proportional changes in the Disabilities of the Arm, Shoulder, and Hand (DASH) scores were determined. Outcomes were categorized as failed, partially successful, and successful based on final follow-up.

RESULTS

Patients were referred following arthroscopic shoulder surgeries (35.4%), shoulder arthroplasties (24.6%), open shoulder procedures (21.5%), and combined open and arthroscopic procedures (18.5%). The mean time to referral was 7.6 months. Nerve injuries involved brachial plexus (33) and individual and multiple peripheral nerve branches (23 and 7, respectively). Twenty-five (38%) nerve injuries demonstrated spontaneous recovery. Thirty-five patients underwent surgical intervention, of which 27 were successful, 3 were partially successful, and 3 failed.

CONCLUSIONS

This is the largest series of patients with iatrogenic nerve injury following shoulder surgeries to date. Our data demonstrate a lack of timely referral to nerve surgeons, especially after arthroscopy. There continues to be a variable injury pattern even among similar surgeries. Despite this, timely surgical intervention, when indicated, can lead to favorable outcomes.

Dental Pulp Stem Cell-Derived Exosomes Promote Sciatic Nerve Regeneration via Optimizing Schwann Cell Function

Repair strategies for injured peripheral nerve have achieved great progresses in recent years. However, the clinical outcomes remain unsatisfactory. Recent studies have found that exosomes secreted by dental pulp stem cells (DPSC-exos) have great potential for applications in nerve repair. In this study, we evaluated the effects of human DPSC-exos on improving peripheral nerve regeneration. Initially, we established a coculture system between DPSCs and Schwann cells (SCs) in vitro to assess the effect of DPSC-exos on the activity of embryonic dorsal root ganglion neurons (DRGs) growth in SCs. We extracted and labeled human DPSC-exos, which were subsequently utilized in uptake experiments in DRGs and SCs. Subsequently, we established a rat sciatic nerve injury model to evaluate the therapeutic potential of DPSC-exos in repairing sciatic nerve damage. Our findings revealed that DPSC-exos significantly promoted neurite elongation by enhancing the proliferation, migration, and secretion of neurotrophic factors by SCs. In vivo, DPSC-exos administration significantly improved the walking behavior, axon regeneration, and myelination in rats with sciatic nerve injuries. Our study underscores the vast potential of DPSC-exos as a therapeutic tool for tissue-engineered nerve construction.

Pioneering a paradigm shift in tissue engineering and regeneration with polysaccharides and proteins-based scaffolds: A comprehensive review

In the realm of modern medicine, tissue engineering and regeneration stands as a beacon of hope, offering the promise of restoring form and function to damaged or diseased organs and tissues. Central to this revolutionary field are biological macromolecules-nature's own blueprints for regeneration. The growing interest in bio-derived macromolecules and their composites is driven by their environmentally friendly qualities, renewable nature, minimal carbon footprint, and widespread availability in our ecosystem. Capitalizing on these unique attributes, specific composites can be tailored and enhanced for potential utilization in the realm of tissue engineering (TE). This review predominantly concentrates on the present research trends involving TE scaffolds constructed from polysaccharides, proteins and glycosaminoglycans. It provides an overview of the prerequisites, production methods, and TE applications associated with a range of biological macromolecules. Furthermore, it tackles the challenges and opportunities arising from the adoption of these biomaterials in the field of TE. This review also presents a novel perspective on the development of functional biomaterials with broad applicability across various biomedical applications.

Biodegradable Electrospun Conduit with Aligned Fibers Based on Poly(lactic-co-glycolic Acid) (PLGA)/Carbon Nanotubes and Choline Bitartrate Ionic Liquid

Functionally active aligned fibers are a promising approach to enhance neuro adhesion and guide the extension of neurons for peripheral nerve regeneration. Therefore, the present study developed poly(lactic-co-glycolic acid) (PLGA)-aligned electrospun mats and investigated the synergic effect with carbon nanotubes (CNTs) and Choline Bitartrate ionic liquid (Bio-IL) on PLGA fibers. Morphology, thermal, and mechanical performances were determined as well as the hydrolytic degradation and the cytotoxicity. Results revealed that electrospun mats are composed of highly aligned fibers, and CNTs were aligned and homogeneously distributed into the fibers. Bio-IL changed thermal transition behavior, reduced glass transition temperature (Tg), and favored crystal phase formation. The mechanical properties increased in the presence of CNTs and slightly decreased in the presence of the Bio-IL. The results demonstrated a decrease in the degradation rate in the presence of CNTs, whereas the use of Bio-IL led to an increase in the degradation rate. Cytotoxicity results showed that all the electrospun mats display metabolic activity above 70%, which demonstrates that they are biocompatible. Moreover, superior biocompatibility was observed for the electrospun containing Bio-IL combined with higher amounts of CNTs, showing a high potential to be used in nerve tissue engineering.

The Impact of the Number of Sutures on Regeneration in Nerve Repair

PURPOSE

The ideal number of sutures for epineural nerve repair is still unclear. Increased number of sutures increases secondary damage and inflammation to the nerve tissue, which negatively affects nerve regeneration. When the number of sutures decreases, the strength of the nerve repair site decreases and nerve endings are fringed, which also negatively affects nerve regeneration. Therefore, each additional suture is not only beneficial but also detrimental. The aim of this study was to find out the ideal number of sutures for nerve repair.

METHODS

Seventy rats were randomly divided into 5 groups. One of the groups was used as a control group, and right sciatic nerves of the rats in other 4 groups were repaired by using 2, 3, 4, or 6 epineural sutures, respectively, after nerve transection. Biomechanical assessment was performed on the nerves collected from these rats at 5 days of follow-up. Functional and histological analyses were evaluated after 12 weeks of follow-up.

RESULTS

It was found that an increase in the number of sutures enhances resistance to tensile force in general. However, there was no significant biomechanical difference between the 6-sutured group in which the most sutures were used and the 4-sutured group. In functional examinations, overall successful results were obtained in the group with 4 sutures. In histological examinations, there was no statistical difference between the control group, 2-sutured groups, and 4-sutured groups in terms of connective tissue index. However, it was observed that the group with 6 sutures had a higher connective tissue index than the control group and groups with 2 and 4 sutures. In terms of regeneration index, it was found that repair with 4 sutures was superior to repair with 2 and 6 sutures. No difference was found between any of the suture groups according to the diameter change index.

CONCLUSIONS

These results indicate that repair with 4 sutures is the best method of epineural repair that provides both strength and regeneration. These findings will contribute to both the repair of clinically similar nerves and the standardization of rat nerve studies.

Application of Adipose Stem Cells in 3D Nerve Guidance Conduit Prevents Muscle Atrophy and Improves Distal Muscle Compliance in a Peripheral Nerve Regeneration Model

BACKGROUND

Peripheral nerve injuries (PNIs) represent a significant clinical problem, and standard approaches to nerve repair have limitations. Recent breakthroughs in 3D printing and stem cell technologies offer a promising solution for nerve regeneration. The main purpose of this study was to examine the biomechanical characteristics in muscle tissue distal to a nerve defect in a murine model of peripheral nerve regeneration from physiological stress to failure.

METHODS

In this experimental study, we enrolled 18 Wistar rats in which we created a 10 mm sciatic nerve defect. Furthermore, we divided them into three groups as follows: in Group 1, we used 3D nerve guidance conduits (NGCs) and adipose stem cells (ASCs) in seven rats; in Group 2, we used only 3D NGCs for seven rats; and in Group 3, we created only the defect in four rats. We monitored the degree of atrophy at 4, 8, and 12 weeks by measuring the diameter of the tibialis anterior (TA) muscle. At the end of 12 weeks, we took the TA muscle and analyzed it uniaxially at 10% stretch until failure.

RESULTS

In the group of animals with 3D NGCs and ASCs, we recorded the lowest degree of atrophy at 4 weeks, 8 weeks, and 12 weeks after nerve reconstruction. At 10% stretch, the control group had the highest Cauchy stress values compared to the 3D NGC group (0.164 MPa vs. 0.141 MPa, p = 0.007) and the 3D NGC + ASC group (0.164 MPa vs. 0.123 MPa, p = 0.007). In addition, we found that the control group (1.763 MPa) had the highest TA muscle stiffness, followed by the 3D NGC group (1.412 MPa), with the best muscle elasticity showing in the group in which we used 3D NGC + ASC (1.147 MPa). At failure, TA muscle samples from the 3D NGC + ASC group demonstrated better compliance and a higher degree of elasticity compared to the other two groups (p = 0.002 and p = 0.008).

CONCLUSIONS

Our study demonstrates that the combination of 3D NGC and ASC increases the process of nerve regeneration and significantly improves the compliance and mechanical characteristics of muscle tissue distal to the injury site in a PNI murine model.

The fabrication of the chitosan-based bioink for in vitro tissue repair and regeneration: A review

The repair and regeneration of the injured tissues or organs is a major challenge for biomedicine, and the emerging 3D bioprinting technology as a class of promising techniques in biomedical research for the development of tissue engineering and regenerative medicine. Chitosan-based bioinks, as the natural biomaterials, are considered as ideal materials for 3D bioprinting to design and fabricate the various scaffold due to their unique dynamic reversibility and fantastic biological properties. Our review aims to provide an overview of chitosan-based bioinks for in vitro tissue repair and regeneration, starting from modification of chitosan that affect these bioprinting processes. In addition, we summarize the advances in chitosan-based bioinks used in the various 3D printing strategies. Moreover, the biomedical applications of chitosan-based bioinks are discussed, primarily centered on regenerative medicine and tissue modeling engineering. Finally, current challenges and future opportunities in this field are discussed. The combination of chitosan-based bioinks and 3D bioprinting will hold promise for developing novel biomedical scaffolds for tissue or organ repair and regeneration.

Retrograde peripheral nerve regeneration from sensory to motor pathways in rats: a new experimental concept in nerve repair

BACKGROUND

The polarity of nerve grafts does not interfere with axon growth. Our goal was to investigate whether axons can regenerate in a retrograde fashion within sensory pathways and then extend into motor pathways, leading to muscle reinnervation.

METHODS

Fifty-four rats were randomized into four groups. In Group 1, the ulnar nerve was connected end-to-end to the superficial radial nerve after neurectomy of the radial nerve in the axilla. In Group 2, the ulnar nerve was connected end-to-end to the radial nerve distal to the humerus; the radial nerve then was divided in the axilla. In Group 3, the radial nerve was divided in the axilla, but no nerve reconstruction was performed. In Group 4, the radial nerve was crushed in the axilla. Over 6 months, we behaviorally assessed the recovery of toe spread in the right operated-upon forepaw by lifting the rat by its tail and lowering it onto a flat surface. Six months after surgery, rats underwent reoperation, nerve transfers were tested electrophysiologically, and the posterior interosseous nerve (PIN) was removed for histological evaluation.

RESULTS

Rats in the crush group recovered toe spread between 5 and 8 days after surgery. Rats with nerve transfers demonstrated electrophysiological and histological findings of nerve regeneration but no behavioral recovery.

CONCLUSIONS

Ulnar nerve axons regrew into the superficial radial nerve and then into the PIN to reinnervate the extensor digitorum communis. We were unable to demonstrate behavioral recovery because rats cannot readapt to cross-nerve transfer.

Techniques and graft materials for repairing peripheral nerve defects

Peripheral nerve defects refer to damage or destruction occurring in the peripheral nervous system, typically affecting the limbs and face. The current primary approaches to address peripheral nerve defects involve the utilization of autologous nerve transplants or the transplantation of artificial material. Nevertheless, these methods possess certain limitations, such as inadequate availability of donor nerve or unsatisfactory regenerative outcomes post-transplantation. Biomaterials have been extensively studied as an alternative approach to promote the repair of peripheral neve defects. These biomaterials include both natural and synthetic materials. Natural materials consist of collagen, chitosan, and silk, while synthetic materials consist of polyurethane, polylactic acid, and polycaprolactone. Recently, several new neural repair technologies have also been developed, such as nerve regeneration bridging technology, electrical stimulation technology, and stem cell therapy technology. Overall, biomaterials and new neural repair technologies provide new methods and opportunities for repairing peripheral nerve defects. However, these methods still require further research and development to enhance their effectiveness and feasibility.

The Muscle Shortening Maneuver: a noninvasive approach to the treatment of peroneal nerve injury. A case report

BACKGROUND

The treatment of peripheral nerve injuries is a debated topic. The Muscle Shortening Maneuver (MSM), a physiotherapy approach, is noninvasive and free of side effects; it consists of a muscle shortening and a solicitation in traction applied simultaneously.

OBJECTIVE

The focus of this report is to describe the effects of the MSM combined with walking retraining in a patient with incomplete injury of the peroneal nerve.

DESCRIPTION

The patient was a 17-year-old man, who underwent osteotomy surgery of the proximal two-thirds of the fibula, due to an Ewing sarcoma that caused a partial injury of the left peroneal nerve. Our assessment plan of the left ankle movement ability comprised range of movement, muscle strength, and surface electromyography (EMG); and a gait analysis was conducted by using an iPhone application. MSM and walking retraining were administered twice and once a week, respectively, for 4 weeks.

OUTCOMES

The active range of movement substantially improved in dorsiflexion (≥15°), whereas slightly decreased in plantar flexion (-5°). Aside from the tibialis anterior, an increase in muscle strength was detected. Surface EMG showed an increased activation, particularly in the peroneus longus. A decrease in gait speed and step length was recorded from the gait analysis, with a better bilateral symmetry.

CONCLUSIONS

Positive outcomes were reported without evidence of risk or adverse events for the participant.

Immediate sciatic nerve reconstruction using an ipsilateral common peroneal nerve graft at the time of sarcoma resection

BACKGROUND

Concomitant resection of the sciatic nerve along with a malignant tumor is no longer a contraindication for limb-sparing surgery, as most of these patients remain ambulatory. However, sciatic nerve reconstruction after sarcoma resection is not commonly performed. Restoration of nerve function can improve patient quality of life. We describe our experience with four patients who underwent sciatic nerve reconstruction using an ipsilateral common peroneal nerve graft at the time of sarcoma resection.

METHODS

Because of the low chance of peroneal nerve recovery, the ipsilateral peroneal trunk was used as a graft to reconstruct the tibial trunk of the sciatic nerve. Two patients were men and two were women. Mean age was 45.3 years (range, 15-62). Mean sciatic nerve defect length was 9.4 cm (range, 8.5-12.0). Proximal thigh defects (three patients) were reconstructed with a double cable; the one patient with a distal thigh defect underwent single cable reconstruction. Mean operation time was 492 min (range, 428-682).

RESULTS

Mean length of the harvested peroneal trunks was 21 cm (range, 11-26). Mean graft length was 11.9 cm (range, 11-13). Postoperative course was uneventful in all four patients. One patient died of sarcoma lung metastasis and could not be evaluated. Three patients were followed for more than 2 years. Two patients achieved British Medical Research Council grade 4 plantar flexion; the remaining patient achieved grade 5 plantar flexion and grade 4 toe flexion. Semmes-Weinstein monofilament sensory testing showed loss of protective sensation on the plantar surface in all three. Musculoskeletal Tumor Society scores at last follow-up were 60.0%, 70.0%, and 43.3%, respectively.

CONCLUSIONS

Immediate sciatic nerve reconstruction using an ipsilateral common peroneal nerve graft avoids reconstruction delay and scar tissue formation, which is advantageous for nerve recovery. This technique may be considered when sciatic nerve resection is anticipated during sarcoma resection.

Zwitterionic Conductive Hydrogel-Based Nerve Guidance Conduit Promotes Peripheral Nerve Regeneration in Rats

In recent years, conductive biomaterials have been widely used to enhance peripheral nerve regeneration. However, most biomaterials use electronic conductors to increase the conductivity of materials. As information carriers, electronic conductors always transmit discontinuous electrical signals, while biological systems essentially transmit continuous signals through ions. Herein, an ion-based conductive hydrogel was fabricated by simple copolymerization of the zwitterionic monomer sulfobetin methacrylate and hydroxyethyl methacrylate. Benefiting from the excellent mechanical stability, suitable electrical conductivity, and good cytocompatibility of the zwitterionic hydrogel, the Schwann cells cultured on the hydrogel could grow and proliferate better, and dorsal root ganglian had an increased neurite length. The zwitterionic hydrogel-based nerve guidance conduits were then implanted into a 10 mm sciatic nerve defect model in rats. Morphological analysis and electrophysiological data showed that the grafts achieved a regeneration effect close to that of the autologous nerve. Overall, our developed zwitterionic hydrogel facilitates efficient and efficacious peripheral nerve regeneration by mimicking the electrical and mechanical properties of the extracellular matrix and creating a suitable regeneration microenvironment, providing a new material reserve for the repair of peripheral nerve injury.

Mechanisms of Wharton's Jelly-derived MSCs in enhancing peripheral nerve regeneration

Warton's jelly-derived Mesenchymal stem cells (WJ-MSCs) play key roles in improving nerve regeneration in acellular nerve grafts (ANGs); however, the mechanism of WJ-MSCs-related nerve regeneration remains unclear. This study investigated how WJ-MSCs contribute to peripheral nerve regeneration by examining immunomodulatory and paracrine effects, and differentiation potential. To this end, WJ-MSCs were isolated from umbilical cords, and ANGs (control) or WJ-MSCs-loaded ANGs (WJ-MSCs group) were transplanted in injury animal model. Functional recovery was evaluated by ankle angle and tetanic force measurements up to 16 weeks post-surgery. Tissue biopsies at 3, 7, and 14 days post-transplantation were used to analyze macrophage markers and interleukin (IL) levels, paracrine effects, and MSC differentiation potential by quantitative real-time polymerase chain reaction (RT-qPCR) and immunofluorescence staining. The WJ-MSCs group showed significantly higher ankle angle at 4 weeks and higher isometric tetanic force at 16 weeks, and increased expression of CD206 and IL10 at 7 or 14 days than the control group. Increased levels of neurotrophic and vascular growth factors were observed at 14 days. The WJ-MSCs group showed higher expression levels of S100β; however, the co-staining of human nuclei was faint. This study demonstrates that WJ-MSCs' immunomodulation and paracrine actions contribute to peripheral nerve regeneration more than their differentiation potential.

Nerve Regeneration with a Scaffold Incorporating an Absorbable Zinc-2% Iron Alloy Filament to Improve Axonal Guidance

Peripheral nerve damage that results in lost segments requires surgery, but currently available hollow scaffolds have limitations that could be overcome by adding internal guidance support. A novel solution is to use filaments of absorbable metals to supply physical support and guidance for nerve regeneration that then safely disappear from the body. Previously, we showed that thin filaments of magnesium metal (Mg) would support nerve regeneration. Here, we tested another absorbable metal, zinc (Zn), using a proprietary zinc alloy with 2% iron (Zn-2%Fe) that was designed to overcome the limitations of both Mg and pure Zn metal. Non-critical-sized gaps in adult rat sciatic nerves were repaired with silicone conduits plus single filaments of Zn-2%Fe, Mg, or no metal, with autografts as controls. After seventeen weeks, all groups showed equal recovery of function and axonal density at the distal end of the conduit. The Zn alloy group showed some improvements in early rat health and recovery of function. The alloy had a greater local accumulation of degradation products and inflammatory cells than Mg; however, both metals had an equally thin capsule (no difference in tissue irritation) and no toxicity or inflammation in neighboring nerve tissues. Therefore, Zn-2%Fe, like Mg, is biocompatible and has great potential for use in nervous tissue regeneration and repair.

Potential Application of Orofacial MSCs in Tissue Engineering Nerve Guidance for Peripheral Nerve Injury Repair

Injury to the peripheral nerve causes potential loss of sensory and motor functions, and peripheral nerve repair (PNR) remains a challenging endeavor. The current clinical methods of nerve repair, such as direct suture, autografts, and acellular nerve grafts (ANGs), exhibit their respective disadvantages like nerve tension, donor site morbidity, size mismatch, and immunogenicity. Even though commercially available nerve guidance conduits (NGCs) have demonstrated some clinical successes, the overall clinical outcome is still suboptimal, especially for nerve injuries with a large gap (≥ 3 cm) due to the lack of biologics. In the last two decades, the combination of advanced tissue engineering technologies, stem cell biology, and biomaterial science has significantly advanced the generation of a new generation of NGCs incorporated with biological factors or supportive cells, including mesenchymal stem cells (MSCs), which hold great promise to enhance peripheral nerve repair/regeneration (PNR). Orofacial MSCs are emerging as a unique source of MSCs for PNR due to their neural crest-origin and easy accessibility. In this narrative review, we have provided an update on the pathophysiology of peripheral nerve injury and the properties and biological functions of orofacial MSCs. Then we have highlighted the application of orofacial MSCs in tissue engineering nerve guidance for PNR in various preclinical models and the potential challenges and future directions in this field.

Second Harmonic Generation Microscopy as a Novel Intraoperative Assessment of Rat Median Nerve Injury

PURPOSE

Nerves that are functionally injured but appear macroscopically intact pose the biggest clinical dilemma. Second Harmonic Generation (SHG) Microscopy may provide a real-time assessment of nerve damage, with the ultimate goal of allowing surgeons to accurately quantify the degree of nerve damage present. The aim of this study was to demonstrate the utility of SHG microscopy to detect nerve damage in vivo in an animal model.

METHODS

Ten Sprague-Dawley rats were anesthetized and prepared for surgery. After surgical exposure and using a custom-made stretch applicator, the right median nerves were stretched by 20%, corresponding to a high strain injury, and held for 5 minutes. The left median nerve served as a sham control (SC), only being placed in the applicator for 5 minutes with no stretch. A nerve stimulator was used to assess the amount of stimulation required to induce a flicker and contraction of the paw. Nerves were then imaged using a multiphoton laser scanning microscope.

RESULTS

Immediately after injury (day 0), SHG images of SC median nerves exhibited parallel collagen fibers with linear, organized alignment. In comparison with SC nerves, high strain nerves demonstrated artifacts indicative of nerve damage consisting of wavy, undulating fibers with crossing fibers and tears, as well as a decrease in the linear organization, which correlated with an increase in the mean stimulation required to induce a flicker and contraction of the paw.

CONCLUSIONS

Second Harmonic Generation microscopy may provide the ability to detect an acute neural stretch injury in the rat median nerve. Epineurial collagen disorganization correlated with the stimulation required for nerve function.

CLINICAL RELEVANCE

In the future, SHG may provide the ability to visualize nerve damage intraoperatively, allowing for better clinical decision-making. However, this is currently a research tool and requires further validation before translating to the clinical setting.

Focal Application of Neurotrophic Factors Augments Outcomes of Nerve-Muscle-Endplate Grafting Technique for Limb Muscle Reinnervation

BACKGROUND

 We have developed a novel muscle reinnervation technique called "nerve-muscle-endplate grafting (NMEG) in the native motor zone (NMZ)." This study aimed to augment the outcomes of the NMEG-NMZ (NN) by focal application of exogenous neurotrophic factors (ENFs) for limb reinnervation.

METHODS

 Adult rats were used to conduct NN plus ENF (NN/ENF) and autologous nerve grafting (ANG, technique control). The nerve innervating the left tibialis anterior (TA) muscle was resected and the denervated TA was immediately treated with NN/ENF or ANG. For NN procedure, an NMEG pedicle was taken from the lateral gastrocnemius muscle and transferred to the NMZ of the denervated TA. For ANG, the nerve gap was bridged with sural nerve. Three months after treatment, the extent of functional and neuromuscular recovery was assessed by measuring static toe spread, maximal muscle force, wet muscle weight, regenerated axons, and innervated motor endplates (MEPs).

RESULTS

 NN/ENF resulted in 90% muscle force recovery of the treated TA, which is far superior to ANG (46%) and NN alone (79%) as reported elsewhere. Toe spread recovered up to 89 and 49% of the control for the NN/ENF and ANG groups, respectively. The average wet muscle weight was 87 and 52% of the control for muscles treated with NN/ENF and ANG, respectively. The mean number of the regenerated axons was 88% of the control for the muscles treated with NN/ENF, which was significantly larger than that for the ANG-repaired muscles (39%). The average percentage of the innervated MEPs in the NN/ENF-treated TA (89%) was higher compared with that in the ANG-repaired TA (48%).

CONCLUSION

 ENF enhances nerve regeneration and MEP reinnervation that further augment outcomes of NN. The NN technique could be an alternative option to treat denervated or paralyzed limb muscles caused by traumatic nerve injuries or lesions.

Application of Electrical Stimulation to Enhance Axon Regeneration Following Peripheral Nerve Injury

Enhancing axon regeneration is a major focus of peripheral nerve injury research. Although peripheral axons possess a limited ability to regenerate, their functional recovery is very poor. Various activity-based therapies like exercise, optical stimulation, and electrical stimulation as well as pharmacologic treatments can enhance spontaneous axon regeneration. In this protocol, we use a custom-built cuff to electrically stimulate the whole sciatic nerve for an hour prior to transection and repair. We used a Thy-1-YFP-H mouse to visualize regenerating axon profiles. We compared the regeneration of axons from nerves that were electrically stimulated to nerves that were not stimulated (untreated). Electrically stimulated nerves had longer axon growth than the untreated nerves. We detail how variations of this method can be used to measure acute axon growth.

Cell-free therapy based on extracellular vesicles: a promising therapeutic strategy for peripheral nerve injury

Peripheral nerve injury (PNI) is one of the public health concerns that can result in a loss of sensory or motor function in the areas in which injured and non-injured nerves come together. Up until now, there has been no optimized therapy for complete nerve regeneration after PNI. Exosome-based therapies are an emerging and effective therapeutic strategy for promoting nerve regeneration and functional recovery. Exosomes, as natural extracellular vesicles, contain bioactive molecules for intracellular communications and nervous tissue function, which could overcome the challenges of cell-based therapies. Furthermore, the bioactivity and ability of exosomes to deliver various types of agents, such as proteins and microRNA, have made exosomes a potential approach for neurotherapeutics. However, the type of cell origin, dosage, and targeted delivery of exosomes still pose challenges for the clinical translation of exosome therapeutics. In this review, we have focused on Schwann cell and mesenchymal stem cell (MSC)-derived exosomes in nerve tissue regeneration. Also, we expressed the current understanding of MSC-derived exosomes related to nerve regeneration and provided insights for developing a cell-free MSC therapeutic strategy for nerve injury.

Methylcobalamin in Combination with Early Intervention of Low-Intensity Pulsed Ultrasound Potentiates Nerve Regeneration and Functional Recovery in a Rat Brachial Plexus Injury Model

This study evaluated and compared the functional recovery and histopathological outcomes of treatment involving low-intensity pulsed ultrasound (LIPUS) and methylcobalamin (B12) on brachial plexus injury (BPI) in an experimental rat model. Three days after BPI, the rats were assigned to receive either LIPUS or methylcobalamin alone or in combination consecutively for 12 days. Serial changes in sensory and motor behavioral responses, as well as morphological and immunohistochemical changes for substance P (SP), ionized calcium-binding adapter molecule 1 (iba1), brain-derived neurotrophic factor (BDNF), and S100 were examined 28 days after BPI as the outcome measurements. Early intervention of LIPUS and methylcobalamin, whether alone or in combination, augmented the sensory and motor behavioral recovery as well as modulated SP and iba1 expression in spinal dorsal horns, BDNF, and S100 in the injured nerve. Moreover, the combined therapy with its synergistic effect gave the most beneficial effect in accelerating functional recovery. In view of the effective initiation of early recovery of sensory and motor functions, treatment with LIPUS and methylcobalamin in combination has a potential role in the clinical management of early-phase BPI.