An alternative to the classical nerve graft for the management of the short nerve gap

Reconstruction of a 4-cm human median nerve gap by including an autogenous nerve slice in a bioabsorbable nerve conduit: case report

Nerve gaps up to 3 cm in length can be reconstructed in the human with a bioabsorbable nerve conduit; however, nerve gaps greater than 3 cm have not been reconstructible in animal models unless a neurotrophic factor, like cultured Schwann cells, was added to the nerve conduit. It is the purpose of this article to present the result of human nerve regeneration across a 4-cm nerve gap in the median nerve at the wrist when a slice of autogenous normal nerve was placed into the middle of a bioabsorbable nerve conduit.

A comparison of polyglycolic acid versus type 1 collagen bioabsorbable nerve conduits in a rat model: an alternative to autografting

PURPOSE

Severe nerve injury with segmental loss requires nerve graft or conduit repair. We compared 2 synthetic, bioabsorbable nerve conduits with the gold standard of autogenous nerve grafting using histopathologic and neurophysiologic analyses.

METHODS

A 10-mm segment of the sciatic nerve of 45 Sprague-Dawley rats was resected, leaving a gap defect. Three experimental groups were used: 15 coaptations using type I collagen nerve conduits, 15 coaptations using polyglycolic acid (PGA) nerve conduits, and 15 coaptations using the excised segments as autogenous nerve grafts. The contralateral legs were used as unoperated controls. After 15 weeks, nerve regeneration was evaluated by measuring isometric muscle contraction force, axonal counting, wet muscle weights, and histology.

RESULTS

Statistically significant differences in the isometric muscle contraction force, axonal counts, and wet muscle weights were found between type I collagen conduit and nerve graft compared to the PGA conduit. Axonal sprouting was less organized and less dense with the PGA conduits when compared to nerve reconstruction with the type I collagen conduits and nerve grafts.

CONCLUSIONS

Type I collagen conduits and autografts produced comparable results, which were significantly better than PGA conduits. The use of type I collagen conduit is a reliable alternative to nerve grafting for gaps up to 10 mm in length.

Efficacy of 780-nm laser phototherapy on peripheral nerve regeneration after neurotube reconstruction procedure (double-blind randomized study)

OBJECTIVE

This pilot double-blind randomized study evaluated the efficacy of 780-nm laser phototherapy on the acceleration of axonal growth and regeneration after peripheral nerve reconstruction by polyglycolic acid (PGA) neurotube.

BACKGROUND DATA

The use of a guiding tube for the reconstruction of segmental loss of injured peripheral nerve has some advantages over the regular nerve grafting procedure. Experimental studies have shown that laser phototherapy is effective in influencing nerve regeneration.

METHODS

The right sciatic nerve was transected, and a 0.5-cm nerve segment was removed in 20 rats. A neurotube was placed between the proximal and the distal parts of the nerve for reconnection of nerve defect. Ten of 20 rats received post-operative, transcutaneous, 200-mW, 780-nm laser irradiation for 14 consecutive days to the corresponding segments of the spinal cord (15 min) and to the reconstructed nerve (15 min).

RESULTS

At 3 months after surgery, positive somato-sensory evoked responses were found in 70% of the irradiated rats (p = 0.015), compared to 30% of the non-irradiated rats. The Sciatic Functional Index in the irradiated group was higher than in the non-irradiated group (p < 0.05). Morphologically, the nerves were completely reconnected in both groups, but the laser-treated group showed an increased total number of myelinated axons.

CONCLUSION

The results of this study suggest that postoperative 780-nm laser phototherapy enhances the regenerative process of the peripheral nerve after reconnection of the nerve defect using a PGA neurotube.

Reconstruction of the human median nerve in the forearm with the Neurotube™

Reconstruction of the median nerve in the forearm traditionally has required multiple interfascicular interposition autologous nerve grafts. Recovery of two-point discrimination, even in young adults, has been reported rarely. Two patients, aged 43 and 61, are reported with 5-year follow-up of median nerve reconstruction in the distal forearm in which multiple interposition bioabsorbable polyglycolic acid conduits (Neurotube) were used to bridge the 3-cm nerve defects. Four separate 2.3-mm diameter, 4.0-cm long conduits were used in each patient. Sensory re-education was used for rehabilitation. Each patient recovered two-point discrimination with good localization in the thumb, index, and middle finger by 2 years after the nerve reconstruction. Both patients recovered abductor pollicis brevis function.

Enhancement of Peripheral Nerve Regeneration Using Bioabsorbable Polymer Tubes Packed With Fibrin Gel

Nerve conduit tubes were developed using bioabsorbable polymer membranes, and the effects of tube shape--straight or bellows-shaped tubes--and the fibrin gel filling were investigated. The mechanical properties of the tubes were examined by in vitro tests, and their effectiveness for peripheral nerve regeneration was determined by grafting into experimentally transected sciatic nerves of rats. The bellows tube showed mechanically superior properties, and when used with the fibrin gel, it induced superior tissue formation of myelinated nerve fibers as compared to other tube types. The total area of myelinated axons regenerated in the fibrin-filled bellows tube was comparable to that of an isograft control, whereas those of the other tubes demonstrated inferior regeneration. This result suggests that the mechanically superior bellows tube filled with fibrin gel is an effective graft alternative for peripheral nerve regeneration.

Endoscopically assisted sural nerve harvest for upper extremity posttraumatic nerve defects: an evaluation of functional outcomes

BACKGROUND

Peripheral nerve injuries in the upper extremity often require interposition of sural nerve grafts for reconstruction. Due to the poor donor-site appearance with standard techniques, and the potential for trauma to the nerve because of poor visualization during the harvest when the stepladder technique is used, the endoscope has been employed for nerve harvest.

METHODS

From January of 1997 until December of 2003, 15 patients with an average age of 27.5 years with posttraumatic upper limb nerve defects of the ulnar, median, or posterior interosseous nerves (crush, cutting, or avulsion injuries) underwent reconstruction with endoscopically harvested sural nerve. The nerves were harvested using atraumatic techniques under video monitor visualization. The functional results of sensation and motor function were assessed using British Medical Research Council scales.

RESULTS

All patients regained at least cutaneous pain and tactile sensibility, with most regaining two-point discrimination (nine patients achieved S3+). Two patients achieved complete recovery (S4). The 11 patients with motor nerve involvement achieved between M1+ and M5 after the initial reconstruction. Eight patients required a total of one immediate and nine secondary procedures to achieve the final outcome. The procedures included tenolysis (three patients), intrinsic tendon transfers (four patients), and opponensplasty (three patients). At the 4-year mean follow-up, grip power was M5 in 13 patients (86.7 percent) and M4 in two patients (13.3 percent).

CONCLUSIONS

Upper extremity sensory and motor nerve defects can be reconstructed with interposition of endoscopically harvested sural nerve grafts. The procedure is reliable, quick, and atraumatic, and results in reasonable motor and sensory recovery.

Bilateral Cavernous Nerve Interposition Grafting During Radical Retropubic Prostatectomy: Memorial Sloan-Kettering Cancer Center Experience

PURPOSE

Cavernous nerve graft is an option for men requiring bilateral cavernous nerve resection for cancer control during radical prostatectomy. We determined the success rate and identified determinants of success of bilateral cavernous nerve grafting following resection of the 2 nerves during radical prostatectomy in patients who were potent preoperatively.

MATERIALS AND METHODS

We retrospectively reviewed the records of 44 consecutive patients who underwent bilateral nerve grafting from 1999 to 2004. Postoperative erectile function was defined as the achievement of erections satisfactory for intercourse with or without oral medication. We calculated cumulative erectile function recovery rates using Kaplan-Meier curves. The log rank test was used to compare variables affecting erectile function recovery with p <0.0083 considered significant after adjusting for the number of variables evaluated using the Bonferroni correction.

RESULTS

The overall 5-year cumulative recovery of erectile function permitting penetration was 34% and the rate of consistent penetration was 11%. None of the analyzed variables were significantly associated with recovery of postoperative erectile function, including patient age (p = 0.3), incomplete bilateral cavernous nerve resection (p = 0.045), sural nerve grafts compared to genitofemoral or ilioinguinal nerves as donor sites (p = 0.067), post-radiation salvage radical prostatectomy (p = 0.15), neoadjuvant hormone therapy (p = 0.7) and comorbidities (p = 0.15) or medications (p = 0.4) affecting EF.

CONCLUSIONS

Bilateral cavernous nerve grafts might be beneficial in select patients. A definitive answer awaits the performance of a multi-institutional, randomized, controlled trial.

Luminal fillers in nerve conduits for peripheral nerve repair

The use of nerve conduits as an alternative for nerve grafting has a long experimental and clinical history. Luminal fillers, factors introduced into these nerve conduits, were later developed to enhance the nerve regeneration through conduits. Though many luminal fillers have been reported to improve nerve regeneration, their use has not been subjected to systematic review. This review categorizes the types of fillers used, the conduits associated with fillers, and the reported performance of luminal fillers in conduits to present a preference list for the most effective fillers to use over specific distances of nerve defect.

Tissue engineered nerve constructs: where do we stand?

Driven by enormous clinical need, interest in peripheral nerve regeneration has become a prime focus of research and area of growth within the field of tissue engineering. While using autologous donor nerves for bridging peripheral defects remains today's gold standard, it remains associated with high donor site morbidity and lack of full recovery. This dictates research towards the development of biomimetic constructs as alternatives. Based on current concepts, this review summarizes various approaches including different extracellular matrices, scaffolds, and growth factors that have been shown to promote migration and proliferation of Schwann cells. Since neither of these concepts in isolation is enough, although each is gaining increased interest to promote nerve regeneration, various combinations will need to be identified to strike a harmonious balance. Additional factors that must be incorporated into tissue engineered nerve constructs are also unknown and warrant further research efforts. It seems that future directions may allow us to determine the "missing link".

Photoengineering of neural tissue repair processes in peripheral nerves and the spinal cord: research development with clinical applications

The purpose of the present paper is to provide our data on the effects of phototherapy on peripheral nerve recovery. The aim is to call attention to an issue that still requires much research to elucidate the biological mechanisms through which phototherapy exerts its effects on nerve tissue, and to provide clinicians with the basis for planning clinical trials on the use of phototherapy for enhancing post-traumatic nerve regeneration.

Maximum intraoperative elongation of the rat sciatic nerve with tissue expander: Functional, neurophysiological, and histological assessment

The purpose of this study was to assess the maximum rapid intraoperative elongation of the rat sciatic nerve with the use of tissue expander, and its possible functional recovery. One hundred and eight rats were divided into five groups, and their right sciatic nerves were expanded with a 10-cc, 12-cc, 14-cc, 16-cc, and 18-cc expander, respectively, for 1 h. The functional recovery of the nerve was assessed at intervals up to 3 months, using the sciatic function index (SFI), neurophysiological indices, and histology. The maximum intraoperative elongation was observed in group IV (16-cc volume of tissue expander), at about 23.83%. SFI decreased between the first and seventh postoperative days, but gradually recovered, reaching preoperative values in all groups according to the formulas of De Medinaceli et al. (Exp. Neurol. 77:634-643, 1982) and Bain et al. (Plast. Reconstr. Surg. 83:129-136, 1989). Latency and motor conduction velocity demonstrated deterioration after expansion, which peaked after surgery. Recovery was gradually completed by the end of the experiment. The histological findings indicated minor aberrations immediately after expansion and maximal demyelination with axonal disruption on day 15. The reparative process started by day 30 and continued until day 90, when almost no histological changes were observed. In conclusion, intraoperative nerve expansion successfully elongates the rat sciatic nerve up to 23.83%. But it causes functional and morphological abnormalities, which are of moderate to severe degree, are of short duration, and are reversible. Intraoperative nerve expansion might be a valuable solution in the treatment of short nerve gaps, but its clinical application still needs to be evaluated.

A utilização do tubo de ácido poliglicólico e FK506 na regeneração de nervos periféricos

Grandes perdas de tecido neural não permitem a reparação através de anastomose primária. Nesses casos, a auto-enxertia de nervo é considerada tratamento de escolha. O tubo sintético à base de ácido poliglicólico é uma opção para enxertia de nervo. O FK506 é um imunossupressor que aumenta a taxa de regeneração neural "in vivo" e "in vitro". O objetivo deste trabalho foi comparar, em ratos, o grau de regeneração neural, utilizando análise histológica, contagem do número de axônios mielinizados regenerados e análise funcional, obtida com a interposição de enxerto autógeno (grupo A), tubo de ácido poliglicólico (grupo B) e da associação do tubo de ácido poliglicólico à administração de FK506 (grupo C) em defeitos de 5 mm no nervo ciático. Foi observado a formação de neuroma apenas no grupo A. Os grupos B e C apresentaram padrões histológicos semelhantes. A avaliação quantitativa do número de axônios mielinizados regenerados determinou que: 1) o grupo B apresentou em média um menor número em ralação aos demais grupos; 2) não houve diferença significativa entre o grupo controle A e o grupo C. Na recuperação funcional, não houve diferença estatisticamente significativa entre os três grupos, a despeito das diferenças histológicas qualitativas e quantitativas verificadas.

La réparation nerveuse périphérique : 30 siècles de recherche

INTRODUCTION

Nerve injury compromises sensory and motor functions. Techniques of peripheral nerve repair are based on our knowledge regarding regeneration. Microsurgical techniques introduced in the late 1950s and widely developed for the past 20 years have improved repairs. However, functional recovery following a peripheral mixed nerve injury is still incomplete.

STATE OF ART

Good motor and sensory function after nerve injury depends on the reinnervation of the motor end plates and sensory receptors. Nerve regeneration does not begin if the cell body has not survived the initial injury or if it is unable to initiate regeneration. The regenerated axons must reach and reinnervate the appropriate target end-organs in a timely fashion. Recovery of motor function requires a critical number of motor axons reinnervating the muscle fibers. Sensory recovery is possible if the delay in reinnervation is short. Many additional factors influence the success of nerve repair or reconstruction. The timing of the repair, the level of injury, the extent of the zone of injury, the technical skill of the surgeon, and the method of repair and reconstruction contribute to the functional outcome after nerve injury.

CONCLUSION

This review presents the recent advances in understanding of neural regeneration and their application to the management of primary repairs and nerve gaps.

Nerve repair by means of tubulization: literature review and personal clinical experience comparing biological and synthetic conduits for sensory nerve repair

Nerve repair is usually accomplished by direct suture when the two stumps can be approximated without tension. In the presence of a nerve defect, the placement of an autologous nerve graft is the current gold standard for nerve restoration. However, over the last 20 years, an increasing number of research articles reported on the use of non-nervous tubes (tubulization) for repairing nerve defects. The clinical employment of tubes (both biological and synthetic) as an alternative to autogenous nerve grafts is mainly justified by the limited availability of donor tissue for nerve autografts and the related morbidity. In addition, tubulization was proposed as an alternative to direct nerve sutures in order to create optimal conditions for nerve regeneration over the short empty space intentionally left between two nerve stumps. This paper outlines recent important advances in this field. Different tubulization techniques proposed so far are described, focusing in particular on studies that reported on the employment of tubes with patients. Our personal clinical experience on tubulization repair of sensory nerve lesions (digital nerves), using both biological and synthetic tubes, is presented, and the clinical results are compared. In our case series, both types of tubes led to good clinical results. Finally, we speculate about the prospects in the clinical application of tubulization for peripheral nerve repair.

Neurotube for facial nerve repair

Facial nerve reconstruction for lesions with nerve gaps frequently require autologous or tubulized grafts of biological or synthetic origin. Neurotube, a bioabsorbable polyglycolic acid tube, represents a valid solution for this kind of defect in emergency and planned surgery. Seven posttraumatic lesions of terminal branches of the facial nerve were repaired by means of Neurotube from September 1999-September 2001. The nerve gap size ranged between 1-3 cm. Nerve regeneration was evaluated at 7-12 months of follow-up when muscle recovery function was examined. Muscle function was very good in 1 case, good in 4, and fair in 2 (71% positive results). No intolerance or discomfort was reported or observed. Neurotube is useful for the reconstruction of facial nerve lesions with a small nerve gap (less then 3 cm) when a direct anastomosis of the two stumps is not possible, or when the suture appears to be in tension. It is a valid alternative to autologous and biological tubulized grafts. The limits of this method are: 1) it can only be used with gaps of less than 3 cm; 2) it is quite costly; 3) there are reports of possible intolerance; and 4) it is not suitable for lesions of the proximal part of the facial nerve.

A new method of selecting Schwann cells from adult mouse sciatic nerve

We describe a method of using laminin for the selection and purification of Schwann cells in vitro. We also studied the viability of the selected cells suspended in alginate beads both in vitro and in vivo. We observed that the homogeneity of the Schwann cell culture increased with each round of laminin selection and reached 85-90% after five passages. The viability of cells after incubation within an alginate bead in vivo was between 73 and 76% compared with greater than 90% viability for cells that were maintained in monolayer culture. This new method of serial selection using laminin-coated surfaces has optimized the purification of a Schwann cell culture expanded from cells harvested from the adult sciatic nerve of a mouse. This method has the advantage of being technically easier than other methods described and results in a Schwann cell culture that is 80-90% homogenous.

Microwave irradiated collagen tubes as a better matrix for peripheral nerve regeneration

Collagen is one of the best materials used for nerve guide preparation due to its biocompatibility and desirable tensile strength. In this work, we have compared regeneration and functional reinnervation after sciatic nerve resection with bioresorbable crosslinked collagen guides in 10 mm gap. The crosslinking was carried out either with glutaraldehyde (GTA) or microwave irradiation (MWI). The multilayered collagen membrane used for nerve guides are prepared by lamellar evaporation technique. Functional evaluations of the regenerated nerves were performed by measuring the sciatic functional index (SFI), nerve conduction velocity (NCV), and electromyography (EMG). Transmission electron microscopic studies showed growth of axonal cable with fewer myelinated axons, Schwann cells and more unmyelinated axons present in the case of group treated with uncrosslinked collagen tubes after 1 month of implantation. However, we have observed more myelinated axons in the case of autograft, GTA, and MWI crosslinked collagen tube implants across the gap of 1 cm after the same period of implantation. Smaller myelinated fiber diameter was observed in the case of GTA crosslinked collagen tube group when compared with the autograft and MWI collagen tube groups. There were more myelinated axons during the 3rd and 6th months postoperatively using these conduits as substantiated by light microscopic studies of the regenerated nerve. The conduction velocity and recovery index improved significantly after 5 months reaching the normal values in the autograft and MWI crosslinked collagen groups compared to GTA and uncrosslinked collagen tubes.

In vivo induction and delivery of nerve growth factor, using HEK-293 cells

Tissue-engineering strategies offer hope to patients facing functional impairment after nerve injury. We have previously demonstrated that HEK-293 cells can release nerve growth factor (NGF) in vitro, using an inducible system of expression. In this study, our objective was to assess the efficacy of the NGF delivery system in vivo, using nude rats. HEK-293 cells were transfected with human NGF cDNA. Ponasterone A (PonA) was used as the inducing agent. NGF collection chambers were implanted subcutaneously in nude rats. Sealed chambers were filled with one of the following: (1) DMEM, (2) untransfected 293 cells (EcR-293) plus PonA, (3) untransfected EcR-293 without PonA, (4) transfected 293 cells (hNGF-EcR-293) plus PonA, or (5) transfected hNGF-EcR-293 without PonA. Chambers were aspirated 24, 48, and 120 h postimplantation. NGF secretion was analyzed in the following ways: (1) NGF protein expression bioactivity was assessed in a PC-12 cell bioassay, and (2) the concentration of secreted NGF was quantified by NGF ELISA. NGF quantification by ELISA reached a maximal release of 12.9 +/- 3.57 ng/mL at 120 h. PC-12 cells exposed to media from induced transfected HEK-293 cell chambers demonstrated higher levels of differentiation compared with controls. We conclude that hNGF-EcR-293 cells can inducibly secrete bioactive NGF when exposed to the induction agent PonA. This regulated delivery system can secrete bioactive NGF for up to 5 days in vivo. We believe this regulated delivery system will be useful for tissue-engineered nerve constructs.

Bridging a 30-mm nerve defect using collagen filaments

This article describes a 30-mm regeneration of severed peripheral nerve axons along collagen filaments. Two thousand or 4000 31-mm-long collagen filaments were grafted to bridge a 30-mm defect of the rat sciatic nerve. A collagen tube was grafted as a control. The mean number and mean fiber diameter of regenerated myelinated axons were 330 +/- 227 and 2.7 +/- 0.9 microm in the distal end of the 2000 collagen-filaments nerve guide, and 564 +/- 275 and 2.5 +/- 1.1 microm in the distal end of the 4000 collagen-filaments nerve guide at 12 weeks postoperatively, whereas in the distal end of the collagen tube, no regenerated axon was found. These results suggest that the collagen filaments guide axons of the rat's sciatic nerve to regenerate for 30 mm and act as a scaffold for axonal regeneration. Thirty-millimeter nerve regeneration of a 1-mm-diameter rat sciatic nerve by an artificial nerve guarantees a clinical application of the implant which should be very important for patients and surgeons.

Peripheral nerve regeneration through guidance tubes

Biological nerve grafts have been extensively utilized in the past to repair peripheral nerve injuries. More recently, the use of synthetic guidance tubes in repairing these injuries has gained in popularity. This review focuses on artificial conduits, nerve regeneration through them, and an account of various synthetic materials that comprise these tubes in experimental animal and clinical trials. It also lists and describes several biomaterial considerations one should regard when designing, developing, and manufacturing potential guidance channel candidates. In the future, it it likely that the most successful synthetic nerve conduit will be one that has been fabricated with some of these strategies in mind.

The Role of Topically Administered FK506 (Tacrolimus) at the Time of Facial Nerve Repair Using Entubulation Neurorrhaphy in a Rabbit Model

Peripheral facial nerve palsy is a common sequela of traumatic craniofacial injury, often resulting in dramatic and sometimes permanent functional deficits. Exogenous agents and methods of repair that accelerate axonal regeneration would be of great benefit to the multitude of patients with facial nerve injuries. The objective of this study was to evaluate the effect of FK506 at the time of facial nerve repair using entubulation neurorrhaphy, and to compare entubulation neurorrhaphy versus interposition autograft in critical facial nerve gap defects. The study design was a prospective, randomized, blinded animal study with a control group. Twenty-five New Zealand White rabbits were assigned to 4 experimental groups and a control group. The buccal branch of the facial nerve was used in all procedures. Group 1 was the control group. Rabbits in group 2 underwent sham surgery. Group 3 was an interposition autograft group in which a 6-mm segment of nerve was transacted, flipped, and followed by epineural repair. Groups 4 and 5 underwent transection followed by entubulation neurorrhaphy with topical administration of either a carrier molecule (group 4) or an FK506 carrier molecule (group 5). Outcome measures included daily subjective assessment of upper lip movement; electromyographic studies at weeks 3, 5, and 8 postoperatively; and blinded quantitative histomorphometric evaluation after 8 weeks. All rabbits in all groups were noted to have spontaneous movement after 8 weeks, with 1 rabbit in group 5 obtaining the highest functional score among all study groups. Electrophysiologic studies showed polyphasic potentials, indicating reinnervation in 1 rabbit in group 5. Histomorphometric examination of group 5 rabbits revealed a similar cross-sectional area distal to transection and remyelination. Other groups showed decreased cross-sectional area and/or incomplete remyelination distal to the transection. FK506 applied topically at the time of facial nerve repair using entubulation neurorrhaphy demonstrated superior results in nerve regeneration versus entubulation neurorrhaphy carrier protein alone, and interposition autograft.

Controlled release of nerve growth factor enhances sciatic nerve regeneration

Based on previous studies demonstrating the potential of growth factors to enhance peripheral nerve regeneration, we developed a novel growth factor delivery system to provide sustained delivery of nerve growth factor (NGF). This delivery system uses heparin to immobilize NGF and slow its diffusion from a fibrin matrix. This system has been previously shown to enhance neurite outgrowth in vitro, and in this study, we evaluated the ability of this delivery system to enhance nerve regeneration through conduits. We tested the effect of controlled NGF delivery on peripheral nerve regeneration in a 13-mm rat sciatic nerve defect. The heparin-containing delivery system was studied in combination with three doses of NGF (5, 20, or 50 ng/mL) and the results were compared with positive controls (isografts) and negative controls (fibrin alone, NGF alone, and empty conduits). Nerves were harvested at 6 weeks postoperatively for histomorphometric analysis. Axonal regeneration in the delivery system groups revealed a marked dose-dependent effect. The total number of nerve fibers at both the mid-conduit level and in the distal nerve showed no statistical difference for NGF doses at 20 and 50 ng/mL from the isograft (positive control). The results of this study demonstrate that the incorporation of a novel delivery system providing controlled release of growth factors enhances peripheral nerve regeneration and represents a significant contribution toward enhancing nerve regeneration across short nerve gaps.

Growth factor enhancement of peripheral nerve regeneration through a novel synthetic hydrogel tube

OBJECT

The authors' long-term goal is repair of peripheral nerve injuries by using synthetic nerve guidance devices that improve both regeneration and functional outcome relative to an autograft. They report the in vitro processing and in vivo application of synthetic hydrogel tubes that are filled with collagen gel impregnated with growth factors.

METHODS

Poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (PHEMA-MMA) porous 12-mm-long tubes with an inner diameter of 1.3 mm and an outer diameter of 1.8 mm were used to repair surgically created 10-mm gaps in the rat sciatic nerve. The inner lumen of the tubes was filled with collagen matrix alone or matrix supplemented with either neurotropin-3 at 1 microg/ml, brain-derived neurotrophic factor at 1 microg/ml, or acidic fibroblast growth factor (FGF-1) at 1 or 10 microg/ml. Nerve regeneration through the growth factor-enhanced tubes was assessed at 8 weeks after repair by histomorphometric analysis at the midgraft level and in the nerve distal to the tube repair. The tubes were biostable and biocompatible, and supported nerve regeneration in more than 90% of cases. Nerve regeneration was improved in tubes in which growth factors were added, compared with empty tubes and those containing collagen gel alone (negative controls). Tubes filled with 10 microg/ml of FGF-1 dispersed in collagen demonstrated regeneration comparable to autografts (positive controls) and showed significantly better regeneration than the other groups.

CONCLUSIONS

The PHEMA-MMA tubes augmented with FGF-1 in their lumens appear to be a promising alternative to autografts for repair of nerve injuries. Studies are in progress to assess the long-term biocompatibility of these implants and to enhance regeneration further.

Management of neuromas

After nerve injury and regeneration, significant pain may be associated with the scar and altered sensation observed within the distribution of the injured nerve. A bulbous swelling may form at the severed nerve end, constituting a traumatic neuroma. The development of a painful neuroma may be more disabling to the patient than an area of anesthesia or even loss of motor function. Effective treatment of the painful neuroma remains a difficult problem. Diminished productivity, alterations in patient lifestyle, and possible progression to chronic pain syndromes must be considered within the scope of neuroma management, and treatment must focus on alleviating the pain and restoring the functional loss caused by the nerve injury. Careful patient selection is the cornerstone of successful outcomes. Once the patient has been selected, the surgical management of the painful neuroma throughout the body is based on basic principles that vary only slightly from region to region. Using these tenets, a neuroma management algorithm has been developed based on the pathophysio-logy of the neuroma, the results of experimental studies, review of patient outcomes, and understanding the psychology of pain in the surgical patient.

Nerve guide material made from fibronectin: assessment of in vitro properties

We have previously used orientated mats of fibronectin as conduits to repair short gaps in peripheral nerves. Here we describe the in vitro properties of a new material in the form of large cables produced from a fibronectin-enriched solution with potential as a conduit for longer nerve defects. Large cables of fibronectin were made up to 14 cm long x 1.5 cm in diameter. When freeze dried, scanning electron microscopy revealed a predominant fiber orientation. Dried cables hydrated rapidly to 1.6 and 4.8 times their original length and diameter, respectively. Once hydrated these cables had pores that ranged from 10 to 100 microm through which Schwann cells and fibroblasts were able to grow in vitro and align with the axis of the fibrils by contact guidance. Furthermore, the porosity of the cable was enhanced by the natural dissolution of protein over a 3-week duration in culture with cells, such that 50- to 200-microm pores were observed. This study suggests that large fibronectin cables are a suitable alternative to the original fibronectin mats to guide components of the peripheral nerves and so to act as conduits with potential use in guiding regeneration across long nerve defects.

30 mm regeneration of rat sciatic nerve along collagen filaments

This paper describes 30 mm regeneration of peripheral nerve axons along collagen filaments; 31-mm-long collagen filaments or collagen tube were grafted to bridge a 30-mm defect of rat sciatic nerve. The mean number and the diameter of regenerated myelinated axons were 330+/-227 and 2.7+/-0.9 microm at the distal end of the collagen-filaments 12 weeks postoperatively; while at the distal end of the tube no axon was found.

Influence of bioresorbable, unsintered hydroxyapatite/poly-L-lactide composite films on spinal cord, nerve roots, and epidural space

The effect of forged unsintered hydroxyapatite/poly-L-lactide (u-HA/PLLA) composite films on spinal cord and nerve roots and its degradation behavior and osteoconductivity in epidural space were compared with those of calcined HA (c-HA)/PLLA and unfilled PLLA films. Partial laminectomy was performed on 20 rabbits, and u-HA/PLLA and PLLA films were implanted in the intervertebral space. Total laminectomy was performed on 30 rabbits to implant u-HA/PLLA, c-HA/PLLA, and PLLA films in both epidural and subcutaneous spaces. For up to 50 weeks, there were no histological changes in the spinal cord or nerve root, and no inflammatory cell infiltration into the epidural space around the films. The rate of decrease in viscosity average molecular weight of both composite films was initially higher than that of PLLA but eventually became lower, although there was no difference in the degradation behavior of the three films in either the epidural or subcutaneous spaces after 50 weeks. Scanning electron microscopic and energy-dispersive X-ray analysis indicated calcium phosphate deposits on the surface of composite films with new bone formation from 4 weeks. The u-HA/PLLA composite film therefore has good biocompatibility, osteoconductivity, and fast primary degradation rate, which may prove compatible with application to spinal surgery.

Regeneration of canine peroneal nerve with the use of a polyglycolic acid-collagen tube filled with laminin-soaked collagen sponge: a comparative study of collagen sponge and collagen fibers as filling materials for nerve conduits

A novel artificial nerve conduit was developed and its efficiency was evaluated on the basis of promotion of peripheral nerve regeneration across an 80-mm gap in dogs. The nerve conduit was made of a polyglycolic acid-collagen tube filled with laminin-soaked collagen sponge. Conduits filled with either sponge- or fiber-form collagen were implanted into an 80-mm gap of the peroneal nerve (five dogs for each form). Twelve months postoperatively nerve regeneration was superior in the sponge group both morphometrically (percentage of neural tissue: fiber: 39.7 +/- 5.2, sponge: 43.0 +/- 4.5, n=3) and electrophysiologically (fiber: CMAP 1.06 +/- 0.077, SEP 1.32 +/- 0.127 sponge: CMAP 1.04 +/- 0.106, SEP 1.24 +/- 0.197, n=5), although these differences were not statistically significant. The observed regeneration was complementary to successful results reported previously in the same model, in which collagen fibers exclusively were used. The results indicate a possible superiority of collagen sponge over collagen fibers as filling materials. In addition, the mass-producibility, superior scaffolding potential, and capacity for gradual release of soluble factors of the sponge provide make it an attractive alternative to fine fibers, which are both technologically difficult and costly to produce. This newly developed nerve conduit has the potential to enhance peripheral nerve regeneration across longer gaps commonly encountered in clinical settings.

Factors that influence peripheral nerve regeneration: an electrophysiological study of the monkey median nerve

Regeneration in the peripheral nervous system is often incomplete though it is uncertain which factors, such as the type and extent of the injury or the method or timing of repair, determine the degree of functional recovery. Serial electrophysiological techniques were used to follow recovery from median nerve lesions (n = 46) in nonhuman primates over 3 to 4 years, a time span comparable with such lesions in humans. Nerve gap distances of 5, 20, or 50mm were repaired with nerve grafts or collagen-based nerve guide tubes, and three electrophysiological outcome measures were followed: (1) compound muscle action potentials in the abductor pollicis brevis muscle, (2) the number and size of motor units in reinnervated muscle, and (3) compound sensory action potentials from digital nerve. A statistical model was used to assess the influence of three variables (repair type, nerve gap distance, and time to earliest muscle reinnervation) on the final recovery of the outcome measures. Nerve gap distance and the repair type, individually and concertedly, strongly influenced the time to earliest muscle reinnervation, and only time to reinnervation was significant when all three variables were included as outcome predictors. Thus, nerve gap distance and repair type exert their influence through time to muscle reinnervation. These findings emphasize that factors that control early axonal outgrowth influence the final level of recovery attained years later. They also highlight that a time window exists within which axons must grow through the distal nerve stump in order for recovery after nerve lesions to be optimal. Future work should focus on interventions that may accelerate the growth of axons from the lesion site into the distal nerve stump.

Axonal regeneration into Schwann cell grafts within resorbable poly(alpha-hydroxyacid) guidance channels in the adult rat spinal cord

Axonal growth and myelination in a SC graft contained in a resorbable tubular scaffold made of poly(D,L-lactic acid) (PLA50) or high molecular weight poly(L-lactic acid) mixed with 10% poly(L-lactic acid) oligomers (PLA(100/10)) were studied for up to 4 months after implantation in the completely transected adult rat thoracic spinal cord. The PLA50 tubes collapsed soon after implantation and, consequently, compressed the graft inside, leading to only occasional thin cables with SCs and a low number of myelinated axons: 17 +/- 6 at 1 and 158 +/- 11 at 2 months post-grafting. The cable contained 32 +/- 23 blood vessels at 2 weeks, 55 +/- 33 at 1 month and 46 +/- 30 at 2 months after implantation. PLA(100/10) tubes, on the other hand, were found to break up into large pieces, which compressed and sometimes protruded into the tissue cable inside. At all time points studied, however, cables contained SCs and were well vascularized with 414 +/- 47 blood vessels at 2 weeks, 437 +/- 139 at 1, 609 +/- 134 at 2 and 396 +/- 95 at 4 months post-grafting. The number of myelinated axons was 712 +/- 509 at 1 month, 1819 +/- 837 at 2 months and 609 +/- 132 at 4 months post implantation. These results demonstrated that fiber growth and myelination into a SC graft contained in a resorbable PLA(100/10) tube increases over the first 2 months post-implantation but decreases thereafter. Changes in geometry of both types of polymer tubes were detrimental to axonal regeneration. Future research should explore the use of polymers that better retain the appropriate mechanical, geometrical and permeability properties over time.

Nerve regeneration through an epineurial sheath: its functional aspect compared with nerve and vein grafts

Although nerve graft is still the only reliable choice in repair of defects in peripheral nerve structure, it has the disadvantage of donor nerve morbidity and of sometimes being unavailable. It has long been researched in alternate nerve grafts with other materials. Studies have shown that nerves could regenerate across short nerve gaps through various conduits, such as veins, pseudosheaths, and bioabsorbable tubes. Despite encouraging studies, their functional results remain unclear. The present study used 40 rats, in which nerve grafts, vein grafts, and epineurial tubes were placed into 1-cm gaps in sciatic nerves created by resection. In one group, sciatic nerves were denuded of the surrounding epineurium, to assess the possible morbidity caused by epineurial sheath technique. At 2, 4, 8, 12, 20, and 28 weeks, functional assessment of nerve regeneration was performed using walking track analysis. The number of myelinated fibers and fiber diameters was measured and electron microscopic evaluation performed. Functionally, the index values were very close to each other in nerve graft and epineurial sheath groups. Morphometric analysis showed significance between the groups. The result of denuded sciatic nerve group was the same as the base track values. It was concluded that the ready availability of epineurial sheath as a conduit to span short nerve gaps could eliminate the morbidity associated with nerve graft harvest and capitalize on the potential benefits of neurotrophism in directing nerve regeneration.

Collagen filaments as a scaffold for nerve regeneration

This article describes repair of peripheral nerve defect using collagen filaments instead of tubes. Many tube-shaped nerve guides induce regeneration of severed peripheral nerve axons within a limited distance. Substantial regeneration of nerve axons has not been reported without a tubular conduit. Here we show the regeneration of peripheral nerve axons along filaments of collagen without a tube. Cables of collagen filaments were grafted to repair 20-mm defects of rat sciatic nerves. Nerve autografts and collagen tubes were grafted as controls. The mean number and the mean fiber diameter of regenerated myelinated axons were approximately 4800 and 3.3 microm in the distal end of the nerve autograft at 8 weeks postoperatively while in the distal end of the collagen-filaments nerve guide, they were approximately 5500 and 2.3 microm. Collagen tubes failed to bridge the nerve defect. Histologic studies suggest that nerve axons regenerated substantially along the collagen filaments.

Reconstruction of a painful post-traumatic medial plantar neuroma with a bioabsorbable nerve conduit: a case report

Although nerve injuries to feet may be common, primary repair of a damaged nerve in the foot is rare. Secondary digital nerve reconstruction in the foot has not been previously reported. This report describes a patient with post-traumatic neuroma of medial plantar nerve who was treated by neuroma resection; the nerve defect was reconstructed with bioabsorbable nerve conduit. This case illustrates successful, secondary reconstruction of nerve injury in the foot using a new surgical technique. A bioabsorbable polyglycolic acid nerve conduit eliminated the need for a short nerve graft and was effective in relieving the neuroma pain by providing an appropriate distal site for neural regeneration.

The use of autogenous vein grafts for inferior alveolar and lingual nerve reconstruction

PURPOSE

This study evaluated whether an autogenous vein graft forms a satisfactory conduit for nerve regeneration.

PATIENTS AND METHODS

Fifteen patients received a total of 16 autogenous vein grafts to repair continuity defects of the inferior alveolar (6) and lingual nerves (10) nerves. All were treated between 4 and 10 months after injury. At surgery, the postresection defects ranged from 2 to 14 mm. All lingual nerves were repaired with saphenous vein grafts from an intraoral approach and all inferior alveolar nerves were repaired with facial vein grafts inserted from an extraoral approach.

RESULTS

Lingual nerve repair in 3 cases where the gap between the nerve ends was 5 mm or less resulted in some return of sensation. In 7 cases where the gap was between 5 and 14 mm, there was no return of sensation. In the 6 inferior alveolar nerve repairs there was some return of sensation in all cases and there was good return of sensation in 3 cases. One patient redeveloped dysesthesia in the inferior alveolar nerve and subsequently had a neurectomy. Histologic material was available from this case.

CONCLUSIONS

It appears that a vein graft can form a physiologic conduit for nerve regeneration. The results are more successful with shorter gaps, which indicates that, in some respects, the vein acts like a barrier membrane. The increased success rate in the inferior alveolar nerve repair may be because the vein remains straight and patent in the inferior alveolar canal. The lack of success with a long lingual nerve gap repair may be because the vein is collapsed or kinked by movement of the tongue, which may inhibit neural regeneration. Therefore, vein grafts should not be used for long lingual nerve continuity defects.

Axonal regeneration into acellular nerve grafts is enhanced by degradation of chondroitin sulfate proteoglycan

Although the peripheral nerve has the potential to regenerate after injury, degenerative processes may be essential to promote axonal growth into the denervated nerve. One hypothesis is that the nerve contains growth inhibitors that must be neutralized after injury for optimal regeneration. In the present study, we tested whether degradation of chondroitin sulfate proteoglycan, a known inhibitor of axon growth, enhances the growth-promoting properties of grafts prepared from normal donor nerves. Excised segments of rat sciatic nerve were made acellular by freeze-killing before treatment with chondroitinase ABC. Chondroitinase-dependent neoepitope immunolabeling showed that chondroitin sulfate proteoglycan was thoroughly degraded throughout the treated nerve segments. In addition, neuronal cryoculture assays revealed that the neurite-promoting activity of acellular nerves was significantly increased by chondroitinase treatment. Control and chondroitinase-treated acellular nerves were then used as interpositional grafts in a rat nerve injury model. Axonal regeneration into the grafts was assessed 4 and 8 d after implantation by growth-associated protein-43 immunolabeling. At both time points, the number of axons regenerating into acellular grafts treated with chondroitinase was severalfold greater than in control grafts. Growth into the chondroitinase-treated grafts was pronounced after only 4 d, suggesting that the delay of axonal growth normally associated with acellular grafts was attenuated as well. These findings indicate that chondroitinase treatment significantly enhanced the growth-promoting properties of freeze-killed donor nerve grafts. Combined with the low immunogenicity of acellular grafts, the ability to improve axonal penetration into interpositional grafts by preoperative treatment with chondroitinase may be a significant advancement for clinical nerve allografting.

Effects of FK506 on nerve regeneration and reinnervation after graft or tube repair of long nerve gaps

We compared the effects of FK506 administration on regeneration and reinnervation after sciatic nerve resection and repair with an autologous graft or with a silicone tube leaving a 6-mm gap in the mouse. Functional reinnervation was assessed by noninvasive methods to determine recovery of motor, sensory, and sweating functions in the hindpaw over 4 months after operation. Morphometric analysis of the regenerated nerves was performed at the end of follow-up. The nerve graft allowed for faster and higher levels of reinnervation in the four functions tested than silicone tube repair. Treatment with FK506 (for the first 9 weeks only) resulted in a slight, although not significant, improvement of the onset of reinnervation and of the maximal degree of recovery achieved after autografting. The recovery of pain sensibility and of the compound nerve action potentials in the digital nerves, which directly depend on axonal regeneration, showed better progression with FK506 than reinnervation of muscles and sweat glands, which require reestablishment of synaptic contacts with target cells. The myelinated fibers in the regenerated nerve showed a more mature appearance in the FK506-treated rats. However, FK506 showed a marginal effect in situations in which regeneration was limited, as in a silicone tube bridging a 6-mm gap in the mouse sciatic nerve. In conclusion, treatment with FK506 improved the rate of functional recovery after nerve resection and autograft repair.

Tissue response to silicone tubes used to repair human median and ulnar nerves

Silicone tubes of appropriate sizes were used to enclose the injured zone of transsected ulnar and median nerves in the human forearm as an alternative to conventional microsurgical repair of the nerve trunk. A gap measuring 3-5 mm was left intentionally between the nerve ends inside the tube. The clinical early results from a prospective randomised study that compared these two principles have recently been presented. Seven patients (five men and two women), aged 15-49 years (median 20) were reexplored 12-44 months (median 22) after the initial procedure because of local discomfort from the tube in four patients. There was a new nerve structure bridging the former gap and in most cases it was impossible to distinguish the site of the injury. In all cases there was a thin capsule around the silicone tube that microscopically consisted of connective tissue with thin walls and no signs of inflammation, granuloma or macrophages (n = 4), while in two cases a mild foreign body reaction was seen at a single site (n = 1) or at patchy areas (n = 1). These results indicate that after more than one year there is a limited tissue reaction around silicone tubes used to repair median and ulnar nerves in humans.

Superior muscle reinnervation after autologous nerve graft or poly-L-lactide-epsilon-caprolactone (PLC) tube implantation in comparison to silicone tube repair

Recovery after peripheral nerve injury depends not only on the amount of reinnervation, but also on its accuracy. The rat sciatic nerve was subjected to an 8 mm long gap lesion repaired either by autograft (AG, n = 6) or tubulization with impermeable silicone tube (SIL, n = 6) or permeable tube of poly-L-lactide-epsilon-caprolactone (PLC, n = 8). Recordings of the compound muscle action potential (CMAP) from gastrocnemius (mGC), tibialis anterior (mTA) and plantar (mPL) muscles were performed 90 days after injury to assess the amount of muscle reinnervation. The CMAP amplitude achieved in mGC, mTA and mPL was similar in after nerve autograft (39%, 42%, 22% of control values) and PLC tube implantation (37%, 36%, 24%) but lower with SIL tube (29%, 30%, 14%). The nerve fascicles projecting into each of these muscles were then transected and retrograde tracers (Fluoro Gold, Fast Blue, DiI) were applied to quantify the percentage of motoneurons with single or multiple branches to different targets. The total number of labeled motoneurons for the three muscles did not differ in autografted rats (1186 +/- 56; mean +/- SEM) with respect to controls (1238 +/- 82), but was reduced with PLC tube (802 +/- 101) and SIL tube (935 +/- 213). The percentage of neurons with multiple projections was lower after autograft and PLC tube (6%) than with SIL tube (10%). Considering the higher CMAP amplitude and lower number of neurons with multiple projections, PLC nerve conduits seem superior to SIL tubes and a suitable alternative to autografts for the repair of long gaps.

Peripheral nerve regeneration along collagen filaments

This paper describes the regeneration of severed peripheral nerve axons along collagen filaments without a tube. Two thousand collagen filaments were grafted to bridge 20 mm defects of rat sciatic nerve. The number of myelinated axons was approximately 4800 in the distal end of the nerve autograft at 8 weeks postoperatively; while in the collagen-filaments nerve guide it was 5500. The results suggested the collagen filaments guided regenerating axons effectively.