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

Bridging a peripheral nerve defect using collagen filaments

We describe bridging a peripheral nerve defect using collagen filaments instead of a tube. Cords of collagen filaments were grafted to bridge 20-mm defects of rat sciatic nerves. Nerve autografts were grafted as the control. The mean number and the mean fiber diameter of regenerated myelinated axons were approximately 4,800 and 3.3 microm, respectively, in the distal end of the nerve autograft and approximately 5,500 and 2.3 microm, respectively, in the distal end of the collagen-filaments nerve guide 8 weeks after surgery. The mean number and the mean fiber diameter of regenerated myelinated axons were approximately 6,900 and 3.1 microm, respectively, in the distal end of the nerve autograft and approximately 6,300 and 3.3 microm, respectively, in the distal end of the collagen-filaments nerve guide 25 weeks after surgery. Histologic studies suggested that the collagen filaments guided regenerating axons effectively. This new procedure offers a possible solution for the need to sacrifice a healthy nerve and for the shortage of graft material available for the repair of severed nerves.

Biodegradable p(DLLA-?-CL) nerve guides versus autologous nerve grafts: Electromyographic and video analysis

The aim of this study was to evaluate the functional effects of bridging a gap in the sciatic nerve of the rat with either a biodegradable copolymer of DL-lactide and epsilon-caprolactone [p(DLLA-epsilon-CL)] nerve guide or an autologous nerve graft. Electromyograms (EMGs) of the gastrocnemius (GC) and tibialis anterior (TA) muscles were recorded 3.5 and 5 months after bridging the nerve gaps. Furthermore, the rats' gait was recorded on video and the quality of the gait was analyzed. EMG patterns of the contralateral nonoperated side were essentially normal. The EMG patterns on the operated side were irregular in all animals, but the quality of gait was better in the nerve guide group. We conclude that the surgical technique (nerve guide or nerve graft) does not influence the occurrence of abnormal EMG patterns, but gait improves to a greater extent when the nerve gap is bridged by a nerve guide.

Peripheral nerve regeneration using bioresorbable macroporous polylactide scaffolds

The ability of DRG-derived neurons to survive and attach onto macroporous polylactide (PLA) foams was assessed in vitro. The foams were fabricated using a thermally induced polymer-solvent phase separation. Two types of pore structures, namely oriented or interconnected pores, can be produced, depending on the mechanism of phase separation, which in turn can be predicted by the thermodynamics of the polymer-solvent pair. Coating of the porous foams with polyvinylalcohol (PVA) considerably improved the wettability of the foams and allowed for cell culture. The in vitro biocompatibility of the PVA-coated supports was demonstrated by measuring cell viability and neuritogenesis. Microscopic observations of the cells seeded onto the polymer foams showed that the interconnected pore networks were more favorable to cell attachment than the anisotropic ones. The capacity of highly oriented foams to support in vivo peripheral nerve regeneration was studied in rats. A sciatic nerve gap of 5-mm length was bridged with a polymer implant showing macrotubes of 100 microm diameter. At 4 weeks postoperatively, the polymer implant was still present. It was well integrated and had restored an anatomic continuity. An abundant cell migration was observed at the outer surface of the polymer implant, but not within the macrotubes. This dense cellular microenvironment was found to be favorable for axogenesis.

A randomized prospective study of polyglycolic acid conduits for digital nerve reconstruction in humans

This article reports the first randomized prospective multicenter evaluation of a bioabsorbable conduit for nerve repair. The study enrolled 98 subjects with 136 nerve transections in the hand and prospectively randomized the repair to two groups: standard repair, either end-to-end or with a nerve graft, or repair using a polyglycolic acid conduit. Two-point discrimination was measured by a blinded observer at 3, 6, 9, and 12 months after repair. There were 56 nerves repaired in the control group and 46 nerves repaired with a conduit available for follow-up. Three patients had a partial conduit extrusion as a result of loss of the initially crushed skin flap. The overall results showed no significant difference between the two groups as a whole. In the control group, excellent results were obtained in 43 percent of repairs, good results in 43 percent, and poor results in 14 percent. In those nerves repaired with a conduit, excellent results were obtained in 44 percent, good results in 30 percent, and poor results in 26 percent (p = 0.46). When the sensory recovery was examined with regard to length of nerve gap, however, nerves with gaps of 4 mm or less had better sensation when repaired with a conduit; the mean moving two-point discrimination was 3.7 +/- 1.4 mm for polyglycolic acid tube repair and 6.1 +/- 3.3 mm for end-to-end repairs (p = 0.03). All injured nerves with deficits of 8 mm or greater were reconstructed with either a nerve graft or a conduit. This subgroup also demonstrated a significant difference in favor of the polyglycolic acid tube. The mean moving two-point discrimination for the conduit was 6.8 +/- 3.8 mm, with excellent results obtained in 7 of 17 nerves, whereas the mean moving two-point discrimination for the graft repair was 12.9 +/- 2.4 mm, with excellent results obtained in none of the eight nerves (p < 0.001 and p = 0.06, respectively). This investigation demonstrates improved sensation when a conduit repair is used for nerve gaps of 4 mm or less, compared with end-to-end repair of digital nerves. Polyglycolic acid conduit repair also produces results superior to those of a nerve graft for larger nerve gaps and eliminates the donor-site morbidity associated with nerve-graft harvesting.

Peripheral nerve regeneration across an 80-mm gap bridged by a polyglycolic acid (PGA)-collagen tube filled with laminin-coated collagen fibers: a histological and electrophysiological evaluation of regenerated nerves

We evaluated peripheral nerve regeneration across an 80-mm gap using a novel artificial nerve conduit. The conduit was made of a polyglycolic acid (PGA)-collagen tube filled with laminin-coated collagen fibers. Twelve beagle dogs underwent implantation of the nerve conduit across an 80-mm gap in the left peroneal nerve. In four other dogs used as negative controls, the nerve was resected and left unconnected. Histological observation showed that numerous unmyelinated and myelinated nerve fibers, all smaller in diameter and with a thinner myelin sheath than normal nerve fibers, regrew through and beyond the gap 12 months after implantation. The distribution of the regenerated axonal diameters was different from that of the normal axonal diameters. Compound muscle action potentials, motor evoked potentials, and somatosensory evoked potentials were recorded in most animals 3 months after implantation. Peak amplitudes and latencies recovered gradually, which indicating the functional establishment of the nerve connection with the target organs. In addition to the ordinary electrophysiological recoveries, potentials with distinct latencies originating from Aalpha, Adelta and C fibers became distinguishable at the 6th lumbar vertebra following stimulation of the peroneal nerve distal to the gap 12 months after implantation. The pattern of walking without load was restored to almost normal 10-12 months after implantation. Neither electrophysiological nor histological restoration was obtained in the controls. Our nerve conduit can guide peripheral nerve elongation and lead to favorable functional recovery across a wider nerve gap than previously reported artificial nerve conduits.

Functional assessment of the rat sciatic nerve following intraoperative expansion: the effect of recovery duration on behavioural, neurophysiological, and morphological measures

The purpose of this study was to investigate the feasibility of rapid intraoperative elongation of the rat sciatic nerve with the use of tissue expander and to assess its functional recovery. Out of 51 rats 43 had their right sciatic nerve expanded with a 5-ml intraoperative expander over 1 hr and 8 were sham-operated controls. The functional recovery of the nerve was assessed at intervals up to 4 months using the Sciatic Functional index (SFI), neurophysiological indices, and histology. Intraoperative expansion elongated the rat sciatic nerve by about 13%. SFI decreased on the first postoperative day and started to recover by Day 7, reaching almost preoperative values by Days 14 and 30 according to De Medinaceli and Bain-Mackinnon-Hunter formulas, respectively. Latency and motor conduction velocity demonstrated a deterioration after expansion which peaked on Day 1. Recovery started by Day 7 and reached preoperative levels by 60 days. The histological findings indicated minor aberrations immediately after expansion and maximal demyelination with minimal axonal disruption on Day 1. The reparative process started by Day 7 and continued till Day 120 when almost no histological changes were observed. In conclusion, intraoperative nerve expansion successfully elongates the rat sciatic nerve. It also causes functional and morphological abnormalities which are of low to moderate degree, have a 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 25-year perspective of peripheral nerve surgery: evolving neuroscientific concepts and clinical significance

In spite of an enormous amount of new experimental laboratory data based on evolving neuroscientific concepts during the last 25 years peripheral nerve injuries still belong to the most challenging and difficult surgical reconstructive problems. Our understanding of biological mechanisms regulating posttraumatic nerve regeneration has increased substantially with respect to the role of neurotrophic and neurite-outgrowth promoting substances, but new molecular biological knowledge has so far gained very limited clinical applications. Techniques for clinical approximation of severed nerve ends have reached an optimal technical refinement and new concepts are needed to further increase the results from nerve repair. For bridging gaps in nerve continuity little has changed during the last 25 years. However, evolving principles for immunosuppression may open new perspectives regarding the use of nerve allografts, and various types of tissue engineering combined by bioartificial conduits may also be important. Posttraumatic functional reorganizations occurring in brain cortex are key phenomena explaining much of the inferior functional outcome following nerve repair, and increased knowledge regarding factors involved in brain plasticity may help to further improve the results. Implantation of microchips in the nervous system may provide a new interface between biology and technology and developing gene technology may introduce new possibilities in the manipulation of nerve degeneration and regeneration.

Expanded polytetrafluoroethylene entubulation of the rabbit inferior alveolar nerve

OBJECTIVE

The purpose of this study was to evaluate the use of an expanded polytetrafluoroethylene conduit in the treatment of a 6. 0-mm gap in the rabbit inferior alveolar nerve and compare the results with those of an autogenous interpositional tibial nerve graft.

STUDY DESIGN

The inferior alveolar nerves of 5 adult New Zealand White female rabbits (10 nerves) were exposed bilaterally, and a 6-mm segment of each nerve was resected. On one side, chosen at random, the gap was immediately bridged through use of an 8.0 x 2. 0-mm expanded polytetrafluoroethylene conduit; on the other side, the gap was grafted with an autogenous tibial nerve graft. Two randomly selected nerves served as sham-dissected controls. At 15 weeks after surgery, the animals were killed and the entire nerve segments were harvested and prepared according to standard fixation and embedding techniques. The sections were examined histomorphometrically to quantify the degree of axonal regeneration through definition of fascicular number, total fascicular surface area, axonal density, and mean axonal diameter at 3 locations along the repair site.

RESULTS

Light microscopic examination revealed the presence of disorganized neural tissue in both groups, with slightly more fibrovascular interfascicular tissue in the expanded polytetrafluoroethylene group. Histomorphometric analysis revealed no significant differences between groups for most of the measured variables. The mean axonal diameter varied between groups, and the fascicular number was greater in the expanded polytetrafluoroethylene group at the middle site.

CONCLUSIONS

This study demonstrates that regeneration of the inferior alveolar nerve can occur across a 6.0-mm gap through an expanded polytetrafluoroethylene tube with results comparable to those of an autogenous nerve graft, significant donor site morbidity being avoided. The significant differences between groups were probably due to greater containment of regenerating axonal fibers in the expanded polytetrafluoroethylene group.

Sutures alone are sufficient to support regeneration across a gap in the continuity of the sciatic nerve in rats

We have proposed that it is sufficient to provide a simple substratum on which regenerating axons may traverse a gap in a peripheral nerve. To test this hypothesis we set up a new experimental model in which sutures were used to bridge a 10 mm long defect in a peripheral nerve. A defect was created bilaterally in 25 rat sciatic nerves. The cut ends of the nerve were joined by three laps of a continuous suture, on one side with 8/0 polyamide (non-absorbable) and on the other with 8/0 polyglactin (absorbable), leaving a 7 mm gap. At two weeks a matrix that contained capillaries, fibroblast-like cells, and mononuclear cells had formed between the nerve endings, and the sutures were surrounded by foreign-body-like tissue reactions. At four weeks axons had grown into the distal nerve segment on both sides in 65%-90% of the cases as indicated by a response to the pinch reflex test and immunocytochemistry for presence of neurofilament protein. Axons were organised in minifascicles and these tended to grow larger as the demarcation of the entire regenerated segment by a perineurial-like structure improved with time. At 12 weeks axonal counts of cross-sections of the distal tibial trunk showed many myelinated nerve fibres but no significant difference in axonal counts or degree of myelination between the polyamide and polyglactin sides. The results show that conventional sutures alone are sufficient to support regeneration across a short gap in a peripheral nerve, a method that may be of potential clinical value.

Modulation of peripheral nerve regeneration: a tissue-engineering approach. The role of amnion tube nerve conduit across a 1-centimeter nerve gap

A new type of a biodegradable nerve graft conduit material, the amnion tube, has been developed in our laboratory. To test the tube in the peripheral nerve regeneration process, it was initially applied across a 1-cm sciatic nerve gap in rats and was compared with other nerve conduit materials. We used male Sprague-Dawley rats as our animal model. The experiment included 66 rats that were randomly assigned into five groups: autograft (n = 17), amnion tube (n = 19), silicone tube (n = 20), no repair (n = 7), and sham group (n = 3). The process of peripheral nerve regeneration was evaluated at 2, 4, 10, and 17 weeks following injury and repair by using morphologic and functional assessments of the outcome of nerve regeneration in each animal. Nerve regeneration across the amnion tube nerve conduit was comparable with that seen in autograft and superior to that of the silicone group. A uniform nerve tissue was seen filling and crossing the amnion conduit, and the regenerated nerve from the proximal stump reached the distal end and was undifferentiated from the normal nerve tissues. At 4 months, the amnion tube biodegraded and no longer could be identified and differentiated from the nerve tissues. The amnion tube animal group showed a number of axons very close to that in the nerve autograft group (37,157 versus 33,054). Functional recovery at a 2- to 4-week interval was significantly statistically higher only in the amnion tube animal group (p = 0.01). However, the improvement disappeared between 10 and 17 weeks. In conclusion, the amnion tube is a potential ideal nerve conduit material secondary to its unique characteristics: it contains important neurotropic factors, is biodegradable, provokes a very weak immune response, is semiflexible, is readily available, and is easily manufactured into different sizes and diameters.

Spatiotemporal progress of nerve regeneration in a tendon autograft used for bridging a peripheral nerve defect

We have previously shown that a tendon autograft from the rat tail can support regeneration across a gap in the continuity of the rat sciatic nerve. In this study, we characterized the spatiotemporal progress of regeneration in such a graft bridging a 10-mm defect in the sciatic nerve of the rat. Regeneration was assessed 7, 10, 14, or 18 days postoperatively, by immunocytochemistry for axons, Schwann cells, and macrophages and histochemistry for blood vessels. Axonal regrowth into the grafts showed an initial delay period of 6.8 days, whereafter axons grew at a rate of 1.0 mm/day. Schwann cells grew into the grafts from both the proximal and distal nerve segments, proximally just ahead of the axonal front. Macrophages were initially preferentially located at the periphery of the grafts, but gradually increased inside the grafts. Blood vessels entered the grafts from both the proximal and distal aspects of the severed nerve. The onset of vascularization appeared to coincide with axonal regeneration into the grafts.

Effects of nerve growth factor on nerve regeneration through a vein graft across a gap

The limited availability of donor sites for nerve grafts and their inherent associated morbidity continue to stimulate research toward finding suitable alternatives. In the following study, the effect of direct administration of nerve growth factor (NGF) into a nerve conduit across a gap was tested in a rat sciatic nerve model. A 1-cm segment of the right sciatic nerve in Sprague-Dawley rats was resected, and the gap was then bridged using one of three methods: group I (NGF-treated group, n = 12), a vein graft filled with NGF (100 ng in 0.3-ml phosphate buffered saline); group II (control group, n = 12), a vein graft filled with phosphate buffered saline only; group III (standard nerve graft, n = 11), a resected segment of the sciatic nerve. All animals were evaluated at 3 and 5 weeks by behavioral testing and at 5 weeks by electrophysiologic testing. At 3 weeks, sensory testing showed that the latency to a noxious stimulus in group I animals (8.0 +/- 5.4 sec, mean +/- SD) was significantly lower than that of group II animals (13.2 +/- 6.5 sec), indicating that sensory recovery was superior in the animals receiving NGF. The mean latency of animals in group III was 12.9 +/- 6.5 sec, but the difference between the latencies of group I and group III did not reach statistical significance. At 5 weeks, there was no difference in sensory testing between groups. Motor function in groups I and III as measured by walk pattern analysis was superior to that of group II at 5 weeks (toe spread ratios 0.66 +/- 0.09, 0.48 +/- 0.07, and 0.69 +/- 0.09 for groups I, II, and III, respectively). Mean motor conduction velocities across the 1-cm gap were 8.6 +/- 4.7 m/sec, 2.5 +/- 0.7 m/sec, and 6.9 +/- 2.9 m/sec in groups I, II, and III respectively. The difference between groups I and III was not statistically significant, but the motor conduction velocity of group II was significantly slower than that of either group I or III (p < 0.002). The positive effects of NGF on regeneration of nerves across a gap seen in this study suggest that it may be useful for treating peripheral nerve injuries in combination with autogenous vein grafts.

Local administration of neurotrophic growth factor in subcutaneous silicon chambers enhances the regeneration of the sensory component of the rat sciatic nerve

An experimental model for local administration of neurotrophic growth factor (NGF) in peripheral nerve lesions is tested. The model consists of a subcutaneous reservoir connected to the sciatic nerve neurorrhaphy. The right sciatic nerves were exposed, severed, and repaired at a level 1.5 cm proximal to their trifurcation. Then, a dome-shaped silicone reservoir connected to the proximal end of a silicone tube was placed subcutaneously in the dorsum of the experimental animal. The distal end of the connecting tube was located in the nerve neurorrhaphy. Two experimental groups were made: Group A (n = 90) received daily doses of a solution containing NGF-7S during the first 4 weeks after surgery and a single weekly dose thereafter. Within this group, three subgroups of 30 rats each were made: A-4 sacrificed 4 weeks after surgery, A-8 sacrificed after 8 weeks, and A-12 after 12 weeks. Group B (n = 90) received the same vehicle solution without NGF under the same schedule and volume as in Group A. Three subgroups were also made as in Group A depending on the survival period. In order to locate the neurons in the dorsal root ganglia, the retrograde tracer horseradish peroxidase was administered at the proximal stump of the sciatic nerve (tibialis branch), which was severed 1 cm distal to the sciatic trifurcation. In respect of the nonoperated side, the percentage between the number of dorsal root ganglia neurons in the NGF-treated group was significantly higher than in the control group (P < 0.001). These results demonstrate that percutaneous administration of multiple doses of NGF in this model enhances sensory nerve regeneration after sciatic lesions evaluated by horseradish peroxidase labeling of dorsal root ganglia neurons.

Neuronal survival using a resorbable synthetic conduit as an alternative to primary nerve repair

Clinically optimal situations for primary nerve repair are rarely observed. Crushed nerve ends result in either suboptimal repair or a need for nerve grafting. Functional results after nerve surgery are relatively poor, including major sensory deficits, which may be due to the death of primary sensory neurons that follows the nerve injury. The aim of this study was to determine if using polyhydroxybutyrate (PHB), a resorbable nerve conduit, could be an alternative to primary nerve repair in reducing loss of neurons. The superficial radial nerves in 20 cats were sectioned bilaterally and primarily repaired microsurgically by the use of two different strategies; either wrapping the nerve ends in sheets of PHB or epineurally suturing of the nerve. After 6 or 12 months, the surviving neurons within the dorsal root ganglia [C5-T1] were counted. No statistically significant differences were found between the two methods. This may imply a future possibility of using PHB as a synthetic nerve graft in situations where suboptimal primary repair or nerve grafts are the alternatives.

Magnetically aligned collagen gel filling a collagen nerve guide improves peripheral nerve regeneration

Bioresorbable collagen nerve guides filled with either magnetically aligned type I collagen gel or control collagen gel were implanted into 4- or 6-mm surgical gaps created in the sciatic nerve of mice and explanted 30 and 60 days postoperation (dpo) for histological and immunohistochemical evaluation. The hypothesis was that contact guidance of regenerating axons and/or invading nonneuronal cells to the longitudinally aligned collagen fibrils would improve nerve regeneration. The criterion for regeneration was observation of regenerating myelinated fibers distal to the nerve guide. Consistent with previous studies showing poor regeneration in 6-mm gaps at 60 dpo with entubulation repair, only one of six mice exhibited regeneration with control collagen gel. In contrast, four of four mice exhibited regeneration with magnetically aligned collagen gel, including the appearance of nerve fascicle formation. The numbers of myelinated fibers were less than the uninjured nerve in all groups, however, which may have been due to rapid resorption of the nerve guides. An attempt to increase the stability of the collagen gel, and thereby the directional information presented by the aligned collagen fibrils, by crosslinking the collagen with ribose before implantation proved detrimental for regeneration.

A new resorbable wrap-around implant as an alternative nerve repair technique

Poly-3-hydroxybutyrate (PHB), a bacterial storage product, is available as bioabsorbable sheets and has been used in this study for primary nerve repair. The aim was to assess axonal regeneration following such repair and determine the inflammatory response to PHB. In 20 adult cats, the transected superficial radial nerve was wrapped in PHB sheets, while primary epineural repair was carried out in the contralateral limb. At 6 and 12 months, the repair sites were assessed immunohistochemically for macrophage infiltration and myelinated axons were counted in the distal nerve. Mean macrophage counts across the whole width of the nerve in both groups at 6 and 12 months showed no statistically significant difference. Nor was there any significant difference between the two groups at both time-points in axon counts, axon diameter, myelin thickness and g-ratio. There was a statistically significant increase in fibre diameters at 12 months, indicating that fibres were undergoing continuous maturation.

A comparison of peripheral nerve repair using an absorbable tubulization device and conventional suture in primates

Median nerve regeneration was studied in 30 adult primates after repair by microsurgical suture or tubulization with a nonwoven, bioabsorbable, polyglycolic acid device. The two methods were compared electrophysiologically and histologically 6 and 12 months after repair. The electrophysiology included recording of electrically evoked compound action potentials and subsequent determination of threshold, conduction velocity, amplitude, and area above the baseline for each component. Measurements were obtained before nerve transection and at the time of biopsy by stimulating both proximal and distal to the transection site. Analysis of all electrophysiological parameters revealed no statistically significant differences (p less than 0.05) between the two repair techniques. Histopathology included examination of cross sections proximal and distal to the repair sites and longitudinal sections through the coaptation site. End organs (Meissner's and Pacinian corpuscles and muscle) were sectioned to determine the degree of reinnervation. No significant differences between the repair techniques were observed by histological analysis of these sections. These evaluations indicated that the tubulization repair technique produced results comparable to that of the suture technique.

Poly(alpha-hydroxyacids) for application in the spinal cord: resorbability and biocompatibility with adult rat Schwann cells and spinal cord

Future surgical strategies to restore neurological function in the damaged human spinal cord may involve replacement of nerve tissue with cultured Schwann cells using biodegradable guiding implants. We have studied the in vitro and in vivo degradability of various aliphatic polyesters as well as their effects on rat Schwann cells in vitro and on spinal cord tissue in vivo. In vitro, cylinders made of poly(D,L-lactic-co-glycolic acid) 50:50 (PLA25GA50) started to degrade at 7 days, compared with 28 days for cylinders made of poly(D,L-lactic acid) (PLA50). This faster degradation of PLA25GA50 was reflected by a much higher absorption of water. In vivo, after implantation of PLA25GA50 or PLA50 cylinders between the stumps of a completely transected adult rat spinal cord, the decrease in molecular weight of both polymers was similar to that found in vitro. In vitro degradation of poly(L-lactic acid) (PLA100) mixed with increasing amounts of PLA100 oligomers also was determined. The degradation rate of PLA100 mixed with 30% oligomers was found to be similar to that of PLA50. In vitro, PLA25GA50 and the breakdown products had no adverse effect on the morphology, survival, and proliferation of cultured rat Schwann cells. In vivo, PLA25GA50 cylinders were integrated into the spinal tissue 2 weeks after implantation, unlike PLA50 cylinders. At all time points after surgery, the glial and inflammatory response near the lesion site was largely similar in both experimental and control animals. At time points later than 1 week, neurofilament-positive fibers were found within PLA25GA50 cylinders or the remains thereof. Growth-associated protein 43, which is indicative of regenerating axons, was observed in fibers in the vicinity of the injury site and in the remains of PLA25GA50 cylinders. The results suggest that poly(alpha-hydroxyacids) are likely candidates for application in spinal cord regeneration paradigms involving Schwann cells.

Motor versus sensory neuron regeneration through collagen tubules

Differences in regeneration of sensory and motor nerves were studied in rats to determine the effects of entubulation with collagen conduits. The rat sciatic nerve was repaired either with a 10-mm saline-filled gap or with a no-gap end-to-end repair cuffed within collagen tubules. These repairs were compared with the standard epineurial repairs. The populations of regenerated motor and sensory neurons in the peroneal nerves of all repairs were compared against the populations of normal peroneal neurons using horseradish peroxidase retrograde labeling. The epineurial repair resulted in regeneration of 65 percent (409 +/- 150) of motor neurons and 79 percent (2127 +/- 516) of sensory neurons (n = 6). The no-gap end-to-end repair in a collagen tubule resulted in regeneration of 53 percent (338 +/- 203) of motor and 70 percent (1893 +/- 794) of sensory neurons (n = 7). In the 10-mm gap repair, only 6.2 percent (39 +/- 18) of motor neurons but 63 percent (1710 +/- 557) of sensory neurons regenerated (n = 5). These results show that collagen entubulation supports nerve regeneration in end-to-end nerve repairs comparably to standard epineurial suture repairs. With the 10-mm gap repairs in collagen tubules, sensory neurons regenerated consistently better than motor neurons in the same environment. Therefore, intrinsic differences exist between motor and sensory neuron regeneration in the same nerve.

The development of bioartificial nerve grafts for peripheral-nerve regeneration

This article describes recent, significant scientific advances leading to the development of the bioartificial nerve graft. Schwann cells, which play an active role in the repair and function of peripheral nerves, are used to seed a synthetic, often resorbable conduit, which is then used to bridge and repair nerve gaps caused by injury or disease. By enhancing the rate and extent of regeneration, the bioartificial nerve graft holds great promise for improving recovery in the peripheral (and central) nervous system.

Gore-Tex tubing as a conduit for repair of lingual and inferior alveolar nerve continuity defects: a preliminary report

PURPOSE

This report describes the results of using a Gore-Tex (Gore Company, Flagstaff, AZ) tube as a conduit for repair of continuity defects in the inferior alveolar or lingual nerves.

PATIENTS AND METHODS

Seven nerve repairs were performed in five patients (M:F = 1:4) with an age range of 16 to 56 years. The duration from injury to repair ranged from 4 to 30 months. Two inferior alveolar and five lingual nerves were repaired.

RESULTS

All seven patients had anesthesia by objective testing preoperatively and had a continuity defect at the time of operation. The size of the defects ranged from 2 to 15 mm. Two of the seven patients had some return of sensation, occurring in defects of 3 mm or smaller.

CONCLUSION

The results of this pilot study indicate that Gore-Tex tubing may not be effective in the repair of continuity defects except in those defects 3 mm or smaller, in which it may act as a protective barrier membrane rather than as a conduit.

Influence of collagen and laminin gels concentration on nerve regeneration after resection and tube repair

In order to assess the usefulness of collagen and laminin gels prefilling nerve chambers to enhance nerve regeneration, we compared reinnervation of target organs after sciatic nerve resection leaving gaps of 4 or 6 mm followed by repair with silicone tubes in different groups of mice. Tubes were prefilled with saline solution, collagen gels, or laminin-containing gels at different concentrations. Functional reinnervation was assessed by noninvasive methods to quantitate recovery of sweating, nociceptive, sensory, and motor functions in the hindpaw repeatedly during 4-5 months postoperation. The increase in gap length between nerve stumps delayed the beginning and reduced the degree of functional recovery achieved. Reinnervation started earlier and achieved slightly higher levels with collagen gel diluted at 1.28 mg/ml than with more concentrated (1.92 and 2.56 mg/ml) collagen gels and with saline-prefilled tubes bridging a 4-mm gap. Recovery was also better with diluted (4 mg/ml) than with concentrated (12 mg/ml) laminin-containing gel, although lower than with collagen gels and saline. By prefilling silicone tubes bridging a 6-mm gap, a length considered limiting for regeneration in the mouse sciatic nerve, with diluted collagen or laminin gels, both matrices allowed for higher levels of recovery and for successful regeneration in a higher proportion of mice than saline solution. The laminin gel performed slightly better than the collagen gel.

Nerve xenograft transplantation. Immunosuppression with FK-506 and RS-61443

An experimental model has been developed to study the potential transplantation of nerve xenografts using the newer immunosuppressive agents RS-61443 and FK-506. Sciatic nerve grafts of 2 cm were transplanted from donor Golden Syrian hamsters into a 0.5 cm gap in the sciatic nerve of recipient Lewis rats. Walking track analysis, somatosensory evoked potentials and histology demonstrated improved regeneration across the nerve xenografts that had been immunosuppressed with RS-61443 and FK-506 compared with non-immunosuppressed controls, but the function never approached that seen in control isografts. Regeneration across nerve xenografts immunosuppressed with FK-506 was better than xenografts immunosuppressed with RS-61443.

Tubular versus conventional repair of median and ulnar nerves in the human forearm: early results from a prospective, randomized, clinical study

Injury to a peripheral nerve is followed by local synthesis and release of neurotrophic factors of importance for the regeneration process. This concept was adopted for repair of transected human median and ulnar nerves in the forearm. As an alternative to conventional microsurgical repair of the nerve trunk, silicone tubes of appropriate size were used to enclose the injury zone, intentionally leaving a gap measuring 3-4 mm between the nerve ends inside the tube. The early results from a prospective, randomized, clinical study comparing this principle with conventional microsurgical technique for repair of human median and ulnar nerves, is presented. Eighteen patients (14 men and 4 women), aged 12-72 (mean, 29.5) years, were randomized to either tubulization (11 cases) or conventional microsurgical repair (7 cases). A battery of tests for sensory and motor functions of the hand were carried out at regular intervals for up to 1 year after surgery. The results show no difference between the both techniques, with the exception of perception of touch, which showed a significant difference (p < .05) at the 3-month checkup in favor of the tubulization technique. At re-exploration 11 months after the initial procedure (1 case), the former gap was replaced by regenerated nerve tissue in direct continuity with the proximal and distal parts of the nerve trunk, the exact level of the former injury being impossible to identify. Study data demonstrate an intrinsic capacity of human major nerve trunks to reconstruct themselves in a preformed space when an optimal environment is offered and the surgical trauma is minimized.

Nerve regeneration across a 25-mm gap bridged by a polyglycolic acid-collagen tube: a histological and electrophysiological evaluation of regenerated nerves

In the study reported here we have examined the nerve regeneration that occurs over a 25-mm gap using a novel biodegradable nerve guide tube. The tube was a composite of polyglycolic acid (PGA) mesh coated with collagen which was filled with neurotrophic factors. The left sciatic nerve of ten adult cats was dissected. The stumps were connected by the tube, and fixed gap. Histological examinations carried out 4-16 months after implantation of the tube revealed regeneration of well vascularized nerve tissue. Regeneration of both myelinated, unmyelinated axons and Schwann cells was confirmed by electron microscopy 5 months after surgery. Following injection of horseradish peroxidase (HRP) into a site peripheral to the regenerated segment of the sciatic nerves, motoneurons in the ventral horn of the spinal cord, afferent terminals in the medial portion of the dorsal column of the medulla oblongata, and sensory afferent nerve terminals in the dorsal horn of the spinal cord were labelled. Electrophysiological examinations revealed restoration of evoked electromyograms and sensory evoked potentials (SEPs) recorded from the cerebral cortex as well as the spinal cord. We also found that some of the regenerated motor axons exhibited branching in the regenerated segments. In two cases, a single motoneuronal axon from the regenerated side projected to both flexors and extensors, simultaneously. Our results indicate that the PGA-collagen composite tube is a promising tool for use as a nerve guide tube in peripheral nerve regeneration.

Rapid Intraoperative Facial Nerve Expansion

The repair of nerve length defect presents a reconstructive challenge after trauma and oncologic resection. This study examined rapid intraoperative nerve expansion as a method of repairing nerve length defects with the cat facial nerve model. We compared expanded nerves with grafted nerves and intact nerves 1 year after repair using the criteria of gross function (symmetry and blink reflex according to a modified House scale), electromyography thresholds, nerve-conduction velocity, morphology, and axon count. Three of the five expanded nerves regenerated, and all of the grafted nerves regenerated. Functional results were similar for the regenerated expanded and the grafted facial nerves, and both methods achieved an equivalent level of function. The facial nerves of the regenerated expanded group, grafted group, and intact group had mean electromyography thresholds of 132 mV, 98 mV, and 134 mV, respectively, and mean conduction velocities of 48.3 mg/second, 47.9 m/second, and 44.7 m/second, respectively. Morphologic examination of all five expanded nerves immediately after the expansion process revealed an intact fascicular structure. However, 1 year after excision of the expanded segment and repair, only three of the five nerves regenerated. Axon count at 1 year was as follows: 404 for the regenerated expanded nerves, 449 for the grafted nerves, and 403 for the intact nerves. The potential advantages of rapid intraoperative nerve expansion over nerve grafting for the repair of nerve gap defects include a single suture line and absence of donor site morbidity. This pilot study demonstrates that rapid intraoperative nerve expansion and regeneration is possible and can be used to repair a nerve length deficit. The development of a rapid and reliable method of intraoperative nerve expansion deserves further study.

Nerve coaptation studies with and without a gap in rabbits

Appropriate matching of proximal and distal fibers is a major objective when suturing a lacerated nerve. Recent studies suggest that neurotropic factors may influence motor/sensory specificity and affect the functional outcome. This was studied in animal models by direct coaptation of cut nerve ends inside a 5-mm collagen tube with and without appropriate sensory/motor alignment, as well as in models where the cut nerve ends were placed in a 10-mm collagen tube with a 5-mm gap, with and without appropriate sensory/motor alignment. The radial nerve of 49 New Zealand white rabbits was chosen because it has distinct motor and sensory divisions. The animals were killed at 24 weeks and electrophysiologic, histologic, and muscle contraction studies were performed. Axon counts and diameters were measured from the distal motor and sensory stumps. Nerve conduction velocity, dry muscle weight, and motor axon counts were not statistically different between the groups. The malaligned group without a gap had better regeneration in sensory nerves than other groups. The muscle contraction force of the malaligned group without a gap was significantly less than the other groups. The malaligned group with a 5-mm gap had the same muscle contraction force as the aligned group without a gap. In this study, a short nerve gap lessened the misdirection of motor fibers after nerve-end coaptation.

Sciatic nerve regeneration in the rat after frozen muscle grafting. A comparative study using somatosensory evoked potentials

In an experimental study, somatosensory evoked potentials were used to evaluate sciatic nerve regeneration in the rat after 12 mm-long conventional nerve grafting, vascularized nerve grafting and frozen muscle grafting. This experimental method was found to be technically easy and highly reproducible. No statistical difference was found between the three groups concerning amplitude of the negative electrical wave recorded at the cortex level after distal stimulation. Conduction velocities were found to be significantly higher in both the vascularized nerve group and the frozen muscle group, compared with the conventional nerve grafting group. The frozen muscle grafting technique is valuable as it gives good experimental results, is easy to carry out and causes minimal damage to the donor site.

The role of conduits in nerve repair: a review

The restoration of effective and meaningful axonal function following peripheral nerve injury continues to be a considerable clinical challenge. The use of conduits to bridge the gap between severed ends is a contemporary experimental maneuver that isolates the microenvironment of regenerating axons. Entubulation has allowed analysis and manipulation of putative influences upon nerve regeneration. A review is provided of the research efforts that have explored the neurobiological and mechanical factors that guide nerve regeneration within conduits. Levels of specificity, from tissue specific growth to end-organ specific growth, are outlined within the framework of the theories of Neurotropism, Contact Guidance and Neurotrophism. Included are investigations utilizing different conduit materials and the few clinical applications of these conduits. A number of chamber manipulations, extra-cellular matrix substrates and growth factors and their molecular receptors have been implicated in enhanced regeneration specificity. This information has been extended to the conduit model. The interposition of healthy nerve segments into conduits is proposed as a means of extending the length of successful nerve regeneration.

Different muscle graft denaturing methods and their use for nerve repair

In an attempt to enhance recovery through denatured muscle grafts we have used different methods to denature muscle, either using dry heat in a microwave oven or by warming in sterile distilled water. Axonal regeneration was studied at intervals from day 5 to day 60 after insertion of the muscle grafts and compared to results found in frozen-thawed muscle grafts and in autologous nerve grafts used as controls. Axonal regeneration, Schwann cell behaviour and the degree of inflammation were quantified using immunohistochemical techniques and computerised image analysis. Autologous nerve grafts supported the highest rates and volumes of axonal regeneration until day 30 when the microwaved muscle grafts had the highest values for axonal immunostaining and at 60 days the highest level of Schwann cell immunoreactivity. We conclude that microwave heating is suitable as an alternative denaturing method for successful muscle grafts and has a potential clinical use.

An experimental study of lingual nerve repair using epineurial sutures or entubulation

The recovery of the mechanosensitive afferent fibres in the lingual branch of the trigeminal nerve has been studied using electrophysiological techniques in cats, after two methods of nerve repair. After nerve section the lingual nerve was repaired by either epineurial sutures or by entubulation. 12 weeks after either method of repair the properties of the regenerated fibres were significantly different from normal, but following repair with epineurial suture they were closer to normal than after repair by entubulation. After entubulation the fibres had a greater reduction in conduction velocity, a greater increase in force threshold, and the adaptation times were faster. The results suggest that epineurial suture should be preferred clinically.

Biological performance of a degradable poly(lactic acid-epsilon-caprolactone) nerve guide: influence of tube dimensions

One of the ways to reconstruct a nerve defect is to use a biodegradable nerve guide. The aim of this study was to establish a nerve guide constructed of an amorphous copolymer of lactic acid-caprolactone. A pilot study was set up to elucidate the effect of the tube dimensions on nerve regeneration. Four types of nerve guides, with internal diameters ranging from 1.12-1.23 mm and wall thicknesses ranging from 0.34-0.68, were tested for this purpose. We evaluated the biodegradation, foreign body reaction and nerve regeneration by light microscopy, after three different implantation times (1, 2, and 3 months). After 2 months, we observed that all types of nerve guides had changed from a transparent to an opaque and swollen state, and that they had lost their strength. The foreign body reaction was characterized by the presence of giant cells and fibroblasts surrounding the degrading nerve guide. From this pilot study, we conclude that nerve guide type 1, with an internal diameter of 1.23 mm and a wall thickness of 0.34 mm, can ensure nerve regeneration in the case of a 1-cm gap in the sciatic nerve of the rat. Nerve guides types 3 and 4, with relatively small lumens, show nerve compression due to a more pronounced swelling of the degrading tube.

The reinnervation of the tongue and salivary glands after two methods of lingual nerve repair in the cat

The recovery of fibres in the chorda tympani after repair by epineurial suture or entubulation was investigated. The combined trunk of the chorda tympani and lingual branch of the trigeminal nerve was sectioned unilaterally, repaired using either epineurial sutures or entubulation, and allowed to recover for 12 weeks. The properties of gustatory, thermosensitive and mechanosensitive units, and the return of vasomotor and secretomotor responses were then investigated. After repair by epineurial suture, integrated whole-nerve activity recorded from the chorda tympani during stimulation of the tongue with gustatory or thermal stimuli was reduced in all areas of the tongue when compared to controls. After entubulation repair, little or no activity could be recorded. Recordings made from 57 single units in the chorda tympani after repair by epineurial suture revealed a greater proportion of purely mechanosensitive units and fewer gustatory units than in the controls. Fewer units were spontaneously active, they had lower maximum discharge frequencies, and produced fewer impulses when stimulated. Recordings made from 61 single units after repair by entubulation revealed receptor characteristics with greater differences from controls than after epineurial suture and there was only one gustatory and one thermosensitive unit. Vasomotor responses were completely restored after repair by epineurial suture, but some responses were smaller after entubulation repair. Secretomotor responses were significantly smaller after both methods of repair and there was no difference between the two groups.

Peripheral nerve repair using a poly(organo)phosphazene tubular prosthesis

Nerve regeneration experiments were carried out using tubular nerve guides of poly[(ethylalanato)1.4(imidazolyl)0.6phosphazene] (PEIP). By means of in vivo tests, this polymer was found to be biodegradable and transformed into harmless products. The tubular nerve guides were prepared by deposition of the dissolved polymer on a glass capillary tube, followed by evaporation of the solvent (methylene dichloride). After transectioning, rat sciatic nerve stumps were immediately sutured into the ends of 10-mm-long polymer tubes. On removal of the prosthesis, after implantation for 45 d, a tissue cable was found bridging the nerve stumps in all cases. Histological analysis revealed that the tissue cable was essentially composed of a regenerated nerve fibre bundle. A parallel series of experiments was undertaken to compare the use of silicone tubes that are not biodegradable and are most frequently used for studies of nerve regeneration with tubulization techniques. The advantages of biodegradable PEIP tubular nerve guides used for peripheral nerve repair are discussed.

Vein conduits for repair of nerves with a prolonged gap or in unfavourable conditions: an analysis of three failed cases

Clinical failure of vein conduits for repair of four nerves in three cases is reported. Two digital nerves with gaps of 5.0 cm and 5.8 cm, respectively, and two median nerves with gaps of 4.0 cm and 5.0 cm were repaired with vein conduits. The digital nerves were repaired secondarily with insertion of nerve tissue slices. The median nerve lacerations were associated with compound soft tissue injuries and were repaired primarily by interfascicular vein conduits. There was no detectable recovery of sensibility in autonomous areas of these nerves and no sign of recovery of the innervated muscles during follow-up. Re-exploration revealed that the vein conduits used for repair of the median nerves were constricted by surrounding scar tissue and axon regeneration was precluded. The critical length for nerve regeneration in human beings and wound conditions unfavorable to nerve regeneration are discussed. This report suggests that vein conduits are not indicated in nerve gaps over 5.0 cm or in primary repair of nerves with compound injuries.

Invaginated vein graft as nerve conduit: an experimental study

Vein grafts have been used for nerve repair in experimental and clinical studies. However, some concerns about their collapsability and the presence of valves which could block axonal growth have been put forth. We propose a modification to eliminate these potential problems by turning the vein inside out, obtaining an "invaginated" vein graft. We performed an experimental study on 61 adult Wistar rats, divided into 3 groups: control (non-operated) (n = 11); immediate repair, with 3 subgroups: invaginated vein graft (n = 10), vein graft (n = 10), and nerve graft (n = 10); and delayed repair, with 2 subgroups: invaginated vein graft (n = 10) and nerve graft (n = 10). Delayed repair was performed 3 to 4 weeks following division of the nerve. Electromyographical (EMG) assessment was performed in all operated animals at 2, 4, and 6 months after immediate reconstruction, and at 1 and 4 months after delayed repair. At the end of the study, all nerves were excised and a morphometric analysis was performed. We conclude that vein grafts are as useful as nerve grafts in immediate and delayed nerve repair, as there were no significant functional or histologic differences. We found no significant differences between invaginated vein grafts and non-invaginated vein grafts. However, electrophysiological results were slightly superior in the former. Regenerated axons were small, grouped in minifascicles with thin myelin sheaths. The venous adventitia did not interfere with axonal growth.

Effect of basic fibroblast growth factor and alpha-melanocytic stimulating hormone on nerve regeneration through a collagen channel

An experimental study on the rat sciatic nerve was performed to evaluate nerve regeneration through a collagen guide and to study the effects of alpha-melanocytic stimulating hormone (alpha-MSH) and basic fibroblast growth factor (b-FGF) in accelerating axonal elongation. After transection, nerves were repaired over a 7 mm gap using a placental collagen type IV guide. The channel was filled with either a b-FGF solution or an alpha-MSH solution or was produced with b-FGF incorporated into the guide. Four weeks later, only groups in which b-FGF had been injected or incorporated displayed a significant somatosensory evoked potential response. Histological and quantitative analysis of nerve fibres confirmed the existence of nerve continuity in groups receiving an alpha-MSH solution or a channel containing b-FGF. These results demonstrate that alpha-MSH in solution and b-FGF incorporated into a collagen type IV channel enhance peripheral nerve regeneration. However, at 4 weeks, only b-FGF (3 ng) restores functional activity.

Regeneration across 'stepping-stone' nerve grafts

The ability of small nerve segments interposed between synthetic conduits to increase the total nerve gap distance across which successful nerve regeneration would occur was studied. Fifty adult male Lewis rats were randomized into five groups. In Group I a segment of resected sciatic nerve was repaired by a nerve graft. Group II had alternating silicone tubing/nerve graft/silicone tubing replacement of the resected nerve segment (single stepping stone group). Group III had silicone tubing/nerve graft/silicone tubing/nerve graft/silicone tubing repair of the nerve deficit (double stepping stone). Group IV had a single long silicone conduit repair. Group V control underwent a sham operation. Nerve regeneration was evaluated using walking track pattern analysis, electrophysiologic assessment and histomorphological evaluation. 'Stepping stone nerve grafts' enhanced regeneration across nerve gaps in comparison to a single long conduit, but were inferior to a single long nerve graft. In the repair of long nerve gaps, the use of multiple short conduits with interposed short nerve segments could provide a source of trophic factors to enhance regeneration.

Management of major penetrating glass injuries to the upper extremities in children and adolescents

Penetrating glass injuries are a common cause of severe neurovascular damage, both in adults and in children. Frequently, an innocent skin wound disguises the extensive nature of the injuries beneath. Nineteen children and adolescents (ages 3-16 years) with a mean age of 9 years who sustained upper extremity penetrating glass wounds were evaluated retrospectively in order (1) to determine the incidence of unappreciated significant neurologic, musculotendonous, or vascular injury; (2) to provide indications for intraoperative evaluation under anesthesia; and (3) to further define the role of microneurorrhaphy in this population. Twelve patients sustained injuries above the elbow and seven patients injuries distal to the elbow. Above the elbow, the structures injured in order of frequency were the median nerve (75%), the brachial artery (58%), the ulnar nerve (50%), the musculocutaneous nerve (33%), sensory nerves of the arm and forearm and venae commitantes (42% each), the radial nerve (25%), and the chords of the brachial plexus (8%). Distal to the elbow, the ulnar nerve was the most frequently involved (71%), followed by the ulnar artery (57%), the flexor carpi ulnaris (57%), the superficialis and profundus flexor tendons (43%), the median nerve (43%), and the palmaris longus and flexor carpi radialis (14% each). Early exploration is critical to successful management. Vascular repairs and or microneurorrhaphy were necessary in all cases. A detailed follow-up evaluation to assess the results of these repairs was carried out from 4 to 9 years postsurgery. There were no clinical problems related to the vascular reconstructions. The results of the nerve repairs in this small series of children and adolescents were remarkably good.(ABSTRACT TRUNCATED AT 250 WORDS)

Group fascicular vein grafts with interposition of nerve slices for long ulnar nerve defects: report of three cases

Group fascicular vein grafts with interposition of nerve slices were designed for reconstruction of three ulnar nerves with defects of 2.5-4.5 cm. The veins were taken from superficial veins in the forearm and reversed to bridge the fascicles in both stumps. Normal nerve slices were sectioned from fascicles in the proximal stump and inserted inside the corresponding vein conduits. Postoperatively, the Tinel's sign was detected across the vein conduits, and electromyography showed reinnervation of intrinsic muscles of the hands. Follow-up for more than 2 years revealed motor recovery to M4 and sensory recovery to S3-S4 in these three cases. This technique may be a promising alternative to group fascicular nerve grafting for long defects in peripheral nerve trunks.

Long-term evaluation of nerve regeneration in a biodegradable nerve guide

Nerve regeneration using artificial biodegradable conduits is of increasing interest. The aim of this study is to evaluate the regeneration and maturation of a nerve after long-term implantation (2 years) of a biodegradable poly-L-lactide/poly-epsilon-caprolactone (PLLA/PCL) copolymeric nerve guide in the sciatic nerve of the rat. After harvesting, we evaluated both the regenerated nerves and the controls, using light microscopy, transmission electron microscopy, and morphometric techniques. Remnants of biomaterial were still present after 2 years of implantation, but the foreign body reaction was very mild at this stage, due to the rounded shapes of the polymer debris. Morphometric analysis showed significant differences between the regenerated nerve and the normal sciatic nerve: the number of myelinated fibers is higher, and the mean fiber diameter of the myelinated fibers in the regenerated nerve is smaller. In conclusion, the results demonstrate that the new PLLA/PCL nerve guide can provide optimal conditions for regeneration and maturation of damaged nerves.