Radial nerve repair using an autologous denatured muscle graft: comparison with outcomes of nerve graft repair

Tendon Transfers, Nerve Grafts, and Nerve Transfers for Isolated Radial Nerve Palsy: A Systematic Review and Analysis

BACKGROUND

Isolated radial nerve palsy is a debilitating injury that may potentially be reconstructed with either tendon transfers, nerve grafts, or nerve transfers. Currently, there is no consensus on the optimal technique for reconstruction. We performed a systematic review and analysis to determine which surgical intervention provides the best clinical outcomes.

METHODS

A systematic review was conducted according to PRISMA guidelines. Twenty-nine papers met inclusion criteria. Grading scales of function and strength were converted into a tripartite scoring system to compare outcomes between techniques. χ2 analyses were performed with a P value < .05.

RESULTS

Seven hundred fifty-four patients were analyzed. Tendon transfers resulted in the highest percentage of good outcomes (82%) and the lowest percentage of poor outcomes (9%). Tendon transfers were superior to nerve grafts and nerve transfers for restoration of wrist extension. Nerve transfers for wrist extension were superior to nerve transfers for finger extension. Nerve grafts and nerve transfers had equivalent rates of good and poor clinical outcomes.

CONCLUSIONS

This study analyzed reported outcomes of tendon transfers, nerve grafts, and nerve transfers for reconstruction of isolated radial nerve palsy. On pooled analysis, tendon transfers had higher rates of superior clinical outcomes as compared with nerve transfers and nerve grafts. Tendon transfers should be considered first-line reconstruction for isolated radial nerve palsy as nerve-based reconstruction is less predictable and reproducible.

A Brief History of Peripheral Nerve Surgery in Serbia

Peripheral nerve surgery in Serbia has become the most fruitful subsection of national neurosurgery, with international recognition of Serbian surgeons and institutions. We chronicle landmark events in the history of the field in Serbia, highlighting the development of the field over time and outlining future prospects. This manuscript provides an example of the development of peripheral nerve surgery and associated training in a challenging social, political, and economic context and may guide the development of peripheral nerve surgery care and training in other settings.

Reconstruction of the Rat Sciatic Nerve by Using Biodegradable and Non-Biodegradable Conduits

The aim of the study was to compare two types of conduits made of either non-resorbable Reperen or resorbable Tissucol for their effects on the regeneration of the rat sciatic nerve under conditions of stump diastasis.

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.

Comparison of Conduits Fabricated by Fresh and Predegenerated Skeletal Muscles for Peripheral Nerve Repairing

ABSTRACT

Reconstruction of peripheral nerve injury remains a challenge for clinical medicine. Previous reports have confirmed that external oblique muscle-fabricated nerve conduit (EMC) could effectively be used to promote peripheral nerve regeneration. In this study, we compared between conduits fabricated from fresh muscle and conduits fabricated from predegenerated muscle for the repair of peripheral nerve defects in a mouse sciatic nerve transection model. We found that the number, diameter, and myelin sheath thickness of the myelinated nerve fibers of the regenerative nerve in the EMC group were larger than those of the predegenerated-EMC (P-EMC) group eight weeks after surgery. The sciatic function index and gastrocnemius wet-weight mass ratio in the EMC group were higher than those in the P-EMC group. The Bcl-2/Bax ratio and the number of Schwann cell nucleus in the proximal nerve stumps in the EMC group were greater than those in the P-EMC group. In conclusion, our results confirmed that the use of fresh skeletal muscle nerve conduit increased the Bcl-2/Bax ratio and promoted the survival of Schwann cells of the proximal nerve stump compared with that of predegenerated skeletal muscle nerve conduits, thus achieving better functional recovery after sciatic nerve defect.

Clinical outcomes report in different brachial plexus injury surgeries: a systematic review

Brachial plexus injury is a lesion that results in loss of function of the arm, and there are multiple ways of surgically approaching its treatment. Controlled trials that compare all surgical repair strategies and their clinical outcomes have not been performed. A systematic review was conducted to identify all articles that reported clinical outcomes in different surgeries (nerve transfer, nerve graft, neurolysis, end-to-end, multiple interventions, and others). Advanced search in PubMed was performed using the Mesh terms "brachial plexus injury" as the main topic and "surgery" as a subtopic, obtaining a total of 2153 articles. The clinical data for eligibility extraction was focused on collecting motor, sensory, pain, and functional recovery. A statistical analysis was performed to find the superior surgical techniques in terms of motor recovery, through the assessment of heterogeneity between groups, and of relationships between surgery and motor recovery. The frequency and the manner in which clinical outcomes are recording were described. The differences that correspond to the demographics and procedural factors were not statistically significant among groups (p > 0.05). Neurolysis showed the highest proportion of motor recovery (85.18%), with significant results between preoperative and post-operative motor assessment (p = 0.028). The proportion of motor recovery in each group according to the surgical approach differed significantly (X² = 82.495, p = 0.0001). The motor outcome was the most reported clinical outcome (97.56%), whereas the other clinical outcomes were reported in less than 15% of the included articles. Unexpectedly, neurolysis, a technique displaced by new surgical alternatives such as nerve transfer/graft, demonstrated the highest proportion of motor recovery. Clinical outcomes such as pain, sensory, and functional recovery were infrequently reported. These results introduce the need to re-evaluate neurolysis through comparative clinical trials, as well as to standardize the way in which clinical outcomes are reported.

Donor nerve graft assessment for covering thumb nerve defects: a cadaveric study

BACKGROUND

Even though several studies reported donor autologous nerve grafts for digital nerve defects, there is no report in the literature regarding acceptable graft for thumb nerves. The purpose of this study is to provide guidelines for autologous nerve graft selection by detecting similarities between thumb nerve zones and donor nerve with regard to the number of fascicles and cross-sectional area.

MATERIALS AND METHODS

Five cadavers were used in this study. An anatomical zoning system was defined for thumb nerves (zones 1, 2, 3). Sural nerve (SN), medial antebrachial cutaneous nerve (MABCN), lateral antebrachial cutaneous nerve (LABCN), posterior interosseous nerve (PIN), and anterior interosseous nerve (AIN) were selected as donor nerve grafts. The number of fascicles and surface area (mm2) was defined.

RESULTS

The mean of the fascicle number in zone 1, zone 2, zone 3, AIN, PIN, LABCN, MABCN, and SN were 3.8, 4.7, 6.1, 2.2, 1.8, 4.5, 3.1, and 6.4, respectively. The mean of the surface area in zone 1, zone 2, zone 3, AIN, PIN, LABCN, MABCN, and SN were 2.19, 6.26, 4.04, 1.58, 0.71, 5.00, 3.01, and 8.06, respectively.

CONCLUSIONS

LABCN is the best choice for all zones that has fascicular matching with all three zones of thumb nerves and caliber matching with zones 2 and 3. In zone 1, the best nerve graft is MABCN which has both suitable caliber and fascicle count.

The Effect of Muscle Graft With Nerve Growth Factor and Laminin on Sciatic Nerve Repair in Rats

Introduction:

Peripheral nerve injury is one of the most common damages that lead to physical disability. Considering the similarity between the coatings of skeletal muscles and nerve fibers, we conducted this research to determine the effect of muscle graft with Nerve Growth Factor (NGF) and Laminin (L) on nerve repair.

Methods:

We cut a 10-mm length of the sciatic nerve from 42 female Wistar rats (Weight: 200±250 g) and equally divided the rats into three groups. In the muscle graft+NGF+laminin group, the degenerated skeletal muscle was sutured with proximal and distal ends of the transected sciatic nerve. Then, NGF (100 ng) and laminin (1.28 mg/mL) were injected into the muscle graft. In the muscle graft group, normal saline was injected into the muscle graft. In the control group, 10 mm of the sciatic nerve was removed without any treatment. Functional recovery was assessed based on Sciatic Functional Index (SFI). Also, tracing motor neurons and histological studies were performed to evaluate nerve repair. The obtained data were analyzed by ANOVA test.

Results:

The Mean±SD SFI value significantly increased in the muscle graft+NGF+laminin (−76.6±2.9) and muscle graft (−82.1±3.5) groups 60 days after the injury compared to the control group. The Mean±SD number of labeled motor neurons significantly increased in the muscle graft+NGF+laminin (78.6±3.1) and muscle graft (61.3±6.1) groups compared to the control group (P<0.001). The mean number of myelinated axons in the distal segments of the muscle graft+NGF+laminin increased significantly compared to the muscle graft group.

Conclusion:

These findings suggest that muscle graft followed by NGF and laminin administration have therapeutic effects on nerve repair.

Polypyrrole/polylactic acid nanofibrous scaffold cotransplanted with bone marrow stromal cells promotes the functional recovery of spinal cord injury in rats

AIMS

The objective of this study was to analyze the efficacy of polypyrrole/polylactic acid (PPy/PLA) nanofibrous scaffold cotransplanted with bone marrow stromal cells (BMSCs) in promoting the functional recovery in a rat spinal cord injury (SCI).

METHODS

Female Sprague-Dawley rats were randomly divided into three groups (n = 18/group): control group, PPy/PLA group, and PPy/PLA/BMSCs group. The SCI was induced in all rats. Consequently, rats in PPy/PLA/BMSCs group were transplanted with 1 × 105 BMSCs after implantation of PPy/PLA, while those in the PPy/PLA group were implanted with PPy/PLA only; no implantation was performed in the control group. Six weeks after surgery, immunofluorescence microscopy, electron microscope, and polymerase chain reaction (PCR) techniques were performed to assess the changes in the injured spinal cord tissues.

RESULTS

Electrophysiology and locomotor function testing suggested that PPy/PLA nanofibrous scaffold cotransplanted with BMSCs could promote the functional recovery of the spinal cord. Six weeks after the operation, lower amount of scar tissue was found in the PPy/PLA group compared with the control group. Abundant neurofilament (NF) and neuron-specific marker (NeuN) positive staining, and myelin formations were detected in the injured area. In addition, the transplantation of BMSCs not only improved the efficacy of PPy/PLA but also managed to survive well and was differentiated into neural and neuroglial cells.

CONCLUSIONS

The implantation of PPy/PLA nanofibrous scaffold and BMSCs has a great potential to restore the electrical conduction and to promote functional recovery by inhibiting the scar tissue formation, promoting axon regeneration, and bridging the gap lesion.

Covalent crosslinking of graphene oxide and carbon nanotube into hydrogels enhances nerve cell responses

Healing of nerve injuries is a critical medical issue. Biodegradable polymeric conduits are a promising therapeutic solution to provide guidance for axon growth in a given space, thus helping nerve heal. Extensive studies in the past decade reported that conductive materials could effectively increase neurite and axon extension in vitro and nerve regeneration in vivo. In this study, graphene oxide and carbon nanotubes were covalently functionalized with double bonds to obtain crosslinkable graphene oxide acrylate (GOa) sheets and carbon nanotube poly(ethylene glycol) acrylate (CNTpega). An electrically conductive reduced GOa-CNTpega-oligo(polyethylene glycol fumarate) (OPF) hydrogel (rGOa-CNTpega-OPF) was successfully fabricated by chemically crosslinking GOa sheets and CNTpega with OPF chains followed by in situ chemical reduction in l-ascorbic acid solution. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging showed homogenous distribution of GOa/CNTpega carbon content in the rGOa-CNTpega-OPF composite hydrogel, resulting in a significant increase of electrical conductivity compared with neutral OPF without carbon content. Cell studies showed excellent biocompatibility and distinguished PC12 cell proliferation and spreading on the rGOa-CNTpega-OPF composite hydrogel. Fluorescent microscopy imaging demonstrated robustly stimulated neurite development in these cells on a conductive rGOa-CNTpega-OPF composite hydrogel compared with that on neutral OPF hydrogels. These results illustrated a promising potential for the rGOa-CNTpega-OPF composite hydrogel to serve as conduits for neural tissue engineering.

Factors predicting sensory and motor recovery after the repair of upper limb peripheral nerve injuries

OBJECTIVE:

To investigate the factors associated with sensory and motor recovery after the repair of upper limb peripheral nerve injuries.

DATA SOURCES:

The online PubMed database was searched for English articles describing outcomes after the repair of median, ulnar, radial, and digital nerve injuries in humans with a publication date between 1 January 1990 and 16 February 2011.

STUDY SELECTION:

The following types of article were selected: (1) clinical trials describing the repair of median, ulnar, radial, and digital nerve injuries published in English; and (2) studies that reported sufficient patient information, including age, mechanism of injury, nerve injured, injury location, defect length, repair time, repair method, and repair materials. SPSS 13.0 software was used to perform univariate and multivariate logistic regression analyses and to investigate the patient and intervention factors associated with outcomes.

MAIN OUTCOME MEASURES:

Sensory function was assessed using the Mackinnon-Dellon scale and motor function was assessed using the manual muscle test. Satisfactory motor recovery was defined as grade M4 or M5, and satisfactory sensory recovery was defined as grade S3⁺ or S4.

RESULTS:

Seventy-one articles were included in this study. Univariate and multivariate logistic regression analyses showed that repair time, repair materials, and nerve injured were independent predictors of outcome after the repair of nerve injuries (P < 0.05), and that the nerve injured was the main factor affecting the rate of good to excellent recovery.

CONCLUSION:

Predictors of outcome after the repair of peripheral nerve injuries include age, gender, repair time, repair materials, nerve injured, defect length, and duration of follow-up.

Conductive PPY/PDLLA conduit for peripheral nerve regeneration

The significant drawbacks and lack of success associated with current methods to treat critically sized nerve defects have led to increased interest in neural tissue engineering. Conducting polymers show great promise due to their electrical properties, and in the case of polypyrrole (PPY), its cell compatibility as well. Thus, the goal of this study is to synthesize a conducting composite nerve conduit with PPY and poly(d, l-lactic acid) (PDLLA), assess its ability to support the differentiation of rat pheochromocytoma 12 (PC12) cells in vitro, and determine its ability to promote nerve regeneration in vivo. Different amounts of PPY (5%, 10%, and 15%) are used to synthesize the conduits resulting in different conductivities (5.65, 10.40, and 15.56 ms/cm, respectively). When PC12 cells are seeded on these conduits and stimulated with 100 mV for 2 h, there is a marked increase in both the percentage of neurite-bearing cells and the median neurite length as the content of PPY increased. More importantly, when the PPY/PDLLA nerve conduit was used to repair a rat sciatic nerve defect it performed similarly to the gold standard autologous graft. These promising results illustrate the potential that this PPY/PDLLA conducting composite conduit has for neural tissue engineering.

A biosynthetic nerve guide conduit based on silk/SWNT/fibronectin nanocomposite for peripheral nerve regeneration

As a contribution to the functionality of nerve guide conduits (NGCs) in nerve tissue engineering, here we report a conduit processing technique through introduction and evaluation of topographical, physical and chemical cues. Porous structure of NGCs based on freeze-dried silk/single walled carbon nanotubes (SF/SWNTs) has shown a uniform chemical and physical structure with suitable electrical conductivity. Moreover, fibronectin (FN) containing nanofibers within the structure of SF/SWNT conduits produced through electrospinning process have shown aligned fashion with appropriate porosity and diameter. Moreover, fibronectin remained its bioactivity and influenced the adhesion and growth of U373 cell lines. The conduits were then implanted to 10 mm left sciatic nerve defects in rats. The histological assessment has shown that nerve regeneration has taken places in proximal region of implanted nerve after 5 weeks following surgery. Furthermore, nerve conduction velocities (NCV) and more myelinated axons were observed in SF/SWNT and SF/SWNT/FN groups after 5 weeks post implantation, indicating a functional recovery for the injured nerves. With immunohistochemistry, the higher S-100 expression of Schwann cells in SF/SWNT/FN conduits in comparison to other groups was confirmed. In conclusion, an oriented conduit of biocompatible SF/SWNT/FN has been fabricated with acceptable structure that is particularly applicable in nerve grafts.

Sensory recovery outcome after digital nerve repair in relation to different reconstructive techniques: meta-analysis and systematic review

Good clinical outcome after digital nerve repair is highly relevant for proper hand function and has a significant socioeconomic impact. However, level of evidence for competing surgical techniques is low. The aim is to summarize and compare the outcomes of digital nerve repair with different methods (end-to-end and end-to-side coaptations, nerve grafts, artificial conduit-, vein-, muscle, and muscle-in-vein reconstructions, and replantations) to provide an aid for choosing an individual technique of nerve reconstruction and to create reference values of standard repair for nonrandomized clinical studies. 87 publications including 2,997 nerve repairs were suitable for a precise evaluation. For digital nerve repairs there was practically no particular technique superior to another. Only end-to-side coaptation had an inferior two-point discrimination in comparison to end-to-end coaptation or nerve grafting. Furthermore, this meta-analysis showed that youth was associated with an improved sensory recovery outcome in patients who underwent digital replantation. For end-to-end coaptations, recent publications had significantly better sensory recovery outcomes than older ones. Given minor differences in outcome, the main criteria in choosing an adequate surgical technique should be gap length and donor site morbidity caused by graft material harvesting. Our clinical experience was used to provide a decision tree for digital nerve repair.

Peripheral nerve repair with epimysium conduit

Autologous tissues such as skeletal muscle have high biocampatibility and can effectively promote nerve regeneration compared to other biological and artificial materials; however, the reasonable and effective application of skeletal muscle requires further study. The purpose of this investigation was to assess the possibility of preparing a hollow nerve conduit, termed the epimysium conduit (EMC), using thin crimps of epimysium with skeletal muscle fibers and evaluate its effectiveness in repairing peripheral nerve defects. We prepared nerve conduits containing lumen with the external oblique muscle of the CAG-EFGP transgenic mice using microsurgical techniques for bridge repair of a 5-mm long sciatic nerve defect in wild-type mice. Systematic histological and functional assessments of the regenerated nerves were performed 8 and 12 weeks after surgery. EMC was found to effectively repair the sciatic nerve defect with significantly greater effectiveness than artificial conduits; however, the repair effect of EMC was lower than that of autologous nerve grafting for some parameters. In addition, our findings showed that some EMC-derived cell components migrated into the region of the regenerated nerves and contributed to reconstruction. Based on these findings, we conclude that a hollow conduit prepared with epimysium and a few skeletal muscle fibers is ideal for repairing peripheral nerve defects, and the cell components in the grafts contribute to nerve regeneration and structural remodeling, which provides an alternative option for the emergency primary repair of peripheral nerve defects in clinical practice.

Peripheral nerve reconstruction with collagen tubes filled with denatured autologous muscle tissue in the rat model

Conventional nerve conduits lack cellular and extracellular guidance structures critical for bridging larger defects. In this study, an exogenous matrix for axonal regeneration was provided by pretreated muscle tissue. In 24 rats, 14-mm sciatic nerve segments were resected and surgically reconstructed using one of the following methods: autograft (AG); bovine type I collagen conduit; (MDM) collagen tube filled with modified denatured autologous muscle tissue. For 8 weeks, functional regeneration was evaluated by footprint and video gait analysis. Evaluation was complemented by electrophysiology, as well as qualitative and quantitative structural assessment of nerves and target muscles. Group AG was superior both structurally and functionally, showing higher axon counts, a more normal gait pattern, and less severe muscle atrophy. Fiber quality (fiber size and myelin thickness) was highest in group MDM, possibly related to the myelin-producing effect of muscular laminin. However, axon count was lowest in this group, and ultrastructural analysis of the denatured muscle tissue showed areas of incomplete denaturation that had acted as a mechanical barrier for regenerating axons. In light of these results, the often advocated use of muscular exogenous matrix for peripheral nerve reconstruction is reviewed in the literature, and its clinical application is critically discussed. In conclusion, combined muscle tubes may have a positive influence on nerve fiber maturation. However, muscle pretreatment is not without risks, and denaturation processes need to be further refined.

Shaping the military wound: issues surrounding the reconstruction of injured servicemen at the Royal Centre for Defence Medicine

The conflict in Afghanistan has produced injuries similar to those produced from military conflicts for generations. What distinguishes the modern casualty of the conflict in Afghanistan from those of other conflicts is the effectiveness of modern field medical care that has led to individuals surviving with injuries, which would have been immediately fatal even a few years ago. These patients present several challenges to the reconstructive surgeon. These injured individuals present early challenges of massive soft-tissue trauma, unstable physiology, complex bony and soft-tissue defects, unusual infections, limited reconstructive donor sites, peripheral nerve injuries and traumatic amputations. Late challenges to rehabilitation include the development of heterotopic ossification in amputation stumps. This paper outlines the approach taken by the reconstructive team at the Royal Centre for Defence Medicine in managing these most difficult of reconstructive challenges.

PDLLA/chondroitin sulfate/chitosan/NGF conduits for peripheral nerve regeneration

Biodegradable PDLLA/Chondroitin sulfate/Chitosan(PDLLA/CS/CHS) nerve conduits with potentially good biocompatibility and good mechanical property feasible for surgical manipulation have been developed in our previous work. The purpose of this study was to investigate their possible application in repairing damaged nerves and the effect of nerve growth factor (NGF). The PDLLA/CS/CHS/NGF nerve conduits were prepared by immobilizing NGF onto the PDLLA/CS/CHS nerve conduits with carbodiimide. Adult Sprague-Dawley (SD) rats weighing 200-250 g were used as the animal model. The conduits were employed to bridge the 10 mm defects in the sciatic nerve of the SD rats. Nerve conduction velocities (NCVs) were clearly detected in both nerve conduits after 3 months of implantation, indicating a rapid functional recovery for the disrupted nerves. The results of histological sections showed that the internal sides of the conduits were compact enough to prevent the connective tissues from ingrowth. Combined with the strong mechanical properties, good nerve regeneration ability and non-toxicity of its degradation products, PDLLA/CS/CHS nerve conduits would be expected to be useful materials to repair nerve damage and NGF can effectively promote the regeneration of peripheral nerve defect.

Clinical outcomes following median to radial nerve transfers

PURPOSE

To evaluate the clinical outcomes in patients with radial nerve palsy who underwent nerve transfers using redundant fascicles of median nerve (innervating the flexor digitorum superficialis and flexor carpi radialis muscles) to the posterior interosseous nerve and the nerve to the extensor carpi radialis brevis.

METHODS

This was a retrospective review of the clinical records of 19 patients with radial nerve injuries who underwent nerve transfer procedures using the median nerve as a donor nerve. All patients were evaluated using the Medical Research Council (MRC) grading system. The mean age of patients was 41 years (range, 17-78 y). All patients received at least 12 months of follow-up (range, 20.3 ± 5.8 mo). Surgery was performed at a mean of 5.7 ± 1.9 months postinjury.

RESULTS

Postoperative functional evaluation was graded according to the following scale: grades MRC 0/5 to MRC 2/5 were considered poor outcomes, whereas an MRC grade of 3/5 was a fair result, 4/5 was a good result, and 4+/5 was an excellent outcome. Postoperatively, all patients except one had good to excellent recovery of wrist extension. A total of 12 patients recovered good to excellent finger and thumb extension, 2 had fair recovery, and 5 had poor recovery.

CONCLUSIONS

The radial nerve is commonly injured, causing severe morbidity in affected patients. The median nerve provides a reliable source of donor nerve fascicles for radial nerve reinnervation. The important nuances of both surgical technique and motor reeducation critical for the success of this transfer have been identified and are discussed.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Ciliary neurotrophic factor-coated polylactic-polyglycolic acid chitosan nerve conduit promotes peripheral nerve regeneration in canine tibial nerve defect repair

A variety of nerve conduits incorporated with chemical and biological factors have been developed to further stimulate nerve regeneration. Although most of the nerve guides in studies are basically limited to bridge a short gap of nerve defect in rat models, it is vital to evaluate effects of conduits on nerve regeneration over distance greater than 20 mm, or more clinically relevant nerve gap lengths in higher mammals. In this study, a poly(lactide-co-glycolide) (PLGA) nerve conduit, treated with pulsed plasma and coated with ciliary neurotrophic factor (CNTF) as well as chitosan, was used to repair 25-mm-long canine tibial nerve defects in eighteen cross-bred dogs. The canines were randomly divided into three groups (n = 6), a 25-mm segment of the tibial nerve was removed and replaced by a PLGA/chitosan-CNTF nerve conduit, PLGA/chitosan conduit and autologous nerve grafts were performed as the control. The results were evaluated by general observation, electromyogram testing, S-100 histological immunostaining, and image analysis at 3 months after operation. The histological results demonstrated that the PLGA/chitosan-CNTF conduits and PLGA/chitosan conduits were capable of leading the damaged axons through the lesioned area. Through the comparison of the three groups, the results in PLGA/chitosan-CNTF conduits group were better than that of PLGA/chitosan conduits group, while they were similar to autologous nerve grafts group. Therefore, CNTF-coated PLGA/chitosan nerve conduits could be an alternative artificial nerve conduit for nerve regeneration.

Construction of tissue engineered nerve grafts and their application in peripheral nerve regeneration

Surgical repair of severe peripheral nerve injuries represents not only a pressing medical need, but also a great clinical challenge. Autologous nerve grafting remains a golden standard for bridging an extended gap in transected nerves. The formidable limitations related to this approach, however, have evoked the development of tissue engineered nerve grafts as a promising alternative to autologous nerve grafts. A tissue engineered nerve graft is typically constructed through a combination of a neural scaffold and a variety of cellular and molecular components. The initial and basic structure of the neural scaffold that serves to provide mechanical guidance and optimal environment for nerve regeneration was a single hollow nerve guidance conduit. Later there have been several improvements to the basic structure, especially introduction of physical fillers into the lumen of a hollow nerve guidance conduit. Up to now, a diverse array of biomaterials, either of natural or of synthetic origin, together with well-defined fabrication techniques, has been employed to prepare neural scaffolds with different structures and properties. Meanwhile different types of support cells and/or growth factors have been incorporated into the neural scaffold, producing unique biochemical effects on nerve regeneration and function restoration. This review attempts to summarize different nerve grafts used for peripheral nerve repair, to highlight various basic components of tissue engineered nerve grafts in terms of their structures, features, and nerve regeneration-promoting actions, and finally to discuss current clinical applications and future perspectives of tissue engineered nerve grafts.

Evaluation of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) conduits for peripheral nerve regeneration

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) was investigated for possible application in repairing damaged nerves. Porous nerve conduits with both uniform wall porosity and non-uniform wall porosity were prepared using a particle leaching method. Adult Sprague-Dawley (SD) rats weighing 200-250 g were used as the animal model. The conduits were employed to bridge the 10mm defects in the sciatic nerve of the Sprague-Dawley (SD) rats. Mechanical tests showed that the PHBHHx nerve conduits had proper mechanical properties including maximal loads of 3.1N and 1.3N for the conduits with non-uniform wall porosity and with uniform wall porosity, respectively, and maximal stresses of 2.3 MPa and 0.94 MPa for the conduits with non-uniform wall porosity and with uniform wall porosity, respectively. At the same time, both types of conduits were permeable to three compounds tested including glucose, lysozyme and bovine serum albumin, indicating the suitability of the conduits for free exchanges of nutrients. Compound Muscle Action Potentials (CMAPs) were clearly observed in both types of the PHBHHx nerve conduits after 1 month of implantation, indicating a rapid functional recovery for the disrupted nerves. The results of histological sections demonstrated that the internal sides of the conduits with non-uniform wall porosity were compact enough to prevent the connective tissues from ingrowth penetration. After implantation for 3 months in the rats, the conduits with uniform wall porosity and those with non-uniform wall porosity lost 24% and 20% of their original weight average molecular weights, respectively. Combined with the strong mechanical properties, good nerve regeneration ability and non-toxicity of its degradation products, PHBHHx nerve conduits can be developed into a useful material to repair nerve damage.

Expression of ATF3 and axonal outgrowth are impaired after delayed nerve repair

Background

A delay in surgical nerve repair results in impaired nerve function in humans, but mechanisms behind the weakened nerve regeneration are not known. Activating transcription factor 3 (ATF3) increases the intrinsic growth state of injured neurons early after injury, but the role of long-term changes and their relation to axonal outgrowth after a delayed nerve repair are not well understood. ATF3 expression was examined by immunohistochemistry in motor and sensory neurons and in Schwann cells in rat sciatic nerve and related to axonal outgrowth after transection and delayed nerve repair (repair 0, 30, 90 or 180 days post-injury). Expression of the neuronal cell adhesion molecule (NCAM), which is expressed in non-myelinating Schwann cells, was also examined.

Results

The number of neurons and Schwann cells expressing ATF3 declined and the length of axonal outgrowth was impaired if the repair was delayed. The decline was more rapid in motor neurons than in sensory neurons and Schwann cells. Regeneration distances over time correlated to number of ATF3 stained neurons and Schwann cells. Many neurofilament stained axons grew along ATF3 stained Schwann cells. If nerve repair was delayed the majority of Schwann cells in the distal nerve segment stained for NCAM.

Conclusion

Delayed nerve repair impairs nerve regeneration and length of axonal outgrowth correlates to ATF3 expression in both neurons and Schwann cells. Mainly non-myelinating Schwann cells (NCAM stained) are present in distal nerve segments after delayed nerve repair. These data provide a neurobiological basis for the poor outcomes associated with delayed nerve repair. Nerve trunks should, if possible, be promptly repaired.