Human Sciatic Nerve Research Articles

Focused gluteal region dissection on the human sciatic nerve

Dissection provides an understanding of human anatomy that is difficult to achieve solely with the use of textbooks. The knowledge obtained from anatomical dissection has allowed medical practitioners the ability to understand the anatomy that forms that basis of a particular clinical presentation, and more effectively treat the condition. These conditions include piriformis syndrome and sciatica. Clinical conditions may also arise due to anatomical variations which are rare presentations, absences, or arrangements of structures. The ultimate goal of the dissection in this report was to discern the pathway of the sciatic nerve and its divisions. In this report, the dissection of the gluteal region of a left leg from a female cadaver is detailed. The findings reveal two anatomical variations, a high division of the sciatic nerve and a muscular slip lateral to the long head of the biceps femoris. Additional research is needed to determine the implications of these anatomical variations in the clinical context. This prosection will be an important educational resource for future students, and could not have been possible without the generous donors.

Organization of the Fibrous Component of Connective Tissue Paraneural Structures in Different Periods of Ontogenesis

Background: The steady increase in road traffic accidents, seasonal injuries leading to damage to the peripheral nerves of the extremities, as well as the military conflicts that are becoming more frequent now actualize research aimed at improving the diagnosis, treatment, and prevention of post-traumatic changes in the nerve trunks of the extremities. The frequency of peripheral nerve injuries varies from 1.5% to 13% of all injuries in peacetime; and during hostilities, it reaches 20%, and disability is 60%. At the same time, specific destructive changes in the nerves of the extremities after their traumatic injury require extraordinary organizational, therapeutic, and functional approaches to their restoration. The purpose of this study was to evaluate the dynamics of changes in the fibrous component of the paraneurium connective tissue structures in different periods of ontogenesis. Methods and Results: The study consisted of two stages. At the first stage, to study changes in the paraneurium connective tissue of the sciatic nerve (SN) in vivo, ultrasound was performed using an RS85 ultrasound scanner (Samsung Medison, South Korea, 2021) and two linear transducers, LA4-18B and LA2-9A. The thickness of the SN and the surrounding paraneurium were measured, and their structural organization was evaluated. The inclusion criterion was the absence of pathology from the peripheral nervous system. All subjects were divided into four age groups (15 people in each group): Group 1 (0-11 years), Group 2 (12-25 years), Group 3 (26-40 years), and Group 4 (41-60 years). The second stage was performed on cadaveric material of the paraneurium connective tissue of the SN of persons of both sexes, of different ages, whose cause of death was not related to diseases or injuries of the nervous system. To determine the qualitative and quantitative ratio of collagen fibers of different degrees of maturity in the connective tissue structures of the paraneurium tissue of the sciatic nerve, polarization microscopy (MicMed-6, Lomo, Russia) was applied, and the basic principle of double refraction, which in combination with Sirius red staining, made it possible to differentiate types I and III collagen. The amount of each collagen type was determined by analyzing the color gamut after Sirius red staining in polarizing light. Fibers containing type I collagen had a red glow, while those containing type III collagen had a green glow. The ratio of collagen types was calculated using the Fiji program (USA, 2022). US examination revealed the presence of a non-pronounced bilateral asymmetry in the structural organization of the paraneurium and an increase in the thickness of the SN with age, from 0-11 years to the age group of 41-60 years. Polarization microscopy of micro-preparations of the human sciatic nerve with paraneurium structures made it possible to analyze the density of the fibers of the paraneurium connective tissue and identify types I and III of collagen. At the age of 11, the amount of type I collagen fibers was maximum (69.74±0.41%), and type III collagen fibers amounted to 30.26±0.44%. Further, with increasing age, the amount of collagen III significantly diminished. The ratio of type I to type III collagen increased with patient age, with the highest ratio in the age group 41-60 years. Conclusion: The revealed dynamics of changes are quite comparable with the age-related features of connective tissue since it is this tissue that makes up the morphological substrate of the paraneurium of the sciatic nerve.

Assessment of Human Epineural Conduit of Different Size Diameters on Efficacy of Nerve Regeneration and Functional Outcomes.

Different types of nerve conduits are used to bridge peripheral nerve gaps when a tension-free repair is unattainable. To best support nerve regeneration, naturally occurring conduits have been tested. Since allografts offer an unlimited source of epineurium, we have developed human epineural conduit (hEC) as a novel technology to bridge nerve gaps. Considering acellular properties, and lack of immunogenic response, epineurium-derived conduits represent an attractive material, when compared with nerve allografts that require systemic immunosuppression. In this study, we introduce the hEC as a novel naturally occurring material applied for repair of nerve gaps after trauma. We tested the application of hEC created from human sciatic nerve in the restoration of 20 mm sciatic nerve defects in the nude rat model. Four experimental groups were studied: group 1: no repair control (n = 6), group 2: autograft control (n = 6), group 3: matched diameter hEC (n = 6), and group 4: large diameter hEC (n = 6). Functional tests of toe-spread and pin prick were performed at 1, 3, 6, 9, 12 weeks after repair. At 12 weeks, nerve samples were collected for immunostaining of Laminin B, S-100, glial fibrillary acidic protein (GFAP), nerve growth factor (NGF), vascular endothelial growth factor (VEGF), von Willebrand factor, and histomorphometric analysis of myelin thickness, axonal density, fiber diameter, and percentage of the myelinated nerve fibers. Muscle samples were gathered for gastrocnemius muscle index (GMI) and muscle fiber area ratio measurements. Best functional recovery, as well as GMI, was revealed for the autograft group, and was comparable to the matched hEC group. Significant differences were revealed between matched and large hEC groups in expression of S100 (p = 0.0423), NGF (p = 0.269), VEGF (p = 0.0003) as well as in percentage of myelinated fibers (p < 0.001) and axonal density (p = 0.0003). We established the feasibility of hEC creation. The innovative method introduces an alternative technique to autograft repair of nerve defects.

Application of Human Epineural Conduit Supported with Human Mesenchymal Stem Cells as a Novel Therapy for Enhancement of Nerve Gap Regeneration

Various therapeutic methods have been suggested to enhance nerve regeneration. In this study, we propose a novel approach for enhancement of nerve gap regeneration by applying human epineural conduit (hEC) supported with human mesenchymal stem cells (hMSC), as an alternative to autograft repair. Restoration of 20 mm sciatic nerve defect with hEC created from human sciatic nerve supported with hMSC was tested in 4 experimental groups (n = 6 each) in the athymic nude rat model (Crl:NIH-Foxn1rnu): 1 - No repair control, 2 - Autograft control, 3 - Matched diameter hEC filled with 1 mL saline, 4 - Matched diameter hEC supported with 3 × 106 hMSC. Assessments included: functional tests: toe-spread and pinprick, regeneration assessment by immunofluorescence staining: HLA-1, HLA-DR, NGF, GFAP, Laminin B, S-100, VEGF, vWF and PKH26 labeling; histomorphometric analysis of myelin thickness, axonal density, fiber diameter and myelinated nerve fibers percentage; Gastrocnemius Muscle Index (GMI) and muscle fiber area ratio. Best sensory and motor function recovery, as well as GMI and muscle fiber area ratio, were observed in the autograft group, and were comparable to the hEC with hMSC group (p = 0.038). Significant improvements of myelin thickness (p = 0.003), fiber diameter (p = 0.0296), and percentage of myelinated fibers (p < 0.0001) were detected in hEC group supported with hMSC compared to hEC with saline controls. At 12-weeks after nerve gap repair, hEC combined with hMSC revealed increased expression of neurotrophic and proangiogenic factors, which corresponded with improvement of function comparable with the autograft control. Application of our novel hEC supported with hMSC provides a potential alternative to the autograft nerve repair.Graphical

Blood-Nerve Barrier (BNB) Pathology in Diabetic Peripheral Neuropathy and In Vitro Human BNB Model.

In diabetic peripheral neuropathy (DPN), metabolic disorder by hyperglycemia progresses in peripheral nerves. In addition to the direct damage to peripheral neural axons, the homeostatic mechanism of peripheral nerves is disrupted by dysfunction of the blood–nerve barrier (BNB) and Schwann cells. The disruption of the BNB, which is a crucial factor in DPN development and exacerbation, causes axonal degeneration via various pathways. Although many reports revealed that hyperglycemia and other important factors, such as dyslipidemia-induced dysfunction of Schwann cells, contributed to DPN, the molecular mechanisms underlying BNB disruption have not been sufficiently elucidated, mainly because of the lack of in vitro studies owing to difficulties in establishing human cell lines from vascular endothelial cells and pericytes that form the BNB. We have developed, for the first time, temperature-sensitive immortalized cell lines of vascular endothelial cells and pericytes originating from the BNB of human sciatic nerves, and we have elucidated the disruption to the BNB mainly in response to advanced glycation end products in DPN. Recently, we succeeded in developing an in vitro BNB model to reflect the anatomical characteristics of the BNB using cell sheet engineering, and we established immortalized cell lines originating from the human BNB. In this article, we review the pathologic evidence of the pathology of DPN in terms of BNB disruption, and we introduce the current in vitro BNB models.

Morphometric analysis of the epineurial and endoneurial blood vessels of the human sciatic nerve in relation to aging

The aim of this research is to perform an analysis of the epineurial and endoneurial blood vessels in relation to aging. The research is conducted on samples of the human sciatic nerve of 12 case (age from 27 to 89). The histological sections are stained by streptavidin-biotin method of detecting the presence of Type IV collagen. After morphometric analysis the following stereological parameters have been calculated: the number of blood vessels per unit of area, the volume density of the blood vessels and the surface density of the blood vessels of the epineurium and endoneurium. An additional diameter measurement is performed for the endoneural blood vessels. In order to perform a more detailed analysis, the cases were classified into three age groups, the first (27–48 years), the second (49–70 years) and, the third (over 70 years). The bivariate correlation analysis showed that the number of blood vessels of the endoneurium, their volume and surface densities in relation to age produced a statistically significant positive correlation. One Way ANOVA test demonstrated a statistically significant increase in the number of endoneurial blood vessels in the age group III when compared the age group I and, in addition, it showed a significant decrease in the diameter of the age group II when compared to the age group I. Paired t – test shows a statistically significant higher number of endoneurial blood vessels in relation to the epineurial, namely, in the age group III. The volume and surface density of the epineurial blood vessels is significantly higher than the endoneurial in both the I and II age group. Age brings about significant changes of the endoneurial vascular network of the sciatic nerve due to the increase in density of the endoneurial blood vessels, their volume and surface densities. Consequently, in the cases older than 70 years, the number of endoneurial blood vessels significantly exceeds the number of epineurial blood vessels.

Three-dimensional reconstruction of internal fascicles and microvascular structures of human peripheral nerves.

Biofabricated nanostructured and microstructured scaffolds have exhibited great potential for nerve tissue regeneration and functional restoration, and prevascularization and biotransportation within 3D fascicle structures are critical. Unfortunately, an ideal internal fascicle and microvascular model of human peripheral nerves is lacking. In this study, we used microcomputed tomography (microCT) to acquire high-resolution images of the human sciatic nerve. We propose a novel deep-learning network technique, called ResNetH3D-Unet, to segment fascicles and microvascular structures. We reconstructed 3D intraneural fascicles and microvascular topography to quantify the fascicle volume ratio (FVR), microvascular volume ratio (MVR), microvascular to fascicle volume ratio (MFVR), fascicle surface area to volume ratio (FSAVR), and microvascular surface area to volume ratio (MSAVR) of human samples. The frequency distributions of the fascicle diameter, microvascular diameter, and fascicle-to-microvasculature distance were analyzed. The obtained microCT analysis and reconstruction provided high-resolution microstructures of human peripheral nerves. Our proposed ResNetH3D-Unet method for fascicle and microvasculature segmentation yielded a mean intersection over union (IOU) of 92.1% (approximately 5% higher than the U-net IOU). The 3D reconstructed model showed that the internal microvasculature runs longitudinally within the internal epineurium and connects to the external vasculature at some points. Analysis of the 3D data indicated a 48.2±3% FVR, 23.7±1.8% MVR, 4.9±0.5% MFVR, 7.26±2.58mm-1 FSAVR, and 1.52±0.52mm-1 MSAVR. A fascicle diameter of 0.98mm, microvascular diameter of 0.125mm, and microvasculature-to-fascicle distance of 0.196mm were most frequent. This study provides fundamental data and structural references for designing bionic scaffolding constructs with 3D microvascular and fascicle distributions.

Another (Internal) Epineurium: Beyond the Anatomical Barriers of Nerves.

The epineurium has been accepted as the outer anatomical barrier of the peripheral nerves. Our objective was to characterize the microanatomy of the layers surrounding nerves using different tissue-specific staining methods. Two hundred forty-two cross sections of human sciatic and median nerves, and brachial plexuses of eight fresh unembalmed cadavers, were examined. The samples were fixed in formaldehyde solution and stained with hematoxylin-eosin, Masson's trichrome, or epithelial membrane antigen under standard conditions. Because epithelial membrane antigen only stains the perineurium, we demonstrated using hematoxylin-eosin and Masson's trichrome that there were different collagen layers inside and outside the nerves. All fascicles had a collagen layer that surrounded the perineurium and were in close contact with it, with no adipose tissue between them. Unlike the perineurium, this layer, an "internal epineurium," contained no cells, and it surrounded one or a small group of fascicles. Bundling these fascicles or small groups of fascicles together was the true epineurium, and between the true and internal epineurium, we consistently found an adipose-containing compartment. More proximal to this, the tibial and common peroneal nerves were bundled together by another collagen layer, the circumneurium, which also had a fat-cell-containing compartment deep to it. There were scattered collagen fibers among the adipocytes. Using tissue-specific staining, we were able to demonstrate a collagen layer, the "internal epineurium." Outside the nerves, we identified several fat-containing concentric compartments. Those compartments were limited by collagen fiber layers that were also similar to the epineurium. Clin. Anat. 33:199-206, 2020. © 2019 Wiley Periodicals, Inc.

Mechanics of anesthetic needle penetration into human sciatic nerve

Nerve blocks are frequently performed by anesthesiologists to control pain. For sciatic nerve blocks, the optimal placement of the needle tip between its paraneural sheath and epineurial covering is challenging, even under ultrasound guidance, and frequently results in nerve puncture. We performed needle penetration tests on cadaveric isolated paraneural sheath (IPS), isolated nerve (IN), and the nerve with overlying paraneural sheath (NPS), and quantified puncture force requirement and fracture toughness of these specimens to assess their role in determining the clinical risk of nerve puncture. We found that puncture force (123 ± 17 mN) and fracture toughness (45.48 ± 9.72 J m−2) of IPS was significantly lower than those for NPS (1440 ± 161 mN and 1317.46 ± 212.45 Jm−2, respectively), suggesting that it is not possible to push the tip of the block needle through the paraneural sheath only, without pushing it into the nerve directly, when the sheath is lying directly over the nerve. Results of this study provide a physical basis for tangential placement of the needle as the ideal situation for local anesthetic deposition, as it allows for the penetration of the sheath along the edge of the nerve without entering the epineurium.

Morphometric analysis of the diameter and g-ratio of the myelinated nerve fibers of the human sciatic nerve during the aging process.

Myelinated nerve fibers suffer from different degrees of atrophy with age. The success of subsequent regeneration varies. The aim of this research was to analyze myelinated fibers of the human sciatic nerve during the aging process. Morphometric analysis was performed on 17 cases with an age range from 9 to 93years. The outer and inner diameter of 100 randomly selected nerve fibers was measured in each of the cases evaluated, and the g-ratio (axonal diameter/outer diameter of the whole nerve fiber) of each was calculated. Scatter plots of the diameters and g-ratios of the analyzed fibers were then analyzed. Nerve fibers of each case were classified into three groups according to the g-ratio values: group I (g-ratio lower than 0.6), group II (g-ratio from 0.6 to 0.7) and group III (g-ratio higher than 0.7). Afterwards, nerve fibers of group II were further classified into small and large subgroups. The percentages of each group of nerve fibers were computed for each case and these values were used for correlational and bivariate linear regression analysis. The percentage of myelinated nerve fibers with large diameter and optimal g-ratio of the sciatic nerve declines significantly with age. This is accompanied by a simultaneous significant increase in the percentage of small myelinated fibers with g-ratio values close to 1 that occupy the upper left quadrant of the scatter plot. It can be concluded that aging of the sciatic nerve is associated with significant atrophy of large myelinated fibers. Additionally, a significant increase in regenerated nerve fibers with thinner myelin sheath is observed with age, which, together with the large myelinated fiber atrophy, might be the cause of the age-related decline in conduction velocity. A better understanding of the changes in aging peripheral nerves might improve interpretation of their pathological changes, as well as comprehension of their regeneration in individuals of different age.

Somatotopic fascicular organization of the human sciatic nerve demonstrated by MR neurography

Objectives:To investigate whether the human sciatic nerve might have a consistent somatotopic organization according to proximal fascicle input by spinal nerves.Methods:Twelve patients (55.3 ± 15.5 years) with confirmed lesions of either the L5 or S1 spinal nerve root underwent magnetic resonance neurography of sciatic nerve fascicles including thigh and knee levels (T2-weighted sequence with fat saturation, repetition time/echo time 7,552/52 milliseconds, voxel size 0.27 × 0.27 × 3.0 mm3). Twenty healthy subjects and 12 additional patients with an established diagnosis of peripheral polyneuropathy served as 2 separate age- and sex-matched control groups. Two blinded readers assessed patients and controls for presence of distinct lesion patterns. Spatial maps of normalized T2 signal were rendered after segmentation and coregistration of sciatic nerve voxels to detect fascicle lesion patterns.Results:A clear somatotopic distribution of nerve fascicles was observed on cross-sections along the entire course of the sciatic nerve and was distinct between patients with L5 and those with S1 lesions. Fascicles emerging from L5 were ordered in anterolateral positions within sciatic nerve cross-sections, while fascicles emerging from S1 appeared posteromedially. Visual assessment discriminated these somatotopic lesions in all cases from both healthy and polyneuropathy controls.Conclusion:A distinct pattern of somatotopy was identified within the sciatic nerve according to proximal fascicle input by L5 and S1 spinal nerves. Knowledge of human nerve somatotopy may have clinically useful implications in imaging-aided diagnosis of neuropathies.

Are human peripheral nerves sensitive to X-ray imaging?

Diagnostic imaging techniques play an important role in assessing the exact location, cause, and extent of a nerve lesion, thus allowing clinicians to diagnose and manage more effectively a variety of pathological conditions, such as entrapment syndromes, traumatic injuries, and space-occupying lesions. Ultrasound and nuclear magnetic resonance imaging are becoming useful methods for this purpose, but they still lack spatial resolution. In this regard, recent phase contrast x-ray imaging experiments of peripheral nerve allowed the visualization of each nerve fiber surrounded by its myelin sheath as clearly as optical microscopy. In the present study, we attempted to produce high-resolution x-ray phase contrast images of a human sciatic nerve by using synchrotron radiation propagation-based imaging. The images showed high contrast and high spatial resolution, allowing clear identification of each fascicle structure and surrounding connective tissue. The outstanding result is the detection of such structures by phase contrast x-ray tomography of a thick human sciatic nerve section. This may further enable the identification of diverse pathological patterns, such as Wallerian degeneration, hypertrophic neuropathy, inflammatory infiltration, leprosy neuropathy and amyloid deposits. To the best of our knowledge, this is the first successful phase contrast x-ray imaging experiment of a human peripheral nerve sample. Our long-term goal is to develop peripheral nerve imaging methods that could supersede biopsy procedures.

Peripheral Neuropathy: Assessment of Proximal Nerve Integrity By Diffusion Tensor Imaging

We investigated the utility of diffusion tensor imaging (DTI) for detecting neuropathic changes in proximal nerve segments in patients with peripheral neuropathy. Twenty-one individuals with (n = 11) and without (n = 10) peripheral neuropathy underwent DTI of a defined sciatic nerve segment. Patients and controls were evaluated by clinical examination and nerve conduction studies at baseline and 6 months after the initial DTI scan. The mean fractional anisotropy (FA) value was significantly lower in sciatic nerves from patients with peripheral neuropathy as compared with controls. Sciatic nerve FA values correlated with clinical disability scores and electrophysiological parameters of axonal damage at baseline and 6 months after MRI scan. DTI-derived FA values are a sensitive measure to discriminate healthy from functionally impaired human sciatic nerve segments. DTI of proximal nerve segments may be useful for estimating the proximal axonal degeneration burden in patients with peripheral neuropathies.

Structure-Activity Relationship of Nerve-Highlighting Fluorophores

Nerve damage is a major morbidity associated with numerous surgical interventions. Yet, nerve visualization continues to challenge even the most experienced surgeons. A nerve-specific fluorescent contrast agent, especially one with near-infrared (NIR) absorption and emission, would be of immediate benefit to patients and surgeons. Currently, there are only three classes of small molecule organic fluorophores that penetrate the blood nerve barrier and bind to nerve tissue when administered systemically. Of these three classes, the distyrylbenzenes (DSBs) are particularly attractive for further study. Although not presently in the NIR range, DSB fluorophores highlight all nerve tissue in mice, rats, and pigs after intravenous administration. The purpose of the current study was to define the pharmacophore responsible for nerve-specific uptake and retention, which would enable future molecules to be optimized for NIR optical properties. Structural analogs of the DSB class of small molecules were synthesized using combinatorial solid phase synthesis and commercially available building blocks, which yielded more than 200 unique DSB fluorophores. The nerve-specific properties of all DSB analogs were quantified using an ex vivo nerve-specific fluorescence assay on pig and human sciatic nerve. Results were used to perform quantitative structure-activity relationship (QSAR) modeling and to define the nerve-specific pharmacophore. All DSB analogs with positive ex vivo fluorescence were tested for in vivo nerve specificity in mice to assess the effect of biodistribution and clearance on nerve fluorescence signal. Two new DSB fluorophores with the highest nerve to muscle ratio were tested in pigs to confirm scalability.

Comparison of viscoelasticity between normal human sciatic nerve and amniotic membrane.

Sciatic nerve tissue was obtained from the gluteus maximus muscle segment of normal human cadavers and amniotic membrane tissue was obtained from healthy human puerperant placentas. Both tissues were analyzed for their stress relaxation and creep properties to determine suitability for transplantation applications. Human amniotic membrane and sciatic nerve tissues had similar tendencies for stress relaxation and creep properties. The stress value of the amniotic membrane stress relaxation group decreased to a greater extent compared with the sciatic nerve stress relaxation group. Similarly, the stress value of the amniotic membrane creep group increased to a greater extent compared with the sciatic nerve creep group. The stress relaxation curve for human amniotic membrane and sciatic nerve showed a logarithm correlation, while the creep curve showed an exponential correlation. These data indicate that amniotic membrane tissue has better stress relaxation and creep properties compared with sciatic nerve tissue.

An artery accompanying the sciatic nerve (arteria comitans nervi ischiadici) and the position of the hip joint: a comparative histological study using chick, mouse, and human foetal specimens

Birds and reptiles always carry a long and thick artery accompanying the sciatic nerve (i.e., the sciatic artery), whereas mammals do not. We attempted to demonstrate a difference in courses of the nerve and artery in fetuses in relation with the hip joint posture. Eight mid-term human fetuses (15-18 weeks), five mouse fetuses (E18) and five chick embryos (11 days after incubation) were examined histologically. Thin feeding arteries in the sciatic nerve were consistently observed in human fetuses in spite of the long, inferiorly curved course of the nerve around the ischium. The tissue around the human sciatic nerve was not so tight because of the medial and inferior shift of the nerve away from the hip joint. The fetal hip joint position differed among the species, being highly flexed in humans and almost at right angle flexion in mice and chicks. Because of deep adduction of the hip joint in the mouse, the knee was located near the midline of the body. The mouse sciatic nerve ran through the tight tissue along the head of the femur, whereas the chick nerve ran through the loose space even in the gluteal region. In birds, evolution of the pelvis including the hip joint without adduction seemed to make the arterial development possible. In mammals, highly flexed or adducted hip joint seemed to be one of the disturbing factors against development of the long and thick artery. A slight change in posture may cause significant arterial variation.

Comparison of viscoelasticity between normal human sciatic nerve and amniotic membrane

Comparison of viscoelasticity between normal human sciatic nerve and amniotic membrane

Similarities and dissimilarities of the blood supplies of the human sciatic, tibial, and common peroneal nerves

The aim was to investigate the arterial supply of the sciatic, tibial, and common peroneal nerves. Thirty-six lower limbs of 18 human fetuses were studied. The fetuses had been fixed in buffered formalin and the blood vessels injected with barium sulfate. Fetal age ranged from 12 to 28 weeks of gestation. Microdissection of the fetal lower extremities was done under ×5 magnifying lenses. The sciatic nerves of 10 lower extremities were dissected and excised and radiographs taken. The extraneural arterial chain of the sciatic nerve was composed of 2-6 arterial branches of the inferior gluteal artery, the medial circumflex femoral artery, the perforating arteries, and the popliteal artery. The extraneural arterial chain of tibial nerve was composed of 2-5 arteries, which were branches of the popliteal, the peroneal, and the posterior tibial arteries. Radiographs showed the presence of complete intraneural arterial chains in the sciatic and tibial nerves, formed from anastomosing vessels. Dissection showed that, in 97.2% of the specimens, the common peroneal nerve was supplied only by one popliteal artery branch, the presence of which was confirmed radiologically. The sciatic and tibial nerves are supplied by numerous arterial branches of different origins, which provide for collateral circulation. In contrast, the common peroneal nerve is most frequently supplied only by one elongated longitudinal blood vessel, a branch of the popliteal artery. Such a vascular arrangement may make the common peroneal nerve less resistant to stretching and compression.

Strain and stress variations in the human amniotic membrane and fresh corpse autologous sciatic nerve anastomosis in a model of sciatic nerve injury.

A 10-mm long sciatic nerve injury model was established in fresh normal Chinese patient cadavers. Amniotic membrane was harvested from healthy maternal placentas and was prepared into multilayered, coiled, tubular specimens. Sciatic nerve injury models were respectively anastomosed using the autologous cadaveric sciatic nerve and human amniotic membrane. Tensile test results showed that maximal loading, maximal displacement, maximal stress, and maximal strain of sciatic nerve injury models anastomosed with human amniotic membrane were greater than those in the autologous nerve anastomosis group. The strain-stress curves of the human amniotic membrane and sciatic nerves indicated exponential change at the first phase, which became elastic deformation curves at the second and third phases, and displayed plastic deformation curves at the fourth phase, at which point the specimens lost their bearing capacity. Experimental findings suggested that human amniotic membranes and autologous sciatic nerves exhibit similar stress-strain curves, good elastic properties, and certain strain and stress capabilities in anastomosis of the injured sciatic nerve.

Probabilistic modeling of selective stimulation of the human sciatic nerve with a flat interface nerve electrode

Ankle control is critical to both standing balance and efficient walking. The hypothesis presented in this paper is that a Flat Interface Nerve Electrode (FINE) placed around the sciatic nerve with a fixed number of contacts at predetermined locations and without a priori knowledge of the nerve's underlying neuroanatomy can selectively control each ankle motion. Models of the human sciatic nerve surrounded by a FINE of varying size were created and used to calculate the probability of selective activation of axons within any arbitrarily designated, contiguous group of fascicles. Simulations support the hypothesis and suggest that currently available implantable technology cannot selectively recruit each target plantar flexor individually but can restore plantar flexion or dorsiflexion from a site on the sciatic nerve without spillover to antagonists. Successful activation of individual ankle muscles in 90% of the population can be achieved by utilizing bipolar stimulation and/or by using a cuff with at least 20 contacts.