Misdirection and guidance of regenerating axons after experimental nerve injury and repair

Intercostal nerve transfer in management of biceps and triceps co-contraction in brachial plexus birth palsy

OBJECTIVE

Brachial plexus birth palsy (BPBP) is often caused by traction during birth. In some cases, reinnervation occurs during spontaneous recovery and it causes involuntary co-contraction between antagonistic muscles. When it comes up between the biceps and triceps muscles, smooth active motion of the elbow joint is impaired. We are presenting outcomes of intercostal nerve (ICN) to radial nerve transfer to minimize elbow motion abnormality due to co-contraction.

METHODS

We present five cases (two males and three females) of biceps and triceps co-contraction in BPBP patients treated from 2005 to 2018. The mean age at surgery was 9.36 years (range, 4.8-16.4 years). They were treated by ICNs transfer to motor branch of the radial nerve to the triceps muscle. Preoperative electromyography was done in all cases to confirm biceps and triceps co-contraction and to assess the contractile status of both muscles. A 10-s flexion extension test was done pre and postoperatively to assess the efficacy of our procedure.

RESULTS

The postop course was uneventful. No donor site morbidity or respiratory complications were recorded in any patient. The mean postoperative follow-up period was 83.9 months (range, 53.6-135.5 months). At the final follow-up, elbow flexion was M4 in the Medical Research Council (MRC) grading scale in all five patients and elbow extension was graded M4 or M4- in all five patients. There was significant increase in the 10 s flexion extension test results delineating the effectiveness of the procedure.

CONCLUSIONS

ICNs transfer to motor branch of the radial nerve to the triceps muscle for management of biceps and triceps co-contraction in BPBP is a good option with minimal morbidity and good success rate.

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.

Morphological Methods to Evaluate Peripheral Nerve Fiber Regeneration: A Comprehensive Review

Regeneration of damaged peripheral nerves remains one of the main challenges of neurosurgery and regenerative medicine, a nerve functionality is rarely restored, especially after severe injuries. Researchers are constantly looking for innovative strategies for tackling this problem, with the development of advanced tissue-engineered nerve conduits and new pharmacological and physical interventions, with the aim of improving patients' life quality. Different evaluation methods can be used to study the effectiveness of a new treatment, including functional tests, morphological assessment of regenerated nerve fibers and biomolecular analyses of key factors necessary for good regeneration. The number and diversity of protocols and methods, as well as the availability of innovative technologies which are used to assess nerve regeneration after experimental interventions, often makes it difficult to compare results obtained in different labs. The purpose of the current review is to describe the main morphological approaches used to evaluate the degree of nerve fiber regeneration in terms of their usefulness and limitations.

Electrical Stimulation of Distal Tibial Nerve During Stance Phase of Walking May Reverse Effects of Unilateral Paw Pad Anesthesia in the Cat

Cutaneous feedback from feet is involved in regulation of muscle activity during locomotion, and the lack of this feedback results in motor deficits. We tested the hypothesis that locomotor changes caused by local unilateral anesthesia of paw pads in the cat could be reduced/reversed by electrical stimulation of cutaneous and proprioceptive afferents in the distal tibial nerve during stance. Several split-belt conditions were investigated in four adult female cats. In addition, we investigated the effects of similar distal tibial nerve stimulation on overground walking of one male cat that had a transtibial, bone-anchored prosthesis for 29 months and, thus, had no cutaneous/proprioceptive feedback from the foot. In all treadmill conditions, cats walked with intact cutaneous feedback (control), with right fore- and hindpaw pads anesthetized by lidocaine injections, and with a combination of anesthesia and electrical stimulation of the ipsilateral distal tibial nerve during the stance phase at 1.2× threshold of afferent activation. Electrical stimulation of the distal tibial nerve during the stance phase of walking with anesthetized ipsilateral paw pads reversed or significantly reduced the effects of paw pad anesthesia on several kinematic variables, including lateral center of mass shift, cycle and swing durations, and duty factor. We also found that stimulation of the residual distal tibial nerve in the prosthetic hindlimb often had different effects on kinematics compared with stimulation of the intact hindlimb with paw anesthetized. We suggest that stimulation of cutaneous and proprioceptive afferents in the distal tibial nerve provides functionally meaningful motion-dependent sensory feedback, and stimulation responses depend on limb conditions.

Micropattern-based nerve guidance conduit with hundreds of microchannels and stem cell recruitment for nerve regeneration

Guiding the regrowth of thousands of nerve fibers within a regeneration-friendly environment enhances the regeneration capacity in the case of peripheral nerve injury (PNI) and spinal cord injury (SCI). Although clinical treatments are available and several studies have been conducted, the development of nerve guidance conduits (NGCs) with desirable properties, including controllable size, hundreds of nerve bundle-sized microchannels, and host stem-cell recruitment, remains challenging. In this study, the micropattern-based fabrication method was combined with stem-cell recruitment factor (substance P, SP) immobilization onto the main material to produce a size-tunable NGC with hundreds of microchannels with stem-cell recruitment capability. The SP-immobilized multiple microchannels aligned the regrowth of nerve fibers and recruited the host stem cells, which enhanced the functional regeneration capacity. This method has wide applicability in the modification and augmentation of NGCs, such as bifurcated morphology or directional topographies on microchannels. Additional improvements in fabrication will advance the regeneration technology and improve the treatment of PNI/SCI.

Platelet-rich plasma loaded nerve guidance conduit as implantable biocompatible materials for recurrent laryngeal nerve regeneration

Vocal cord paralysis caused by recurrent laryngeal nerve (RLN) injury during thyroidectomy results in hoarseness, aspiration, and dyspnea. We evaluated the usefulness of nerve guidance conduits (NGCs) constructed from an asymmetric polycaprolactone (PCL)/Pluronic F127 porous membrane and filled with platelet-rich plasma (PRP) for functional RLN regeneration. We evaluated the proliferation and migration of Schwann cells (SCs) after PRP treatment in vitro. For the in vivo study, rabbits were divided into a non-loaded NGC group and a PRP-loaded NGC group. The left RLNs were resected and interposed with the NGCs. Functional and histological examinations of the vocal cords were performed. SC proliferation and migration increased in a PRP dose-dependent manner, with the PRP increasing the levels of neurotrophic factors, myelin-associated glycoprotein, and ERK. In vivo, the PRP group showed significantly better vocal cord mobility and less vocalis muscle atrophy than the non-loaded NGC group. Histologically, the ingrowth of nerve endings occurred more rapidly in the PRP group, and acetylcholinesterase, neurofilament, and S-100 expression in neural endings were significantly higher in the PRP group. Furthermore, transmission electron microscopy showed that myelinated axons were more tightly packed in the PRP group. This study shows that PRP-loaded NGCs provide a favorable environment for neural regeneration and suggests that this technique has therapeutic potential for promoting RLN recovery.

ESWT Diminishes Axonal Regeneration following Repair of the Rat Median Nerve with Muscle-In-Vein Conduits but Not after Autologous Nerve Grafting

Investigations reporting positive effects of extracorporeal shockwave therapy (ESWT) on nerve regeneration are limited to the rat sciatic nerve model. The effects of ESWT on muscle-in-vein conduits (MVCs) have also not been investigated yet. This study aimed to evaluate the effects of ESWT after repair of the rat median nerve with either autografts (ANGs) or MVCs. In male Lewis rats, a 7 mm segment of the right median nerve was reconstructed either with an ANG or an MVC. For each reconstructive technique, one group of animals received one application of ESWT while the other rats served as controls. The animals were observed for 12 weeks, and nerve regeneration was assessed using computerized gait analysis, the grasping test, electrophysiological evaluations and histological quantification of axons, blood vessels and lymphatic vasculature. Here, we provide for the first time a comprehensive analysis of ESWT effects on nerve regeneration in a rat model of median nerve injury. Furthermore, this study is among the first reporting the quantification of lymphatic vessels following peripheral nerve injury and reconstruction in vivo. While we found no significant direct positive effects of ESWT on peripheral nerve regeneration, results following nerve repair with MVCs were significantly inferior to those after ANG repair.

Nerve transfer with 3D-printed branch nerve conduits

Background

Nerve transfer is an important clinical surgical procedure for nerve repair by the coaptation of a healthy donor nerve to an injured nerve. Usually, nerve transfer is performed in an end-to-end manner, which will lead to functional loss of the donor nerve. In this study, we aimed to evaluate the efficacy of 3D-printed branch nerve conduits in nerve transfer.

Methods

Customized branch conduits were constructed using gelatine-methacryloyl by 3D printing. The nerve conduits were characterized both in vitro and in vivo. The efficacy of 3D-printed branch nerve conduits in nerve transfer was evaluated in rats through electrophysiology testing and histological evaluation.

Results

The results obtained showed that a single nerve stump could form a complex nerve network in the 3D-printed multibranch conduit. A two-branch conduit was 3D printed for transferring the tibial nerve to the peroneal nerve in rats. In this process, the two branches were connected to the distal tibial nerve and peroneal nerve. It was found that the two nerves were successfully repaired with functional recovery.

Conclusions

It is implied that the two-branch conduit could not only repair the peroneal nerve but also preserve partial function of the donor tibial nerve. This work demonstrated that 3D-printed branch nerve conduits provide a potential method for nerve transfer.

Slow progression of sciatic nerve degeneration and regeneration after loose ligation through microglial activation and decreased KCC2 levels in the mouse spinal cord ventral horn

Peripheral nerve injury affects motor functions. To reveal the mechanisms underlying motor dysfunction and recovery after nerve compression, which have not been precisely examined, we investigated the temporal relationship among changes in motor function, nerve histopathology, and marker molecule expression in the spinal cord after loose ligation of the mouse sciatic nerve. After ligation, sciatic motor function suddenly declined, and axons gradually degenerated. During degeneration, galanin was localized in motor neuron cell bodies. Then, in the ventral horn, microglia were activated, and expression of choline acetyltransferase (ChAT), a synthetic enzyme of acetylcholine, and potassium chloride co-transporter 2 (KCC2), which shifts the action of γ-amino butyric acid (GABA) and glycine to inhibitory, decreased. Motor function recovery was insufficient although axonal regeneration was complete. ChAT levels gradually recovered during axonal regeneration. When regeneration was nearly complete, microglial activation declined, and KCC2 expression started to increase. The KCC2 level sufficiently recovered when axonal regeneration was complete, suggesting that the excitatory action of GABA/glycine may participate in axonal regeneration. Furthermore, these changes proceeded slower than those after severance, suggesting that loose ligation, compression, may mediate slower progression of degeneration and regeneration than severance, and these changes may cause the motor dysfunction and its recovery.

A Dual-Modal Magnetic Resonance/Photoacoustic Imaging Tracer for Long-Term High-Precision Tracking and Facilitating Repair of Peripheral Nerve Injuries

Neuroanatomical tracing is considered a crucial technique to assess the axonal regeneration level after injury, but traditional tracers do not meet the needs of in vivo neural tracing in deep tissues. Magnetic resonance (MR) and photoacoustic (PA) imaging have high spatial resolution, great penetration depth, and rich contrast. Fe₃ O₄ nanoparticles may work well as a dual-modal diagnosis probe for neural tracers, with the potential to improve nerve regeneration. The present study combines antegrade neural tracing imaging therapy for the peripheral nervous system. Fe₃ O₄ @COOH nanoparticles are successfully conjugated with biotinylated dextran amine (BDA) to produce antegrade nano-neural tracers, which are encapsulated by microfluidic droplets to control leakage and allow sustained, slow release. They have many notable advantages over traditional tracers, including dual-modal real-time MR/PA imaging in vivo, long-duration release effect, and limitation of uncontrolled leakage. These multifunctional anterograde neural tracers have potential neurotherapeutic function, are reliable and may be used as a new platform for peripheral nerve injury imaging and treatment integration.

Recombinant COL6 α2 as a Self-Organization Factor That Triggers Orderly Nerve Regeneration Without Guidance Cues

Collagen VI (COL6) in the microenvironment was recently identified as an extracellular signal that bears the function of promoting orderly axon bundle formation. However, the large molecular weight of COL6 (≈2,000 kDa) limits its production and clinical application. It remains unclear whether the smaller subunit α chains of COL6 can exert axon bundling and ordering effects independently. Herein, based on a dorsal root ganglion (DRG) ex vivo model, the contributions of three main COL6 α chains on orderly nerve bundle formation were analyzed, and COL6 α2 showed the largest contribution weight. A recombinant COL6 α2 chain was produced and demonstrated to promote the formation of orderly axon bundles through the NCAM1-mediated pathway. The addition of COL6 α2 in conventional hydrogel triggered orderly nerve regeneration in a rat sciatic nerve defect model. Immunogenicity assessment showed weaker immunogenicity of COL6 α2 compared to that of the COL6 complex. These findings suggest that recombinant COL6 α2 is a promising material for orderly nerve regeneration.

Improvement of Walking Analysis using the Sciatic Function Index for Sciatic Nerve Function in Injured Rat Model Treated with Low-Intensity Aerobics

BACKGROUND: Sciatica is a disease of the peripheral nerves. Sciatica indicates that there is damage to the peripheral nerves in the sciatic nerves. Factors that can affect this disease include gender, posture, parity, age, genetic factors, and occupation. Some of the pathophysiological conditions of sciatica include the pathology of the intervertebral disc, dorsal root, and sciatic nerve itself. The results of standard therapy with surgery have not been effective and very expensive. Therefore, research on therapy in sciatica cases still needs to be done and evaluated. Physical exercise treatment (aerobic] is necessary for this therapy in sciatica cases due to promote the function of peripheral nerves. AIM: This study aimed to determine the effect of aerobic exercise treatment on peripheral nerve injury and its relationship to walking function during injury-induced peripheral nerve regeneration. METHODS: This study was an experimental study with a post-test. he study sample consisted of Male Sprague-Dawley rats with an age of about 2-3 months divided into three groups. Control group was conducted by surgery without clamping/injuring the peripheral nerves. The treatment for second group (P1) was clamping/injury of peripheral nerve and given the treatment of physical exercise with aerobics. The treatment for third group (P2) was clamping/injury of peripheral nerve and not given the treatment of physical exercise with aerobics. The intensity of giving physical exercise treatment with aerobic that is carried out is for 42 days. Nerve functional evaluation was carried out using the sciatic function index (SFI) method. Histological staining for sciatic was used hematoxylin-Eosin (HE) staining and immunohistochemistry with Growth Associated Protein 43 (GAP43) [Bioss, bs-0154R] and S100 antibody [ab52642]. This research was  approved by Animal  Ethics Committee of University of Indonesia protocol (No.19-07-0852). RESULTS: There was a significant change between the 7th and 14th days (p<0.001; paired t-test) in the P1 treatment. Improvement in nerve function was found on the 14th day after being given aerobic treatment. This is indicated by the data average change in SFI scores on days 7 and 4 was from -144 to 34. This data is also supported by footprint changes for injured hindfoot data. CONCLUSION: Low intensity aerobics treatment improve the walking function and nerve function in sciatic nerve injury on day 14. This is due to the effect of physical exercise on the injured sciatic nerve.

Nerve bundle formation during the promotion of peripheral nerve regeneration: collagen VI-neural cell adhesion molecule 1 interaction

The formation of nerve bundles, which is partially regulated by neural cell adhesion molecule 1 (NCAM1), is important for neural network organization during peripheral nerve regeneration. However, little is known about how the extracellular matrix (ECM) microenvironment affects this process. Here, we seeded dorsal root ganglion tissue blocks on different ECM substrates of peripheral nerve ECM-derived matrix-gel, Matrigel, laminin 521, collagen I, and collagen IV, and observed well-aligned axon bundles growing in the peripheral nerve ECM-derived environment. We confirmed that NCAM1 is necessary but not sufficient to trigger this phenomenon. A protein interaction assay identified collagen VI as an extracellular partner of NCAM1 in the regulation of axonal fasciculation. Collagen VI interacted with NCAM1 by directly binding to the FNIII domain, thereby increasing the stability of NCAM1 at the axolemma. Our in vivo experiments on a rat sciatic nerve defect model also demonstrated orderly nerve bundle regeneration with improved projection accuracy and functional recovery after treatment with 10 mg/mL Matrigel and 20 μg/mL collagen VI. These findings suggest that the collagen VI-NCAM1 pathway plays a regulatory role in nerve bundle formation. This study was approved by the Animal Ethics Committee of Guangzhou Medical University (approval No. GY2019048) on April 30, 2019.

Comparison between normal and reverse orientation of graft in functional and histomorphological outcomes after autologous nerve grafting: An experimental study in the mouse model

BACKGROUND

Autologous nerve grafting has been considered the gold standard for the treatment of irreparable nerve gaps. However, the choice of effective proximodistal orientation of autografts (normal or reversed) is controversial. Therefore, we compared functional and histological outcomes between normal and reversed orientations of autografts in a mouse sciatic nerve model.

MATERIALS AND METHODS

Thirty C57BL/6J mice weighing 20-25 g were assigned to the donor, normally oriented autograft, and reverse-oriented autograft groups (n = 10 per group). A 10-mm section of the sciatic nerve was harvested from a donor mouse. Half the harvested nerve was grafted onto an irreparable gap in a recipient mouse using either a normal or reversed orientation. The sciatic functional index (SFI) was measured biweekly for up to 12 weeks postoperatively. Morphological analysis was performed using immunofluorescence staining for neurofilament (NF) and myelin protein zero (P0) in cross-sectional and whole-mount nerve preparations in 12 weeks postoperatively. Additionally, morphological analysis of the tibialis anterior muscle was performed using hematoxylin and eosin staining. NF or P0-expressing axons were counted and cross-sectional area (CSA) and minimum Feret's diameter of myofibers were measured.

RESULTS

The SFI recovered gradually up to 12 weeks after autografting, but there were no significant differences in the SFI between the normal and reversed orientations. The number of NF-expressing axons in center of graft was significantly higher in the normal orientation than in the reversed orientation (P < .05). However, there were no significant differences in the number and mean intensity of P0-expressing axons between the orientations. The CSA of myofibers was significantly larger in the normal orientation than in the reversed orientation (P < .05).

CONCLUSIONS

Normally oriented autografts promote axonal regrowth and prevent neurogenic muscular atrophy compared with reverse-oriented autografts. However, despite these positive histomorphometric effects, the proximodistal orientation of the autograft does not affect functional outcomes.

Peripheral Nerve Healing: So Near and Yet So Far

Peripheral nerve injuries represent a considerable portion of chronic disability that especially affects the younger population. Prerequisites of proper peripheral nerve injury treatment include in-depth knowledge of the anatomy, pathophysiology, and options in surgical reconstruction. Our greater appreciation of nerve healing mechanisms and the development of different microsurgical techniques have significantly refined the outcomes in treatment for the past four decades. This work reviews the peripheral nerve regeneration process after an injury, provides an overview of various coaptation methods, and compares other available treatments such as autologous nerve graft, acellular nerve allograft, and synthetic nerve conduits. Furthermore, the formation of neuromas as well as their latest treatment options are discussed.

A systematic review and meta-analysis of studies comparing muscle-in-vein conduits with autologous nerve grafts for nerve reconstruction

The gold-standard method for reconstruction of segmental nerve defects, the autologous nerve graft, has several drawbacks in terms of tissue availability and donor site morbidity. Therefore, feasible alternatives to autologous nerve grafts are sought. Muscle-in-vein conduits have been proposed as an alternative to autologous nerve grafts almost three decades ago, given the abundance of both tissues throughout the body. Based on the anti-inflammatory effects of veins and the proregenerative environment established by muscle tissue, this approach has been studied in various preclinical and some clinical trials. There is still no comprehensive systematic summary to conclude efficacy and feasibility of muscle-in-vein conduits for reconstruction of segmental nerve defects. Given this lack of a conclusive summary, we performed a meta-analysis to evaluate the potential of muscle-in-vein conduits. This work’s main findings are profound discrepancies regarding the results following nerve repair by means of muscle-in-vein conduits in a preclinical or clinical setting. We identified differences in study methodology, inter-species neurobiology and the limited number of clinical studies to be the main reasons for the still inconclusive results. In conclusion, we advise for large animal studies to elucidate the feasibility of muscle-in-vein conduits for repair of segmental defects of critical size in mixed nerves.

Three-Dimensional Engineered Peripheral Nerve: Toward a New Era of Patient-Specific Nerve Repair Solutions

Reconstruction of peripheral nerve injuries (PNIs) with substance loss remains challenging because of limited treatment solutions and unsatisfactory patient outcomes. Currently, nerve autografting is the first-line management choice for bridging critical-sized nerve defects. The procedure, however, is often complicated by donor site morbidity and paucity of nerve tissue, raising a quest for better alternatives. The application of other treatment surrogates, such as nerve guides, remains questionable, and it is inefficient in irreducible nerve gaps. More importantly, these strategies lack customization for personalized patient therapy, which is a significant drawback of these nerve repair options. This negatively impacts the fascicle-to-fascicle regeneration process, critical to restoring the physiological axonal pathway of the disrupted nerve. Recently, the use of additive manufacturing (AM) technologies has offered major advancements to the bioengineering solutions for PNI therapy. These techniques aim at reinstating the native nerve fascicle pathway using biomimetic approaches, thereby augmenting end-organ innervation. AM-based approaches, such as three-dimensional (3D) bioprinting, are capable of biofabricating 3D-engineered nerve graft scaffolds in a patient-specific manner with high precision. Moreover, realistic in vitro models of peripheral nerve tissues that represent the physiologically and functionally relevant environment of human organs could also be developed. However, the technology is still nascent and faces major translational hurdles. In this review, we spotlighted the clinical burden of PNIs and most up-to-date treatment to address nerve gaps. Next, a summarized illustration of the nerve ultrastructure that guides research solutions is discussed. This is followed by a contrast of the existing bioengineering strategies used to repair peripheral nerve discontinuities. In addition, we elaborated on the most recent advances in 3D printing and biofabrication applications in peripheral nerve modeling and engineering. Finally, the major challenges that limit the evolution of the field along with their possible solutions are also critically analyzed.

[Research progress of peripheral nerve mismatch regeneration]

Objective

To review the research progress of peripheral nerve mismatch regeneration, and to provide reference for its related basic research and clinical treatment.

Methods

The pathophysiology of peripheral nerve after injury, several main factors affecting the mismatch regeneration of peripheral nerve, and the fate of axon after mismatch regeneration were summarized by referring to the relevant literature at home and abroad in recent years.

Results

Distal pathways and target organs can selectively affect the mismatch regeneration of peripheral nerves; different phenotypes of Schwann cells have different effects on the mismatch regeneration of peripheral nerves; studying the mechanism of action of exosomes from different Schwann cells on different types of axons can provide a new direction for solving the mismatch regeneration of peripheral nerves.

Conclusion

Peripheral nerve mismatch regeneration is affected by various factors. However, the specific mechanism and characteristics of these factors remain to be further studied.

Peripheral Nerve Regeneration and Muscle Reinnervation

Injured peripheral nerves but not central nerves have the capacity to regenerate and reinnervate their target organs. After the two most severe peripheral nerve injuries of six types, crush and transection injuries, nerve fibers distal to the injury site undergo Wallerian degeneration. The denervated Schwann cells (SCs) proliferate, elongate and line the endoneurial tubes to guide and support regenerating axons. The axons emerge from the stump of the viable nerve attached to the neuronal soma. The SCs downregulate myelin-associated genes and concurrently, upregulate growth-associated genes that include neurotrophic factors as do the injured neurons. However, the gene expression is transient and progressively fails to support axon regeneration within the SC-containing endoneurial tubes. Moreover, despite some preference of regenerating motor and sensory axons to “find” their appropriate pathways, the axons fail to enter their original endoneurial tubes and to reinnervate original target organs, obstacles to functional recovery that confront nerve surgeons. Several surgical manipulations in clinical use, including nerve and tendon transfers, the potential for brief low-frequency electrical stimulation proximal to nerve repair, and local FK506 application to accelerate axon outgrowth, are encouraging as is the continuing research to elucidate the molecular basis of nerve regeneration.

Extradural Contralateral C7 Nerve Root Transfer in a Cervical Posterior Approach for Treating Spastic Limb Paralysis: A Cadaver Feasibility Study

STUDY DESIGN

Anatomic study in nine fresh-frozen cadavers.

OBJECTIVE

To confirm the anatomical feasibility of transferring the extradural ventral roots (VRs) and dorsal roots (DRs) of contralateral C7 nerves to those of the ipsilateral C7 nerves respectively through a cervical posterior approach.

SUMMARY OF BACKGROUND DATA

The contralateral C7 nerve root transfer technique makes breakthrough for treating spastic limb paralysis. However, its limitations include large surgical trauma and limited indications.

METHODS

Nine fresh-frozen cadavers (four females and five males) were placed prone, and the feasibility of exposing the bilateral extradural C7 nerve roots, separation of the extradural C7 VR and DR, and transfer of the VR and DR of the contralateral C7 to those of the ipsilateral C7 on the dural mater were assessed. The pertinent distances and the myelography results of each specimen were analyzed. The acetylcholinesterase (AChE) and antineurofilament 200 (NF200) double immunofluorescent staining were preformed to determine the nerve fiber properties.

RESULTS

A cervical posterior midline approach was made and the laminectomy was performed to expose the bilateral extradural C7 nerve roots. After the extradural C7 VR and DR are separated, the VR and DR of the contralateral C7 have sufficient lengths to be transferred to those of the ipsilateral C7 on the dural mater. The myelography results showed that the spinal cord is not compressed after the nerve anastomosis. The AChE and NF200 double immunofluorescent staining showed the distal ends of the contralateral C7 VRs were mostly motor nerve fibers, and the distal ends of the contralateral C7 DRs were mostly sensory nerve fibers.

CONCLUSION

Extradural contralateral C7 nerve root transfer in a cervical posterior approach for treating spastic limb paralysis is anatomically feasible.

LEVEL OF EVIDENCE

5.

Disinhibition of Human Primary Somatosensory Cortex After Median Nerve Transection and Reinnervation

Despite state-of-the-art surgical and postoperative treatment, median nerve transection causes lasting impaired hand function due to limitations in the nerve’s reinnervation ability. The defective innervation and thus controllability of the affected hand can shape the brain’s control of manual behaviors. Earlier studies of changes in the processing of tactile stimuli have focused mainly on stimulation of the reinnervated hand and lack sufficient control over the brain’s use of the tactile input in perceptual terms. Here we used fMRI to measure brain activity (BOLD-signal) in 11 people with median nerve injury and healthy controls (N = 11) when performing demanding tactile tasks using the tip of either the index or little finger of either hand. For the nerve-injured group, the left median nerve had been traumatically transected in the distal forearm and surgically repaired on average 8 years before the study. The hand representation of their contralesional (right) primary somatosensory cortex (S1) showed greater activity compared to controls when the left reinnervated index finger was used, but also when the left-hand little finger and the fingers of the right hand innervated by uninjured nerves were used. We argue that the overall increase in activity reflects a general disinhibition of contralesional S1 consistent with an augmented functional reorganizational plasticity being an ongoing feature of chronic recovery from nerve injury. Also, the nerve-injured showed increased activity within three prefrontal cortical areas implicated in higher-level behavioral processing (dorsal anterior cingulate cortex, left ventrolateral prefrontal and right dorsolateral prefrontal cortex), suggesting that processes supporting decision-making and response-selection were computationally more demanding due to the compromised tactile sensibility.

The course of recovery of locomotor function over a 10-week observation period in a rat model of femoral nerve resection and autograft repair

BACKGROUND

A great extent of knowledge on peripheral nerve regeneration has been gathered using the rat sciatic nerve model. The femoral nerve model of the rat offers an interesting alternative, as it lacks disadvantageous features such as automutilation. For the analysis of locomotor behavior in rats after sciatic nerve injury, the CatWalk^™ XT Gait Analysis System is often used. However, lesions of the femoral nerve in the rat have yet remained unstudied with this method.

MATERIAL AND METHODS

Ten male Sprague Dawley rats were evaluated with the CatWalk XT to study their gait after a 6-mm resection of the right femoral nerve and reconstruction with an autologous nerve graft. Animals were observed for 10 weeks after surgery.

RESULTS

Print Area, Print Length, Swing Speed, and Duty Cycle decreased to a minimum of 40% of baseline 2 weeks after surgery. Swing Time was elevated more than twofold at this time point. However, all these parameters recovered back to >90% of baseline values at 10 weeks after surgery. This degree of functional recovery has not been reported after sciatic nerve resection and autograft repair. Base of support varied minimally postoperatively in contrast to a strong decrement after sciatic nerve resection and repair.

CONCLUSION

We hereby provide a comprehensive in-depth analysis of how to study functional recovery after injury of the femoral nerve in the rat via the CatWalk XT. We place special emphasis on highlighting the differences between the femoral nerve and sciatic nerve injury model in this context.

The Evolving Neural Tissue Engineering Landscape of India

The healthcare sector in India is witnessing unprecedented advancement. Tissue engineering has become an integral part of healthcare and medicine, particularly where treatments involve functional restoration of any injured or deceased part of the body. Not falling behind much with the progressing medical and healthcare sector of India, tissue engineering is also gaining momentum in the country. Out of several arenas of tissue engineering, India has made its mark in orthopedic and bone regeneration, cosmetic and skin regeneration, and very importantly neural regeneration. There are several articles reviewing the progress and prospects of orthopedic and skin regeneration research in India. However, there is no systematic review on progress, prospects, and pitfalls associated with neural tissue engineering in Indian context. The existing ones mainly focus on the technical advancements in the field from a global perspective. Therefore, it is worthwhile to have an organized look at the evolving neural tissue engineering landscape of India. This review will walk the readers systematically through different aspects of the topic. The review starts with an introduction to the nervous system to help readers appreciate the complexity that must be dealt with while engineering neural tissue. This is followed with a global picture of the neural tissue engineering, prominent research groups working on neural tissue engineering in India, factors that have and are currently molding the prospects of this field, and concluding with an overall perspective on present and future of neural tissue engineering in India.

A Subtle Network Mediating Axon Guidance: Intrinsic Dynamic Structure of Growth Cone, Attractive and Repulsive Molecular Cues, and the Intermediate Role of Signaling Pathways

A fundamental feature of both early nervous system development and axon regeneration is the guidance of axonal projections to their targets in order to assemble neural circuits that control behavior. In the navigation process where the nerves grow toward their targets, the growth cones, which locate at the tips of axons, sense the environment surrounding them, including varies of attractive or repulsive molecular cues, then make directional decisions to adjust their navigation journey. The turning ability of a growth cone largely depends on its highly dynamic skeleton, where actin filaments and microtubules play a very important role in its motility. In this review, we summarize some possible mechanisms underlying growth cone motility, relevant molecular cues, and signaling pathways in axon guidance of previous studies and discuss some questions regarding directions for further studies.

Polyethylene Glycol: The Future of Posttraumatic Nerve Repair? Systemic Review

Peripheral nerve injury is a common posttraumatic complication. The precise surgical repair of nerve lesion does not always guarantee satisfactory motor and sensory function recovery. Therefore, enhancement of the regeneration process is a subject of many research strategies. It is believed that polyethylene glycol (PEG) mediates axolemmal fusion, thus enabling the direct restoration of axon continuity. It also inhibits Wallerian degeneration and recovers nerve conduction. This systemic review, performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, describes and summarizes published studies on PEG treatment efficiency in various nerve injury types and repair techniques. Sixteen original experimental studies in animal models and one in humans were analyzed. PEG treatment superiority was reported in almost all experiments (based on favorable electrophysiological, histological, or behavioral results). To date, only one study attempted to transfer the procedure into the clinical phase. However, some technical aspects, e.g., the maximal delay between trauma and successful treatment, await determination. PEG therapy is a promising prospect that may improve the surgical treatment of peripheral nerve injuries in the clinical practice.

Convergent end-to-end neurorrhaphy: An alternative technique for dual innervation of the gastrocnemius muscle in rats

INTRODUCTION

Muscle contraction generated by electrical impulses simultaneously originating from two different neural sources may be an interesting treatment alternative for long term facial palsy. An experimental model was designed to compare single and dual innervation of the gastrocnemius muscle (GM) in rats.

METHODS

Fifty adult Wistar rats underwent transection of their right peroneal nerve and were divided into five groups (n = 10): control (C), tibial nerve section (TS), tibial nerve primary end-to-end neurorrhaphy (PEE), tibial nerve primary repair associated with end-to-side peroneal-to-tibial nerve transfer (PRES), and tibial nerve repair by convergent end-to-end (CEE) neurorrhaphy between the proximal stumps of the tibial and peroneal nerves to the distal stump of the tibial nerve. The outcomes were assessed 12 weeks after the experiment by walking track, electromyography, GM mass index, and histomorphometric analysis of the distal tibial nerve.

RESULTS

The functional recovery of the PRES (-33.77 ± 24.13) and CEE (-42.15 ± 31.14) groups was greater (P < 0.003) than the PEE group (-80.26 ± 17.20). The CEE group (18.35 ± 7.84) showed greater amplitude (P = 0.006) than the PEE group (8.2 ± 4.64). There was no difference in the muscle mass index among the reinnervation groups (P > 0.705). Histologic analysis revealed greater (P < 0.002) axonal density in the CEE group (126.70 ± 15.01) compared to PEE (99.70 ± 12.82) and PRES (92.00 ± 19.17) groups.

CONCLUSIONS

The dual innervation techniques showed earlier and greater functional recovery of the GM than did the single innervation technique. The CEE group showed a 40% higher number of regenerated axons in the distal tibial nerve stump.

Regeneration of Transected Recurrent Laryngeal Nerve Using Hybrid-Transplantation of Skeletal Muscle-Derived Stem Cells and Bioabsorbable Scaffold

Hybrid transplantation of skeletal muscle-derived multipotent stem cells (Sk-MSCs) and bioabsorbable polyglyconate (PGA) felt was studied as a novel regeneration therapy for the transected recurrent laryngeal nerve (RLN). Sk-MSCs were isolated from green fluorescence protein transgenic mice and then expanded and transplanted with PGA felt for the hybrid transplantation (HY group) into the RLN transected mouse model. Transplantation of culture medium (M group) and PGA + medium (PGA group) were examined as controls. After eight weeks, trans-oral video laryngoscopy demonstrated 80% recovery of spontaneous vocal-fold movement during breathing in the HY group, whereas the M and PGA groups showed wholly no recoveries. The Sk-MSCs showed active engraftment confined to the damaged RLN portion, representing favorable prevention of cell diffusion on PGA, with an enhanced expression of nerve growth factor mRNAs. Axonal re-connection in the HY group was confirmed by histological serial sections. Immunohistochemical analysis revealed the differentiation of Sk-MSCs into Schwann cells and perineurial/endoneurial cells and axonal growth supportive of perineurium/endoneurium. The number of axons recovered was over 86%. These results showed that the stem cell and cytokine delivery system using hybrid transplantation of Sk-MSCs/PGA-felt is a potentially practical and useful approach for the recovery of transected RLN.

Cocontraction measured with short-range stiffness was higher in obstetric brachial plexus lesions patients compared to healthy subjects

We suggest short range stiffness (SRS) at the elbow joint as an alternative diagnostic for EMG to assess cocontraction. Elbow SRS is compared between obstetric brachial plexus lesion (OBPL) patients and healthy subjects (cross-sectional study design). Seven controls (median 28years) and five patients (median 31years) isometrically flexed and extended the elbow at rest and three additional torques [2.1,4.3,6.4Nm] while a fast stretch stimulus was applied. SRS was estimated in silico using a neuromechanical elbow model simulating the torque response from the imposed elbow angle. SRS was higher in patients (250±36Nm/rad) than in controls (150±21Nm/rad, p=0.014), except for the rest condition. Higher elbow SRS suggested greater cocontraction in patients compared to controls. SRS is a promising mechanical alternative to assess cocontraction, which is a frequently encountered clinical problem in OBPL due to axonal misrouting.

Regenerative peripheral neuropathic pain: novel pathological pain, new therapeutic dimension

After peripheral nerve damage, injured or stressed primary sensory neurons (PSNs) transmitting pathological pain (pathopain) sensitize central nervous system (CNS) neural circuits and determine behavioral phenotypes of peripheral neuropathic pain (PNP). Therefore, phenotypic profiling of pathopain-transmitting PSNs is vital for probing and discovering PNP conditions. Following peripheral nerve injuries (PNIs), PNP might be potentially transmitted by distinct classes of damaged or stressed PSNs, such as axotomized PSNs without regeneration (axotomy-non-regenerative neurons), axotomized PSNs with accurate regeneration (axotomy-regenerative neurons), and spared intact PSNs adjacent to axotomized neurons (axotomy-spared neurons). Both axotomy-non-regenerative neurons and axotomy-spared neurons have been definitely shown to participate in specific PNP transmission. However, whether axotomy-regenerative neurons could transmit PNP with unique features has remained unclear. Recent studies in rodent models of axonotmesis have clearly demonstrated that axotomy-regenerative neurons alone transmit persistent pathological pain with unique behavioral phenotypes. In this review, we exclusively review this novel category of PNP, reasonably term it ‘regenerative peripheral neuropathic pain’, and finally discuss its potential clinical significance as a new therapeutic dimension for PNIs beyond nerve regeneration.

Nociceptive and Neuronal Evaluation of the Sciatic Nerve of Wistar Rats Subjected to Compression Injury and Treated with Resistive Exercise

Background. To investigate the climb stairs resistance exercise on nociception and axonal regeneration in the sciatic nerve of rats. Methods. 24 Wistar rats were divided: control group (CG—no injury), exercise group (EG—no injury with physical exercise), lesion group (LG—injury, but without exercise), and treated group (LEG—injury and physical exercise). LG and LEG were subjected to sciatic nerve compression with hemostat. From the 3rd day after injury began treatment with exercise, and after 22 days occurs the removal of a nerve fragment for morphological analysis. Results. Regarding allodynia, CG obtained values less than EG (p = 0.012) and larger than LG and LEG (p < 0.001). Histological results showed that CG and EG had normal appearance, as LG and LEG showed up with large amounts of inflammatory infiltration, degeneration and disruption of nerve fibers, and reduction of the myelin sheath; however LEG presented some regenerated fibers. From the morphometric data there were significant differences, for nerve fiber diameter, comparing CG with LG and LEG and comparing axon diameter and the thickness of the myelin of the CG to others. Conclusion. Climb stairs resistance exercise was not effective to speed up the regenerative process of axons.

Combined use of Y-tube conduits with human umbilical cord stem cells for repairing nerve bifurcation defects

Given the anatomic complexity at the bifurcation point of a nerve trunk, enforced suturing between stumps can lead to misdirection of nerve axons, thereby resulting in adverse consequences. We assumed that Y-tube conduits injected with human umbilical cord stem cells could be an effective method to solve such problems, but studies focused on the best type of Y-tube conduit remain controversial. Therefore, the present study evaluated the applicability and efficacy of various types of Y-tube conduits containing human umbilical cord stem cells for treating rat femoral nerve defects on their bifurcation points. At 12 weeks after the bridging surgery that included treatment with different types of Y-tube conduits, there were no differences in quadriceps femoris muscle weight or femoral nerve ultrastructure. However, the Y-tube conduit group with longer branches and a short trunk resulted in a better outcome according to retrograde labeling and electrophysiological analysis. It can be concluded from the study that repairing a mixed nerve defect at its bifurcation point with Y-tube conduits, in particular those with long branches and a short trunk, is effective and results in good outcomes.

Comparative outcome measures in peripheral regeneration studies

Traumatic peripheral nerve injuries are common and often result in partial or permanent paralysis, numbness of the affected limb, and debilitating neuropathic pain. Experimental animal models of nerve injury have utilized a diversity of outcome measures to examine functional recovery following injury. Four primary categories of outcome measures of regenerative success including retrograde labeling with counts of regenerating neurons, immunohistochemistry and histomorphometry, reinnervation of target muscles, and behavioral analysis of recovery will be reviewed. Validity of different outcome measures are discussed in context of hindlimb, forelimb, and facial nerve injury models. Severity of nerve injury will be highlighted, and comparisons between nerve crush injury and more severe transection and neuroma-in-continuity nerve injury paradigms will be evaluated. The case is made that specific outcome measures may be more sensitive to assessing functional recovery following nerve injury than others. This will be discussed in the context of the lack of association between certain outcome measures of nerve regeneration. Examples of inaccurate conclusions from specific outcome measures will also be considered. Overall, researchers must therefore take care to select appropriate outcome measures for animal nerve injury studies dependant on the specific experimental interventions and scientific questions addressed.

Femoral nerve regeneration and its accuracy under different injury mechanisms

Surgical accuracy has greatly improved with the advent of microsurgical techniques. However, complete functional recovery after peripheral nerve injury has not been achieved to date. The mechanisms hindering accurate regeneration of damaged axons after peripheral nerve injury are in urgent need of exploration. The present study was designed to explore the mechanisms of peripheral nerve regeneration after different types of injury. Femoral nerves of rats were injured by crushing or freezing. At 2, 3, 6, and 12 weeks after injury, axons were retrogradely labeled using 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil) and True Blue, and motor and sensory axons that had regenerated at the site of injury were counted. The number and percentage of Dil-labeled neurons in the anterior horn of the spinal cord increased over time. No significant differences were found in the number of labeled neurons between the freeze and crush injury groups at any time point. Our results confirmed that the accuracy of peripheral nerve regeneration increased with time, after both crush and freeze injury, and indicated that axonal regeneration accuracy was still satisfactory after freezing, despite the prolonged damage.

Femoral nerve regeneration and its accuracy under different injury mechanisms

Surgical accuracy has greatly improved with the advent of microsurgical techniques. However, complete functional recovery after peripheral nerve injury has not been achieved to date. The mechanisms hindering accurate regeneration of damaged axons after peripheral nerve injury are in urgent need of exploration. The present study was designed to explore the mechanisms of peripheral nerve regeneration after different types of injury. Femoral nerves of rats were injured by crushing or freezing. At 2, 3, 6, and 12 weeks after injury, axons were retrogradely labeled using 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (Dil) and True Blue, and motor and sensory axons that had regenerated at the site of injury were counted. The number and percentage of Dil-labeled neurons in the anterior horn of the spinal cord increased over time. No significant differences were found in the number of labeled neurons between the freeze and crush injury groups at any time point. Our results confirmed that the accuracy of peripheral nerve regeneration increased with time, after both crush and freeze injury, and indicated that axonal regeneration accuracy was still satisfactory after freezing, despite the prolonged damage.

Growth factor choice is critical for successful functionalization of nanoparticles

Nanoparticles (NPs) show new characteristics compared to the corresponding bulk material. These nanoscale properties make them interesting for various applications in biomedicine and life sciences. One field of application is the use of magnetic NPs to support regeneration in the nervous system. Drug delivery requires a functionalization of NPs with bio-functional molecules. In our study, we functionalized self-made PEI-coated iron oxide NPs with nerve growth factor (NGF) and glial cell-line derived neurotrophic factor (GDNF). Next, we tested the bio-functionality of NGF in a rat pheochromocytoma cell line (PC12) and the bio-functionality of GDNF in an organotypic spinal cord culture. Covalent binding of NGF to PEI-NPs impaired bio-functionality of NGF, but non-covalent approach differentiated PC12 cells reliably. Non-covalent binding of GDNF showed a satisfying bio-functionality of GDNF:PEI-NPs, but turned out to be unstable in conjugation to the PEI-NPs. Taken together, our study showed the importance of assessing bio-functionality and binding stability of functionalized growth factors using proper biological models. It also shows that successful functionalization of magnetic NPs with growth factors is dependent on the used binding chemistry and that it is hardly predictable. For use as therapeutics, functionalization strategies have to be reproducible and future studies are needed.

Cryostat Slice Irregularities May Introduce Bias in Tissue Thickness Estimation: Relevance for Cell Counting Methods

Stereological techniques using the optical disectors require estimation of final section thickness, but frozen tissue irregularities may interfere with this estimation. Cryostat slices from rodent nerve tissues (dorsal root ganglia, spinal cord, and brain), cut at 16, 40, and 50 μm, were digitized with a confocal microscope and visualized through 3D software. Geometric section thickness of tissue (T geom) was defined as tissue volume/area. Maximal section thicknesses (T max), from the top to the bottom of the section, were measured in a random sample of vertical ZX planes. Irregularities were mostly related to blood vessels traversing the tissue and neuronal somas protruding over the cut surfaces, with other neuron profiles showing a fragmented appearance. Irregularities contributed to increasing the distance between the tops and bottoms of slices sectioned in different laboratories. Significant differences were found between T max and T geom for all thickness studies and counting frames (p<0.01). The T geom/T max average rate was 68.4-85.7% in volumes around cell profiles (∼600-1,200 μm2) and 83.3-91.8% in subcellular samples (∼25-160 μm2). Confocal microscopy may help to assess tissue irregularities, which might lead to an overestimation of tissue volume if section thickness is estimated by focusing on the top and bottom of the sections.

[Traumatic nerve damage: causes, approaches and prognosis]

Whereas minor injuries to peripheral nerves merely lead to a circumscribed damage of the myelin sheath which is completely healed within 3 months, penetrating injuries lead to degeneration of the distal axonal fragment (Waller degeneration) and simultaneously to time-dependent alterations in the effector organs, in the perikarya in the medulla and spinal ganglia as well as in the brain. Animal experimental studies and also findings in humans confirm that the conditions for regeneration of nerve fibers are most favorable in the first days and weeks following injury. Therefore, for optimal therapy it should be clarified as early as possible whether there is a chance for reinnervation using exclusively conservative therapy or whether an operative reconstruction is necessary due to the severity of structural damage. Imaging investigation procedures, such as neurosonography and magnetic resonance (MR) neurography can provide decisive information on this aspect. As a rule, the decision on the indications for a nerve operation should be made within the first 3 months. Even with optimal therapy the healing process of severe neural injuries is often unsatisfactory. For some years novel procedures for improvement of nerve regeneration have been tested in animal experiments which involve totally different points in the healing process. It is hoped that with these approaches procedures for improvement in the treatment of nerve injuries in humans can be developed in the near future.

Extensive motor axonal misrouting after conservative treatment of obstetric brachial plexus lesions

AIM

The aim of this cross-sectional study was to assess systematically motor function and motor misrouting in adults with conservatively treated obstetric brachial plexus lesion (OBPL).

METHOD

Seventeen adults with OBPL (median age 38y; five males, 12 females) and 16 comparison participants (median age 26y; eight males, eight females) were investigated. Motor function in the group with OBPL was assessed through passive and active motion, muscle strength of the deltoid, biceps, and triceps muscles, and Mallet aggregate score and five subscores. Motor misrouting was quantified by electrically stimulating each of 10 arm muscles and recording activity from the other nine in response to this. Motor function and motor misrouting were statistically analysed using the Mann-Whitney U test and Spearman's correlation coefficient.

RESULTS

Motor function testing showed excellent strength but poor functional Mallet scores. Participants with OBPL had significantly more motor misrouting than comparison participants (Mann-Whitney U=31.5 [df=28], p<0.001, median difference=-4.00, 95% confidence interval [CI]=-7.00 to -1.00). Most misrouting was observed when stimulating the biceps (Mann-Whitney U=38.5 [df=31], p<0.001, median difference=-3.00, 95% CI -3.00 to -1.00), deltoid (Mann-Whitney U=68.5 [df=31], p=0.003, median difference=-1.0, 95% CI=-4.00 to 0.00 <0.001) and brachioradialis muscles (Mann-Whitney U=72.0 [df=31], p=0.002, median difference <0.001, 95% CI=-3.00 to 0.00 <0.001). There were no significant correlations between the presence of motor misrouting and impairment of motor function.

INTERPRETATION

There is extensive motor misrouting in conservatively treated OBPL. The presence of this, in addition to motor functional impairment, suggests that motor misrouting should be further studied in OBPL.