Processed nerve allografts for peripheral nerve reconstruction: A multicenter study of utilization and outcomes in sensory, mixed, and motor nerve reconstructions

Repair of Sciatic Nerve Defect in Rats With Acellular Nerve Allograft Carrying Vascular Endothelial Cells

BACKGROUND

Acellular nerve allografts (ANAs) were developed to replace the autologous nerve grafts (ANGs) to fill the peripheral nerve defects. Poor vascularization relative to ANGs has been a limitation of application of ANAs.

METHODS

A total of 60 female Sprague-Dawley rats were assigned 3 groups. The rats in A group received ANGs, the rats in B group received ANAs, and the rats in C group were transplanted with ANA carrying endothelial cells (ANA + ECs). In the 1st, 2nd, 4th, and 12th postoperative weeks, 5 rats were selected from each group for evaluating sciatic function index (SFI), electrophysiology, maximum tetanic force recovery rate, tibialis anterior muscle weights recovery rate, and microvessel density. In the 12th postoperative week, the nerves were harvested and stained with toluidine blue and observed under an electron microscope to compare nerve fibers, myelin width, and G-ratio.

RESULTS

All the rats survived. In the first and second postoperative weeks, more microvessels were found in the ANA + EC group. In the 12th postoperative week, the nerve fibers were more numerous, and G-ratio was smaller in the C group compared with the B group. The compound muscle action potential and maximum tetanic force recovery rate in the tibialis anterior muscle in the C group were better than those in the B group in the 12th postoperative week. The A group showed better performances in electrophysiology, maximum tetanic force, muscle wet weight, and nerve regeneration.

CONCLUSION

ANA + ECs can promote early angiogenesis, promoting nerve regeneration and neurological function recovery.

Material matters: Degradation products affect regenerating Schwann cells

Devices to treat peripheral nerve injury (PNI) must balance many considerations to effectively guide regenerating nerves across a gap and achieve functional recovery. To enhance efficacy, design features like luminal fillers have been explored extensively. Material choice for PNI devices is also critical, as the determining factor of device mechanics, and degradation rate and has increasingly been found to directly impact biological response. This study investigated the ways in which synthetic polymer materials impact the differentiation state and myelination potential of Schwann cells, peripheral nerve glia. Microporous substrates of polycaprolactone (PCL), poly(lactide-co-glycolide) (PLGA) 85:15, or PLGA 50:50 were chosen, as materials already used in nerve repair devices, representing a wide range of mechanics and degradation profiles. Schwann cells co-cultured with dorsal root ganglion (DRG) neurons on the substrates expressed more mature myelination proteins (MPZ) on PLGA substrates compared to PCL. Changes to myelination and differentiation state of glia were reflected in adhesion proteins expressed by glia, including β-dystroglycan and integrin α6, both laminin binding proteins. Importantly, degradation products of the polymers affected glial expression independently of direct attachment. Fast degrading PLGA 50:50 substrates released measurable amounts of degradation products (lactic acid) within the culture period, which may push Schwann cells towards glycolytic metabolism, decreasing expression of early transcription factors like sox10. This study shows the importance of understanding not only material effects on attachment, but also on cellular metabolism which drives myelination responses.

Insights on the Choice and Preparation of the Donor Nerve in Corneal Neurotization for Neurotrophic Keratopathy: A Narrative Review

The article introduces neurotrophic keratopathy (NK), a condition resulting from corneal denervation due to various causes of trigeminal nerve dysfunctions. Surgical techniques for corneal neurotization (CN) have evolved, aiming to restore corneal sensitivity. Initially proposed in 1972, modern approaches offer less invasive options. CN can be performed through a direct approach (DCN) directly suturing a sensitive nerve to the affected cornea or indirectly (ICN) through a nerve auto/allograft. Surgical success relies on meticulous donor nerve selection and preparation, often involving multidisciplinary teams. A PubMed research and review of the relevant literature was conducted regarding the surgical approach, emphasizing surgical techniques and the choice of the donor nerve. The latter considers factors like sensory integrity and proximity to the cornea. The most used are the contralateral or ipsilateral supratrochlear (STN), and the supraorbital (SON) and great auricular (GAN) nerves. Regarding the choice of grafts, the most used in the literature are the sural (SN), the lateral antebrachial cutaneous nerve (LABCN), and the GAN nerves. Another promising option is represented by allografts (acellularized nerves from cadavers). The significance of sensory recovery and factors influencing surgical outcomes, including nerve caliber matching and axonal regeneration, are discussed. Future directions emphasize less invasive techniques and the potential of acellular nerve allografts. In conclusion, CN represents a promising avenue in the treatment of NK, offering tailored approaches based on patient history and surgical expertise, with new emerging techniques warranting further exploration through basic science refinements and clinical trials.

Assessing the Efficacy of Allogeneic Nerve Grafts in Trigeminal Nerve Repair: A Systematic Review

PURPOSE

Our primary objective was to assess the efficacy of allogeneic nerve grafts in inferior alveolar nerve or lingual nerve repair. We hypothesized that using allogeneic nerve grafts would be effective, as evidenced by achieving high rates of functional sensory recovery (FSR). Additionally, we looked if sex, time from injury to repair, etiology of nerve damage, and graft length affected outcomes.

METHODS

A systematic review following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines was conducted. PubMed and Scopus databases were searched using specific search strategies to generate eligible studies. Inclusion criteria encompassed studies reporting use of allogeneic grafts, assessing FSR using either Medical Research Council Scale or Neurosensory Testing, and published within the past 15 years.

RESULTS

Across 10 studies conducted between 2011 and 2023, analysis was performed on 149 patients and 151 reconstructed nerves. Allogeneic nerve grafts showed an average FSR rate of 88.0%. Kaplan-Meier analysis of time to FSR postoperatively revealed that of those achieving FSR, 80% achieved it within 6 months and 98% achieved it by 1 year. The mean graft length was 29.92 mm ± 17.94 mm. The most common etiology for nerve damage was third molar extractions (23.3%). Sex distribution among patients revealed that 85 were female (57.0%) and 64 were male (43.0%).

CONCLUSION

Our primary hypothesis was supported as nerve allografts achieved high rates of FSR. FSR was achieved in normative timeframes, which is 6 to 12 months postoperatively. Furthermore, allografts reduced the risk of posttraumatic trigeminal neuropathy. Time from injury to repair, graft length, etiology of nerve damage, and sex did not affect FSR. As the assessed variables in our study did not affect outcomes, there needs to be a more nuanced approach to understanding and addressing various factors influencing sensory recovery.

The effectiveness of acellular nerve allografts compared to autografts in animal models: A systematic review and meta-analysis

BACKGROUND

Treatment of nerve injuries proves to be a worldwide clinical challenge. Acellular nerve allografts are suggested to be a promising alternative for bridging a nerve gap to the current gold standard, an autologous nerve graft.

OBJECTIVE

To systematically review the efficacy of the acellular nerve allograft, its difference from the gold standard (the nerve autograft) and to discuss its possible indications.

MATERIAL AND METHODS

PubMed, Embase and Web of Science were systematically searched until the 4th of January 2022. Original peer reviewed paper that presented 1) distinctive data; 2) a clear comparison between not immunologically processed acellular allografts and autologous nerve transfers; 3) was performed in laboratory animals of all species and sex. Meta analyses and subgroup analyses (for graft length and species) were conducted for muscle weight, sciatic function index, ankle angle, nerve conduction velocity, axon count diameter, tetanic contraction and amplitude using a Random effects model. Subgroup analyses were conducted on graft length and species.

RESULTS

Fifty articles were included in this review and all were included in the meta-analyses. An acellular allograft resulted in a significantly lower muscle weight, sciatic function index, ankle angle, nerve conduction velocity, axon count and smaller diameter, tetanic contraction compared to an autologous nerve graft. No difference was found in amplitude between acellular allografts and autologous nerve transfers. Post hoc subgroup analyses of graft length showed a significant reduced muscle weight in long grafts versus small and medium length grafts. All included studies showed a large variance in methodological design.

CONCLUSION

Our review shows that the included studies, investigating the use of acellular allografts, showed a large variance in methodological design and are as a consequence difficult to compare. Nevertheless, our results indicate that treating a nerve gap with an allograft results in an inferior nerve recovery compared to an autograft in seven out of eight outcomes assessed in experimental animals. In addition, based on our preliminary post hoc subgroup analyses we suggest that when an allograft is being used an allograft in short and medium (0-1cm, > 1-2cm) nerve gaps is preferred over an allograft in long (> 2cm) nerve gaps.

Neurosensory recovery of inferior alveolar nerve gap reconstruction: a systematic review

Numerous procedures can potentially injure the inferior alveolar nerve during oral and maxillofacial surgery, eventually causing loss or alteration of local sensitivity. When its total rupture occurs, a conduit, such as an autogenous graft, can be used to join it. Due to the morbidity resulting from this technique, alternative forms of sensorineural repair have been investigated. This systematic review includes an electronic search of PubMed, Embase, LILACS, and Web of Science databases, in addition to a grey literature and manual search. Article selection was performed by two independent researchers following a predetermined inclusion criterion: human studies evaluating the regression of sensorineural disorders after any form of grafting (autogenous, allogeneic, and synthetic). Of the 789 studies, 648 were analysed. Only 11 articles met the eligibility criteria. After analysing the results, it was noted that regaining normal sensitivity was uncommon, but the majority of reconstructed nerves recovered their protective abilities. Allografts showed success rates similar to autogenous grafts, making them a viable alternative. However, clinical trials are still needed to provide solid evidence. Prognosis for sensory recovery was impacted by grafting time and patient age.

Surgery for mononeuropathies

Advancement in microsurgical techniques and innovative approaches including greater use of nerve and tendon transfers have resulted in better peripheral nerve injury (PNI) surgical outcomes. Clinical evaluation of the patient and their injury factors along with a shift toward earlier time frame for intervention remain key. A better understanding of the pathophysiology and biology involved in PNI and specifically mononeuropathies along with advances in ultrasound and magnetic resonance imaging allow us, nowadays, to provide our patients with a logical and sophisticated approach. While functional outcomes are constantly being refined through different surgical techniques, basic scientific concepts are being advanced and translated to clinical practice on a continuous basis. Finally, a combination of nerve transfers and technological advances in nerve/brain and machine interfaces are expanding the scope of nerve surgery to help patients with amputations, spinal cord, and brain lesions.

Sensory Outcomes for Inferior Alveolar Nerve Reconstruction with Allograft following Free Fibula Mandible Reconstruction

BACKGROUND

As patient survival with head and neck cancer has improved, treatment goals have had to evolve to focus on improving quality of life. Traditionally, patients who have undergone mandibulectomy are left with an insensate chin and lower lip secondary to resection of the inferior alveolar nerve (IAN). The purpose of this study was to critically evaluate the authors' initial experience using processed nerve allografts (PNA) for IAN reconstruction following oncologic mandibulectomy and reconstruction with free fibula osteocutaneous flaps and to assess their patients' sensory outcomes.

METHODS

The authors performed a retrospective review of the first 32 patients who underwent immediate IAN reconstruction with PNA at the time of oncologic mandibulectomy and mandible reconstruction with free fibula osteocutaneous flaps at The University of Texas M. D. Anderson Cancer Center over a 1-year period. Semmes-Weinstein filament sensory testing was conducted at multiple surgical follow-up appointments to evaluate the quality of sensory recovery.

RESULTS

Thirteen of the 32 patients underwent postoperative Semmes-Weinstein filament testing. All 13 patients demonstrated partial return of sensation. At a mean follow-up of 8.33 months, the average level of sensation was 60.93% that of the unaffected side of the lower lip.

CONCLUSIONS

Patients were consistently afforded improvement in lower lip sensation using PNA-based IAN grafting as an adjunct to free fibula-based mandible reconstruction. The procedure adds no additional surgical morbidity and has shown consistent positive results.

Acellular Nerve Allografts in Major Peripheral Nerve Repairs: An Analysis of Cases Presenting With Limited Recovery

BACKGROUND

Acellular nerve allografts have been used successfully and with increasing frequency to reconstruct nerve injuries. As their use has been expanded to treat longer gap, larger diameter nerve injuries, some failed cases have been reported. We present the histomorphometry of 5 such cases illustrating these limitations and review the current literature of acellular nerve allografts.

METHODS

Between 2014 and 2019, 5 patients with iatrogenic nerve injuries to the median or ulnar nerve reconstructed with an AxoGen AVANCE nerve allograft at an outside hospital were treated in our center with allograft excision and alternative reconstruction. These patients had no clinical or electrophysiological evidence of recovery, and allograft specimens at the time of surgery were sent for histomorphological examination.

RESULTS

Three patients with a median and 2 with ulnar nerve injury were included. Histology demonstrated myelinated axons present in all proximal native nerve specimens. In 2 cases, axons failed to regenerate into the allograft and in 3 cases, axonal regeneration diminished or terminated within the allograft.

CONCLUSIONS

The reported cases demonstrate the importance of evaluating the length and the function of nerves undergoing acellular nerve allograft repair. In long length, large-diameter nerves, the use of acellular nerve allografts should be carefully considered.

Use of acellular dermal matrix in peripheral nerve reconstruction: an experimental study on rat sciatic nerve defect

BACKGROUND

In patients with nerve tissue defects, the use of autologous nerve grafts is the standard method of treatment. Alternatives to autologous, nerve grafts have attracted the attention of reconstructive surgeons. In this study, the results of nerve repairs using acellular dermal matrix (ADM) in an experimental rat sciatic nerve defect model are presented.

METHODS

Thirty-six Sprague-Dawley rats were randomized into 5 groups: Group 1: control group, Group 2: negative control group (n = 6), Group 3: autologous nerve graft group (n = 10), Group 4: donor site entubulated with ADM group (n = 10); and Group 5: nerve graft entubulated with ADM group (n = 10). The animals in each group were evaluated for electrophysiologic functions, gastrocnemius muscle weight and histomorphology on the 3rd and 6th month.

RESULTS

The compound muscle action potential was observed to be distinctly lower in Groups 3, 4 and 5 in comparison to the control group. In Group 4, the gastrocnemius ratio (GCR) values on the 6th month were statistically significantly lower than the GCR values in Group 3 and Group 5, The histological scores and myelinated axonal counts in Group 5 were statistically significantly higher than the values in Group 3 and Group 4.

CONCLUSION

The results of this study showed that wrapping ADM around nerve grafts resulted in better outcomes with respect to nerve healing.

Update on Upper Limb Neuroma Management

Painful terminal neuromas in the upper limb due to nerve injury are common. Neuroma symptoms include a sharp and burning sensation, cold intolerance, dysesthesia, pain, numbness, and paresthesia. These symptoms could have a negative impact on the functional ability of the patient and quality of life. In addition, Prostheses use might be abandoned by amputees due to neuroma-induced pain. Many clinicians face challenges while managing neuromas. Contemporary "active" methods like regenerative peripheral nerve interface (RPNI), targeted muscle reinnervation (TMR), and processed nerve allograft repair (PNA) are replacing the conventional "passive" approaches such as excision, transposition, and implantation techniques. RPNI involves inducing axonal sprouting by transplanting the free end of a peripheral nerve into a free muscle graft. TMR includes reassigning the role of the peripheral nerve by the transfer of the distal end of a pure sensory or a mixed peripheral nerve to a motor nerve of a nearby muscle segment. To give the peripheral nerve a pathway to re-innervate its target tissue, PNA entails implanting a sterile extracellular matrix prepared from decellularized and regenerated human nerve tissue with preserved epineurium and fascicles. Of these, RPNI and TMR appear to hold a promising treatment for nerve-ending neuromas and prevent their relapse. In contrast, PNA may reduce neuroma pain and allow meaningful nerve repair. The aim of this article is to provide an overview of the newer approaches of TMR, RPNI, and PNA and discuss their implications, surgical techniques, and reported consequences.

Nerve regeneration conduit from inverted human umbilical cord vessel in the treatment of proper palmar digital nerve sections

Treatment of digital nerve injuries, particularly in case of a gap, is challenging. Recovery of finger sensitivity is often incomplete and can impair personal and occupational activity. The need for better nerve regeneration has given rise to alternative treatments such as nerve conduits. This study aimed to evaluate the safety and efficacy of a conduit of freeze-dried inverted human umbilical cord vessel for regeneration in digital nerve section. Twenty-three patients with a mean nerve gap of 6.11 mm (range 2-30 mm and static 2-point discrimination (s2PD) > 15 mm underwent surgical repair of digital nerve section using a nerve regeneration conduit. The primary endpoint was recovery of sensitivity after conduit implantation. Secondary endpoints comprised progression of pain, functional symptoms, pressure threshold, hand-specific symptoms and disabilities, and restored innervation. Mean follow-up was 10.1 ± 4.1 months (range 1-14 months). Sensitivity recovered progressively in the months following implantation. There was a mean decrease of 8.54 mm in s2PD between baseline and last follow-up (p < 0.001). Complete innervation recovered in 83.3% of cases at last follow-up. Pressure threshold and hand-related quality of life improved significantly and symptoms due to nerve sectioning (pain, cold intolerance, hypoesthesia, hyperesthesia) resolved almost completely. There were no safety issues related to the nerve conduit. These results indicate that freeze-dried inverted human umbilical vessels can be a safe and effective option as conduit for digital nerve regeneration.

Efficacy of Nerve-Derived Hydrogels to Promote Axon Regeneration Is Influenced by the Method of Tissue Decellularization

Injuries to large peripheral nerves are often associated with tissue defects and require reconstruction using autologous nerve grafts, which have limited availability and result in donor site morbidity. Peripheral nerve-derived hydrogels could potentially supplement or even replace these grafts. In this study, three decellularization protocols based on the ionic detergents sodium dodecyl sulfate (P1) and sodium deoxycholate (P2), or the organic solvent tri-n-butyl phosphate (P3), were used to prepare hydrogels. All protocols resulted in significantly decreased amounts of genomic DNA, but the P2 hydrogel showed the best preservation of extracellular matrix proteins, cytokines, and chemokines, and reduced levels of sulfated glycosaminoglycans. In vitro P1 and P2 hydrogels supported Schwann cell viability, secretion of VEGF, and neurite outgrowth. Surgical repair of a 10 mm-long rat sciatic nerve gap was performed by implantation of tubular polycaprolactone conduits filled with hydrogels followed by analyses using diffusion tensor imaging and immunostaining for neuronal and glial markers. The results demonstrated that the P2 hydrogel considerably increased the number of axons and the distance of regeneration into the distal nerve stump. In summary, the method used to decellularize nerve tissue affects the efficacy of the resulting hydrogels to support regeneration after nerve injury.

Controlling axonal regeneration with acellular nerve allograft limits neuroma formation in peripheral nerve transection: An experimental study in a swine model

BACKGROUND

Symptomatic neuromata are a common indication for revision surgery following amputation. Previously described treatments, including traction neurectomy, nerve transposition, targeted muscle re-innervation, and nerve capping, have provided inconsistent results or are technically challenging. Prior research using acellular nerve allografts (ANA) has shown controlled termination of axonal regrowth in long grafts. The purpose of this study was to determine the ability of a long ANA to prevent neuroma formation following transection of a peripheral nerve in a swine model.

MATERIALS AND METHODS

Twenty-two adult female Yucatan miniature swine (Sus scrofa; 4-6 months, 15-25 kg) were assigned to control (ulnar nerve transection only, n = 10), treatment (ulnar transection and coaptation of 50 mm ANA, n = 10), or donor (n = 2) groups. Nerves harvested from donor group animals were treated to create the ANA. After 20 weeks, the transected nerves including any neuroma or graft were harvested. Both qualitative (nerve architecture, axonal sprouting) and quantitative histologic analyses (myelinated axon number, cross sectional area of nerve tissue) were performed.

RESULTS

Qualitative histologic analysis of control specimens revealed robust axon growth into dense scar tissue. In contrast, the treatment group revealed dwindling axons in the terminal tissue, consistent with attenuated neuroma formation. Quantitative analysis revealed a significantly decreased number of myelinated axons in the treatment group (1232 ± 540) compared to the control group (44,380 ± 7204) (p < .0001). Cross sectional area of nerve tissue was significantly smaller in treatment group (2.83 ± 1.53 mm² ) compared to the control group (9.14 ± 1.19 mm² ) (p = .0012).

CONCLUSIONS

Aberrant axonal growth is controlled to termination with coaptation of a 50 mm ANA in a swine model of nerve injury. These early results suggest further investigation of this technique to prevent and/or treat neuroma formation.

Current Trends in the Reconstruction and Rehabilitation of Jaw following Ablative Surgery

Simple Summary

The Maxilla and mandible provide skeletal support for of the middle and lower third of our faces, allowing for the normal functioning of breathing, chewing, swallowing, and speech. The ablative surgery of jaws in the past often led to serious disfigurement and disruption in form and function. However, with recent strides made in computer-assisted surgery and patient-specific implants, the individual functional reconstruction of the jaw is evolving rapidly and the prompt rehabilitation of both the masticatory function and aesthetics after jaw resection has been made possible. In the present review, the recent advancements in jaw reconstruction technology and future perspectives will be discussed.

Abstract

The reconstruction and rehabilitation of jaws following ablative surgery have been transformed in recent years by the development of computer-assisted surgery and virtual surgical planning. In this narrative literature review, we aim to discuss the current state-of-the-art jaw reconstruction, and to preview the potential future developments. The application of patient-specific implants and the “jaw-in-a-day technique” have made the fast restoration of jaws’ function and aesthetics possible. The improved efficiency of primary reconstructive surgery allows for the rehabilitation of neurosensory function following ablative surgery. Currently, a great deal of research has been conducted on augmented/mixed reality, artificial intelligence, virtual surgical planning for soft tissue reconstruction, and the rehabilitation of the stomatognathic system. This will lead to an even more exciting future for the functional reconstruction and rehabilitation of the jaw following ablative surgery.

Failed Acellular Nerve Allografts: A Critical Review

BACKGROUND

Acellular nerve allograft (ANA) occupies an increasingly prominent role in the treatment of peripheral nerve reconstruction. There is demonstrable efficacy; however, some grafts fail to support axonal regrowth and the reasons for this are unclear. This study examines the ANA experience in a specialized peripheral nerve surgery department to discuss the clinical and histological findings in failed cases.

METHOD

Failed ANA grafts were identified from a prospective database using Medical Research Council Classification (MRCC) S3 and M3 as thresholds for success. Cases in which ANA grafting was indicated for nerve related pain and dysesthesia but where no subjective improvement in symptoms occurred were also included. Patients requiring revision surgery after ANA grafting were also considered failures. Cases were then examined in conjunction with a literature review to identify possible mechanisms of failure, including detailed histological analysis in 2 cases.

RESULTS

Eight failed procedures were identified from a database of 99 separate allograft records on 74 patients. This included procedures for 2 tibial nerves, 2 superficial radial nerves, 2 median nerves, 1 digital nerve and a lateral cord brachial plexus injury (male/female, 5:3; age range, 24-54 years). Allograft length range 25 to 120 mm. One postoperative infection was identified. Histological findings in 2 cases included adequate vascularization of allograft material without subsequent axonal regeneration, a reduction of large myelinated fibers proximal to a tibial nerve allograft in the setting of a chronic injury, and a preference for small rather than large fiber regeneration.

CONCLUSIONS

This article reports instances of ANA graft failure in a variety of contexts, for which the primary reasons for failure remain unclear. The etiology is likely to be multifactorial with both patient, graft and surgeon factors contributing to failure. Further clinical and histological analysis of ANA failures will improve our understanding of the mechanisms of graft failure.

Innovations in Peripheral Nerve Injury: Current Concepts and Emerging Techniques to Improve Recovery

Despite the surgical advances in treatment of peripheral nerve injuries, consistent recovery of function is limited suggesting that a multimodal approach is required to optimize nerve regeneration. This approach should include advanced surgical repair techniques, as well as tissue engineering, cellular therapies, and application of local and systemic modulators of neuroregeneration. Further research is needed to advance these therapies from the laboratory to clinical practice, and to further understand how these treatments and techniques can act in concert to optimize functional nerve regeneration.

Regulation of Schwann Cell and DRG Neurite Behaviors within Decellularized Peripheral Nerve Matrix

Decellularized nerve hydrogels (dNHs) containing bioactive molecules are promising biomaterials for peripheral nerve injury (PNI) treatment and have been extensively applied in clinical and preclinical practice. However, most previous research projects studied their influences on nerve-related cellular behaviors in two dimensions (2D) without taking hydrogel biomechanics into consideration. The molecular mechanisms underlying the beneficial microenvironment provided by dNHs also remain unclear. In this study, dNHs from rat sciatic nerves were prepared, and their effects on Schwann cell (SC) and dorsal root ganglion (DRG) neurite behaviors were evaluated and compared to commercial rat tail type I collagen (Col) hydrogels in three-dimensional (3D) environments. We found that dNHs could promote SC proliferation and neurite outgrowth, and both the hydrogel mechanics and components contributed to the dNH functionalization. Through proteomics analysis, we found that laminin (LAM) and type V collagen (COLV) exclusively and abundantly existed in dNHs. By adding exogenous LAM and COLV into Col hydrogels, we demonstrated that they regulated SC gene expression and that LAM could promote SC spreading and neurite outgrowth, while COLV improved SC proliferation. Lastly, dNHs were fabricated into paper-like, aligned nerve scaffolds through unidirectional freezing to expand the dNH applications in PNI treatment.

[Use of acellular allogeneic nerve transplants for nerve defects of the hand : Experience from a German hand surgery center]

Peripheral nerve injuries are often encountered in traumatological care. The aim of this manuscript is to provide initial data, experiences and performance reports from Germany in the implantation of acellular human nerve transplants in peripheral sensory nerve defects of the hand and to put these data in the context of a comprehensive review of the literature. Of the patients 4 (7 digital nerves) were examined 6 months postoperatively and 5 patients (6 digital nerves) were examined 1 year after the operation (3 were also at the 6‑month examination). All patients had a clinical improvement after nerve reconstruction (≥ S3 according to the classification of sensory recovery of the Medical Research Council modified by Mackinnon and Dellon). Disadvantages of our clinical study are the small number of patients, the inhomogeneity (primary and secondary nerve reconstruction) and the lack of comparison with other nerve reconstruction methods.

Biomaterial and Therapeutic Approaches for the Manipulation of Macrophage Phenotype in Peripheral and Central Nerve Repair

Injury to the peripheral or central nervous systems often results in extensive loss of motor and sensory function that can greatly diminish quality of life. In both cases, macrophage infiltration into the injury site plays an integral role in the host tissue inflammatory response. In particular, the temporally related transition of macrophage phenotype between the M1/M2 inflammatory/repair states is critical for successful tissue repair. In recent years, biomaterial implants have emerged as a novel approach to bridge lesion sites and provide a growth-inductive environment for regenerating axons. This has more recently seen these two areas of research increasingly intersecting in the creation of 'immune-modulatory' biomaterials. These synthetic or naturally derived materials are fabricated to drive macrophages towards a pro-repair phenotype. This review considers the macrophage-mediated inflammatory events that occur following nervous tissue injury and outlines the latest developments in biomaterial-based strategies to influence macrophage phenotype and enhance repair.

Comparison of mesenchymal stem cell attachment efficiency in acellular neural graft for peripheral nerve regeneration

Decellularized nerve allograft is an alternative to autologous nerve graft for nerve defects but has shown inferior clinical outcomes. Mesenchymal stem cells can play a key role in improving nerve regeneration of decellularized nerve allografts. The purpose of this study was to compare different mesenchymal stem cell seeding methods and to find the most efficient way to attach cells to nerve grafts for peripheral nerve regeneration. Wharton's jelly mesenchymal stem cells were collected from human umbilical cords and were seeded in the acellular nerve graft in five different ways as follows: PBS injection, fibrin glue drop, Matrigel drop, bioreactor, and Matrigel injection. A 6-mm sciatic nerve defect of Sprague-Dawley rats was bridged using mesenchymal stem cells-laden acellular nerve grafts according to the five seeding methods. Two days after implantation, the nerve tissue was biopsied and analyzed by the immunofluorescence staining of nuclei. The number of Wharton's jelly mesenchymal stem cells (+ h Nuclei) was counted in the inside, outside, and the total area of the graft sections under 200X magnification. The highest efficiency of mesenchymal stem cell attachment inside the graft and the highest total number of attached mesenchymal stem cells was observed in the group using Matrigel injection (p < 0.0001). This study showed mesenchymal stem cells can be more effectively attached to decellularized nerve graft using the injection method with Matrigel than other static or dynamic seeding methods in vivo.

A Retrospective Case Series of Peripheral Mixed Nerve Reconstruction Failures Using Processed Nerve Allografts

BACKGROUND

Favorable rates of meaningful recovery (≥M3/S3) of processed nerve allografts (PNAs) for mixed and motor nerve injuries have been reported, but there are few reports of patients having complete PNA failure (M0/S0). The purpose of this study was to describe the outcomes, including rate of complete failures, in a case series of patients who underwent PNA for peripheral mixed nerve reconstructions.

METHODS

A retrospective review of outcomes between May 2018 to September 2020 was performed. Consecutive patients who underwent nerve reconstruction (>15 mm) with PNA for a peripheral mixed nerve injury of the upper or lower extremity were eligible. Those who returned to clinic for a 10-month postoperative visit were included in this study. The primary outcome was whether the patient was defined as having a complete failure (M0/S0).

RESULTS

A total of 22 patients underwent a PNA during the time period; 14 patients participated in follow-up and were included (average age: 34.7 years) with a mean follow-up of 11.9 months. The average gap length was 46.4 mm (range 15-110 mm). At their 10-month postoperative visit, no patients had any motor or sensory improvement; all patients were deemed as having complete failure. Four patients underwent or were planned for subsequent revision surgery.

CONCLUSIONS

In this study, we demonstrated a high number of complete failures, with all 14 included patients sustaining a complete failure (100% failure rate) at a minimum 10-month follow-up visit. Failure in this case series was not observed to affect one nerve type, location, or be related to preoperative injury size.

Clinical Outcomes and Patient Satisfaction After Corneal Neurotization

PURPOSE

The aim of this study was to assess clinical outcomes of corneal neurotization (CN) and determine patient perception of postoperative results.

METHODS

This was a retrospective study involving 29 eyes in 28 patients who underwent CN. Chart review data included demographic and clinical history; ophthalmic examination including visual acuity, ocular surface quality, and corneal sensation; surgical technique; and postoperative course. Subjective self-reported patient outcomes of surgical success were also assessed. Only eyes with at least 6 months of follow-up were included in the statistical analysis.

RESULTS

A total of 24 eyes and 23 patients were included in statistical analyses. The median postoperative follow-up time was 12.2 months (interquartile range 10.9-18.5 mo). Twenty-three eyes (92%) achieved improvement in ocular surface quality. Eleven of 13 (85%) demonstrated healing of persistent epithelial defects at their last follow-up. Patients gained a median of 2.3 cm in Cochet-Bonnet esthesiometry measurements of sensation. No significant difference was found between preoperative and postoperative visual acuity. All 17 patients who provided self-assessment of their surgical outcome indicated they would undergo CN again if given the choice. Most of the patients reported that the postoperative pain was tolerable, with a median pain score of 3.0 on a 10-point scale (interquartile range 0.0-4.0). Sixteen patients (94%) reported full or partial return of skin sensation along the donor nerve distribution.

CONCLUSIONS

CN provides improvement in corneal health and sensibility, with high patient satisfaction and minimal postoperative pain and morbidity.

Nerve guidance conduit development for primary treatment of peripheral nerve transection injuries: A commercial perspective

Commercial nerve guidance conduits (NGCs) for repair of peripheral nerve discontinuities are of little use in gaps larger than 30 mm, and for smaller gaps they often fail to compete with the autografts that they are designed to replace. While recent research to develop new technologies for use in NGCs has produced many advanced designs with seemingly positive functional outcomes in animal models, these advances have not been translated into viable clinical products. While there have been many detailed reviews of the technologies available for creating NGCs, none of these have focussed on the requirements of the commercialisation process which are vital to ensure the translation of a technology from bench to clinic. Consideration of the factors essential for commercial viability, including regulatory clearance, reimbursement processes, manufacturability and scale up, and quality management early in the design process is vital in giving new technologies the best chance at achieving real-world impact. Here we have attempted to summarise the major components to consider during the development of emerging NGC technologies as a guide for those looking to develop new technology in this domain. We also examine a selection of the latest academic developments from the viewpoint of clinical translation, and discuss areas where we believe further work would be most likely to bring new NGC technologies to the clinic. STATEMENT OF SIGNIFICANCE: NGCs for peripheral nerve repairs represent an adaptable foundation with potential to incorporate modifications to improve nerve regeneration outcomes. In this review we outline the regulatory processes that functionally distinct NGCs may need to address and explore new modifications and the complications that may need to be addressed during the translation process from bench to clinic.

Clinical Outcomes of Symptomatic Neuroma Resection and Reconstruction with Processed Nerve Allograft

Background:

Neuromas causing sensory disturbance can substantially affect nerve function and quality of life. Historically, passive termination of the nerve end and proximal relocation to muscle or bone has been performed after neuroma resection, but this method does not allow for neurologic recovery or prevent recurrent neuromas. The use of processed nerve allografts (PNAs) for intercalary reconstruction of nerve defects following neuroma resection is reasonable for neuroma management, although reported outcomes are limited. The purpose of this study was to assess the outcomes of pain reduction and functional recovery following neuroma resection and intercalary nerve reconstruction using PNA.

Methods:

Data on outcomes of PNA use for peripheral nerve reconstruction were collected from a multicenter registry study. The registry database was queried for upper extremity nerve reconstruction with PNA after resection of symptomatic neuroma. Patients completing both pain and quantitative sensory assessments were included in the analysis. Improvement in pain-related symptoms was determined via patient self-reported outcomes and/or the visual analog scale. Meaningful sensory recovery was defined as a score of at least S3 on the Medical Research Council Classification scale.

Results:

Twenty-five repairs involving 21 patients were included in this study. The median interval from injury to reconstruction was 386 days, and the average nerve defect length was 31 mm. Pain improved in 80% of repairs. Meaningful sensory recovery was achieved in 88% of repairs.

Conclusion:

Neuroma resection and nerve reconstruction using PNA can reduce or eliminate chronic peripheral nerve pain and provide meaningful sensory recovery.

Comparison of two different decellularization methods for processed nerve allograft

The use of processed nerve allografts as an alternative to autologous nerve grafts, the gold standard treatment for peripheral nerve defects, is increasing. However, it is not widely used in Korea due to cost and insurance issues. Moreover, the main detergent used in the conventional Hudson method is unavailable. Therefore, a new nerve allograft decellularization process is needed. We aimed to compare the traditional Hudson method with a novel decellularization process that may remove cellular content more efficiently while preserving the extracellular matrix (ECM) structure using low concentration sodium dodecyl sulfate (SDS) and nuclease. After each decellularization process, DNA content was measured in nerve tissue. Masson's trichrome staining and scanning electron microscopy were performed to determine the state of preservation of the ECM. A significantly greater amount of DNA content was removed in the novel method, and the ECM structure was preserved in both methods. For the in vivo study, a 15-mm long sciatic nerve defect was created in two groups of Sprague-Dawley rats, and processed nerve allografts decellularized using the Hudson or novel method were transplanted. Functional and histological recovery results were measured 12 weeks post-transplantation. Ankle contracture angle, maximal isometric tetanic force of the tibialis anterior (TA), and the TA mass were compared between the groups, as well as the percent neural tissue (100 × neural area/intrafascicular area). There was no significant difference in functional and histological nerve recovery between the methods. The novel method is appropriate for developing a processed nerve allograft.

Functional and immunological peculiarities of peripheral nerve allografts

This review addresses the accumulating evidence that live (not decellularized) allogeneic peripheral nerves are functionally and immunologically peculiar in comparison with many other transplanted allogeneic tissues. This is relevant because live peripheral nerve allografts are very effective at promoting recovery after segmental peripheral nerve injury via axonal regeneration and axon fusion. Understanding the immunological peculiarities of peripheral nerve allografts may also be of interest to the field of transplantation in general. Three topics are addressed: The first discusses peripheral nerve injury and the potential utility of peripheral nerve allografts for bridging segmental peripheral nerve defects via axon fusion and axon regeneration. The second reviews evidence that peripheral nerve allografts elicit a more gradual and less severe host immune response allowing for prolonged survival and function of allogeneic peripheral nerve cells and structures. Lastly, potential mechanisms that may account for the immunological differences of peripheral nerve allografts are discussed.

Evidence-Based Approach to Timing of Nerve Surgery: A Review

ABSTRACT

Events causing acute stress to the health care system, such as the COVID-19 pandemic, place clinical decisions under increased scrutiny. The priority and timing of surgical procedures are critically evaluated under these conditions, yet the optimal timing of procedures is a key consideration in any clinical setting. There is currently no single article consolidating a large body of current evidence on timing of nerve surgery. MEDLINE and EMBASE databases were systematically reviewed for clinical data on nerve repair and reconstruction to define the current understanding of timing and other factors affecting outcomes. Special attention was given to sensory, mixed/motor, nerve compression syndromes, and nerve pain. The data presented in this review may assist surgeons in making sound, evidence-based clinical decisions regarding timing of nerve surgery.

Properties Regulation and Biological Applications of Decellularized Peripheral Nerve Matrix Hydrogel

Decellularized peripheral nerve matrix hydrogel (DNM-G) has drawn increasing attention in the field of neural tissue engineering, owing to its high tissue-specific bioactivity, drug/cell delivery capability, and multifunctional processability. However, the mechanisms and influencing factors of DNM-G formation have been rarely reported. To enable potential biological applications, the relationship between gelation conditions (including digestion time and gel concentration) and mechanical properties/stability (sol-gel transition temperature, gelation time, nanotopology, and storage modulus) of the DNM-G were systematically investigated in this study. The adequate-digested decellularized nerve matrix solution exhibited higher mechanical property, shorter gelation time, and a lower gelation temperature. A noteworthy increase of β-sheet proportion was identified through Fourier-transform infrared spectroscopy (FTIR) and circular dichroism (CD) characterizations, which suggested the possible major secondary structure formation during the phase transition. Besides, the DNM-G degraded fast that over 70% mass loss was noted after 4 weeks when immersing in PBS. A natural cross-linking agent, genipin, was gently introduced into DNM-G to enhance its mechanical properties and stability without changing its microstructure and biological performance. As a prefabricated scaffold, DNM-G remarkably increased the length and penetration depth of dorsal root ganglion (DRG) neurites compared to collagen gel. Furthermore, the DNM-G promoted the myelination and facilitated the formation of the morphological neural network. Finally, we demonstrated the feasibility of applying DNM-G in support-free extrusion-based 3D printing. Overall, the mechanical and biological performance of DNM-G can be manipulated by tuning the processing parameters, which is key to the versatile applications of DNM-G in regenerative medicine.

Effectiveness and Biocompatibility of Decellularized Nerve Graft Using an In Vivo Rat Sciatic Nerve Model

BACKGROUND

Decellularized nerve allografting is one of promising treatment options for nerve defect. As an effort to develop more efficient nerve graft, recently we have developed a new decellularization method for nerve allograft. The aim of this study was to evaluate the effectiveness and biocompatibility of nerve graft decellularized by our newly developed method.

METHODS

Forty-eight inbred male Lewis rats were divided into two groups, Group I (autograft group, n = 25), Group II (decellularized isograft group, n = 23). Decellularized nerve grafts were prepared with our newly developed methods using amphoteric detergent and nuclease treatment. Serum cytokine level measurements at 0, 2, and 4 weeks and histologic evaluation for inflammatory cell infiltration at 6 and 16 weeks after nerve graft.

RESULTS

There was no significant difference in mean maximum isometric tetanic force and weight of tibialis anterior muscle or ankle angle at toe-off phase between two groups at 6 and 16 weeks survival time points (p > 0.05). There was no inflammatory cell infiltration in either group and histomorphometric assessments of 6- and 16-week specimens of the isograft group did not differ from those in the autograft group with regard to number of fascicle, cross sectional area, fascicle area ratio, and number of regenerated nerve cells.

CONCLUSION

Based on inflammatory reaction, axonal regeneration, and functional outcomes, our newly developed decellularized nerve grafts were fairly biocompatible and had comparable effectiveness to autografts for nerve regeneration, which suggested it would be suitable for nerve reconstruction as an alternative to autograft.

Facial Reanimation and Reconstruction of the Radical Parotidectomy

Radical parotidectomy may result from treating advanced parotid malignancies invading the facial nerve. Survival is often enhanced with multimodality treatment protocols, including postoperative radiation therapy. In addition to the reconstructive challenge of restoring facial nerve function, patients may be left with a significant cervicofacial concavity and inadequate skin coverage. This should be addressed with stable vascularized tissue that is resistant to radiation-induced atrophy. This article describes a comprehensive strategy, includes the use of the anterolateral thigh free flap, the temporalis regional muscle transfer, motor nerve to vastus lateralis grafts, nerve to masseter transfer, and fascia lata grafts for static suspension.

Intraneural fibrosis and loss of microvascular architecture - Key findings investigating failed human nerve allografts

BACKGROUND

Processed nerve allografts are increasingly used in clinical nerve reconstruction with promising results. However, allograft failure has been reported, leading to chronic pain and persistent loss of function. In the present work, we performed a histological and immunohistochemical analysis of two failed allograft reconstructions of a sensory human nerve one year after primary surgery.

METHODS

Two patients with a superficial radial nerve injury underwent nerve reconstruction with processed nerve allografts. The clinical follow-up was complicated by severe neuropathic pain and absent sensory reinnervation. Consequently, the failed allografts were excised with subsequent histological and immunohistochemical examinations. For that purpose, the collagen content and neurofilament network as well as the blood and lymphatic vasculature were analysed in the center of the specimens.

RESULTS

Histology revealed increased fibrosis, fatty degeneration, and disorganised proliferation of nerve fibres. Moreover, the microvascular network within the allografts was characterised by increased numbers of microvessels, whereas no difference was found concerning the lymphatic vasculature.

CONCLUSION

The herein presented histological and immunohistochemical findings indicate that the failure of human allografts is associated with loss of the physiological microvascular architecture. Future studies elucidating the complex interplay of angiogenesis, lymphangiogenesis and axonal regeneration are required to better understand the mechanisms of human allograft failure.

Clinical Outcome for Surgical Treatment of Traumatic Neuroma With a Processed Nerve Allograft: Results of a Small Prospective Case Series

Processed nerve allografts are used increasingly in the treatment of traumatic neuroma in small sensory nerves. The goal of the present study was to investigate the use of an allograft after different intervals between injury and repair and to analyze results, not only for the success of pain relief, but also for potential recovery of sensation in time. Four patients with painful neuroma in small sensory nerves in the lower extremity were surgically treated with a decellularized allograft. Patients were followed prospectively for at least 1 y. Clinical outcome was assessed using the Likert scale. Recovery of sensation was tested using Semmes-Weinstein monofilaments. In all 4 cases an allograft of 3-cm was used to reconstruct a defect in the superficial peroneal (3) or sural nerve (1) after excision of the neuroma. Complete relief of pain symptoms was achieved in 2 patients: 1 case concerned the reconstruction of a neuroma with an interval of less than 1 y between injury and repair and 1 case a neuroma-in-continuity. Sensation recovered completely in these 2 cases. In the other 2 cases, that had an interval between injury and reconstruction of more than 1 y, there was neither successful pain relief nor recovery of sensation. This prospective study shows that processed nerve allografts can be successful for the reconstruction of small sensory nerves after excision of the traumatic neuroma both for recovery of pain and sensation, but in this small case series only if the interval between injury and reconstruction was <1 y.

Bioactive Nanofiber-Based Conduits in a Peripheral Nerve Gap Management-An Animal Model Study

The aim was to examine the efficiency of a scaffold made of poly (L-lactic acid)-co-poly(ϵ-caprolactone), collagen (COL), polyaniline (PANI), and enriched with adipose-derived stem cells (ASCs) as a nerve conduit in a rat model. P(LLA-CL)-COL-PANI scaffold was optimized and electrospun into a tubular-shaped structure. Adipose tissue from 10 Lewis rats was harvested for ASCs culture. A total of 28 inbred male Lewis rats underwent sciatic nerve transection and excision of a 10 mm nerve trunk fragment. In Group A, the nerve gap remained untouched; in Group B, an excised trunk was used as an autograft; in Group C, nerve stumps were secured with P(LLA-CL)-COL-PANI conduit; in Group D, P(LLA-CL)-COL-PANI conduit was enriched with ASCs. After 6 months of observation, rats were sacrificed. Gastrocnemius muscles and sciatic nerves were harvested for weight, histology analysis, and nerve fiber count analyses. Group A showed advanced atrophy of the muscle, and each intervention (B, C, D) prevented muscle mass decrease (p < 0.0001); however, ASCs addition decreased efficiency vs. autograft (p < 0.05). Nerve fiber count revealed a superior effect in the nerve fiber density observed in the groups with the use of conduit (D vs. B p < 0.0001, C vs. B p < 0.001). P(LLA-CL)-COL-PANI conduits with ASCs showed promising results in managing nerve gap by decreasing muscle atrophy.

Surgical Treatment of Abdominal Wall Neuromas

Neuromas are an under-recognized contributor to chronic abdominal pain. Other than after mesh inguinal hernia repair, surgical management of painful abdominal wall neuromas has not been well established in the literature.

Evidence-Based Approach to Nerve Gap Repair in the Upper Extremity: A Review of the Literature and Current Algorithm for Surgical Management

The upper extremity is the most common site for nerve injuries. In most cases, direct repair can be performed, but when a critical gap occurs, special techniques must be used to enhance nerve regeneration and allow recovery of sensory and motor functions. These techniques include the use of autografts, processed nerve allografts, and conduits. However, surprisingly few studies have compared outcomes from the different methods of nerve gap repair in a rigorous fashion. There is a lack of evidence-based guidelines for the management of digital and motor and mixed nerve injuries with a nerve gap. The purpose of this study is to perform a comprehensive literature review and propose a rational algorithm for management of nerve injuries with a critical gap.

Nerve Reconstruction Using Processed Nerve Allograft in the U.S. Military

BACKGROUND

Processed nerve allograft (PNA) is an alternative to autograft for the reconstruction of peripheral nerves. We hypothesize that peripheral nerve repair with PNA in a military population will have a low rate of meaningful recovery (M ≥ 3) because of the frequency of blasting mechanisms and large zones of injury.

METHODS

A retrospective review of the military Registry of Avance Nerve Graft Evaluating Utilization and Outcomes for the Reconstruction of Peripheral Nerve Discontinuities database was conducted at the Walter Reed Peripheral Nerve Consortium. All adult active duty military patients who underwent any peripheral nerve repair with PNA for complete nerve injuries augmented with PNA visit were included. Motor strength and sensory function were reported as a consensus from the multidisciplinary Peripheral Nerve Consortium. Motor and sensory testing was conducted in accordance with the British Medical Research Council.

RESULTS

A total of 23 service members with 25 nerve injuries (3 sensory and 22 mixed motor/sensory) underwent reconstruction with PNA. The average age was 30 years and the majority were male (96%). The most common injury was to the sciatic nerve (28%) from a complex mechanism (gunshot, blast, compression, and avulsion). The average defect was 77 mm. Twenty-four percent of patients achieved a meaningful motor recovery. Longer follow-up was correlated with improved postoperative motor function (r = 0.49 and P = .03).

CONCLUSIONS

The military population had complex injuries with large nerve gaps. Despite the low rate of meaningful recovery (27.3%), large gaps in motor and mixed motor/sensory nerves are difficult to treat, and further research is needed to determine if autograft would achieve superior results.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic, Level III.

Inferior alveolar nerve allogenic repair following mandibulectomy: A systematic review

PURPOSE

Processed nerve allografts (PNA) are an alternative to nerve autografts to reconstruct the inferior alveolar nerve (IAN) when it is damaged. The purpose of this study was to report the results of IAN reconstruction using PNA in the context of aggressive benign mandibular pathology.

MATERIAL AND METHOD

A systematic literature review was performed according to the Preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) statement through the MEDLINE (Pubmed) and SCOPUS (Elsevier) databases. Studies concerning reconstructive surgeries of IAN by PNA, performed at the same time as the surgical resection of the benign pathologies of the mandible were included. The following data were analyzed: gender and patient age, cause of mandibular resection, graft dimensions, sensory recovery at least 6 months after surgery according to the MRC scale, and adverse events related to the intervention.

RESULTS

The initial search yielded 290 studies and 5 were included in the final review. A total of 33 patients underwent 36 IAN reconstructions; 14 patients were female (42.4%) and mean age was 30 years old. The mean length of graft used was 64.0 ± 9.1 mm. The most common pathology that led to nerve resection was ameloblastoma (52%). Among the reconstructions for which follow-up data were available, functional sensory recovery occurred in 92.9% of cases.

CONCLUSION

PNA are a reliable, safe, and effective alternative to nerve autografts for the rehabilitation of the IAN with 92.9% of functional recovery according to the reported literature, avoiding any comorbidity associated with the use of a donor site.

Facial Nerve Repair: Bioengineering Approaches in Preclinical Models

Injury to the facial nerve can occur after different etiologies and range from simple transection of the branches to varying degrees of segmental loss. Management depends on the extent of injury and options include primary repair for simple transections and using autografts, allografts, or conduits for larger gaps. Tissue engineering plays an important role to create artificial materials that are able to mimic the nerve itself without extra morbidity in the patients. The use of neurotrophic factors or stem cells inside the conduits or around the repair site is being increasingly studied to enhance neural recovery to a greater extent. Preclinical studies remain the hallmark for development of these novel approaches and translation into clinical practice. This review will focus on preclinical models of repair after facial nerve injury to help researchers establish an appropriate model to quantify recovery and analyze functional outcomes. Different bioengineered materials, including conduits and nerve grafts, will be discussed based on the experimental animals that were used and the defects introduced. Future directions to extend the applications of processed nerve allografts, bioengineered conduits, and cues inside the conduits to induce neural recovery after facial nerve injury will be highlighted.

Reconstruction of Critical Nerve Defects Using Allogenic Nerve Tissue: A Review of Current Approaches

Regardless of the nerve defect length, nerve injury is a debilitating condition for the affected patient that results in loss of sensory and motor function. These functional impairments can have a profound impact on the patient’s quality of life. Surgical approaches for the treatment of short segment nerve defects are well-established. Autologous nerve transplantation, considered the gold standard, and the use of artificial nerve grafts are safe and successful procedures for short segment nerve defect reconstruction. Long segment nerve defects which extend 3.0 cm or more are more problematic for repair. Methods for reconstruction of long defects are limited. Artificial nerve grafts often fail to regenerate and autologous nerve grafts are limited in length and number. Cadaveric processed/unprocessed nerve allografts are a promising alternative in nerve surgery. This review gives a systematic overview on pre-clinical and clinical approaches in nerve allograft transplantation.

Local FK506 drug delivery enhances nerve regeneration through fresh, unprocessed peripheral nerve allografts

OBJECTIVE

Nerve allografts offer many advantages in the reconstruction of peripheral nerve gaps: they retain their native microstructure, contain pro-regenerative Schwann cells, are widely available, and avoid donor site morbidity. Unfortunately, clinical use of nerve allografts is limited by the need for systemic immunosuppression and its adverse effects. To eliminate the toxicity of the systemic immunosuppressant FK506, we developed a local FK506 drug delivery system (DDS) to provide drug release over 28 days. The study objective was to investigate if the local FK506 DDS enhances nerve regeneration in a rodent model of nerve gap defect reconstruction with immunologically-disparate nerve allografts.

METHODS

In male Lewis rats, a common peroneal nerve gap defect was reconstructed with either a 20 mm nerve isograft from a donor Lewis rat or a 20 mm fresh, unprocessed nerve allograft from an immunologically incompatible donor ACI rat. After 4 weeks of survival, nerve regeneration was evaluated using retrograde neuronal labelling, quantitative histomorphometry, and serum cytokine profile.

RESULTS

Treatment with both systemic FK506 and the local FK506 DDS significantly improved motor and sensory neuronal regeneration, as well as histomorphometric indices including myelinated axon number. Rats with nerve allografts treated with either systemic or local FK506 had significantly reduced serum concentrations of the pro-inflammatory cytokine IL-12 compared to untreated vehicle control rats with nerve allografts. Serum FK506 levels were undetectable in rats with local FK506 DDS.

INTERPRETATION

The local FK506 DDS improved motor and sensory nerve regeneration through fresh nerve allografts to a level equal to that of either systemic FK506 or nerve isografting. This treatment may be clinically translatable in peripheral nerve reconstruction or vascularized composite allotransplantation.

Management of Acute Facial Nerve and Parotid Injuries

Acute soft tissue trauma to the head and neck is a common reason for emergency department presentation and should be appropriately evaluated by a facial plastic surgeon. The evaluation of a patient who has suffered facial trauma should always include a comprehensive facial nerve exam and carry a low threshold of suspicion for parotid duct injury when involving the cheek. Injuries to the facial nerve and parotid duct can result in significant long-term functional, cosmetic, and emotional morbidity, particularly when diagnosis is delayed. In the repair of facial nerve transection, neurorrhaphy technique is primarily based on the ability to obtain tension-free anastomosis and outcomes are in large part related to timing of repair. Parotid duct injuries are generally repaired based on the site of ductal injury. In this article, we present a guide to the relevant anatomy of the facial nerve branches and the parotid duct, the important factors guiding treatment decisions alongside their related risks and benefits, as well as the management of complications of facial nerve neurorrhaphy and parotid duct injuries and repair.

Effects of surface condition of conductive electrospun nanofiber mats on cell behavior for nerve tissue engineering

Electrospun nanofibrous scaffold is a promising implant for peripheral nerve regeneration. Herein, to investigate the effect of surface morphological features and electrical properties of scaffolds on nerve cell behavior, we modified electrospun cellulose (EC) fibrous mats with four kind of soluble conductive polymers derivates (poly (N-(methacryl ethyl) pyrrole) (PMAEPy), poly (N-(2-hydroxyethyl) pyrrole) (PHEPy), poly (3-(Ethoxycarbonyl) thiophene) (P3ECT) and poly (3-thiophenethanol) (P3TE)) by an in-situ polymerization method. The morphological characterization showed that conductive polymers formed aggregated nanoparticles and coatings on the EC nanofibers with the increased fiber diameter further affected the surface properties. Compared with pure EC scaffold, more PC12 cells were adhered and grown on modified mats, with more integral and clearer cell morphology. The results of protein adsorption study indicated that modified EC mats could provide more protein adsorption site due to their characteristic surface morphology, which is beneficial to cell adhesion and growth. The results in this study suggested that these conductive polymers modified scaffolds with special surface morphology have potential applications in neural tissue engineering.

Immediate allograft reconstruction of the infraorbital nerve following resection of polyostotic fibrous dysplasia lesion

Processed nerve allografts (PNA) have increasingly been used as alternative to autogenous nerve grafts to repair nerve injuries in oral-maxillofacial surgeries. This case report describes an immediate PNA reconstruction of infraorbital nerve injury sustained during the ablation of a large expansile polyostotic fibrous dysplasia centered in the left maxilla.

Spider silk nerve graft promotes axonal regeneration on long distance nerve defect in a sheep model

Peripheral nerve injuries with substantial tissue loss require autologous nerve transplantation or alternatively reconstruction with nerve conduits. Axonal elongation after nerve transection is about 1 mm/day. The precise time course of axonal regeneration on an ultrastructural level in nerve gap repair using either autologous or artificial implants has not been described. As peripheral nerve regeneration is a highly time critical process due to deterioration of the neuromuscular junction, this in vivo examination in a large animal model was performed in order to investigate axonal elongation rates and spider silk material degradation in a narrowly delimited time series (20, 30, 40, 50, 90, 120, 150 and 180 days) by using a novel spider silk based artificial nerve graft as a critical prerequisite for clinical translation. Autologous nerves or artificial nerve conduits based on spider silk of the spider species Trichonephila edulis were transplanted in a 6.0 cm nerve defect model in the black headed mutton. At each of the post-implant time point, electrophysiology recordings were performed to assess functional reinnervation of axonal fibers into the implants. Samples were analyzed by histology and immunofluorescence in order to verify the timeline of axonal regeneration including axonal regeneration rates of the spider silk implant and the autologous transplant groups. Spider silk was degraded within 3 month by a light immune response mainly mediated by Langhans Giant cells. In conjunction with behavioral analysis and electrophysiological measurements, the results indicate that the spider silk nerve implant supported an axonal regeneration comparable to an autologous nerve graft which is the current gold standard in nerve repair surgery. These findings indicate that a biomaterial based spider silk nerve conduit is as effective as autologous nerve implants and may be an important approach for long nerve defects.