Management of nerve gaps: autografts, allografts, nerve transfers, and end-to-side neurorrhaphy

Peripheral nerve regeneration with conduits: use of vein tubes

Treatment of peripheral nerve injuries remains a challenge to modern medicine due to the complexity of the neurobiological nerve regenerating process. There is a greater challenge when the transected nerve ends are not amenable to primary end-to-end tensionless neurorraphy. When facing a segmental nerve defect, great effort has been made to develop an alternative to the autologous nerve graft in order to circumvent morbidity at donor site, such as neuroma formation, scarring and permanent loss of function. Tubolization techniques have been developed to bridge nerve gaps and have been extensively studied in numerous experimental and clinical trials. The use of a conduit intends to act as a vehicle for moderation and modulation of the cellular and molecular ambience for nerve regeneration. Among several conduits, vein tubes were validated for clinical application with improving outcomes over the years. This article aims to address the investigation and treatment of segmental nerve injury and draw the current panorama on the use of vein tubes as an autogenous nerve conduit.

Nerve cross-bridging to enhance nerve regeneration in a rat model of delayed nerve repair

There are currently no available options to promote nerve regeneration through chronically denervated distal nerve stumps. Here we used a rat model of delayed nerve repair asking of prior insertion of side-to-side cross-bridges between a donor tibial (TIB) nerve and a recipient denervated common peroneal (CP) nerve stump ameliorates poor nerve regeneration. First, numbers of retrogradely-labelled TIB neurons that grew axons into the nerve stump within three months, increased with the size of the perineurial windows opened in the TIB and CP nerves. Equal numbers of donor TIB axons regenerated into CP stumps either side of the cross-bridges, not being affected by target neurotrophic effects, or by removing the perineurium to insert 5-9 cross-bridges. Second, CP nerve stumps were coapted three months after inserting 0-9 cross-bridges and the number of 1) CP neurons that regenerated their axons within three months or 2) CP motor nerves that reinnervated the extensor digitorum longus (EDL) muscle within five months was determined by counting and motor unit number estimation (MUNE), respectively. We found that three but not more cross-bridges promoted the regeneration of axons and reinnervation of EDL muscle by all the CP motoneurons as compared to only 33% regenerating their axons when no cross-bridges were inserted. The same 3-fold increase in sensory nerve regeneration was found. In conclusion, side-to-side cross-bridges ameliorate poor regeneration after delayed nerve repair possibly by sustaining the growth-permissive state of denervated nerve stumps. Such autografts may be used in human repair surgery to improve outcomes after unavoidable delays.

Management and complications of traumatic peripheral nerve injuries

This article provides an overview of the management of traumatic peripheral nerve injuries. It examines the basic pathophysiology of peripheral nerve injuries, along with the clinical presentation, diagnostic work-up, and treatment options and outcomes for the various classifications of traumatic peripheral nerve injuries.

Power tool injuries to the hand and wrist

Power tool injuries to the hand and wrist are complex injuries which can have a profound impact on the function of the patient. This article gives an overview of the principles, and provides a systematic approach, to the management and rehabilitation of the injured limb and patient required to minimize future disability.

Biocompatibility and characterization of a peptide amphiphile hydrogel for applications in peripheral nerve regeneration

Peripheral nerve injury is a debilitating condition for which new bioengineering solutions are needed. Autografting, the gold standard in treatment, involves sacrifice of a healthy nerve and results in loss of sensation or function at the donor site. One alternative solution to autografting is to use a nerve guide conduit designed to physically guide the nerve as it regenerates across the injury gap. Such conduits are effective for short gap injuries, but fail to surpass autografting in long gap injuries. One strategy to enhance regeneration inside conduits in long gap injuries is to fill the guide conduits with a hydrogel to mimic the native extracellular matrix found in peripheral nerves. In this work, a peptide amphiphile (PA)-based hydrogel was optimized for peripheral nerve repair. Hydrogels consisting of the PA C₁₆GSH were compared with a commercially available collagen gel. Schwann cells, a cell type important in the peripheral nerve regenerative cascade, were able to spread, proliferate, and migrate better on C₁₆GSH gels in vitro when compared with cells seeded on collagen gels. Moreover, C₁₆GSH gels were implanted subcutaneously in a murine model and were found to be biocompatible, degrade over time, and support angiogenesis without causing inflammation or a foreign body immune response. Taken together, these results help optimize and instruct the development of a new synthetic hydrogel as a luminal filler for conduit-mediated peripheral nerve repair.

Activation of the Wnt/β-catenin signaling cascade after traumatic nerve injury

Recent data have shown that preservation of the neuromuscular junction (NMJ) after traumatic nerve injury helps to improve functional recovery with surgical repair via matrix metalloproteinase-3 (MMP3) blockade. As such, we sought to explore additional pathways that may augment this response. Wnt3a has been shown to inhibit acetylcholine receptor (AChR) clustering via β-catenin-dependent signaling in the development of the NMJ. Therefore, we hypothesized that Wnt3a and β-catenin are associated with NMJ destabilization following traumatic denervation. A critical size nerve defect was created by excising a 10-mm segment of the sciatic nerve in mice. Denervated muscles were then harvested at multiple time points for immunofluorescence staining, quantitative real-time PCR, and western blot analysis for Wnt3a and β-catenin levels. Moreover, a novel Wnt/β-catenin transgenic reporter mouse line was utilized to support our hypothesis of Wnt activation after traumatic nerve injury. The expression of Wnt3a mRNA was significantly increased by 2 weeks post-injury and remained upregulated for 2 months. Additionally, β-catenin was activated at 2 months post-injury relative to controls. Correspondingly, immunohistochemical analysis of denervated transgenic mouse line TCF/Lef:H2B-GFP muscles demonstrated that the number of GFP-positive cells was increased at the motor endplate band. These collective data support that post-synaptic AChRs destabilize after denervation by a process that involves the Wnt/β-catenin pathway. As such, this pathway serves as a potential therapeutic target to prevent the motor endplate degeneration that occurs following traumatic nerve injury.

Alternatives to sural nerve grafts in the upper extremity

BACKGROUND

The sural nerve is the most common nerve graft donor despite requiring a second operative limb and causing numbness of the lateral foot. The purposes of this study were to review our experience using nerve autografts in upper extremity nerve reconstruction and develop recommendations for donor selection.

METHODS

A retrospective case series study was performed of all consecutive patients undergoing nerve grafting procedures for upper extremity nerve injuries over an 11-year period (2001-2012).

RESULTS

Eighty-six patients received 109 nerve grafts over the study period. Mean patient age was 42.9 ± 18.3 years; 57 % were male. There were 51 median (59 %), 26 ulnar (30 %), 14 digital (13 %), 13 radial (16 %), and 3 musculocutaneous (4 %) nerve injuries repaired with 99 nerve autografts (71 from upper extremity, 28 from lower extremity). Multiple upper extremity nerve autograft donors were utilized, including the medial antebrachial cutaneous nerve (MABC), third webspace branch of median, lateral antebrachial cutaneous nerve (LABC), palmar cutaneous, and dorsal cutaneous branch of ulnar nerve. By using an upper-extremity donor, a second operative limb was avoided in 58 patients (67 %), and a second incision was avoided in 26 patients (30 %). The frequency of sural graft use declined from 40 % (n = 17/43) to 11 % (n = 7/64).

CONCLUSIONS

Our algorithm for selecting nerve graft material has evolved with our growing understanding of nerve internal topography and the drive to minimize additional incisions, maximize ease of harvest, and limit donor morbidity. This has led us away from using the sural nerve when possible and allowed us to avoid a second operative limb in two thirds of the cases.

Principles of nerve repair in complex wounds of the upper extremity

Peripheral nerve injuries are common in the setting of complex upper extremity trauma. Early identification of nerve injuries and intervention is critical for maximizing return of function. In this review, the principles of nerve injury, patient evaluation, and surgical management are discussed. An evidence-based approach to nerve reconstruction is reviewed, including the benefits and limitations of direct repair and nerve gap reconstruction with the use of autografts, processed nerve allografts, and conduits. Further, the principles and indications of commonly used nerve transfers in proximal nerve injuries are also addressed.

A novel artificial nerve graft for repairing long-distance sciatic nerve defects: a self-assembling peptide nanofiber scaffold-containing poly(lactic-co-glycolic acid) conduit

In this study, we developed a novel artificial nerve graft termed self-assembling peptide nanofiber scaffold (SAPNS)-containing poly(lactic-co-glycolic acid) (PLGA) conduit (SPC) and used it to bridge a 10-mm-long sciatic nerve defect in the rat. Retrograde tracing, behavioral testing and histomorphometric analyses showed that compared with the empty PLGA conduit implantation group, the SPC implantation group had a larger number of growing and extending axons, a markedly increased diameter of regenerated axons and a greater thickness of the myelin sheath in the conduit. Furthermore, there was an increase in the size of the neuromuscular junction and myofiber diameter in the target muscle. These findings suggest that the novel artificial SPC nerve graft can promote axonal regeneration and remyelination in the transected peripheral nerve and can be used for repairing peripheral nerve injury.

Nerve repair: toward a sutureless approach

Peripheral nerve repair for complete section injuries employ reconstructive techniques that invariably require sutures in their application. Sutures are unable to seal the nerve, thus incapable of preventing leakage of important intraneural fluids from the regenerating nerve. Furthermore, sutures are technically demanding to apply for direct repairs and often induce detrimental scarring that impedes healing and functional recovery. To overcome these limitations, biocompatible and biodegradable glues have been used to seal and repair peripheral nerves. Although creating a sufficient seal, they can lack flexibility and present infection risks or cytotoxicity. Other adhesive biomaterials have recently emerged into practice that are usually based on proteins such as albumin and collagen or polysaccharides like chitosan. These adhesives form their union to nerve tissue by either photothermal (tissue welding) or photochemical (tissue bonding) activation with laser light. These biomaterial adhesives offer significant advantages over sutures, such as their capacity to unite and seal the epineurium, ease of application, reduced invasiveness and add the potential for drug delivery in situ to facilitate regeneration. This paper reviews a number of different peripheral nerve repair (or reconstructive) techniques currently used clinically and in experimental procedures for nerve injuries with or without tissue deficit.

Challenges in sciatic nerve repair: anatomical considerations

Object

The object of this study was to highlight the challenge of insufficient donor graft material in peripheral nerve surgery, with a specific focus on sciatic nerve transection requiring autologous sural nerve graft.

Methods

The authors performed an anatomical analysis of cadaveric sciatic and sural nerve tissue. To complement this they also present 3 illustrative clinical cases of sciatic nerve injuries with segmental defects. In the anatomical study, the cross-sectional area (CSA), circumference, diameter, percentage of neural tissue, fat content of the sural nerves, as well as the number of fascicles, were measured from cadaveric samples. The percentage of neural tissue was defined as the CSA of fascicles lined by perineurium relative to the CSA of the sural nerve surrounded by epineurium.

Results

Sural nerve samples were obtained from 8 cadaveric specimens. Mean values and standard deviations from sural nerve measurements were as follows: CSA 2.84 ± 0.91 mm2, circumference 6.67 ± 1.60 mm, diameter 2.36 ± 0.43 mm, fat content 0.83 ± 0.91 mm2, and number of fascicles 9.88 ± 3.68. The percentage of neural tissue seen on sural nerve cross-section was 33.17% ± 4.96%. One sciatic nerve was also evaluated. It had a CSA of 37.50 mm2, with 56% of the CSA representing nerve material. The estimated length of sciatic nerve that could be repaired with a bilateral sural nerve harvest (85 cm) varied from as little as 2.5 cm to as much as 8 cm.

Conclusions

Multiple methods have been used in the past to repair sciatic nerve injury but most commonly, when a considerable gap is present, autologous nerve grafting is required, with sural nerve being the foremost source. As evidenced by the anatomical data reported in this study, a considerable degree of variability exists in the diameter of sural nerve harvests. Conversely, the percentage of neural tissue is relatively consistent across specimens. The authors recommend that the peripheral nerve surgeon take these points into consideration during nerve grafting as insufficient graft material may preclude successful recovery.

Neurite outgrowth on electrospun PLLA fibers is enhanced by exogenous electrical stimulation

OBJECTIVE

Both electrical stimuli (endogenous and exogenous) and topographical cues are instructive to axonal extension. This report, for the first time, investigated the relative dominance of directional topographical guidance cues and directional electrical cues to enhance and/or direct primary neurite extension. We hypothesized the combination of electrical stimulation with electrospun fiber topography would induce longer neurite extension from dorsal root ganglia neurons than the presence of electrical stimulation or aligned topography alone.

APPROACH

To test the hypothesis, neurite outgrowth was examined on laminin-coated poly-L-lactide films or electrospun fibers (2 µm in diameter) in the presence or absence of electrical stimulation. Immunostained neurons were semi-automatically traced using Neurolucida software and morphology was evaluated.

MAIN RESULTS

Neurite extension increased 74% on the aligned fibers compared to film controls. Stimulation alone increased outgrowth by 32% on films or fibers relative to unstimulated film controls. The co-presentation of topographical (fibers) with biophysical (electrical stimulation) cues resulted in a synergistic 126% increase in outgrowth relative to unstimulated film controls. Field polarity had no influence on the directionality of neurites, indicating topographical cues are responsible for guiding neurite extension.

SIGNIFICANCE

Both cues (electrical stimulation and fiber geometry) are modular in nature and can be synergistically applied in conjunction with other common methods in regenerative medicine such as controlled release of growth factors to further influence axonal growth in vivo. The combined application of electrical and aligned fiber topographical guidance cues described herein, if translated in vivo, could provide a more supportive environment for directed and robust axonal regeneration following peripheral nerve injury.

Clinical applications of autografts, conduits, and allografts in repair of nerve defects in the hand: current guidelines

Traumatic nerve injuries are common conditions treated by hand surgeons, and the optimal treatment of a severed nerve requires providing a healthy wound bed, generous trimming to healthy nerve substance, and a minimal-tension approximation. The gold standard for repair of a critical nerve gap has been the nerve autograft. However, results are generally less favorable than direct suture. Autogenous and synthetic conduits and processed nerve allografts have been developed as less morbid and more convenient alternatives to autografts, but the reported outcomes have been uneven. Engineered neural tissues show great promise in inducing nerve regeneration across a gap.

3D nano/microfabrication techniques and nanobiomaterials for neural tissue regeneration

Injuries of the nervous system occur commonly among people of many different ages and backgrounds. Currently, there are no effective strategies to improve neural regeneration; however, tissue engineering provides a promising avenue for regeneration of many tissue types, including the neural context. Functional nerve conduits derived from tissue engineering techniques present bioengineered 3D artificial substitutes for implantation and rehabilitation of injured nerves. In particular, nanotechnology as a versatile vehicle to create biomimetic nanostructured tissue-engineered neural scaffolds provides great potential for the development of innovative and successful nerve grafts. Nanostructured conduits derived from traditional and novel tissue engineering techniques have been shown to be superior for successful neural function construction due to a high degree of biomimetic character. In this paper, we will focus on current progress in developing 3D nano/microstructured neural scaffolds via electrospinning, emerging 3D printing and self-assembly techniques, nanobiomaterials and bioactive cues for enhanced neural tissue regeneration.

In vitro evaluation of cell-seeded chitosan films for peripheral nerve tissue engineering

Natural biomaterials have attracted an increasing interest in the field of tissue-engineered nerve grafts, representing a possible alternative to autologous nerve transplantation. With the prospect of developing a novel entubulation strategy for transected nerves with cell-seeded chitosan films, we examined the biocompatibility of such films in vitro. Different types of rat Schwann cells (SCs)--immortalized, neonatal, and adult-of the chitosan substrate. Both cell types were viable on the biomaterial and showed different metabolic activities and proliferation behavior, indicating cell-type-specific cell-biomaterial interaction. Moreover, the cell types also displayed their typical morphology. In cocultures adult SCs used the BMSCs as a feeder layer and no negative interactions between both cell types were detected. Further, the chitosan films allow neurite outgrowth from dissociated sensory neurons, which is additionally supported on film preseeded with SC-BMSC cocultures. The presented chitosan films therefore demonstrate high potential for their use in tissue-engineered nerve grafts.

Hand reanimation

Brachial plexus disruption, major traumatic amputations, and Volkmann's contracture are all devastating injuries that present difficult reconstructive challenges. Advances in our understanding of nerve injury, regeneration, and refinement of microsurgical techniques have given rise to a number of therapeutic avenues over the last 4 decades. Hand reanimation aims to provide strength, stability, and mobility to a sensate hand. How this is achieved depends on a thorough understanding of the underlying pathophysiology, which in turn dictates what surgical modalities are suitable. Common to all reanimation procedures is the need to ensure full passive range of motion of the target joints prior to definitive surgery. Hand therapy is essential to prevent deleterious sequelae of injury, and to maximize rehabilitation following surgical reconstruction. Options for reanimation include nerve repair, nerve grafting, nerve transfer, tendon transfer, and free functioning muscle transfer.

Nerve gaps

SUMMARY

Peripheral nerve injury is a significant problem affecting greater that 1 million people around the world each year and poses major challenges to the plastic and reconstructive surgeon. When primary nerve repair is not possible, several options for management of the nerve gap include a nerve autograft, nerve conduit, and acellular nerve allograft. For extensive and proximal nerve injuries, cellular nerve allografts and nerve transfers may be considered. This article reviews the indications and outcomes for each option, as in many cases more than one option may be acceptable.

Nerve regeneration across cryopreserved allografts from cadaveric donors: a novel approach for peripheral nerve reconstruction

Object

The use of allografts from cadaveric donors has attracted renewed interest in recent years, and pretreatment with cryopreservation and immunosuppression methods has been investigated to maximize axonal regrowth and minimize allograft rejection. The authors wanted to assess the outcome of treatments of brachial plexus stretch injuries with cryopreserved allografts from cadaveric donors in nonimmunosuppressed patients.

Methods

Ten patients with brachial plexus lesions were submitted to electromyography (EMG) testing 1 and 3 months after a traumatic event and 1 week before surgery to localize and identify the type of lesion. Intraoperative EMG recordings were performed for intraoperative monitoring to select the best surgical strategy, and postoperative EMG was used to follow up patients and determine surgical outcomes. If nerve action potentials (NAPs) were present intraoperatively, neurolysis was performed, whereas muscular/nerve neurotization was performed if NAPs were absent. Cryopreserved allografts obtained from selected cadaveric donors and provided by the tissue bank of Treviso were used for nerve reconstruction in patients who were not treated with immunosuppressive drugs.

Results

The surgical strategy was selected according to the type and site of the nerve lesion and on the basis of IOM results: 14 cryopreserved allografts were used for 7 muscular neurotizations and for 7 nerve neurotizations, and 5 neurolysis procedures were performed. All of the patients had regained motor function at the 1- and 2-year follow-ups.

Conclusions

Some variables may affect functional recovery after allograft surgery, and the outcome of peripheral nerve reconstruction is more favorable when patients are carefully evaluated and selected for the surgery. The authors demonstrated that using cryopreserved allografts from cadaveric donors is a valid surgical strategy to restore function of the damaged nerve without the need for any immunosuppressive treatments. This approach offers new perspectives on procedures for extensive reconstruction of brachial and lumbosacral plexuses.

Profiling circulating microRNA expression in a mouse model of nerve allotransplantation

Background

The lack of noninvasive biomarkers of rejection remains a challenge in the accurate monitoring of deeply buried nerve allografts and precludes optimization of therapeutic intervention. This study aimed to establish the expression profile of circulating microRNAs (miRNAs) during nerve allotransplantation with or without immunosuppression.

Results

Balb/c mice were randomized into 3 experimental groups, that is, (1) untreated isograft (Balb/c → Balb/c), (2) untreated allograft (C57BL/6 → Balb/c), and (3) allograft (C57BL/6 → Balb/c) with FK506 immunosuppression. A 1-cm Balb/c or C57BL/6 donor sciatic nerve graft was transplanted into sciatic nerve gaps created in recipient mice. At 1, 3, 7, 10, and 14 d after nerve transplantation, nerve grafts, whole blood, and sera were obtained for miRNA expression analysis with an miRNA array and subsequent validation with quantitative real-time PCR (qRT-PCR). Three circulating miRNAs (miR-320, miR-762, and miR-423-5p) were identified in the whole blood and serum of the mice receiving an allograft with FK506 immunosuppression, within 2 weeks after nerve allotransplantation. However, these 3 circulating miRNAs were not expressed in the nerve grafts. The expression of all these 3 upregulated circulating miRNAs significantly decreased at 2, 4, and 6 d after discontinuation of FK506 immunosuppression. In the nerve graft, miR-125-3b and miR-672 were significantly upregulated in the mice that received an allograft with FK506 only at 7 d after nerve allotransplantation.

Conclusions

We identified the circulating miR-320, miR-762, and miR-423-5p as potential biomarkers for monitoring the immunosuppression status of the nerve allograft. However, further research is required to investigate the mechanism behind the dysregulation of these markers and to evaluate their prognostic value in nerve allotransplantation.

Limitations of nerve repair of segmental defects using acellular conduits

The authors present the case of a 20-year-old man who, 3 months after his initial injury, underwent repair of a 1.7-cm defect of the ulnar nerve at the wrist; repair was performed with an acellular nerve allograft. Given the absence of clinical or electrophysiological recovery at 8 months postrepair, the patient underwent reexploration, excision of the “regenerated cable,” and rerepair of the ulnar nerve with sural nerve autografts. Histology of the cable demonstrated minimal axonal regeneration at the midpoint of the repair. At the 6- and 12-month follow-ups of the sural nerve graft repair, clinical and electrophysiological evidence of both sensory and motor reinnervation of the ulnar nerve and associated hand muscles was demonstrated. In this report, the authors describe a single case of failed acellular nerve allograft and correlate the results with basic science and human studies reporting length and diameter limitations in human nerve repair utilizing grafts or conduits devoid of viable Schwann cells.

Immunohistochemical, ultrastructural and functional analysis of axonal regeneration through peripheral nerve grafts containing Schwann cells expressing BDNF, CNTF or NT3

We used morphological, immunohistochemical and functional assessments to determine the impact of genetically-modified peripheral nerve (PN) grafts on axonal regeneration after injury. Grafts were assembled from acellular nerve sheaths repopulated ex vivo with Schwann cells (SCs) modified to express brain-derived neurotrophic factor (BDNF), a secretable form of ciliary neurotrophic factor (CNTF), or neurotrophin-3 (NT3). Grafts were used to repair unilateral 1 cm defects in rat peroneal nerves and 10 weeks later outcomes were compared to normal nerves and various controls: autografts, acellular grafts and grafts with unmodified SCs. The number of regenerated βIII-Tubulin positive axons was similar in all grafts with the exception of CNTF, which contained the fewest immunostained axons. There were significantly lower fiber counts in acellular, untransduced SC and NT3 groups using a PanNF antibody, suggesting a paucity of large caliber axons. In addition, NT3 grafts contained the greatest number of sensory fibres, identified with either IB₄ or CGRP markers. Examination of semi- and ultra-thin sections revealed heterogeneous graft morphologies, particularly in BDNF and NT3 grafts in which the fascicular organization was pronounced. Unmyelinated axons were loosely organized in numerous Remak bundles in NT3 grafts, while the BDNF graft group displayed the lowest ratio of umyelinated to myelinated axons. Gait analysis revealed that stance width was increased in rats with CNTF and NT3 grafts, and step length involving the injured left hindlimb was significantly greater in NT3 grafted rats, suggesting enhanced sensory sensitivity in these animals. In summary, the selective expression of BDNF, CNTF or NT3 by genetically modified SCs had differential effects on PN graft morphology, the number and type of regenerating axons, myelination, and locomotor function.

Assessment of in vivo behavior of polymer tube nerve grafts simultaneously with the peripheral nerve regeneration process using scanning electron microscopy technique

In this study, scanning electron microscopy (SEM) has been applied for instantaneous assessment of processes occurring at the site of regenerating nerve. The technique proved to be especially useful when an artificial implant should have been observed but have not yet been extensively investigated before for assessment of nerve tissue. For in vivo studies, evaluation of implant's morphology and its neuroregenerative properties is of great importance when new prototype is developed. However, the usually applied histological techniques require separate and differently prepared samples, and therefore, the results are never a 100% comparable. In our research, we found SEM as a technique providing detailed data both on an implant behavior and the nerve regeneration process inside the implant. Observations were carried out during 12-week period on rat sciatic nerve injury model reconstructed with nerve autografts and different tube nerve grafts. Samples were analyzed with haematoxylin-eosin (HE), immunocytochemical staining for neurofillament and S-100 protein, SEM, TEM, and the results were compared. SEM studies enabled to obtain characteristic pictures of the regeneration process similarly to TEM and histological studies. Schwann cell transformation and communication as well as axonal outgrowth were identified, newly created and matured axons could be recognized. Concurrent analysis of biomaterial changes in the implant (degradation, collapsing of the tube wall, migration of alginate gel) was possible. This study provides the groundwork for further use of the described technique in the nerve regeneration studies.

Type I collagen nerve conduits for median nerve repairs in the forearm

PURPOSE

To evaluate patients with median nerve damage in the distal forearm treated with type 1 collagen nerve conduits.

METHODS

Nine patients with damage to the median nerve in the distal forearm underwent treatment with a type 1 collagen nerve conduit. The nerve gaps ranged between 1 and 2 cm. An independent observer reexamined patients after treatment at a minimal follow-up of 14 months and a mean follow-up of 21 months. Residual pain was evaluated using a visual analog scale. Functional outcome was quantified by assessing static 2-point discrimination, nerve conduction velocity relative to the uninjured limb, and Disabilities of the Arm, Shoulder, and Hand outcome measure scoring. We also recorded quality of life measures including patients' perceived satisfaction with the results and return to work latency.

RESULTS

We observed no implant-related complications. Of 9 patients, 7 were free of pain, and the mean visual analog scale was 0.6. The mean Disabilities of the Arm, Shoulder, and Hand score was 6. The static 2-point discrimination was less than 6 mm in 3 patients, between 6 and 10 mm in 4 patients, and over 10 mm in 2 patients. Six patients reached a status of M4 or higher. Eight patients were satisfied with the procedure and would undergo surgery again.

CONCLUSIONS

This study indicates that purified type 1 bovine collagen conduits are a practical and efficacious method for the repair of median nerves in the distal forearm.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Analysis of lumbar plexopathies and nerve injury after lateral retroperitoneal transpsoas approach: diagnostic standardization

Object

The minimally invasive lateral transpsoas approach has become an increasingly popular means of fusion. The most frequent complication is related to lumbar plexus nerve injuries; these can be diagnosed based on distribution of neurological deficit following the motor and/or sensory nerve injury. However, the literature has failed to provide a clinically relevant description of these complications. With accurate clinical diagnosis, spine practitioners can provide more precise prognostic and management recommendations to include observation, nerve blocks, neurodestructive procedures, medications, or surgical repair strategies. The purpose of this study was to standardize the clinical findings of lumbar plexopathies and nerve injuries associated with minimally invasive lateral retroperitoneal transpsoas lumbar fusion.

Methods

A thorough literature search of the MEDLINE database up to June 2012 was performed to identify studies that reported lumbar plexus and nerve injuries after the minimally invasive lateral retroperitoneal transpsoas approach. Included studies were assessed for described neurological deficits postoperatively. Studies that did attempt to describe nerve-related complications clinically were excluded. A clinically relevant assessment of lumbar plexus nerve injury was derived to standardize early diagnosis and outline prognostic implications.

Results

A total of 18 studies were selected with a total of 2310 patients; 304 patients were reported to have possible plexus-related complications. The incidence of documented nerve and/or root injury and abdominal paresis ranged from 0% to 3.4% and 4.2%, respectively. Motor weakness ranged from 0.7% to 33.6%. Sensory complications ranged from 0% to 75%. A lack of consistency in the descriptions of the lumbar plexopathies and/or nerve injuries as well as a lack of diagnostic paradigms was noted across studies reviewed. Sensory dermal zones were established and a standardized approach was proposed.

Conclusions

There is underreporting of postoperative lumbar plexus nerve injury and a lack of standardization of clinical findings of neural complications related to the minimally invasive lateral retroperitoneal transpsoas approach. The authors provide a diagnostic paradigm that allows for an efficient and accurate classification of postoperative lumbar plexopathies and nerve injuries.

Reconstruction of sciatic nerve after traumatic injury in humans - factors influencing outcome as related to neurobiological knowledge from animal research

Background

The aim was to evaluate what can be learned from rat models when treating patients suffering from a sciatic nerve injury.

Methods

Two patients with traumatic sciatic nerve injury are presented with examination of motor and sensory function with a five-year follow-up. Reconstruction of the nerve injury was performed on the second and third day, respectively, after injury using sural nerve grafts taken from the injured leg. The patients were examined during follow-up by electromyography (EMG), MRI and functionalMRI (fMRI) to evaluate nerve reinnervation, cell death in dorsal root ganglia (DRG) and cortical activation; factors that were related to clinical history in the patients.

Results

One patient regained good motor function of the lower leg and foot, confirmed by EMG showing good activation in the leg muscles and some reinnervation in the foot muscles, as well as some sensory function of the sole of the foot. The other patient regained no motor (confirmed by EMG) or sensory function in the leg or foot. Factors most influential on outcome in two cases were type of injury, nerve gap length and particularly type of reconstruction. A difference in follow-up and rehabilitation likely also influence outcome. MRI did not show any differences in DRG size of injured side compared to the uninjured side. fMRI showed normal activation in the primary somatosensory cortex as a response to cutaneous stimulation of the normal foot. However, none of the two patients showed any activation in the primary somatosensory cortex following cutaneous stimulation of the injured foot.

Conclusions

In decision making of nerve repair and reconstruction data from animal experiments can be translated to clinical practice and to predict outcome in patients, although such data should be interpreted with caution and linked to clinical experience. Rat models may be useful to identify and study factors that influence outcome after peripheral nerve repair and reconstruction; procedures that should be done correctly and with a competent team. However, some factors, such as cognitive capacity and coping, known to influence outcome following nerve repair, are difficult to study in animal models. Future research has to find and develop new paths and techniques to study changes in the central nervous system after nerve injury and develop strategies to utilize brain plasticity during the rehabilitation.

Nerve reconstruction in the hand and upper extremity

In the management of traumatic peripheral nerve injuries, the severity or degree of injury dictates the decision making between surgical management versus conservative management and serial examination. This review explores some of the recent literature, specifically addressing recent basic science advances in end-to-side and reverse end-to-side recovery, Schwann cell migration, and neuropathic pain. The management of nerve gaps, including the use of nerve conduits and acellularized nerve allografts, is examined. Current commonly performed nerve transfers are detailed with focus on both motor and sensory nerve transfers, their indications, and a basic overview of selected surgical techniques.

Adult-brain-derived neural stem cells grafting into a vein bridge increases postlesional recovery and regeneration in a peripheral nerve of adult pig

We attempted transplantation of adult neural stem cells (ANSCs) inside an autologous venous graft following surgical transsection of nervis cruralis with 30 mm long gap in adult pig. The transplanted cell suspension was a primary culture of neurospheres from adult pig subventricular zone (SVZ) which had been labeled in vitro with BrdU or lentivirally transferred fluorescent protein. Lesion-induced loss of leg extension on the thigh became definitive in controls but was reversed by 45–90 days after neurosphere-filled vein grafting. Electromyography showed stimulodetection recovery in neurosphere-transplanted pigs but not in controls. Postmortem immunohistochemistry revealed neurosphere-derived cells that survived inside the venous graft from 10 to 240 post-lesion days and all displayed a neuronal phenotype. Newly formed neurons were distributed inside the venous graft along the severed nerve longitudinal axis. Moreover, ANSC transplantation increased CNPase expression, indicating activation of intrinsic Schwann cells. Thus ANSC transplantation inside an autologous venous graft provides an efficient repair strategy.

C3 peptide promotes axonal regeneration and functional motor recovery after peripheral nerve injury

Peripheral nerve injuries are frequently seen in trauma patients and due to delayed nerve repair, lifelong disabilities often follow this type of injury. Innovative therapies are needed to facilitate and expedite peripheral nerve regeneration. The purpose of this study was to determine the effects of a 1-time topical application of a 26-amino-acid fragment (C3(156-181)), derived from the Clostridium botulinum C3-exoenzyme, on peripheral nerve regeneration in 2 models of nerve injury and repair in adult rats. After sciatic nerve crush, different dosages of C3(156-181) dissolved in buffer or reference solutions (nerve growth factor or C3(bot)-wild-type protein) or vehicle-only were injected through an epineurial opening into the lesion sites. After 10-mm nerve autotransplantation, either 8.0 nmol/kg C3(156-181) or vehicle were injected into the proximal and distal suture sites. For a period of 3 to 10 postoperative weeks, C3(156-181)-treated animals showed a faster motor recovery than control animals. After crush injury, axonal outgrowth and elongation were activated and consequently resulted in faster motor recovery. The nerve autotransplantation model further elucidated that C3(156-181) treatment accounts for better axonal elongation into motor targets and reduced axonal sprouting, which are followed by enhanced axonal maturation and better axonal functionality. The effects of C3(156-181) are likely caused by a nonenzymatic down-regulation of active RhoA. Our results indicate the potential of C3(156-181) as a therapeutic agent for the topical treatment of peripheral nerve repair sites.

Next generation nerve guides: materials, fabrication, growth factors, and cell delivery

Nerve guides are increasingly being used surgically to repair acute peripheral nerve injuries. This is not only due to an increase in the number of commercially available devices, but also clinical acceptance. However, regeneration distance is typically limited to 20-25 mm, in part due to the basic tubular design. A number of experimental studies have shown improvements in nerve regeneration distance when conduits incorporate coatings, internal scaffolds, topographical cues, or the delivery of support cells. Current studies on designing nerve guides for maximizing nerve regeneration focus both on cell-containing and cell-free devices, the latter being clinically attractive as "off the shelf" products. Arguably better results are obtained when conduits are used in conjunction with support cells (e.g., Schwann cells or stem cells) that can improve regeneration distance and speed of repair, and provide informative experimental data on how Schwann and neuronal cells respond in regenerating injured nerves. In this review we discuss the range of current nerve guides commercially available and appraise experimental studies in the context of the future design of nerve guides for clinical use.

Use of adipose-derived stem cells to fabricate scaffoldless tissue-engineered neural conduits in vitro

Peripheral nerve injuries resulting from trauma or disease often necessitate surgical intervention. Although the gold standard for such repairs uses nerve autografts, alternatives that do not require invasive harvesting of autologous nerve tissues are currently being designed and evaluated. We previously established the use of scaffoldless engineered neural conduits (ENCs) fabricated from primary cells as one such alternative in sciatic nerve repair in rats [Baltich et al. (2010) In Vitro Cell Dev Biol Anim 46(5):438-444]. The present study establishes protocols for fabricating neural conduits from adipose-derived stem cells (ASCs) differentiated to either a fibroblast or neural lineage and co-cultured into a three-dimensional (3-D) scaffoldless tissue-ENC. Addition of ascorbic acid-2-phosphate and fibroblast growth factor (FGF)-2 to the medium induced and differentiated ASCs to a fibroblast lineage in more than 90% of the cell population, as confirmed by collagen I expression. ASC-differentiated fibroblasts formed monolayers, delaminated, and formed 3-D conduits. Neurospheres were formed by culturing ASCs on non-adherent surfaces in serum-free neurobasal medium with the addition of epidermal growth factor (EGF) and FGF-2. The addition of 10 ng EGF and 10 ng FGF-2 produced larger and more numerous neurospheres than treatments of lower EGF and FGF-2 concentrations. Subsequent differentiation to glial-like cells was confirmed by the expression of S100. ASC-derived fibroblast monolayers and neurospheres were co-cultured to fabricate a 3-D scaffoldless tissue-ENC. Their nerve-like structure and incorporation of glial-like cells, which would associate with regenerating axons, may make these novel, stem cell-derived neural conduits an efficacious technology for repairing critical gaps following peripheral nerve injury.

Nerve problems in the lower extremity

The article provides an overview of management and repair strategies for lower extremity peripheral nerve injuries. It discusses the indications for autografts, nerve conduits, allografts, end-to-side repairs, primary repair, and nerve transfers. The relative pros and cons of each strategy are discussed, providing a broad overview of treatment options for the management of lower extremity nerve injuries.

Dose and duration of nerve growth factor (NGF) administration determine the extent of behavioral recovery following peripheral nerve injury in the rat

Nerve growth factor (NGF) has been previously shown to support neuron survival and direct neurite outgrowth in vitro, and to enhance axonal regeneration in vivo. However, a systematic analysis of NGF dose and dose duration on behavioral recovery following peripheral nerve injury in rodents has not been previously investigated. Here, we show that NGF promotes a bell shaped dose-response, with an optimal threshold effect occurring at 800 pg/μl. High dose NGF inhibited regeneration. However, this effect could be reversed through functional blockade of p75 receptors, thus implicating these receptors as mediators of the inhibitory response. Longer term evaluation showed that animals administered NGF at 80 ng/day for 3 weeks had greater sensorimotor recovery compared to all other treatment groups. These animals made significantly fewer errors during skilled locomotion, and displayed both increased vertical and fore-aft ground reaction forces during flat surface locomotion. Furthermore, terminal electrophysiological and myological assessments (EMG, wet gastrocnemius muscle weights) corroborated the behavioral data. Overall, these data support the hypothesis that both appropriate dose and duration of NGF are important determinants of behavioral recovery following nerve injury in the rat.