Analysis of upper and lower extremity peripheral nerve injuries in a population of patients with multiple injuries

A (heat) shock to the system promotes peripheral nerve regeneration

Peripheral nerves are easily damaged, resulting in loss of motor and sensory function. Recovery of motor and sensory function after peripheral nerve injury is suboptimal, even after appropriate surgical repair. This is due to the slow rate of axonal elongation during regeneration and atrophic changes that occur in denervated Schwann cells and target muscle with proximal lesions. One way to solve this problem is to accelerate the rate at which the axons regenerate. In this issue of the JCI, Ma and colleagues show that this can be achieved in mice by overexpression of heat shock protein 27, providing hope for enhanced functional recovery in patients after peripheral nerve damage.

Biomaterials for the development of peripheral nerve guidance conduits

Currently, surgical treatments for peripheral nerve injury are less than satisfactory. The gold standard of treatment for peripheral nerve gaps >5 mm is the autologous nerve graft; however, this treatment is associated with a variety of clinical complications, such as donor site morbidity, limited availability, nerve site mismatch, and the formation of neuromas. Despite many recent advances in the field, clinical studies implementing the use of artificial nerve guides have yielded results that are yet to surpass those of autografts. Thus, the development of a nerve guidance conduit, which could match the effectiveness of the autologous nerve graft, would be beneficial to the field of peripheral nerve surgery. Design strategies to improve surgical outcomes have included the development of biopolymers and synthetic polymers as primary scaffolds with tailored mechanical and physical properties, luminal "fillers" such as laminin and fibronectin as secondary internal scaffolds, surface micropatterning, stem cell inclusion, and controlled release of neurotrophic factors. The current article highlights approaches to peripheral nerve repair through a channel or conduit, implementing chemical and physical growth and guidance cues to direct that repair process.

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.

Acellular nerve allografts in peripheral nerve regeneration: a comparative study

INTRODUCTION

Processed nerve allografts offer a promising alternative to nerve autografts in the surgical management of peripheral nerve injuries where short deficits exist.

METHODS

Three established models of acellular nerve allograft (cold-preserved, detergent-processed, and AxoGen-processed nerve allografts) were compared with nerve isografts and silicone nerve guidance conduits in a 14-mm rat sciatic nerve defect.

RESULTS

All acellular nerve grafts were superior to silicone nerve conduits in support of nerve regeneration. Detergent-processed allografts were similar to isografts at 6 weeks postoperatively, whereas AxoGen-processed and cold-preserved allografts supported significantly fewer regenerating nerve fibers. Measurement of muscle force confirmed that detergent-processed allografts promoted isograft-equivalent levels of motor recovery 16 weeks postoperatively. All acellular allografts promoted greater amounts of motor recovery compared with silicone conduits.

CONCLUSION

These findings provide evidence that differential processing for removal of cellular constituents in preparing acellular nerve allografts affects recovery in vivo.

Non-viral genetic transfection of rat Schwann cells with FuGENE HD© lipofection and AMAXA© nucleofection is feasible but impairs cell viability

Purpose:

To determine transfection efficiency of FuGENE HD© lipofection and AMAXA© nucleofection on rat Schwann cells (SC).

Methods:

The ischiadic and median nerves of 6-8 week old Lewis rats were cultured in modified melanocyte-growth medium. SCs were genetically transfected with green fluorescent protein (GFP) as reporter gene using FuGENE HD© lipofection and AMAXA© nucleofection. Transfection rates were determined by visualization of GFP fluorescence under fluorescence microscopy and cell counting. Transfected cell to non-transfected cell relation was determined.

Results:

Purity of Schwann cell culture was 88% as determined by immunohistologic staining. Transfection rate of FuGENE HD© lipofection was 2%, transfection rate of AMAXA© nucleofection was 10%. With both methods, Schwann cells showed pronounced aggregation behavior which made them unfeasible for further cultivation. Settling of Schwann cells on laminin and poly-l-ornithine coated plates was compromised by either method.

Conclusion:

Non-viral transfection of rat SC with FuGENE HD© lipofection and AMAXA© nucleofection is basically possible with a higher transfection rate for nucleofection than for lipofection. As cell viability is compromised by either method however, viral transfection is to be considered if higher efficiency is required.

Potentials and limitations of peripheral nerve injury models in rodents with particular reference to the femoral nerve

Restoration of function after peripheral nerve repair in humans is unsatisfactory. Various causes of poor recovery have been proposed. Still, we do not understand which of these potential factors are indeed detrimental and do not know how to manipulate them experimentally in a clinically feasible way. Future success largely depends on methodological improvement in rodent models. An example of recent progress is the introduction of new functional and anatomical outcome measures in the facial nerve injury paradigm which led to novel insights into facial nerve regeneration and a new therapeutic concept. Less success can be ascribed to the use of the classical spinal nerve model, the sciatic nerve paradigm, not least because of its anatomical and functional complexity making assessment of recovery challenging. A simpler alternative to the sciatic nerve is the femoral nerve model. It offers, alongside with its known usefulness for studies on precision of motor reinnervation, the possibility of reliable functional assessments and a straightforward search of anatomical substrates of dysfunction. The structure-function approach in the femoral nerve paradigm has been useful for testing of novel therapeutic means and analyses of regeneration in mutant mice. The potential of the method has still not been really exploited and its more extensive use may contribute to better understanding of nerve regeneration.

Short-term motor compensations to denervation of feline soleus and lateral gastrocnemius result in preservation of ankle mechanical output during locomotion

Denervation of selected ankle extensors in animals results in locomotor changes. These changes have been suggested to permit preservation of global kinematic characteristics of the hindlimb during stance. The peak ankle joint moment is also preserved immediately after denervation of several ankle extensors in the cat, suggesting that the animal's response to peripheral nerve injury may also be aimed at preserving ankle mechanical output. We tested this hypothesis by comparing joint moments and power patterns during walking before and after denervation of soleus and lateral gastrocnemius muscles. Hindlimb kinematics, ground reaction forces and electromyographic activity of selected muscles were recorded during level, downslope (-50%) and upslope (50%) walking before and 1-3 weeks after nerve denervation. Denervation resulted in increased activity of the intact medial gastrocnemius and plantaris muscles, greater ankle dorsiflexion, smaller knee flexion, and the preservation of the peak ankle moment during stance. Surprisingly, ankle positive power generated in the propulsion phase of stance was increased (up to 50%) after denervation in all walking conditions (p < 0.05). The obtained results suggest that the short-term motor compensation to denervation of lateral gastrocnemius and soleus muscles may allow for preservation of mechanical output at the ankle. The additional mechanical energy generated at the ankle during propulsion can result, in part, from increased activity of intact synergists, the use of passive tissues around the ankle and by the tendon action of ankle two-joint muscles and crural fascia.

Inducible nerve growth factor delivery for peripheral nerve regeneration in vivo

BACKGROUND

HEK-293 cells can be genetically modified to release and regulate nerve growth factor (NGF) in vitro. The aim of this study was to evaluate the impact of this NGF delivery system on peripheral nerve regeneration in vivo.

METHODS

HEK-293 cells were transfected with an ecdysone receptor, NGF cDNA, and herpes simplex virus-thymidine kinase suicide vector. NGF production is induced by ponasterone A and stopped by ganciclovir. A 13-mm sciatic nerve gap was bridged with Silastic conduits in 120 nude rats, and transfected HEK-293 cells were added, induced, and boostered to secrete bioactive NGF.

RESULTS

The induction of the cell line and additional booster with ponasterone A demonstrated significantly higher levels of bioactive NGF, enhanced macroscopic nerve growth, improved functional recovery, and histologic regeneration when compared with control groups after 7, 14, and 21 days, and 2 and 4 months. The treatment with ganciclovir resulted in suppression of the NGF production and decreased functional and histologic outcomes.

CONCLUSIONS

Transfected HEK-293 cells can be regulated to inducibly produce bioactive NGF in vivo over prolonged periods. This tissue-engineered nerve construct including the NGF delivery system is able to improve peripheral nerve regeneration and functional recovery and appears to be superior to nerve isografts.

Three-dimensional alignment of schwann cells using hydrolysable microfiber scaffolds: strategies for peripheral nerve repair

Injuries to the peripheral nervous system affect 1 in 1,000 individuals each year. The implication of sustaining such an injury is considerable with loss of sensory and/or motor function. The economic implications too are extensive running into millions of pounds (or dollars) annually for provision and support. The natural regrowth of peripheral nerves is possible for small gap injuries (of approximately 1-2 mm). However, patients with larger gap injuries require surgical intervention. The "gold standard" for repairing gap injuries is autografting; however, there are problems associated with this approach, and so, the use of nerve guidance conduits (NGC) is a realistic alternative. We outline in this chapter the development of an NGC that incorporates aligned poly-L-lactide fibres for supporting the growth of organised Schwann cells within a three-dimensional scaffold in vitro. A closed loop bioreactor for growing cells within NGC scaffolds is described together with a method of plasma deposition for modifying the microfibre surface chemistry (which improves the ability of Schwann cells to attach) and confocal microscopy for measuring cell viability and alignment within 3D constructs.

A novel motion analysis approach reveals late recovery in C57BL/6 mice and deficits in NCAM-deficient mice after sciatic nerve crush

Assessment of motor abilities after sciatic nerve injury in rodents, in particular mice, relies exclusively on walking track (footprint) analysis despite known limitations of this method. Using principles employed recently for video-based motion analyses after femoral nerve and spinal cord injuries, we have designed and report here a novel approach for functional assessments after sciatic nerve lesions in mice. Functional deficits are estimated by angle and distance measurements on single video frames recorded during beam-walking and inclined ladder climbing. Analyses of adult C57BL/6J mice after crush of the sciatic, tibial, or peroneal nerve allowed the identification of six numerical parameters, detecting impairments of the plantar flexion of the foot and the toe spread. Some of these parameters, as well as footprint functional indices, revealed severe impairment after crush injury of the sciatic or tibial, but not the peroneal nerve, and complete recovery within 3 weeks after lesion. Other novel estimates, however, showed that complete recovery is reached as late as 2-3 months after sciatic nerve crush. These measures detected both tibial and peroneal dysfunction. In contrast to the complete restoration of function in wild-type mice (100%), our new parameters, in contrast to the sciatic functional index, showed incomplete recovery (85%) 90 days after sciatic nerve crush in mice deficient in the neural cell adhesion molecule (NCAM). We conclude that the novel video-based approach is more precise, sensitive, and versatile than established tests, allowing objective numerical assessment of different motor functions in a sciatic nerve injury paradigm in mice.

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.

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.

Phototherapy in peripheral nerve regeneration: From basic science to clinical study

OBJECT

This review summarizes the continuous study of low-power laser radiation treatment of a severely injured peripheral nerve. Laser phototherapy was applied as a supportive factor for accelerating and enhancing axonal growth and regeneration after injury or a reconstructive peripheral nerve procedure. In nerve cell cultures, laser phototherapy was used to stimulate activation of nerve cells.

METHODS

Low-power laser radiation was used for treatment of peripheral nerve injury using a rat sciatic nerve model after crush injury, neurorrhaphy, or neurotube reconstruction. Nerve cell growth and axonal sprouting were investigated using laser phototherapy on embryonic rat brain cultures. The outcome in animal studies facilitated a clinical double-blind, placebo-controlled, randomized study that measured the effectiveness of 780-nm laser phototherapy on patients suffering from incomplete peripheral nerve injuries for 6 months to several years.

RESULTS

Animal studies showed that laser phototherapy has an immediate protective effect, maintains functional activity of the injured nerve, decreases scar tissue formation at the injury site, decreases degeneration in corresponding motor neurons of the spinal cord, and significantly increases axonal growth and myelinization. In cell cultures, laser irradiation accelerates migration, nerve cell growth, and fiber sprouting. A pilot clinical double-blind, placebocontrolled, randomized study showed that in patients with incomplete long-term peripheral nerve injury, 780-nm laser radiation can progressively improve peripheral nerve function, which leads to significant functional recovery.

CONCLUSIONS

Using 780-nm laser phototherapy accelerates and enhances axonal growth and regeneration after injury or a reconstructive peripheral nerve procedure. Laser activation of nerve cells, their growth, and axonal sprouting can be considered as potential treatment of neuronal injury. Animal and clinical studies show the promoting action of phototherapy on peripheral nerve regeneration, making it possible to suggest that the time for broader clinical trials has arrived.

Repairing injured peripheral nerves: Bridging the gap

Peripheral nerve injuries that induce gaps larger than 1-2 cm require bridging strategies for repair. Autologous nerve grafts are still the gold standard for such interventions, although alternative treatments, as well as treatments to improve the therapeutic efficacy of autologous nerve grafting are generating increasing interest. Investigations are still mostly experimental, although some clinical studies have been undertaken. In this review, we aim to describe the developments in bridging technology which aim to replace the autograft. A multi-disciplinary approach is of utmost importance to develop and optimise treatments of the most challenging peripheral nerve injuries.

The role of nerve allografts and conduits for nerve injuries

Nerve repair after transection has variable and unpredictable outcomes. In addition to advancements in microvascular surgical techniques, nerve allografts and conduits are available options in peripheral nerve reconstruction. When tensionless nerve repair is not feasible, or in chronic injuries, autografts have been traditionally used. As substitute to autografts, decellularized allografts and conduits have become available. These conduits can reduce donor site morbidity, functional loss at the donor area in cases where autografts are used, and immune reaction from transplants or unprocessed allografts. The development of new biomaterials for use in conduits, as well as use of cytokines, growth factors, and other luminal fillers, may help in the treatment of acute and chronic nerve injuries. The indications and properties of nerve conduits and allografts are detailed in this article.

Neuropathic pain in patients with upper-extremity nerve injury

PURPOSE

The purpose of this review was to present an analysis of the literature of the outcome studies reported in patients following traumatic upper-extremity (UE) nerve injuries (excluding amputation), to assess the presence of an association between neuropathic pain and outcome in patients following traumatic UE nerve injuries, and to provide recommendations for inclusion of more comprehensive outcome measures by clinicians who treat these patients.

SUMMARY OF KEY POINTS

A Medline and CINAHL literature search retrieved 48 articles. This review identified very few studies of patients with peripheral nerve injury that reported neuropathic pain. When pain was reported, visual analogue or numeric rating scales were most frequently used; standardized questionnaires measuring pain or psychosocial function were rarely administered. Recent evidence shows substantial long-term disability and pain in patients following peripheral nerve injury.

RECOMMENDATION

To better understand neuropathic pain in patients following peripheral nerve injury, future outcome studies should include valid, reliable measures of physical impairment, pain, disability, health-related quality of life, and psychosocial functioning.

Dynamic quantification of host Schwann cell migration into peripheral nerve allografts

Host Schwann cell (SC) migration into nerve allografts is the limiting factor in the duration of immunosuppression following peripheral nerve allotransplantation, and may be affected by different immunosuppressive regimens. Our objective was to compare SC migration patterns between clinical and experimental immunosuppression regimens both over time and at the harvest endpoint. Eighty mice that express GFP under the control of the Schwann cell specific S100 promoter were engrafted with allogeneic, nonfluorescent sciatic nerve grafts. Mice received immunosuppression with either tacrolimus (FK506), or experimental T-cell triple costimulation blockade (CSB), consisting of CTLA4-immunoglobulin fusion protein, anti-CD40 monoclonal antibody, and anti-inducible costimulator monoclonal antibody. Migration of GFP-expressing host SCs into wild-type allografts was assessed in vivo every 3 weeks until 15 weeks postoperatively, and explanted allografts were evaluated for immunohistochemical staining patterns to differentiate graft from host SCs. Immunosuppression with tacrolimus exhibited a plateau of SC migration, characterized by significant early migration (< 3 weeks) followed by a constant level of host SCs in the graft (15 weeks). At the endpoint, graft fluorescence was decreased relative to surrounding host nerve, and donor SCs persisted within the graft. CSB-treated mice displayed gradually increasing migration of host SCs into the graft, without the plateau noted in tacrolimus-treated mice, and also maintained a population of donor SCs at the 15-week endpoint. SC migration patterns are affected by immunosuppressant choice, particularly in the immediate postoperative period, and the use of a single treatment of CSB may allow for gradual population of nerve allografts with host SCs.

Nerve injuries of the upper extremity-expected outcome and clinical examination

Nerve injuries are common in trauma surgery and appear more frequently if the upper extremity is affected. The aim of this study is to estimate possible predictors of the outcome after nerve injury of the upper extremity and to demonstrate feasible tools to follow up postoperative nerve regeneration for the daily clinical practice. During January 2000 until December 2004, a total of 372 nerve lesions of the upper extremity have been treated in our clinic. Patient's age, site of nerve lesion, concomitant injuries, and the timing of surgical repair could be outlined to be significant predictors for clinical outcome. Digital nerve lesions showed the best regenerative capacity. Most predictors of clinical outcome such as patient's age, concomitant injuries, and site of lesion cannot be influenced. But knowing the predictors helps specify the prognosis of nerve regeneration. For the daily clinical practice, static two-point discrimination, location of Tinel's sign, and grip strength measurement seem to be fast and reproducible tools to follow up nerve regeneration at the upper extremity.

Functional outcome and health status of injured patients with peripheral nerve lesions

BACKGROUND

Peripheral nerve lesions (PNLs) can complicate the clinical course and outcome of multiply injured patients. Since this often impedes recovery, it can be a significant burden for both patients and clinicians. The objective of the present study was to investigate the long-term outcome and health status of patients with PNL.

SUBJECTS AND METHODS

Multiply injured patients admitted to an intensive rehabilitation setting were identified. The Barthel and modified Rankin scales (mRS) were administered to all patients at admission, discharge and follow-up. The short form (SF)-36 questionnaire was used at follow-up (mean: 25.3+/-6.5 months).

RESULTS

Seventy-seven multiply injured patients were identified, and 45 (22 male, 23 female; mean age: 59.7+/-21.7 years; range: 19-83 years) were enrolled. Of the injured patients, 22 subjects (10 male and 12 female) had no PNL, while 23 (12 male, 11 female) did. In the PLN group, the mean Barthel scores at admission, discharge and follow-up, respectively, were 33.4+/-17.9, 85.3+/-3.8 and 93.0+/-6.9 (p<0.001) and the median mRS scores were 4 (interquartile range (IQR): 3-5), 3 (IQR: 1-3) and 1 (IQR: 0-2), respectively. In the group without PLN, the mean Barthel scores at admission, discharge and follow-up, respectively, were 30.4+/-14.5, 86.6+/-9.8 and 96.6+/-4.9 (p<0.001) and the median mRS scores were 4 (IQR: 3-5), 2 (IQR: 1-3) and 0.5 (IQR: 0-2). The mean length of hospital stay was 86.7+/-10.8 and 65.6+/-14.6 days in patients with and without PNL, respectively. The SF-36 did not show significant differences between the groups, but the patients with and without PNL reported significant lower mean scores on all items compared to national population norms.

CONCLUSION

Multiply injured patients with and without PNL showed significant improvement and a good long-term outcome after rehabilitation. However, those with PNL had a longer hospital stay and needed more rehabilitation than patients without PNL. Both the groups of patients experienced significant difficulties in the health status.

Motoneuron survival after chronic and sequential peripheral nerve injuries in the rat

OBJECT

Surgical repair of peripheral nerves following chronic nerve injury is associated with poor axonal regeneration and outcome. An underlying possibility is that chronic injuries may increase motoneuron cell death. The hypothesis that substantial motoneuron death follows chronic and sequential nerve injuries was tested in adult rats in this study.

METHODS

Thirty adult male Lewis rats underwent bilateral multistage surgeries. At initial surgery, Fast Blue (FB) tracer was injected at a nerve-crush injury site in the right control femoral motor nerve. The left femoral motor nerve was transected at the same level and either capped to prevent regeneration (Group 1), or repaired to allow axonal regeneration and reinnervation of the target quadriceps muscle (Group 2) (15 rats in each group). After 8 weeks in 6 rats/group, the left femoral nerve was cut and exposed to FB just proximal to prior nerve capping or repair and the rats were evaluated for FB-labeled motoneuron counts bilaterally in the spinal cord (this was considered survival after initial injury). In the remaining 9 animals/group, the left nerve was recut (sequential injury), exposed to FB, and repaired to a fresh distal saphenous nerve stump to permit axonal regeneration. Following another 6 weeks, Fluoro-Gold, a second retrograde tracer, was applied to the cut distal saphenous nerve. This allowed us to evaluate the number of motoneurons that survived (maintained FB labeling) and the number of motoneurons that survived but that also regenerated axons (double labeled with FB and Fluoro-Gold).

RESULTS

A mean number of 350 and 392 FB-labeled motoneurons were found after 8 weeks of nerve injury on the right and the left sides, respectively. This indicated no significant cell death due to initial nerve injury alone. A similar number (mean 390) of motoneurons were counted at final end point at 14 weeks, indicating no significant cell death after sequential and chronic nerve injury. However, only 50% (mean 180) of the surviving motoneurons were double labeled, indicating that only half of the population regenerated their axons.

CONCLUSIONS

The hypothesis that significant motoneuron cell death occurs after chronic and or sequential nerve injury was rejected. Despite cell survival, only 50% of motoneurons are capable of exhibiting a regenerative response, consistent with our previous findings of reduced regeneration after chronic axotomy.

Use of stem cells to augment nerve injury repair

OBJECTIVE

The purpose of this review is to summarize the basic science literature related to chronic nerve injuries, and to then use this as the background to provide emerging insights into the promising role of cellular therapy for nerve injury repair.

METHODS

The literature pertinent to the experimental and clinical aspects of chronic nerve injury was reviewed, as was emerging literature and our own recent experience in using cellular therapy to repair injured nerves.

RESULTS

Peripheral nerves have the potential to regenerate axons and reinnervate end organs. Yet, outcome after peripheral nerve injury, even after nerve repair, remains relatively poor. The single most important quantitative contributor to poor motor recovery is chronic denervation of the distal nerve. Chronic denervation is common because of the often extensive injury zone that prevents any axonal outgrowth or (even if outgrowth occurs) the relatively slow rate of regeneration. As a consequence, the distal nerve remains chronically devoid of regrowing axons. In turn, prolonged denervation of Schwann cells (SCs) seems to be the critical factor that makes them unreceptive for axonal regeneration. Regenerative success was demonstrated when denervated SCs were replaced with healthy SCs cultured from a secondary nerve. This cell-replacement strategy is, however, limited in the clinical setting by the inability to obtain sufficient numbers of cells and the requirement for sacrifice of additional nerve tissue. We, along with several other groups, have therefore begun investigating stem cell therapies to improve the regenerative environment.

CONCLUSION

There are several avenues of stem cell-based approaches to peripheral nerve repair. One of these, skin-derived precursor cells, are easily accessible, autologous adult stem cells that can survive and myelinate in the peripheral nerve environment and become SC-like in their apparent differentiation.

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.

Polymers for Fabricating Nerve Conduits

Peripheral nerve regeneration is a complicated and long-term medical challenge that requires suitable guides for bridging nerve injury gaps and restoring nerve functions. Many natural and synthetic polymers have been used to fabricate nerve conduits as well as luminal fillers for achieving desired nerve regenerative functions. It is important to understand the intrinsic properties of these polymers and techniques that have been used for fabricating nerve conduits. Previously extensive reviews have been focused on the biological functions and in vivo performance of polymeric nerve conduits. In this paper, we emphasize on the structures, thermal and mechanical properties of these naturally derived synthetic polymers, and their fabrication methods. These aspects are critical for the performance of fabricated nerve conduits. By learning from the existing candidates, we can advance the strategies for designing novel polymeric systems with better properties for nerve regeneration.

Ethyl-cyanoacrylate is acutely nontoxic and provides sufficient bond strength for anastomosis of peripheral nerves

Anastomosis is a common technique for the union of severed nerve trunks. This is commonly performed with sutures, a process that can be both time consuming and injurious to tissue. One promising alternative to suturing is the use of adhesives to join the severed segments. Cyanoacrylate-based glues have been used clinically as a surgical adhesive for soft tissues. However, the acute effects of these glues on nerve electrophysiology and the tensile strength of the rejoined tissues have not been evaluated. Using a guinea pig model, we analyzed the mechanical properties of transected sciatic nerves repaired with epineural application of ethyl-cyanoacrylate and the short term consequences of cyanoacrylate application on impulse conduction. Results showed that nerves coapted with ethyl-cyanoacrylate were capable of bearing in vivo forces. Additionally, no acute effects on conduction were observed in uninjured sciatic nerves exposed to ethyl-cyanoacrylate. In conjunction with long term in vivo reports from literature, the current results support the use of cyanoacrylates in nerve repair.

Non-invasive imaging of nerve regeneration

The need for non-invasive imaging of peripheral nerves that can reliably assess extent of nerve fiber degeneration and regeneration is increasingly realized. Availability of such a technology has several immediate clinical and preclinical applications. Diffusion tensor imaging (DTI) is an emerging magnetic resonance based technology that is particularly suited for imaging nerve fiber tracts. This review highlights immediate clinical and preclinical uses of non-invasive imaging of peripheral nerve regeneration and DTI as a potential technology that can fulfill these clinical and research needs.

Practical considerations concerning the use of stem cells for peripheral nerve repair

In this review the authors intend to demonstrate the need for supplementing conventional repair of the injured nerve with alternative therapies, namely transplantation of stem or progenitor cells. Although peripheral nerves do exhibit the potential to regenerate axons and reinnervate the end organ, outcome following severe nerve injury, even after repair, remains relatively poor. This is likely because of the extensive injury zone that prevents axon outgrowth. Even if outgrowth does occur, a relatively slow growth rate of regeneration results in prolonged denervation of the distal nerve. Whereas denervated Schwann cells (SCs) are key players in the early regenerative success of peripheral nerves, protracted loss of axonal contact renders Schwann cells unreceptive for axonal regeneration. Given that denervated Schwann cells appear to become effete, one logical approach is to support the distal denervated nerve environment by replacing host cells with those derived exogenously. A number of different sources of stem/precursor cells are being explored for their potential application in the scenario of peripheral nerve injury. The most promising candidate, transplant cells are derived from easily accessible sources such as the skin, bone marrow, or adipose tissue, all of which have demonstrated the capacity to differentiate into Schwann cell-like cells. Although recent studies have shown that stem cells can act as promising and beneficial adjuncts to nerve repair, considerable optimization of these therapies will be required for their potential to be realized in a clinical setting. The authors investigate the relevance of the delivery method (both the number and differentiation state of cells) on experimental outcomes, and seek to clarify whether stem cells must survive and differentiate in the injured nerve to convey a therapeutic effect. As our laboratory uses skin-derived precursor cells (SKPCs) in various nerve injury paradigms, we relate our findings on cell fate to other published studies to demonstrate the need to quantify stem cell survival and differentiation for future studies.

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.

Vitamin D2 potentiates axon regeneration

To date, the use of autograft tissue remains the "gold standard" technique for repairing transected peripheral nerves. However, the recovery is suboptimal, and neuroactive molecules are required. In the current study, we focused our attention on vitamin D, an FDA-approved molecule whose neuroprotective and neurotrophic actions are increasingly recognized. We assessed the therapeutic potential of ergocalciferol--the plant-derived form of vitamin D, named vitamin D2--in a rat model of peripheral nerve injury and repair. The left peroneal nerve was cut out on a length of 10 mm and immediately autografted in an inverted position. After surgery, animals were treated with ergocalciferol (100 IU/kg/day) and compared to untreated animals. Functional recovery of hindlimb was measured weekly, during 10 weeks post-surgery, using a walking track apparatus and a numerical camcorder. At the end of this period, motor and sensitive responses of the regenerated axons were calculated and histological analysis was performed. We observed that vitamin D2 significantly (i) increased axogenesis and axon diameter; (ii) improved the responses of sensory neurons to metabolites such as KCl and lactic acid; and (iii) induced a fast-to-slow fiber type transition of the Tibialis anterior muscle. In addition, functional recovery was not impaired by vitamin D supplementation. Altogether, these data indicate that vitamin D potentiates axon regeneration. Pharmacological studies with various concentrations of the two forms of vitamin D (ergocalciferol vs. cholecalciferol) are now required before recommending this molecule as a potential supplemental therapeutic approach following nerve injury.

Chapter 25: Phototherapy in peripheral nerve injury: effects on muscle preservation and nerve regeneration

Posttraumatic nerve repair and prevention of muscle atrophy represent a major challenge of restorative medicine. Considerable interest exists in the potential therapeutic value of laser phototherapy for restoring or temporarily preventing denervated muscle atrophy as well as enhancing regeneration of severely injured peripheral nerves. Low-power laser irradiation (laser phototherapy) was applied for treatment of rat denervated muscle in order to estimate biochemical transformation on cellular and tissue levels, as well as on rat sciatic nerve model after crush injury, direct or side-to-end anastomosis, and neurotube reconstruction. Nerve cells' growth and axonal sprouting were investigated in embryonic rat brain cultures. The animal outcome allowed clinical double-blind, placebo-controlled randomized study that measured the effectiveness of 780-nm laser phototherapy on patients suffering from incomplete peripheral nerve injuries for 6 months up to several years. In denervated muscles, animal study suggests that the function of denervated muscles can be partially preserved by temporary prevention of denervation-induced biochemical changes. The function of denervated muscles can be restored, not completely but to a very substantial degree, by laser treatment initiated at the earliest possible stage post injury. In peripheral nerve injury, laser phototherapy has an immediate protective effect. It maintains functional activity of the injured nerve for a long period, decreases scar tissue formation at the injury site, decreases degeneration in corresponding motor neurons of the spinal cord, and significantly increases axonal growth and myelinization. In cell cultures, laser irradiation accelerates migration, nerve cell growth, and fiber sprouting. In a pilot, clinical, double-blind, placebo-controlled randomized study in patients with incomplete long-term peripheral nerve injury, 780-nm laser irradiation can progressively improve peripheral nerve function, which leads to significant functional recovery. A 780-nm laser phototherapy temporarily preserves the function of a denervated muscle, and accelerates and enhances axonal growth and regeneration after peripheral nerve injury or reconstructive procedures. Laser activation of nerve cells, their growth, and axonal sprouting can be considered as potential treatment for neural injury. Animal and clinical studies show the promoting action of phototherapy on peripheral nerve regeneration, which makes it possible to suggest that the time for broader clinical trials has come.

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.

Peripheral nerve regeneration using a keratin-based scaffold: long-term functional and histological outcomes in a mouse model

PURPOSE

The management of peripheral nerve injuries with segmental defects is a challenge to both patient and surgeon. Repairs under tension have a poor prognosis; sensory nerve allografts have donor site morbidity and suboptimal motor recovery, but remain the gold standard. The development of conduit-based repair strategies has evolved and these are promising for sensory nerves and short defects; however, no conduit filler is clinically available that improves motor recovery equivalent to sensory autografts. In this study, motor recovery using keratin-based hydrogel filler was compared with that for sensory nerve autografts and empty conduits.

METHODS

Fifty-four mice were randomized into 3 treatment groups: empty conduit, sural nerve autograft, and keratin hydrogel-filled conduit. Animals were followed for 6 weeks, 3 months, and 6 months. Outcomes included compound motor action potential (CMAP), nerve area, myelinated axon number and density, and myelinated axon diameter.

RESULTS

Neuromuscular recovery with keratin was greater than with empty conduits in most outcome measures. Nerves that regenerated through the keratin hydrogel had lower conduction delays, greater amplitudes, more myelinated axons, and larger axons than nerves that regenerated through empty conduits. Sensory nerve autografts and keratin hydrogel were statistically equivalent in CMAP measurements at 6 months. Moreover, keratin-filled conduits demonstrated greater axon density and larger average axon diameter than both empty conduits and autograft at 6 months.

CONCLUSIONS

In a mouse tibial nerve model, keratin hydrogels significantly improved electrophysiological recovery, compared with empty conduits and sensory nerve autografts, at an early time point of regeneration. Keratin hydrogels also produce long-term electrical and histological results superior to empty conduits and equivalent to sensory nerve autografts.

Digital nerve reconstruction by multiple Y-shaped nerve grafts at the metacarpophalangeal joint level

Digital nerve injuries are common; injuries of the common digital nerves are less frequent than those involving the proper digital nerves. Traditional techniques used to reconstruct peripheral nerves are: direct suture, autologous nerve grafts, autologous vein grafts, vascularised nerve graft and alloplastic nerve grafts. Autologous nerve grafts remain the most common conduits for segmental defects. Difficulties can arise when attempting to repair complex nerve gaps, particularly when joining the proximal stump of the common digital nerve with two distal stumps of proper digital nerves as in lesions involving the web space. We present below a case of such a lesion. We describe the use of the lateral antebrachial cutaneous nerve (LABCN) as donor nerve, by exploiting its natural branchings.