The biology of nerve injury and repair

Biocompatible 3D-Printed Devices With Adipose Stem Cells in the Regenerative Process of Sciatic Nerve Lesions in Rodent Models: An Experimental Study

INTRODUCTION

Peripheral nerve injuries are a significant clinical challenge. The rat sciatic nerve serves as an ideal model for studying nerve regeneration. Extensive research has been conducted to unravel the intricate mechanisms involved in peripheral nerve regeneration, aiming to develop effective therapeutic strategies for nerve injury patients. Research including different types of materials that can be used as nerve guides like synthetic polymers have been investigated for their biocompatibility and molding properties. Among multiple stem cell types, adipose-derived stem cells (ASCs), bone marrow-derived mesenchymal stem cells (BM-MSCs), and induced pluripotent stem cells (iPSCs) have shown neuroprotective and regenerative important properties.

METHODS

The purposes of our study were to develop a protocol for rat sciatic nerve injury treated with 3D-printed guide and adipose stem cells to investigate nerve regeneration through histologic examination and biomechanical characteristics of muscular tissue. We use 20 (100%) male Wistar rats, measuring between 350 g ± 35 g, who underwent complete transection of the right sciatic nerve, resulting in a 1 cm defect. The group was separated into three subgroups: the first subgroup (n = 8) was treated with a 3D-printed guide with adipose stem cells, the second subgroup (n = 8) was treated with a 3D-printed guide without adipose stem cells, and the third subgroup (n = 4) was the control group. At four, eight, and 12 weeks, we measured with ultrasonography the grade of muscular atrophy. At 12 weeks, we harvested the sciatic nerve and performed a histological examination and mechanical investigation of the tibialis anterior muscle.

RESULTS

On the examined specimen of the first subgroup, cross-sectioned nerve structures were present, surrounded by a mature fibro-adipose connective tissue, with blood vessels. In the second subgroup, no nerve structure was observed on the examined sections, but in the polymorphic inflammatory infiltrate and control group, no signs of regeneration were found.

CONCLUSIONS

The present study shows a promising potential when utilizing adipose stem cell-based therapies for promoting peripheral nerve regeneration following large (>1 cm) nerve defects knowing that at this size, regeneration is impossible with known treatments.

Effects of exosomes from mesenchymal stem cells on functional recovery of a patient with total radial nerve injury: A pilot study

BACKGROUND

Peripheral nerve injury can result in significant clinical complications that have uncertain prognoses. Currently, there is a lack of effective pharmacological interventions for nerve damage, despite the existence of several small compounds, peptides, hormones, and growth factors that have been suggested as potential enhancers of neuron regeneration. Despite the objective of achieving full functional restoration by surgical intervention, the persistent challenge of inadequate functional recovery remains a significant concern in the context of peripheral nerve injuries.

AIM

To examine the impact of exosomes on the process of functional recovery following a complete radial nerve damage.

METHODS

A male individual, aged 24, who is right-hand dominant and an immigrant, arrived with an injury caused by a knife assault. The cut is located on the left arm, specifically below the elbow. The neurological examination and electrodiagnostic testing reveal evidence of left radial nerve damage. The sural autograft was utilized for repair, followed by the application of 1 mL of mesenchymal stem cell-derived exosome, comprising 5 billion microvesicles. This exosome was split into four equal volumes of 0.25 mL each and delivered microsurgically to both the proximal and distal stumps using the subepineural pathway. The patient was subjected to a period of 180 d during which they had neurological examination and electrodiagnostic testing.

RESULTS

The duration of the patient's follow-up period was 180 d. An increasing Tinel's sign and sensory-motor recovery were detected even at the 10th wk following nerve grafting. Upon the conclusion of the 6-mo post-treatment period, an evaluation was conducted to measure the extent of improvement in motor and sensory functions of the nerve. This assessment was based on the British Medical Research Council scale and the Mackinnon-Dellon scale. The results indicated that the level of improvement in motor function was classified as M5, denoting an excellent outcome. Additionally, the level of improvement in sensory function was classified as S3+, indicating a good outcome. It is noteworthy that these assessments were conducted in the absence of physical therapy. At the 10th wk post-injury, despite the persistence of substantial axonal damage, the nerve exhibited indications of nerve re-innervation as evidenced by control electromyography (EMG). In contrast to the preceding. EMG analysis revealed a significant electrophysiological enhancement in the EMG conducted at the 6th-mo follow-up, indicating ongoing regeneration.

CONCLUSION

Enhanced comprehension of the neurobiological ramifications associated with peripheral nerve damage, as well as the experimental and therapy approaches delineated in this investigation, holds the potential to catalyze future clinical progress.

Comparative Proteomic Analysis of Differentially Expressed Proteins between Injured Sensory and Motor Nerves after Peripheral Nerve Transection

Peripheral nerve repair and functional recovery depend on the rate of nerve regeneration and the quality of target reinnervation. It is important to fully understand the cellular and molecular basis underlying the specificity of peripheral nerve regeneration, which means achieving corresponding correct pathfinding and accurate target reinnervation for regrowing motor and sensory axons. In this study, a quantitative proteomic technique, based on isobaric tags for relative and absolute quantitation (iTRAQ), was used to profile the protein expression pattern between single motor and sensory nerves at 14 days after peripheral nerve transection. Among a total of 1259 proteins identified, 176 proteins showed the differential expressions between injured motor and sensory nerves. Quantitative RT-PCR and western blot analysis were applied to validate the proteomic data on representative differentially expressed proteins. Functional categorization indicated that differentially expressed proteins were linked to a diverse array of molecular functions, including axonogenesis, response to axon injury, tissue remodeling, axon ensheathment, cell proliferation and adhesion, vesicle-mediated transport, response to oxidative stress, internal signal cascade, and macromolecular complex assembly, which might play an essential role in peripheral motor and sensory nerve regeneration. Overall, we hope that the proteomic database obtained in this study could serve as a solid foundation for the comprehensive investigation of differentially expressed proteins between injured motor and sensory nerves and for the mechanism elucidation of the specificity of peripheral nerve regeneration. Data are available via ProteomeXchange with identifier PXD022097.

Neuroprotective Effects of Ozone Therapy After Sciatic Nerve Cut Injury

A number of antioxidants have been used to treat peripheral nerve injury. However, there are few definitive experimental studies of ozone therapy for peripheral nerve cut injury. We aimed to examine the effects of mild level ozone therapy on sciatic nerve regeneration. One hundred adult male Wistar albino rats were randomly divided into four groups: group 1 (n=20) no cut injury or therapy; group 2 (n=20) sham; group 3 (n=30) nerve cut injury, no therapy; group 4 (n=30) nerve cut injury and ozone therapy. Sciatic functional index (SFI) and withdrawal reflex (WDR) were measured for all groups before nerve cut, at postoperative day 1, and at weeks 2, 4, 6 and 8. More myelinated (M) nerve fibers were observed after nerve cut injury in the ozone-therapy group. Significant differences were seen in plasma SOD (superoxide dismutase), CAT (catalase) and GPx (glutathione peroxidase) activities (p<0.05), and significant functional improvement was observed at postoperative weeks 2 and 4 (p<0.05) after ozone treatment. This is the first study conducted for the purpose of examining the effects of ozone therapy on sciatic nerve cut injury.

Neurotrophin expression and histomorphometric evaluation in Wistar rats subjected to neural mobilization after compression of the median nerve

OBJECTIVE

To evaluate the neurotrophin mRNA expression and axon count in the median nerve of Wistar rats submitted to neural mobilization (NM) after nerve compression.

METHODS

Eighteen animals were randomly divided into G1 (nerve compression only), G2 (NM for 1 min), and G3 (NM for 3 min). For NM, the animals were anesthetized and the right scapula received the mobilization, adapted as indicated for humans, on alternate days, from the third to the 13th postoperative (PO) day, totaling six days of therapy. On the 14th PO day, animals were anesthetized and euthanized. Fragments of the median nerve, distal to the compression procedure, were removed for histomorphometric analysis and expression of neurotrophins, nerve growth factor (NGF), and brain-derived neurotrophic factor (BDNF) by RT-PCR.

RESULTS

Histomorphometric analysis revealed differences in the number of axons in the injured side, which was significantly lower in the injured limb nerve compared to the control limb, whereas the RT-PCR analysis showed no significant differences in the expression of NGF or BDNF.

CONCLUSION

NM treatment did not affect median nerve regeneration, which maintained normal recovery rates.

Laser Therapy in the Treatment of Paresthesia: A Retrospective Study of 125 Clinical Cases

OBJECTIVE

The aim of this retrospective study was to evaluate the effectiveness of laser therapy for acceleration and recovery of nerve sensitivity after orthognathic or minor oral surgeries, by analysis of clinical records of patients treated at the Special Laboratory of Lasers in Dentistry (LELO, School of Dentistry, University of São Paulo), throughout the period 2007-2013.

BACKGROUND DATA

Nerve tissue lesions may occur during various dental and routine surgical procedures, resulting in paresthesia. Laser therapy has been shown to be able to accelerate and enhance the regeneration of the affected nerve tissue; however, there are few studies in the literature that evaluate the effects of treatment with low-power laser on neural changes after orthognathic or minor oral surgeries.

METHODS

A total of 125 clinical records were included, and the data on gender, age, origin of the lesion, nerve, interval between surgery and onset of laser therapy, frequency of laser irradiation (one or two times per week), final evolution, and if there was a need to change the irradiation protocol, were all recorded. These data were related to the recovery of sensitivity in the affected nerve area. Descriptive analyses and modeling for analysis of categorical data (α=5%) were performed.

RESULTS

The results from both analyses showed that the recovery of sensitivity was correlated with patient age (p=0.015) and interval between surgery and onset of laser therapy (p=0.002).

CONCLUSIONS

Within the limits of this retrospective study, it was found that low- power laser therapy with beam emission band in the infrared spectrum (808 nm) can positively affect the recovery of sensitivity after orthognathic or minor oral surgeries.

Swimming does not alter nociception threshold in obese rats submitted to median nerve compression

OBJECTIVES

We, herein, analyzed the effect of swimming on nociception threshold and peripheral nerve regeneration in lean and obese rats submitted to median nerve compression.

METHODS

To induce obesity, newborn male Wistar rats received injections of monosodium glutamate (MSG), whereas the control (CTL) group received saline. The animals were separated into 6 groups; control and obese (CTL and MSG), control and obese with lesion (CTL LES and MSG LES), and control and obese with lesion submitted to physical exercise (CTL LES PE and MSG LES PE).

RESULTS

Median nerve compression reduced nociception threshold in CTL LES and MSG LES rats. Swimming effectively altered nociception only in CTL LES PE animals. Lean and obese animals displayed histological differences, when compared to sedentary animals, and exercise improved axon regeneration in both groups. The brain-derived neurotrophic factor and GAP 43 protein expression was greater in animals submitted to nervous compression without alteration by exercise.

DISCUSSION

In conclusion, swimming, a conservative treatment for peripheral nerve lesions, was not able to improve the nociception threshold in obese rats.

Biomaterial Approaches to Enhancing Neurorestoration after Spinal Cord Injury: Strategies for Overcoming Inherent Biological Obstacles

While advances in technology and medicine have improved both longevity and quality of life in patients living with a spinal cord injury, restoration of full motor function is not often achieved. This is due to the failure of repair and regeneration of neuronal connections in the spinal cord after injury. In this review, the complicated nature of spinal cord injury is described, noting the numerous cellular and molecular events that occur in the central nervous system following a traumatic lesion. In short, postinjury tissue changes create a complex and dynamic environment that is highly inhibitory to the process of neural regeneration. Strategies for repair are outlined with a particular focus on the important role of biomaterials in designing a therapeutic treatment that can overcome this inhibitory environment. The importance of considering the inherent biological response of the central nervous system to both injury and subsequent therapeutic interventions is highlighted as a key consideration for all attempts at improving functional recovery.

Effects of extracorporeal shock wave therapy on functional recovery and neurotrophin-3 expression in the spinal cord after crushed sciatic nerve injury in rats

The study described here investigated the effects of extracorporeal shock wave therapy (ESWT) on functional recovery and neurotrophin-3 expression in the spinal cord after sciatic nerve injury in rats. Forty-five 8-wk-old rats were used and randomly divided into three groups: An experimental group, a control group and a sham group. The experimental group received ESWT after the nerve-crushing damage. The sciatic functional index and Dartfish Software were used to determine the effect of sciatic nerve damage on functional changes. A 1-cm length of spinal cord encompassing the L4-6 level was removed for Western blot analysis. The sciatic functional index significantly changed in both the ESWT and control groups after impairment. In the time course evaluation of the ankle angle in the toe off, the ESWT group had statistically significant increases from day 21 onward. There was a significant difference in neurotrophin-3 expression between the groups on days 1, 7 and 14 after impairment. Early application of ESWT increased the expression of neurotrophin-3 and neurotrophin-3 mRNA, and daily therapy facilitated the activity of macrophages and Schwann cells, which affect the survival and regeneration of neurons.

Peripheral nerve regeneration: experimental strategies and future perspectives

Peripheral nerve injuries represent a substantial clinical problem with insufficient or unsatisfactory treatment options. This review summarises all the events occurring after nerve damage at the level of the cell body, the site of injury and the target organ. Various experimental strategies to improve neuronal survival, axonal regeneration and target reinnervation are described including pharmacological approaches and cell-based therapies. Given the complexity of nerve regeneration, further studies are needed to address the biology of nerve injury, to improve the interaction with implantable scaffolds, and to implement cell-based therapies in nerve tissue engineering.

Action of therapeutic laser and ultrasound in peripheral nerve regeneration

Objective

To assess the efficacy of early therapeutic laser and ultrasound in the regeneration process of an injury in rats.

Methods

We used 24 rats. Eighteen underwent surgery for sciatic nerve compression by a hemostat above the popliteal fossa. The animals were divided into three groups of six animals each. Normal control group. GI: Injured control without therapeutic intervention. GII: laser ArGaAl therapeutic intervention. GIII: therapeutic intervention of Pulsed Ultrasound. We begin therapeutic interventions 24 hours after injury, with daily applications for a period of fourteen consecutive days.

Results

In assessing the girth of the muscles of the right they, the following average decrease (in mm) for each GI: 0.45, GII: 0.42, GIII: 0.40 In relation to travel time, both GII and GIII presented significant difference when compared to GI. In the final evaluation of the IFC, GII excelled in the GIII. As for the healing observed, a major great improvement was observed in GII and GIII.

Conclusion

The results showed that nerve recovery was higher with the laser application. Level of evidence II, Therapeutic Studies - Investigation of the results of treatment.

Low-Level Laser-Accelerated Peripheral Nerve Regeneration within a Reinforced Nerve Conduit across a Large Gap of the Transected Sciatic Nerve in Rats

This study proposed a novel combination of neural regeneration techniques for the repair of damaged peripheral nerves. A biodegradable nerve conduit containing genipin-cross-linked gelatin was annexed using beta-tricalcium phosphate (TCP) ceramic particles (genipin-gelatin-TCP, GGT) to bridge the transection of a 15 mm sciatic nerve in rats. Two trigger points were irradiated transcutaneously using 660 nm of gallium-aluminum arsenide phosphide (GaAlAsP) via laser diodes for 2 min daily over 10 consecutive days. Walking track analysis showed a significant improvement in sciatic functional index (SFI) (P < 0.01) and pronounced improvement in the toe spreading ability of rats undergoing laser stimulation. Electrophysiological measurements (peak amplitude and area) illustrated by compound muscle action potential (CMAP) curves demonstrated that laser stimulation significantly improved nerve function and reduced muscular atrophy. Histomorphometric assessments revealed that laser stimulation accelerated nerve regeneration over a larger area of neural tissue, resulting in axons of greater diameter and myelin sheaths of greater thickness than that observed in rats treated with nerve conduits alone. Motor function, electrophysiological reactions, muscular reinnervation, and histomorphometric assessments all demonstrate that the proposed therapy accelerated the repair of transected peripheral nerves bridged using a GGT nerve conduit.

The brain-derived neurotrophic factor, nerve growth factor, neurotrophin-3, and induced nitric oxide synthase expressions after low-level laser therapy in an axonotmesis experimental model

BACKGROUND DATA

A robust body of evidence has shown that low-level laser therapy (LLLT) improves peripheral nerve regeneration. However, the biochemical background triggered in this process is not yet fully understood.

OBJECTIVE

The purpose of this study was to evaluate the mRNA expression of neurotrophic factors (brain-derived neurotrophic factor [BDNF], nerve growth factor [NGF], and neurotrophin-3, [NT-3]) and also an inflammatory marker (induced nitric oxide synthase [iNOS]) in an axonotmesis experimental model after low-level laser therapy.

METHODS

Thirty-six adult male Wistar rats (250-350 g) were subjected to right sciatic nerve crush injury, and 24 h later, the animals in the three different experimental groups (n=18) were irradiated on a daily basis with helium-neon laser (collimated HeNe laser, continuous emission, wavelength: 632.8 nm, power density: 0.5 mW/cm(2), irradiation time: 20 sec, energy density: 10 J/cm(2)) during 7, 14, and 21 consecutive days, respectively. The control group (n=18) underwent the same procedures, but with the equipment turned off. At the end of the experiments, animals were killed with an overdose of anesthesia to remove samples from the sciatic nerve lesion epicenter to determine the mRNA expression of BDNF, NGF, NT-3 and iNOS enzyme.

RESULTS

Comparisons between groups showed that HeNe laser increased the mRNA expression of both BDNF and NGF factors after 14 days of LLLT, with peak expression at the 21st day. Increase in NT-3 mRNA expression was not observed. In addition, HeNe laser produced iNOS expression reduction, which played an important role in the inflammatory process.

CONCLUSIONS

The reported data could have a relevant practical value because LLLT is a noninvasive procedure, and have revealed significant increase in neurotrophic factor expressions and inflammatory process reduction, opening the possibility of using LLLT as an important aid to nerve regeneration process.

Effects of large-area irradiated laser phototherapy on peripheral nerve regeneration across a large gap in a biomaterial conduit

This paper proposes a novel biodegradable nerve conduit comprising 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) cross-linked gelatin, annexed with β-tricalcium phosphate (TCP) ceramic particles (EDC-Gelatin-TCP, EGT). In this study, the EGT-implant site in rats was irradiated using a large-area 660 nm AlGaInP diode laser (50 mW) to investigate the feasibility of laser stimulation in the regeneration of a 15-mm transected sciatic nerve. The animals were divided into three groups: a sham-irradiated group (EGT/sham); an experimental group undergoing low-level laser (LLL) therapy (EGT/laser); a control group undergoing autologous nerve grafts (autografts). Twelve weeks after implantation, walking track analysis showed a significantly higher sciatic functional index (p < 0.05) and improved toe spreading development in the EGT/laser and autograft groups than in the EGT/sham group. In electrophysiological measurement, both the mean peak amplitude and the area under the compound muscle action potential curves in the EGT/laser and autograft groups showed significantly improved functional recovery than the EGT/sham group (p < 0.05). Compared with the EGT/sham group, the EGT/laser and autograft groups displayed a reduction in muscular atrophy. Histomorphometric assessments revealed that the EGT/laser group had undergone more rapid nerve regeneration than the EGT/sham group. The laser-treated group also presented greater neural tissue area as well as larger axon diameter and thicker myelin sheath than the tube group without the laser treatment, indicating improved nerve regeneration. Thus, these assessments demonstrate that LLL therapy can accelerate the repair of a transected peripheral nerve in rats after being bridged with EGT conduit.

Efeito do laser de baixa intensidade (660 nm) na regeneração do nervo isquiático lesado em ratos

Os nervos periféricos são estruturas que, ao sofrerem lesões, podem originar incapacidades motoras e sensitivas importantes. O laser de baixa intensidade é um dos diversos recursos terapêuticos para promover a regeneração nervosa precoce, mas ainda não há consenso sobre sua utilização. O objetivo deste estudo foi investigar, por meio de avaliação funcional, o efeito da terapia a laser de baixa intensidade (660 nm) na regeneração do nervo isquiático após esmagamento. Foram utilizados 18 ratos (Wistar) submetidos à lesão do nervo isquiático divididos em dois grupos, controle e grupo laser, submetido ao tratamento a laser (AsGaAl, 660 nm, 10J/cm2, 30 mW e 0,06 cm²) por 21 dias no local da lesão. Para a avaliação funcional, foi aplicado o índice funcional do ciático (IFC) no pré-operatório e nos 7º, 14º e 21º dias de pós-operatório. Quando comparados o IFC dos grupos no 14o dia de pós-operatório, foi encontrada melhora significante no grupo laser em relação ao controle. Na amostra analisada e nos parâmetros utilizados, pôde-se constatar que a aplicação do laser foi eficaz na recuperação funcional precoce do nervo ciático esmagado.

Comparative effects of wavelengths of low-power laser in regeneration of sciatic nerve in rats following crushing lesion

Peripheral nerves are structures that, when damaged, can result in significant motor and sensory disabilities. Several studies have used therapeutic resources with the aim of promoting early nerve regeneration, such as the use of low-power laser. However, this laser therapy does not represent a consensus regarding the methodology, thus yielding controversial conclusions. The objective of our study was to investigate, by functional evaluation, the comparative effects of low-power laser (660 nm and 830 nm) on sciatic nerve regeneration following crushing injuries. Twenty-seven Wistar rats subjected to sciatic nerve injury were divided into three groups: group sham, consisting of rats undergoing simulated irradiation; a group consisting of rats subjected to gallium-aluminum-arsenide (GaAlAs) laser at 660 nm (10 J/cm(2), 30 mW and 0.06 cm(2) beam), and another one consisting of rats subjected to GaAlAs laser at 830 nm (10 J/cm(2), 30 mW and 0.116 cm(2)). Laser was applied to the lesion for 21 days. A sciatic functional index (SFI) was used for functional evaluation prior to surgery and on days 7, 14, and 21 after surgery. Differences in SFI were found between group 660 nm and the other ones at the 14th day. One can observe that laser application at 660 nm with the parameters and methods utilised was effective in promoting early functional recovery, as indicated by the SFI, over the period evaluated.

Injury to the radial nerve caused by fracture of the humeral shaft:Timing and neurobiological aspects related to treatment and diagnosis

The radial nerve may not function in association with fractures of the humeral shaft. There are various opinions about the causes and treatment. We report a case of complete rupture of the radial nerve after a fracture of the proximal shaft of the humerus. The nerve injury was treated with grafting and TENDON transfer. Here we discuss diagnoses and treatments including neurobiological aspects of nervous regeneration. We suggest that electrodiagnostic examination after a radial nerve palsy caused by a humeral fracture is done 5-6 weeks after injury and that nerve repair and reconstruction should be done within two, and not later than three, months after injury.

Influence of laser (660 nm) on functional recovery of the sciatic nerve in rats following crushing lesion

With the aim of accelerating the regenerative processes, the objective was to study the influence of gallium-aluminum-arsenide (GaAlAs) laser (660 nm) on functional and histomorphological recovery of the sciatic nerve in rats. The sciatic nerves of 12 Wistar rats were crushed divided into two groups: control and laser therapy. For the latter, GaAlAs laser was utilized (660 nm, 4 J/cm(2), 26.3 mW and 0.63 cm(2) beam), at three equidistant points on the lesion, for 20 days. Comparison of the sciatic functional index (SFI) showed that there was a significant difference only between the pre-lesion value of the laser therapy group and that after the 21st day in the control group. It was concluded that the parameters and methods utilized demonstrated positive results regarding the SFI over the time period evaluated.

Effect of laser therapy (660 nm) on recovery of the sciatic nerve in rats after injury through neurotmesis followed by epineural anastomosis

The aim of this study was to analyze the influence of aluminum gallium arsenide (AlGaAs) laser (660 nm) on the myelin sheath and functional recovery of the sciatic nerve in rats. The sciatic nerves of 12 Wistar rats were subjected to injury through neurotmesis and epineural anastomosis, and the animals were divided into two groups: group 1 was the control and group 2, underwent low-level laser therapy (LLLT). After the injury, AlGaAs laser at 660 nm, 4 J/cm(2), 26.3 mW and beam area of 0.63 cm(2) was administered to three equidistant points on the injury for 20 consecutive days. In the control group the mean area of the myelin impairment was 0.51 (+/- 0.11) on day 21 after the operation, whereas this value was 1.31 (+/- 0.22) in the LLLT group. Student's t-test revealed a P value = 0.0229 for the mean area values of the myelin sheath between the LLLT and control groups. Comparison of the sciatic functional index (SFI) showed that there was no significant difference between the pre-lesion value in the laser therapy group and the control group. The use of AlGaAs laser (660 nm) provided significant changes to the morphometrically assessed area of the myelin sheath, but it did not culminate in positive results for functional recovery in the sciatic nerve of the rats after injury through neurotmesis.

Hand function after nerve repair

Treatment of injuries to major nerve trunks in the hand and upper extremity remains a major and challenging reconstructive problem. Such injuries may cause long-lasting disabilities in terms of lost fine sensory and motor functions. Nowadays there is no surgical repair technique that can ensure recovery of tactile discrimination in the hand of an adult patient following nerve repair while very young individuals usually regain a complete recovery of functional sensibility. Post-traumatic nerve regeneration is a complex biological process where the outcome depends on multiple biological and environmental factors such as survival of nerve cells, axonal regeneration rate, extent of axonal misdirection, type of injury, type of nerve, level of the lesion, age of the patient and compliance to training. A major problem is the cortical functional reorganization of hand representation which occurs as a result of axonal misdirection. Although protective sensibility usually occurs following nerve repair, tactile discriminative functions seldom recover--a direct result of cortical remapping. Sensory re-education programmes are routinely applied to facilitate understanding of the new sensory patterns provided by the hand. New trends in hand rehabilitation focus on modulation of central nervous processes rather than peripheral factors. Principles are being evolved to maintain the cortical hand representation by using the brain capacity for visuo-tactile and audio-tactile interaction for the initial phase following nerve injury and repair (phase 1). After the start of the re-innervation of the hand (phase 2), selective de-afferentation, such as cutaneous anaesthesia of the forearm of the injured hand, allows expansion of the nerve-injured cortical hand representation, thereby enhancing the effects of sensory relearning. Recent data support the view that training protocols specifically addressing the relearning process substantially increase the possibilities for improved functional outcome after nerve repair.