Experimental nerve reconnection: importance of initial repair

Treadmill training of rats after sciatic nerve graft does not alter accuracy of muscle reinnervation

Background and purpose

After peripheral nerve lesions, surgical reconstruction facilitates axonal regeneration and motor reinnervation. However, functional recovery is impaired by aberrant reinnervation.

Materials and methods

We tested whether training therapy by treadmill exercise (9 × 250 m/week) before (run-idle), after (idle-run), or both before and after (run-run) sciatic nerve graft improves the accuracy of reinnervation in rats. Female Lewis rats (LEW/SsNHsd) were either trained for 12 weeks (run) or not trained (kept under control conditions, idle). The right sciatic nerves were then excised and reconstructed with 5 mm of a congenic allograft. One week later, training started in the run-run and idle-run groups for another 12 weeks. No further training was conducted in the run-idle and idle-idle groups. Reinnervation was measured using the following parameters: counting of retrogradely labeled motoneurons, walking track analysis, and compound muscle action potential (CMAP) recordings.

Results

In intact rats, the common fibular (peroneal) and the soleus nerve received axons from 549 ± 83 motoneurons. In the run-idle group, 94% of these motoneurons had regenerated 13 weeks after the nerve graft. In the idle-run group, 81% of the normal number of motoneurons had regenerated into the denervated musculature and 87% in both run-run and idle-idle groups. Despite reinnervation, functional outcome was poor: walking tracks indicated no functional improvement of motion in any group. However, in the operated hindlimb of run-idle rats, the CMAP of the soleus muscle reached 11.9 mV (normal 16.3 mV), yet only 6.3-8.1 mV in the other groups.

Conclusion

Treadmill training neither altered the accuracy of reinnervation nor the functional recovery, and pre-operative training (run-idle) led to a higher motor unit activation after regeneration.

Electrical stimulation to enhance peripheral nerve regeneration: Update in molecular investigations and clinical translation

Peripheral nerve injuries are common and frequently result in incomplete functional recovery even with optimal surgical treatment. Permanent motor and sensory deficits are associated with significant patient morbidity and socioeconomic burden. Despite substantial research efforts to enhance peripheral nerve regeneration, few effective and clinically feasible treatment options have been found. One promising strategy is the use of low frequency electrical stimulation delivered perioperatively to an injured nerve at the time of surgical repair. Possibly through its effect of increasing intraneuronal cyclic AMP, perioperative electrical stimulation accelerates axon outgrowth, remyelination of regenerating axons, and reinnervation of end organs, even with delayed surgical intervention. Building on decades of experimental evidence in animal models, several recent, prospective, randomized clinical trials have affirmed electrical stimulation as a clinically translatable technique to enhance functional recovery in patients with peripheral nerve injuries requiring surgical treatment. This paper provides an updated review of the cellular physiology of electrical stimulation and its effects on axon regeneration, Level I evidence from recent prospective randomized clinical trials of electrical stimulation, and ongoing and future directions of research into electrical stimulation as a clinically feasible adjunct to surgical intervention in the treatment of patients with peripheral nerve injuries.

A single session of brief electrical stimulation enhances axon regeneration through nerve autografts

Nerve graft reconstruction of gap defects may result in poor clinical outcomes, particularly with long regeneration distances. Electrical stimulation (ES) of nerves may improve outcomes in such patients. A single session of ES at 20 Hz for 1 h significantly enhances axon regeneration in animals and human subjects after nerve crush or nerve transection and repair. The objectives of this study were to evaluate if ES enhances axon regeneration through nerve grafts and if there is added benefit of a second, delayed session of ES (serial ES) on axon regeneration as compared to a single session only of ES. In female rats, a gap defect was created in the hindlimb common peroneal (CP) nerve and immediately reconstructed with a 10 mm nerve autograft (Experiment 1) or a 20 mm nerve autograft (Experiment 2). In Experiment 1, rats were randomized to 1 h of CP nerve ES or sham stimulation. In Experiment 2, rats were randomized to control (sham ES + sham ES), single ES (ES + sham ES), or serial ES (ES + ES), which consisted of an initial 1 h session of either ES or sham stimulation of the CP nerve, followed by a second 1 h session of ES or sham stimulation of the CP nerve 4 weeks later. In both experiments, after a 6 week period of nerve regeneration, CP neurons that had regenerated axons distal to the autograft were retrograde labelled for enumeration, and the CP nerve distal to the autograft was harvested for histomorphometry. In Experiment 1, rats that received CP nerve ES had statistically significantly more motor (p < .05) and sensory (p < .05) neurons that regenerated axons distal to the 10 mm nerve autograft, with more myelinated axons on histomorphometry (p < .001). Similarly, in Experiment 2, significantly more motor (p < .01) and sensory (p < .05) neurons regenerated axons distal to the 20 mm nerve autograft after a single session or two sessions of CP nerve ES. There was no significant difference in the number of regenerated motor or sensory neurons between rats with 20 mm CP nerve autografts receiving either one or two sessions of CP nerve ES (p > .05). In conclusion, a single session of ES enhances axon regeneration following nerve autografting with no added effect of a second, delayed session of ES. These findings support previous studies in animals and humans of the robust effect of a single session of ES in promoting nerve regeneration following injury and repair.

Label-free Imaging of Tissue Architecture during Axolotl Peripheral Nerve Regeneration in Comparison to Functional Recovery

Human peripheral nerves hold the potential to regenerate after injuries; however, whether a successful axonal regrowth was achieved can be elucidated only months after injury by assessing function. The axolotl salamander is a regenerative model where nerves always regenerate quickly and fully after all types of injury. Here, de- and regeneration of the axolotl sciatic nerve were investigated in a single and double injury model by label-free multiphoton imaging in comparison to functional recovery. We used coherent anti-Stokes Raman scattering to visualize myelin fragmentation and axonal regeneration. The presence of axons at the lesion site corresponded to onset of functional recovery in both lesion models. In addition, we detected axonal regrowth later in the double injury model in agreement with a higher severity of injury. Moreover, endogenous two-photon excited fluorescence visualized macrophages and revealed a similar timecourse of inflammation in both injury models, which did not correlate with functional recovery. Finally, using the same techniques, axonal structure and status of myelin were visualized in vivo after sciatic nerve injury. Label-free imaging is a new experimental approach that provides mechanistic insights in animal models, with the potential to be used in the future for investigation of regeneration after nerve injuries in humans.

Immediate and complete restoration of peripheral nerve function after injury is attainable by a combination of surgical and chemical interventions

Despite significant advances in almost every other aspect of medicine, physicians are still unable to restore function after nerve injury with any consistency or reliability. The current standard of care (which involves coaptation of the two ends via epineurial sutures) is largely unchanged from its first description over 400 years ago, and unfortunately leads to a recovery that is at best slow (taking months or years) and partial. Encouragingly, two new conceptual approaches are being developed that separately have been shown to improve outcomes. The first approach involves optimization of the mechanical aspects of nerve coaptation (with an emphasis on exceedingly "clean cuts" of the axon ends and moving any suture material far away from the coaptation site). The second approach involves manipulation of the chemical composition of the local environment at the cut ends of the nerve in order to promote re-establishment of membranous continuity. Though neither approach currently leads to results that reach those of uninjured controls, there is reason to believe that these two approaches can be used concurrently. Thus, we hypothesize that immediate and complete restoration of peripheral nerve function after injury is attainable by a combination of surgical and chemical interventions. The combination could be tested in rodents and non-human primates by assessing histology, electrical activity, intracellular diffusion, and functional status and could likely rapidly move to a clinical trial in humans. If the hypothesis is proven to be true, its impact would be profound, as it would positively affect not only recovery after traumatic nerve injury, but also functional status after allotransplantation, as well as introduce the prospects of advanced interfaces between human nerves and computer circuits.

Complete section of proper palmar digital pedicles: Correlation between arterial patency and sensory recovery

Wounds to proper palmar digital (PPD) pedicles are frequent surgical emergencies. A correlation between arterial patency and nerve regeneration, however, has never been demonstrated. Forty-seven patients presenting complete section of a PPD pedicle and having undergone surgical repair of both elements were followed-up at a minimum of one year postoperatively. Doppler ultrasound examination studied arterial patency as well as the degree of stenosis. Neurological examination determined the BMRC score and the existence of cold intolerance, symptomatic neuroma and neurogenic pain. In 32 cases, the artery was permeable; in the remaining 15, arterial thrombosis was identified. In 14 out of the 32 permeable-artery subjects, stenosis had no significant effect; in the remaining 18 cases, circulation was reduced. BMRC scores showed 11 S4 cases, 16 S3+, 16 S3 and 4 S2. Twenty-nine cases of intolerance to cold were identified, along with two cases of neurogenic pain and 17 cases of symptomatic neuroma. A statistically significant correlation was shown between arterial patency and BMRC scores (Chi-square, P=0.0221) and neurological symptoms appeared to be linked to the degree of stenosis. Favorable BMRC scores were observed where the artery was permeable, notably where blood flow was not modified below the repair site. This observation also seemed valid regarding disabling neurogenic symptoms.

Does partial muscle reinnervation preserve future re-innervation potential?

INTRODUCTION

Late revision nerve surgery for incomplete motor recovery due to partial reinnervation would improve muscle function if all muscle fibers were protected from developing denervation atrophy.

METHODS

Sixty immature Sprague-Dawley rats underwent the following tibial nerve manipulations (n = 15/group): group A, partial denervation (two thirds of nerve resected and the remaining one third crushed), revision repair at 8 months; group B, partial denervation; group C, complete denervation, immediate reconstruction; group D, complete denervation, reconstruction at 8 months; and group E, control. Final testing at 11 months included muscle force, weight, and histology.

RESULTS

Muscle weight was significantly (P < 0.05) different among all groups (highest to lowest: E > B > C > A > D), and force was significantly lower in groups A and D compared with E. Muscle fiber cross-sectional area was statistically smaller in group A than in groups B, C, or E.

DISCUSSION

Partial reinnervation still allowed substantial muscle recovery, but it did not preserve the non-innervated muscle fibers. Muscle Nerve 56: 1143-1148, 2017.

End-to-side neurorrhaphy using an electrospun PCL/collagen nerve conduit for complex peripheral motor nerve regeneration

In cases of complex neuromuscular defects, finding the proximal stump of a transected nerve in order to restore innervation to damaged muscle is often impossible. In this study we investigated whether a neighboring uninjured nerve could serve as a source of innervation of denervated damaged muscle through a biomaterial-based nerve conduit while preserving the uninjured nerve function. Tubular nerve conduits were fabricated by electrospinning a polymer blend consisting of poly(ε-caprolactone) (PCL) and type I collagen. Using a rat model of common peroneal injury, the proximal end of the nerve conduit was connected to the side of the adjacent uninjured tibial branch (TB) of the sciatic nerve after partial axotomy, and the distal end of the conduit was connected to the distal stump of the common peroneal nerve (CPN). The axonal continuity recovered through the nerve conduit at 8 weeks after surgery. Recovery of denervated muscle function was achieved, and simultaneously, the donor muscle, which was innervated by the axotomized TB also recovered at 20 weeks after surgery. Therefore, this end-to-side neurorrhaphy (ETS) technique using the electrospun PCL/collagen conduit appears to be clinically feasible and would be a useful alternative in instances where autologous nerve grafts or an adequate proximal nerve stump is unavailable.

Growth hormone treatment enhances the functional recovery of sciatic nerves after transection and repair

INTRODUCTION

Although nerves can spontaneously regenerate in the peripheral nervous system without treatment, functional recovery is generally poor, and thus there is a need for strategies to improve nerve regeneration.

METHODS

The left sciatic nerve of adult rats was transected and immediately repaired by epineurial sutures. Rats were then assigned to one of two experimental groups treated with either growth hormone (GH) or saline for 8 weeks. Sciatic nerve regeneration was estimated by histological evaluation, nerve conduction tests, and rotarod and treadmill performance.

RESULTS

GH-treated rats showed increased cellularity at the lesion site together with more abundant immunoreactive axons and Schwann cells. Compound muscle action potential (CMAP) amplitude was also higher in these animals, and CMAP latency was significantly lower. Treadmill performance increased in rats receiving GH.

CONCLUSION

GH enhanced the functional recovery of the damaged nerves, thus supporting the use of GH treatment, alone or combined with other therapeutic approaches, in promoting nerve repair.

Erythropoietin promotes functional recovery and enhances nerve regeneration after peripheral nerve injury in rats

BACKGROUND AND PURPOSE

EPO has been shown to have beneficial effects in a variety of CNS injury models. The purpose of this study was to evaluate the effects of EPO on nerve regeneration and functional recovery in a rat model of peripheral nerve surgery.

MATERIALS AND METHODS

The sciatic nerve of the rat with a 10-mm defect was bridged with a silicone rubber tube. Forty adult male Sprague-Dawley rats were assigned to the control or experimental groups to receive an intraperitoneal injection of NGF (2000 U/kg daily for 2 weeks) or EPO (5000 U/kg daily for 2 weeks), respectively. Macroscopic, functional, electrophysiologic, ultraminiature, and histologic assessments of nerves were performed 4-8 weeks after surgery.

RESULTS

The results showed that in EPO-treated rats, there was a significant increase in the axon diameter, myelin thickness, and total number of nerve fibers as well as the degree of maturity of regenerated myelinated nerve fibers in comparison with those rats not treated with EPO. In addition, as measured by the SFI and MNCV, the motor function of the re-innervated hind limbs of rats with EPO treatment significantly improved at week 8, whereas there was no significant difference in the motor function between the 2 groups at 4 weeks.

CONCLUSIONS

Our results demonstrated that EPO is able to enhance nerve regeneration and promote functional recovery after peripheral nerve injury in the rat, suggesting the potential clinical application of EPO for the treatment of peripheral nerve injury in humans.

Functional recovery in T13–L1 hemisected rats resulting from peripheral nerve rerouting: role of central neuroplasticity

Background: Functional improvements after spinal cord injury (SCI) have been reported anecdotally following neurotization, in other words, rerouting nerves proximal to injured cord segments to distal neuromuscular targets, although the underlying mechanisms remain largely unknown. Aim: To test our hypothesis that neurotization-mediated recovery is primarily attributable to CNS neuroplasticity that therefore manifests optimal response during particular therapeutic windows, we anastomosed the T12 intercostal nerve to the ipsilateral L3 nerve root 1–4 weeks after T13–L1 midline hemisection in rats. Results: While axonal tracing and electromyography revealed limited reinnervation in the target muscles, neurobehavioral function, as assessed by locomotion, extensor postural thrust and sciatic functional index of SCI rats receiving neurotization 7–10 days postinjury (n = 11), recovered to levels close to non-SCI controls with neurotization only (n = 3), beginning 3–5 weeks postanastomosis. Conversely, hindlimb deficits were unchanged in hemisected controls with sham neurotization (n = 7) or 4 weeks-delayed neurotization (n = 3) and in rats that had undergone T13–L1 transection plus bilateral anastomoses (n = 6). Conclusion: Neurotized SCI animals demonstrated multiparameters of neural reorganization in the distal lumbar cord, including enhanced proliferation of endogenous neural stem cells, increased immunoreactivity of serotonin and synaptophysin, and neurite growth/sprouting, suggesting that anastomosing functional nerves with the nerve stump emerging distal to the hemisection stimulates neuroplasticity in the dysfunctional spinal cord. Our conclusion is validated by the fact that severance of the T13–L1 contralateral cord abolished the postanastomosis functional recovery. Neurotization and its neuroplastic sequelae need to be explored further to optimize clinical strategies of post-SCI functional repair.

Posttraumatic facial nerve regeneration in rabbits

Posttraumatic facial paralysis is a frequent disease. This work studies posttraumatic regeneration of the facial nerve in rabbits. Functional and histological analysis compared injured and normal nerves on opposite sides. The left facial nerve trunk of twenty rabbits were subjected to compression lesion, and sacrificed after two (subgroup AL), four (BL) and six (CL) weeks. Comparison between groups was made by analysing total and partial densities of myelinated axons.

STATISTICAL ANALYSIS

Tukey Method (p<0.05).

RESULTS

There was partial functional recovery after two weeks, and complete recovery after five weeks. Qualitative analysis demonstrated a degenerative pattern in the AL group, with an increased tissue inflammatory process. Evident regeneration signs were observed in the BL group, and almost complete regeneration was seen in the CL group. Normal nerves (N) had an average TD of 15705.59 and average PD of 21800.75. The BL group had an average TD of 10818.55 and an average PD of 15340.56. The CL group had an average TD of 13920.36 and an average PD of 16589.15. The BL group had an average TD of N equal to 68.88%, and the CL group had an average TD of N equal to 88,63% (statistically significant). N showed a significant higher PD than injured nerves. However, this was not statistically different between BL and CL subgroups. Nerve DT was a more reliable method than PD in this study.

Motor reinnervation of a denervated muscle by using a sensory nerve: an experimental study on gluteus maximus muscle of the rat

PURPOSE

This study aimed at developing a new muscle reinnervation technique using a sensory nerve.

METHODS

We attempted innervation of the rat gluteus maximus muscle using the lateral femoral cutaneous nerve (LFCN). We placed the gluteus maximus muscle into the fibroadipose tissue in the distribution of the LFCN in 24 rats. In one group, the original innervation remained intact. In the second and third groups, the muscles were denervated, and in the third group, the proximal end of the nerve to the gluteus maximus was sutured to the distal end of the divided LFCN. We compared muscle reinnervations of the groups by using electrophysiologic evaluation of the muscle contractions, light microscope evaluation of the axonal regenerations, and scanning electron microscope evaluation of the actin-myosin structures of the muscles at the end of an elapsed waiting period.

RESULTS

At the end of electrophysiologic evaluation, the mean area of compound muscle action potentials measured in group 1 was 3.8 ms/mV; in group 2, 0.0; and in group 3 (experimental group), 0.5. Axonal regeneration was observed distal to the coaptation, and actin-myosin structures were mostly spared in group 3.

CONCLUSIONS

This study explored the feasibility of a new flap prefabrication method that aims at developing reinnervation of a denervated muscle by means of a sensory nerve. In light of histologic and electrophysiologic findings, this type of reinnervation is possible.

Suture of transected nerve suppresses expression of BH3-only protein Noxa in nerve-transected motor neurons of C57BL/6J mouse

Disrupted peripheral nerves are typically sutured as spontaneous recovery does not always occur. However, the molecular mechanisms involved in nerve regeneration following end-to-end nerve suture are obscure. Here, we investigated effects of end-to-end nerve suture after peripheral nerve transection on motor neurons, using the C57BL/6J mouse hypoglossal nerve injury model. In this animal model, 60-80% of injured motor neurons gradually progress to neuronal death, while the remaining injured neurons survive and regenerate. Mice were divided into the Cut and Suture groups. In the Cut group, the right hypoglossal nerve was transected. In the Suture group, the right hypoglossal nerve was transected and then was repaired using end-to-end nerve suture. We assessed differences between the Cut and Suture groups by analyzing the neuronal survival rate by thionine staining and the nerve terminal regeneration rate by vesicular acetylcholine transporter (VAChT) immunohistochemistry, which is a marker for cholinergic presynaptic terminal. We found that 82.9% of motor neurons survived in the Suture group, whereas only 39.2% of motor neurons did in the Cut group 56 days after surgery. At that time point, 86% of presynaptic terminals compared to controls were regenerated in the Suture group, and 21% were regenerated in the Cut group. These results demonstrate that peripheral nerve suture prevented death of nerve-transected motor neurons and promoted nerve regeneration. We also examined expression profiles of major survival and death signal-associated genes in hypoglossal nuclei using in situ hybridization and real-time polymerase chain reaction (PCR). Although most of the survival- and death-associated genes were regulated in a similar manner in both groups, expression of BH3-only protein Noxa mRNA was significantly lower in the Suture than in the Cut group. A significant suppression of Noxa expression by the Suture may be a major reason why nerve suture induces survival and regeneration of nerve-injured motor neurons.

Long-term functional results of primary reconstruction of severe forearm injuries

Severe forearm injuries caused by machinery such as a power saw represented about 0.2% of all upper limb injuries operated on in the plastic surgery section of our institute between 1993 and 1997. These are complex and contaminated injuries with severe damage to skin, muscles, tendons, nerves, vessels and bones. Primary repair or reconstruction of all the divided vital structures was carried out in our series of four patients, including one 4-cm cable nerve graft for a median nerve defect. After an average 22-month follow up, the functional results showed grade M4 motor recovery and better than grade S3+ sensory recovery of the hand in all four patients. We suggest that a definitive primary procedure is best when possible. This will achieve a better functional outcome from early neural regeneration, and will reduce the frequency of secondary procedures, cause less scarring, and shorten the duration of hospital stays and rehabilitation periods.

Delayed acetyl-l-carnitine administration and its effect on sensory neuronal rescue after peripheral nerve injury

Protection of sensory neurons after peripheral nerve injury is clinically crucial since inadequate sensory recovery is seriously affected by the death of up to 40% of sensory neurons. Immediate acetyl-L-carnitine (ALCAR) treatment eliminates this cell loss, but may not always be clinically feasible, hence we studied the effect of delaying the initiation of ALCAR treatment. Five groups of rats (n=5 per group) underwent unilateral sciatic nerve axotomy. ALCAR treatment (50 mg/kg/day) was initiated immediately, or after delays of 6 h, 24 h or 7 days after injury. A sham-treated group served as control. L4 and L5 dorsal root ganglia were harvested bilaterally 2 weeks after injury and stereological sensory neuron counts were obtained. Immediate sham treatment provided no neuroprotection (25% loss). Cell loss was eliminated when ALCAR was commenced within<or=24 h of axotomy. No statistically significant neuroprotective effect (18% loss) was evident compared to sham when ALCAR administration was initiated 7 days post-axotomy. When commenced within a clinically applicable time frame ALCAR treatment remains highly neuroprotective, potentially improving clinical outcome following peripheral nerve trauma.

Regeneração pós-traumática do nervo facial em coelhos

A paralisia facial periférica traumática constitui-se em afecção freqüente. OBJETIVO: estudo da regeneração pós-traumática do nervo facial em coelhos, por avaliação funcional histológica dos nervos traumatizados comparados aos normais contralaterais. METODOLOGIA: Vinte coelhos foram submetidos à compressão do tronco do nervo facial esquerdo e sacrificados após duas (grupo AL), quatro (BL) e seis (CL) semanas da lesão. A comparação entre os grupos foi feita pelas densidades total e parcial de axônios mielinizados. ESTUDO ESTATÍSTICO: método de Tukey (p < 0,05). RESULTADOS: Houve recuperação funcional parcial após duas, e completa após cinco semanas. Na análise qualitativa, verificou-se em AL um padrão degenerativo, com maior processo inflamatório tecidual. Em BL, sinais de regeneração neural, praticamente completa em CL. Os nervos normais (N) apresentaram DT média de 15705,59 e DP média de 21800,75. O grupo BL revelou DT média de 10818,55 e DP média de 15340,56 e o CL, DT média de 13920,36 e DP média de 16589,15. BL obteve 68,88%, e o grupo CL, 88,63% da DT de N. N mostrou DP maior que os lesados; porém, esta não evidenciou diferença estatística entre BL e CL. A DT dos nervos revelou-se um método analítico mais fidedigno do que a DP estudada.

[Operative strategies for hand injuries in multiple trauma. A systematic review of the literature]

OBJECTIVE

Hand injuries are not life threatening but crucial in multiple trauma because of their long-term functional results. The goal of this systematic review was to derive recommendations for diagnostic and treatment procedures from a systematic review of the literature.

METHODS

Articles on hand injuries in multiple trauma and articles on clinical trails for isolated hand injuries were systematically collected (MEDLINE, Cochrane, and hand searches) and classified into evidence levels (1 to 5 according to the Oxford system).

RESULTS

The special management of hand injuries in multiple trauma requires accurate diagnostic procedures, differentiated therapy strategies, and adequate timing. Depending on type and extent of the injury, there are substantial differences for primary or secondary operative treatment.

CONCLUSION

Hand injuries represent important lesions in multiple trauma. Due to the life-threatening situation they may be overlooked in the beginning of the treatment. Because of their long-term consequences for function and health-related quality of life, hand injuries require an early and accurate diagnosis and a differentiated treatment strategy.

Long-term evaluation of motor function following intraneural injection of ropivacaine using walking track analysis in rats

BACKGROUND

There is a paucity of data regarding neurologic function following nerve injury. Our objective was the long-term evaluation of motor function following intraneural injection of ropivacaine in rats using the sciatic function index (SFI), derived from walking track analysis.

METHODS

Rats were randomly assigned to one of four groups of 13 animals each. A needle was inserted under magnification into the left sciatic nerve and 0.2 ml of normal saline, formalin 15%, ropivacaine 0.2 or 0.75% were injected intraneurally. The right side was sham operated. Walking track analysis was performed the day before and on days 1, 4, 7, 11, 15, 18, 21, and 67 following intraneural injection. At the end of the experiment (day 67) a semi-quantitative evaluation of neuropathologic changes was performed by three independent observers.

RESULTS

Animals treated with saline and ropivacaine (0.2 and 0.75%) had no detectable impairment of motor function at any time point. In contrast, rats treated with formalin had a complete loss of motor function immediately after the intraneural injection, which persisted until day 21 and returned to normal by day 67. Important histopathologic changes (score=2) with excellent inter-observer agreement were seen only in the group treated with formalin. This applied to both axonal degeneration and Schwann cell density evaluations.

CONCLUSIONS

These findings suggest that intraneural injections of ropivacaine at concentrations routinely used in clinical practice appear to have no deleterious effect on sciatic nerve motor function in this experimental rat model.

Pathway sampling by regenerating peripheral axons

A century ago, Ramon y Cajal described the generalized response of regenerating peripheral axons to their environment. By using mice that express fluorescent proteins in their axons, we are now able to quantify the response of individual axons to nerve transection and repair. Sciatic nerves from nonexpressing mice were grafted into those expressing a yellow variant of green fluorescent protein, then examined at 5, 7, or 10 days after repair. Regeneration was found to be a staggered process, with only 25% of axons crossing the repair in the first week. In the setting of Wallerian degeneration, this stagger will expose growth cones to an evolving menu of molecular cues upon which to base pathway decisions. Many axons arborize, allowing them to interact simultaneously with several pathways. Arborization could serve as the anatomical substrate for specificity generation through collateral pruning. Axons often travel laterally across the face of the distal stump before choosing a pathway. As a result, the average unbranched axon has access to over 100 distal Schwann cell tubes. This extensive access, however, does not ensure correct matching of axon and end organ, suggesting that pathway choice is made on the basis of factors other than end organ identity. These observations explain the failure of refined surgical techniques to restore normal function after nerve injury. The apparent wandering of axons across the repair defies surgical control and mandates a biological approach to reuniting severed axons with appropriate distal pathways.

Investigation of skeletal muscle denervation and reinnervation using magnetic resonance spectroscopy

OBJECTIVE

To determine changes in skeletal muscle metabolism after nerve transection and repair and to correlate metabolic changes with functional recovery.

STUDY DESIGN AND SETTING

Male Wistar rats were divided into 6 experimental groups plus a control group. The posterior tibial nerve was transected and reapproximated. At varying times after surgery (1, 2, 4, 6, or 8 weeks) animals were sacrificed, the gastrocnemius muscle was harvested, and proton nuclear magnetic resonance (NMR) spectroscopy was performed. Functional recovery was measured using the sciatic function index.

RESULTS

Animals undergoing nerve repair all showed functional recovery whereas the nonrepaired nerve group did not. Concentration of glucose and lactate increased after denervation and then returned toward normal. Choline concentration decreased and then returned toward normal. In animals not undergoing nerve repair, the metabolic abnormalities persisted and showed no sign of recovery over the 8-week observation period.

CONCLUSIONS

1H NMR spectroscopy is a potentially useful tool to study changes in skeletal muscle metabolism after motor nerve injury.

SIGNIFICANCE

NMR spectroscopy is rapidly developing into a clinically useful tool. High-field magnets have improved resolution and data acquisition. Basic experiments, such as those described here, will help guide the use of NMR spectroscopy in clinical medicine and will also lead to a better understanding of basic mechanisms of nerve injury and repair.

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.

An analysis of facial nerve function in irradiated and unirradiated facial nerve grafts

PURPOSE

The effect of high-dose radiation therapy on facial nerve grafts is controversial. Some authors believe radiotherapy is so detrimental to the outcome of facial nerve graft function that dynamic or static slings should be performed instead of facial nerve grafts in all patients who are to receive postoperative radiation therapy. Unfortunately, the facial function achieved with dynamic and static slings is almost always inferior to that after facial nerve grafts. In this retrospective study, we compared facial nerve function in irradiated and unirradiated nerve grafts. METHODS AND MATERIALS The medical records of 818 patients with neoplasms involving the parotid gland who received treatment between 1974 and 1997 were reviewed, of whom 66 underwent facial nerve grafting. Fourteen patients who died or had a recurrence less than a year after their facial nerve graft were excluded. The median follow-up for the remaining 52 patients was 10.6 years. Cable nerve grafts were performed in 50 patients and direct anastomoses of the facial nerve in two. Facial nerve function was scored by means of the House-Brackmann (H-B) facial grading system. Twenty-eight of the 52 patients received postoperative radiotherapy. The median time from nerve grafting to start of radiotherapy was 5.1 weeks. The median and mean doses of radiation were 6000 and 6033 cGy, respectively, for the irradiated grafts. One patient received preoperative radiotherapy to a total dose of 5000 cGy in 25 fractions and underwent surgery 1 month after the completion of radiotherapy. This patient was placed, by convention, in the irradiated facial nerve graft cohort.

RESULTS

Potential prognostic factors for facial nerve function such as age, gender, extent of surgery at the time of nerve grafting, preoperative facial nerve palsy, duration of preoperative palsy if present, or number of previous operations in the parotid bed were relatively well balanced between irradiated and unirradiated patients. However, the irradiated graft group had a greater proportion of patients with pathologic evidence of nerve invasion (p = 0.007) and unfavorable type of nerve graft (p = 0.04). Although the irradiated graft cohort had more potentially negative prognostic factors, there was no difference in functional outcome (H-B Grade III or IV) between irradiated and unirradiated graft patients. H-B Grades III, IV, V, and VI were the best postoperative facial nerve functions achieved in 35%, 39%, 13%, and 13% of patients, respectively. The patient with preoperative radiotherapy never recovered any facial nerve function (H-B Grade VI). Median time to best facial nerve function after surgery was longer in the irradiated patients (13.1 vs. 10.8 months), but this was not statistically significant (p = 0.10). Presence of preoperative facial nerve palsy (p = 0.005), duration of preoperative palsy (p = 0.003), and age greater than 60 years at the time of grafting (p = 0. 04) were all negative prognostic factors for achieving a functional facial nerve on univariate analysis. Analysis of age as a continuous variable (p = 0.12) and pathologic evidence of nerve invasion (p = 0. 1) revealed a trend toward negative prognostic factors. Gender, number of previous operations in the parotid bed, extent of surgery at the time of nerve grafting, and type of grafting procedure were not significant prognostic factors. Whether radiotherapy was delivered less than 6 weeks after nerve grafting or more than 6 weeks had no impact on achievement of a functional facial nerve.

CONCLUSION

Negative prognostic factors for achieving a functional facial nerve in our series include the presence of preoperative facial nerve palsy, duration of preoperative palsy, and age greater than 60 years. Radiotherapy was not a negative prognostic factor. Comparing irradiated and unirradiated grafts revealed no difference in best facial nerve function achieved, despite the presence of a greater proportion of negative prognostic factors in

Morphometric and ultrastructural studies of the sciatic nerve regeneration in rats intoxicated with ethanol

The aim of the study was to examine the process of sciatic nerve regeneration and changes in the dorsal root ganglia (from which sensory fibres of the sciatic nerve extend) in animals intoxicated with ethanol. The experiment used 20 rats, divided into two groups: control and treated. The treated animals were intragastrically given 2g/kg b.w. of ethanol in 25% aqueous solution. In both groups the right sciatic nerve was transected and then sutured. After 5 months the animals were anaesthetized. The left and the right spinal dorsal ganglia-L5 and sections from the non-operated and operated sciatic nerves were collected for analysis. Ultrastructural examinations and morphometric measurements were conducted. It was found that ethanol administrated to rats inhibited regeneration of the transected and then sutured sciatic nerve, impairing the growth of axons in the transected nerve and destroying the regenerating sensory ganglion cells. The mechanism of the changes described may be associated with axonal transport disorders or with the suppressed production of biologically active substances, which affect nerve regeneration.

Cryopreservation of peripheral nerve grafts

The utilization of viable biological nerve graft substitutes and nerve allografts raises the problem of nerve storage. To clarify this, rat sciatic nerve segments were harvested and stored in Dulbecco's modified eagle medium. The segments were divided into three groups. In the first group, no cryoprotectant was added, whereas the second had 10% dimethyl sulfoxide (DMSO) added as cryoprotectant. These two groups of nerve segments were subjected to controlled freezing. In a third group, segments were frozen uncontrolled in liquid nitrogen (-196 degrees C). All nerves were replanted orthotopically. Fresh conventional autografts (fourth group) served as control group. Histologically, freezing did not affect the structural elements such as basal lamina tubes and perineurial tissue. Morphometrically, all cryopreserved grafts had significantly reduced axon counts and less myelinization than did controls. Cryoprotected nerves (group 2) showed no different morphometric parameters compared with the group without DMSO (group 1). Controlled freezing was superior to uncontrolled freezing (group 3). Impaired regeneration was attributed mainly to delayed Wallerian degeneration and slower revascularization. Moreover, decreased survival of resident Schwann cells in the graft may impair regeneration due to the lack of neurotrophic, neurotropic, and attachment factors in early regeneration. Grafts subjected to controlled freezing support axonal regeneration to a certain extent, but further studies are required to assess various cooling patterns, cryoprotectants, and graft revascularization.

Methods to evaluate functional nerve recovery in adult rats: walking track analysis, video analysis and the withdrawal reflex

The aim of this study was to compare different methods for the evaluation of functional nerve recovery. Three groups of adult male Wistar rats were studied. In group A, a 12-mm gap between nerve ends was bridged by an autologous nerve graft; in rats of group B we performed a crush lesion of the sciatic nerve and group C consisted of non-operated control rats. The withdrawal reflex, elicited by an electric stimulus, was used to evaluate the recovery of sensory nerve function. To investigate motor nerve recovery we analyzed the walking pattern. Three different methods were used to obtain data for footprint analysis: photographic paper with thickened film developer on the paws, normal white paper with finger paint, and video recordings. The footprints were used to calculate the sciatic function index (SFI). From the video recordings, we also analyzed stepcycles. The withdrawal reflex is a convenient and reproducible test for the evaluation of global sensory nerve recovery. Recording walking movements on video and the analysis of footplacing is a perfect although time-consuming method for the evaluation of functional aspects of motor nerve recovery.

Ischaemia-reperfusion injury of the peripheral nerve: An experimental study

Although the neuropathology of ischaemic fibre degeneration is relatively well known, its pathogenesis is poorly understood. One of the presumed mechanisms is oxidative stress, causing the breakdown of the blood-nerve barrier (BNB) and ending in lipid peroxidation. We evaluated the effect of ischaemia and reperfusion on the sciatic-tibial nerve of the rat and investigated the biochemical, pathological, and functional evidence of BNB disruption and lipid peroxidation. The distal portion and trifurcation of the sciatic nerve were rendered ischaemic by clamping the femoral vessels for 3 h and followed by varying durations of reperfusion. Reperfusion resulted in an increase in lipid peroxidation beginning from the first hour and increasing until the seventh day, followed by a gradual decline over the following weeks. Nerve oedema and ischaemic fibre degeneration (IFD) consistently became more severe and prominent with reperfusion, indicating that oxidative stress damages the BNB and causes IFD. Results of functional testing by the sciatic function index correlated with other parameters as walking track analysis results got worse as reperfusion periods increased. Impairment of walking patterns was more striking after the first day and continued up to the third week. These data indicate that severe ischaemia of the peripheral nerve results in reperfusion injury, functional impairment, and disruption of the BNB. Microvascular events, which may occur during reperfusion, may be important in amplifying the nerve fibre degeneration that initiated during ischaemia.

Effect of nerve repair after unilateral partial facial paralysis on craniofacial growth and development

The effect of partial transection, coaptation, and freezing of the left facial nerve on craniofacial growth and development was investigated. Twelve-day-old New Zealand White rabbits were randomly assigned to four groups: control group (n = 15), nerve ablation group (n = 15) with a surgically induced partial facial paralysis, nerve coaptation group (n = 15) with a surgically induced partial facial paralysis treated by immediate microsurgical nerve coaptation, and nerve freezing group (n = 13) with a freezing-induced partial facial paralysis. All animals were operated on at the age of 12 days; follow-up evaluations were performed at the ages of 2 months (end-point prepubertal growth) and 6 months (full grown). Computerized dorsoventral roentgencephalometric analysis and computer tomographic three-dimensional volumetric measurements were performed at both ages. Roentgencephalometric analysis revealed that the growth disturbances of the nerve ablation group and the nerve coaptation group were analogous. In contrast, in the nerve freezing group, hardly any growth disturbances as compared with the control group were seen. The CT volume measurements revealed a significant left-right difference in maxillary volume at the ages of 2 and 6 months in the nerve coaptation group as compared with the control group. Muscle histomorphometric analysis revealed a shift in muscle fiber composition in the nerve coaptation group and the nerve freezing group, with an increase of type I fibers at the cost of type IIA fibers. This shift was significantly less pronounced in the latter than in the former. Nerve histomorphometric analysis revealed a significant increase in the number of nerve fibers in the nerve coaptation group as compared with the control group. In the nerve freezing group, the increase in the number of nerve fibers was not significantly different as compared with the control group and the nerve coaptation group. Both the equivalent diameter and the myelin area were equally reduced in the nerve coaptation and nerve freezing groups. Thus, the nerve coaptation group and the nerve freezing group did not differ significantly in the extent of nerve recovery, although they differed in the extent of muscle recovery. The extent of muscle recovery, in turn, was related to the extent of abnormal craniofacial growth and development. Indeed, the growth and development were hardly abnormal in the nerve freezing group and as abnormal as after untreated paralysis in the nerve coaptation group. Therefore, factors related to nerve regeneration, other than those assessed by nerve histomorphology, were considered to be responsible for these differences between both groups. The duration of the denervation time was regarded to be considerably shorter in the nerve freezing group than in the nerve coaptation group, resulting in the observed improved muscle recovery. The difference in the degree of axonal malalignment between both groups was considered to be negligible, because of the tolerance toward axonal malalignment at neonatal age.

Recombinant human glial growth factor 2 (rhGGF2) improves functional recovery of crushed peripheral nerve (a double-blind study)

This in vivo double-blind study evaluated the effect of recombinant human glial growth factor 2 (rhGGF2), a Schwann cell mitogen, on the recovery of motor function of rat sciatic nerve following crush injury. Seventy three rats were divided into three groups. Group I (n=5), sham operated; Groups II (n=34) and III (n=34) received a 100 g crush load for 2 h over a 5 mm segment of the sciatic nerve. Group III was treated with 1 mg/kg rhGGF2, via subcutaneous injection one day before nerve crush and daily for the following four days. Group II received an equivalent volume of saline as a control. Motor functional recovery was assessed by calculating the sciatic functional index (SFI) and the recovery rate of tetanic contractile force of the extensor digitorum longus (EDL) muscle. Recovery of nerve function was evident at day 11 after crush in the rhGGF2-treated animals, whereas the nerves in controls were still paralyzed. The rhGGF2-treated animals showed a significant improvement of the SFI between days 11-21 postoperatively when compared to controls. The isometric tetanic contractile force was stronger in the rhGGF2-treated group than in controls, with a significant difference at 40 to 70 Hz stimulus frequencies on day 4. Correlation analysis showed that tetanic contractile force had a linear correlation with the SFI. Histologic assessment indicated that the rhGGF2-treated animals showed less severe degeneration and earlier robust remyelination of axons than controls. The results suggest that treatment with rhGGF2 is effective in promoting nerve regeneration as seen in measurements of functional recovery and qualitative assessment of nerve morphology. The mechanism of GGF's protective effect may be related to its direct action on Schwann cells, stimulating their mitosis as well as inducing neurotrophic factors essential to neuronal maintenance and repair.

The cellular and molecular basis of peripheral nerve regeneration

Functional recovery from peripheral nerve injury and repair depends on a multitude of factors, both intrinsic and extrinsic to neurons. Neuronal survival after axotomy is a prerequisite for regeneration and is facilitated by an array of trophic factors from multiple sources, including neurotrophins, neuropoietic cytokines, insulin-like growth factors (IGFs), and glial-cell-line-derived neurotrophic factors (GDNFs). Axotomized neurons must switch from a transmitting mode to a growth mode and express growth-associated proteins, such as GAP-43, tubulin, and actin, as well as an array of novel neuropeptides and cytokines, all of which have the potential to promote axonal regeneration. Axonal sprouts must reach the distal nerve stump at a time when its growth support is optimal. Schwann cells in the distal stump undergo proliferation and phenotypical changes to prepare the local environment to be favorable for axonal regeneration. Schwann cells play an indispensable role in promoting regeneration by increasing their synthesis of surface cell adhesion molecules (CAMs), such as N-CAM, Ng-CAM/L1, N-cadherin, and L2/HNK-1, by elaborating basement membrane that contains many extracellular matrix proteins, such as laminin, fibronectin, and tenascin, and by producing many neurotrophic factors and their receptors. However, the growth support provided by the distal nerve stump and the capacity of the axotomized neurons to regenerate axons may not be sustained indefinitely. Axonal regenerations may be facilitated by new strategies that enhance the growth potential of neurons and optimize the growth support of the distal nerve stump in combination with prompt nerve repair.

Protective effect of 21-aminosteroid pretreatment in peripheral nerve low-load crush injury in mature and immature rats

The effects of U-74006F (tirilazad mesylate), a 21-aminosteroid antioxidant, on injured peripheral nerve were studied. Twenty-two immature and 44 mature rats were divided equally into two groups. The experimental group received two injections of 3 mg/kg of U-74006F at a 2 hour interval. The control group received the same volumes of a citrate buffer. A 5 mm segment of the sciatic nerve was subjected to a crush load of 100 g for 2 hours. Motor function (sciatic functional index) was assessed to day 48 postoperatively. There was total paralysis of the crushed limb in all rats the first week after crushing. The experimental group had a statistically significant improvement in motor function compared with the controls on days 14, 21, 25, and 28 for the mature rats and on days 11 and 14 for the immature rats. The mature controls attained complete recovery on day 42 and had a significantly slower recovery rate than the immature controls, which had recovered fully by day 25. The recovery rates were almost similar among mature and immature groups pretreated with U-74006F, both of which had fully recovered motor function by day 28. The results indicate that pretreatment with U-74006F can significantly promote peripheral nerve function after low-load crush injury and that the age of the animal influences the rate of peripheral nerve recovery.

The effects of low level laser treatment on recovery of nerve conduction and motor function after compression injury in the rat sciatic nerve

An animal study is presented examining the effect of low level laser (LLL) treatment on nerve regeneration following axonotmesis. Twenty animals received a standardised injury to the right sciatic nerve using a time, load and length sequence (10 min, 150 N, 5 mm) known to cause extensive axonal degeneration of the rat sciatic nerve. The LLL treatment was administered using a hand-held laser probe in light contact with the skin on the dorsal aspect of the hind leg overlying the site of the axonotmesis injury to the sciatic nerve. A group of 10 animals were treated with 6J of LLL (GaAlAs 830 nm) daily for a period of 28 d. Ten more animals were treated daily with a sham exposure setting and served as controls. Nerve function was assessed by a recognised method of walking tract print analysis; the "Sciatic Functional Index" (SFI), and nerve regeneration was assessed by recording the evoked compound action potentials (cAP) in the common peroneal nerve. At 21 d post-injury, the laser-treated group had a significantly lower median SFI than the sham laser-treated group, indicating that the real laser treatment had improved functional recovery in the nerve. However, no differences were found between the evoked cAP parameters that were measured in the laser-treated and sham laser-treated groups. Histological examination reiterated the lack of difference between the two groups. Consequently, the effects of LLL on recovery must have occurred more peripherally to the point measured.

Interpreting nerve morphometry data after experimental traumatic lesions

Morphometric data were obtained in 2 experimental conditions: crush lesions of the sciatic nerve of rats, and transection of this nerve followed by repair. Ratios were used in order to facilitate comprehension of data. Results were compared to those obtained using a method of functional assessment. The study indicated that morphometric data provided a reliable picture of the trophic condition of regenerated nerves but did not correlate with the level of function.

Axonal regeneration into chronically denervated distal stump. 2. Active expression of type I collagen mRNA in epineurium

During the first 2 weeks after an injury to peripheral nerve, endoneurial cells proliferate and express integrin beta 1 and mRNA for collagen types I and III. Clinical results for surgical repair within this time are clearly better than those obtained after delayed (months after original injury) surgery. The question of whether this is due to changes in the proliferative capacity of endoneurial cells or to changes in expression of mRNA for collagen types I and III or integrin beta 1 was studied using rats. The left common peroneal nerve was transected and allowed to degenerate for 3 and 6 months. After these times, the tibial nerve of the same animals were transected, and the fresh proximal stump of the transected tibial nerve was sutured into the chronically denervated distal stump of the common peroneal nerve. At 3 and 6 weeks after the reoperation, samples were collected from the distal stump for morphometry, immunohistochemistry and in situ hybridization. Proliferating cells and Schwann cells were identified by immunohistochemistry. These cells increased markedly in number during the axonal reinnervation. In situ hybridization revealed that in the epineurium and perineurium, which were fibrotic, especially type I but also type III collagen mRNA were highly expressed. The amount of type I collagen mRNA in the endoneurium seemed to increase with progressing axonal reinnervation. Immunostaining for integrin beta 1 was negative in these distal stumps. In the present study the proliferation of endoneurial cells and expression of type I collagen mRNA in the endoneurium were similar to those found after immediate regeneration of transected peripheral nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

CO2 laser repair of the facial nerve: an experimental study in the rat

The facial nerve is often injured by trauma, infection or during the course of tumour resection. Many techniques of nerve anastomosis have been described with the current standard nerve repair using the microscope and monofilament suture. The purpose of this study was to evaluate the CO2 surgical laser as a tool for facial nerve anastomosis. Following preliminary electrical measurements 36 nerves were anastomosed using either laser or conventional monofilament suture. Laser anastomosis had neither beneficial nor detrimental effects on nerve regeneration. This method of anastomosis may be advantageous when surgical access is limited. In addition this study found that the use of CO2 laser as a dissecting or vapourizing tool in proximity to intact facial nerves results in degenerative changes.

The quest for better recovery from peripheral nerve injury: current status of nerve regeneration research

The author reviews relevant nerve regeneration research in the past half-century to give the reader familiarity with the background of current research efforts. Recent research has been aided by newer knowledge of the biology of nerve regeneration. Early efforts to improve nerve regeneration centered on improvements in technical or surgical repairs, with only modest gains. Although current technical improvements with lasers or fibrin glue to repair nerves may show promise, the approach of deMedinaceli et al. combines several new ideas with some improvement experimentally. With the discovery of nerve growth factors and a host of newer nerve growth promoting factors, the biochemical arena has explored. Special tubes to repair nerves enable easy manipulation of the environment to study the effects of various factors on nerve regeneration. Silastic and bioresorbable tubes show the most promise to enhance nerve regeneration by tubulization. Because of the explosion of knowledge and high levels of activity of research, it is apparent that further improvements of nerve regeneration are on the horizon.

Percentage of nerve injuries in which primary repair can be achieved by end-to-end approximation: review of 2,181 nerve lesions

Primary nerve repair yields better results than secondary reconstruction but is not always possible. We reviewed a series of 2,181 fresh nerve injuries of the upper limb. One nerve only was injured in 41% of the patients; two or more in 59%. One thousand four hundred eighty-two injuries (68%) were located in the digits. The injured limb segment was lost or beyond repair in 387 cases (18% of all cases). In the 1,794 remaining injuries, primary treatment was accomplished by end-to-end suture 1,568 times (87%) and by graft 33 times (> 2%) and was impossible in 193 cases (11%).

Autotomy and the sciatic functional index

The rat sciatic nerve serves as a good model of nerve regeneration and, as such, is often used in investigations of nerve repair. After transection of the sciatic nerve, rodents frequently scratch and bite their anesthetic foot, resulting in amputation of one or more toes. This is termed autotomy or autophagy. When these rats are part of a study using the sciatic functional index (SFI), autotomy results in unusable data, since necessary foot landmarks have been removed. It would be helpful, therefore, to be familiar with the phenomenon of autotomy and to know which rats are least likely to mutilate themselves. In our experiment involving 64 rats in which the sciatic nerve was transected and repaired, we found that female Sprague-Dawley rats were significantly less likely to perform autotomy than males (33% vs. 65%, P = .04). In addition, we noted that two-thirds of the autotomies that occurred did so by postoperative week 4 and that tabasco sauce did not decrease this activity. We present our experience and a survey of the literature on autotomy and the SFI.

The functional recovery of peripheral nerves following defined acute crush injuries

This study evaluates the effect of crushing load on functional recovery of the sciatic nerve. Male Sprague-Dawley rats were divided into five groups: sham operation, resected sciatic nerve, and 100 g (13 mm Hg/mm2), 500 g (50 mm Hg/mm2), and 15,000 g (1,000 mm Hg/mm2) of sciatic crush load (groups 1-5). In groups 3-5, a 5-mm segment of sciatic nerve was crushed for 10 min using a specially designed crushing device. Motor functional recovery was assessed from hind-limb walking tracks by calculating a sciatic functional index. There was no detectable functional deficit in the group receiving sham operations, while the resected sciatic nerve group exhibited complete dysfunction for the full duration of the experiment. All groups subjected to crush exhibited an initial deficit that gradually recovered to normal by day 14 (100-g crush), day 39 (500-g crush), and day 53 (15,000-g crush). Histological changes were also related to the initial crushing load and the length of the recovery period. Results indicate that the crushing device described is able to administer an adjustable, defined crush injury to the rat sciatic nerve, and that the functional deficit resulting from such an injury can be easily monitored with a sciatic functional index. The rate of recovery of crushed nerves was directly related to the initial load. All crushed nerves recovered in this experiment, even after the application of a 15,000-g load for 10 min.

Applying "cell surgery" to nerve repair: a preliminary report on the first ten human cases

We have applied a new technique of nerve repair, based on the principles of "cell surgery", to ten nerve lesions of the upper limb. Eight lesions were recent, five to 36 hours; they were divisions of the ulnar nerve (1), median nerve (2), sensory radial nerve (1), palmar and digital nerves (4). One lesion was 15 days old (median nerve). One eight-month-old loss of 4.5 cm. of the median nerve was grafted. In nine out of the ten cases, the short-term results were encouraging. Poor local conditions (fibrosis of the nerve bed) or poor general health (chronic alcoholism) had no adverse influence on the results. In the remaining case, the protocol was not followed in its entirety: it was not possible to crystallise properly the nerve, and trimming was done with scissors in the conventional way instead of smoothly trimming the solidified tips. The functional result in this case is a failure. These preliminary results seem to indicate that correctly applying the technique in its entirety may be more important than local conditions. We think that this technique can be applied to the majority of nerve lesions. The appropriate equipment is absolutely necessary in order to apply the method.

Selective reinnervation: a comparison of recovery following microsuture and conduit nerve repair

Selective reinnervation was studied by comparing the regeneration across a conventional neurorraphy versus a conduit nerve repair. Lewis rats underwent right sciatic nerve transection followed by one of four different nerve repairs (n = 8/group). In groups I and II a conventional neurorraphy was performed and in groups III and IV the proximal and distal stumps were coapted by use of a silicone conduit with an interstump gap of 5 mm. The proximal and distal stumps in groups I and III were aligned anatomically correct and the proximal stump was rotated 180 degrees in groups II and IV (i.e. proximal peroneal nerve opposite the distal tibial nerve and the proximal tibial nerve opposite the distal peroneal nerve). By 14 weeks, there was an equivalent, but incomplete return in sciatic function index (SFI) in groups I, III, and IV as measured by walking track analysis. However, the SFI became unmeasurable by 6 weeks in all group II animals. At 14 weeks, the percent innervation of the tibialis anterior and medial gastronemius muscles by the peroneal and tibial nerves respectively was estimated by selective compound muscle action potential amplitude recordings. When fascicular alignment was reversed, there was greater tibial (P = 0.02) and lesser peroneal (P = 0.005) innervation of the gastrocnemius muscle in the conduit (group IV) versus the neurorraphy (group II) group. This suggests that the gastrocnemius muscle may be selectively reinnervated by the tibial nerve. However, there was no evidence of selective reinnervation of the tibialis anterior muscle. Despite these differences, the functional recovery in both conduit repair groups (III and IV) was equivalent to a correctly aligned microsuture repair (group I) and superior to that in the incorrectly aligned microsuture repair (group II).

Improved imaging of rat hindfoot prints for walking track analysis

Walking track analysis is an investigative technique that allows a researcher to assess objectively the functional capacity of the limb in the rat sciatic nerve model. This study has shown that paint and paper is a better method for imaging the rat foot plantar surface than other methods described in the literature. The block printing paint has the distinct advantage of keeping radial diffusion error to a minimum. Paint more correctly images the important anatomical landmarks of the rat plantar surface. There is better traction (less slippage) rendering the prints easier to interpret. The authors conclude that the paint and paper is a superior method to the other methods currently available.

Microanatomic analysis of the trigeminal nerve and potential nerve graft donor sites

A histologic study was undertaken to define the microanatomic characteristics of two commonly injured peripheral trigeminal nerve branches (lingual and mandibular nerves) and the two nerves most frequently procured for use in their interpositional graft repair (sural and greater auricular nerves). Nerves, obtained from fresh human cadavers, were evaluated for total fascicular area, fascicle number, axon number, axon size, and axon density. The peripheral branches of the trigeminal nerve (third division) were morphometrically similar, with only a slight decrease in axon density in the lingual nerve. Comparisons between the donor nerves, however, showed numerous discrepancies at the axonal level. While the fascicular area of the sural nerve was only slightly smaller, axon numbers and densities were only one-half that of the trigeminal nerves. Although the greater auricular nerve was appreciably smaller in overall size, a much better correlation existed with the trigeminal nerve in axonal qualities. These microanatomic findings raise questions about the potential capability of these graft choices to optimally restore axonal connections between nerve ends in trigeminal nerve repair.