腰椎间盘突出症有限元模型的建立与分析

目的建立人体腰椎运动节段(L3~5)有限元模型,于轴向正压力、前屈、侧弯、后伸及旋转等载荷下研究椎间盘的生物力学特征。方法根据健康成年人腰椎运动节段(L3~5)的CT影像学资料,采用Mimics10.0医学图像处理软件和Geomagic10.0逆向工程软件分别建立腰椎运动节段(L3~5)椎体和椎间盘的几何模型,Ansys软件附加腰椎相关韧带及通过改变椎间盘突出后对应的材料属性,构建正常模型和腰椎间盘突出(L34)模型,运用有限元方法模拟正常椎间盘和突出椎间盘于轴向正压力、前屈、侧弯、后伸和旋转等载荷下生物力学特征参数。结果腰椎运动节段(L3,4)发生椎间盘突出后即改变了椎间盘的应力分布及传递载荷能力,应力主要集中于纤维环之后外侧。结论腰椎运动节段(L34)椎间盘突出后椎间盘的承载功能明显下降。     

人工腰椎间盘置换后下位关节突关节内压力的变化*★

目的：腰椎间盘和关节突关节共同维持腰椎的稳定，任何一个部分的退行性变都将引起另两部分的退变。观察SB Charite人工腰椎间盘假体置换对相邻下位关节突关节内压力的影响，以提供人工椎间盘临床应用的生物力学参数。 方法：实验于2003-03在国防科技大学航天与材料工程学院力学实验室完成。①实验材料：10具新鲜成人尸体腰椎标本，包括L2~5椎体及其椎间盘，死者均为急性脑死亡的健康青壮年。肉眼及X射线观察以排除标本无畸形、退行性变及结构性破坏。剔除椎旁肌肉及其筋膜组织，保留所有的韧带、椎间盘及关节囊并维持其完整性。②实验方法及评估：将Ω状微型电阻式压力传感器置入L4/5关节突关节，分别测量L3/4椎间盘完整和人工椎间盘置换两种状态下轴向（400～2 000 N）、后伸、对侧弯和同侧弯(2~10 N·m)载荷4种工况时L4/5关节突关节内的压力。 结果：纳入成人尸体腰椎标本共10具，均进入结果分析，实验过程中标本无破坏和脱落。轴向、后伸、同侧弯及对侧弯加载条件下，人工椎间盘置换组与椎间盘完整组比较，下位关节突关节内压力差异均无显著性（P > 0.05）。 结论：①人工腰椎间盘置换后相邻下位关节突关节内压力与正常时无明显改变。②人工椎间盘置换在重建腰椎生物力学性能的同时不会引起相邻下位关节突关节内压力的改变。     

人工腰椎间盘置换的有限元模型

背景：国内外已有学者将有限元分析用于脊柱的生物力学模拟，但对人工椎间盘置换前后腰椎生物力学系统的有限元模拟报道较少。 目的：实验建立腰椎运动节段SB-Chaite III型人工椎间盘置换的新型三维有限元模型，并在此基础上进行有限元分析。 设计、时间及地点：观察性实验于2003-12/2004-08在中南大学湘雅医院骨科研究室完成。 对象：选择1名健康成年男性志愿者作为模拟对象,对脊柱T12~S1节段进行层厚2 mm的连续扫描，共获得CT断层图像264幅，并对CT图像每隔15°进行三维重建，获取用于建立三维模型的相关数据。 方法：将CT扫描的腰椎图像结合人体解剖学数据通过3DSMAX软件建模形成正常中国男性L4~5运动节段的三维模型。 主要观察指标：结合SB-Chaite Ⅲ型人工椎间盘的三维模型，用有限元分析软件SAP2000转换成有限元模型。 结果：成功建立了腰椎运动节段的三维模型和有限元模型。L4~5节段SB-Chaite Ⅲ型人工椎间盘置换的有限元模型总节点数为2 542个，包括1 924个Solid单元，592个Area单元，50个Link单元。 结论：通过CT断层扫描、图像数字化处理及计算机辅助设计等方法，可以建立腰椎人工椎间盘置换的有限元模型。     

有限元法分析举重运动员预备提铃动作过程中腰椎节段的受力变化

背景：多年来,国内外学者对腰椎的生物力学特性进行了大量的研究,但是由于腰椎生理结构的复杂性以及研究手段的局限性,很多问题有待于进一步探索,特别是对举重运动员腰部损伤的防治是目前亟待解决的问题。 目的：建立人体完整腰段脊柱三维有限元模型,分析举重运动员预备提铃动作时腰椎节段的受力特点。 方法：引入“组装搭配式”思想,利用Dicom数据,建立人体脊柱腰椎节段(L1~5)完整的、真实的三维有限元模型。并模拟举重运动员预备提铃动作时,各椎体及椎间盘所受应力情况。 结果与结论：举重运动员预备提铃动作时,各椎体应力分布在椎体前下方,此处应力水平明显高于其他部位,椎体后部结构中椎弓根处出现应力集中现象,应力也处于较高水平。椎间盘应力分布在纤维环的中部和前部,但是前部更为明显。此时,不同椎体、腰椎间盘所承受的应力不同,其应力表现为自上向下呈逐渐增大趋势。各椎体的应力值大于其下方椎间盘的应力值,各椎体应力值是其下方椎间盘的四五倍。证实实验所建腰椎节段三维有限元模型可以用于模拟脊柱腰椎节段的生物力学特性研究。     

腰椎运动节段终板凹陷角变化的有限元分析*☆

背景：终板的组织形态改变可通过影响对椎间盘的营养传递最终导致椎间盘的退变。 目的：观察终板凹陷程度变化对腰椎运动节段生物力学的影响。 设计、时间及地点：有限元模型生物力学分析。于2005-01/2007-01在浙江大学医学院附属第二医院骨科生物力学实验室完成。 材料：德国西门子SOMATOM SENSATION 16螺旋CT机。ANSYS有限元分析软件(Inc. Pennsylvania, USA)。 方法：在以往建立的腰椎L4~5运动节段三维非线性有限元模型基础上，采用CAD方法精确构建大、中、小3种不同终板凹陷角的有限元模型，有限元模型的椎间盘前凸角、小关节间隙等其余形态学参数及网格划分均保持一致。垂直压缩、屈曲、伸直、前后剪力5种载荷条件下，分别对3种有限元模型生物力学参数进行测试。 主要观察指标：终板-椎间盘界面应变、椎间盘刚度、髓核内压、椎间盘膨出、纤维环纤维张应力、纤维环基质应力、腰椎后部结构应力以及关节突接触力。 结果：负载条件下，终板凹陷角增加、终板凹陷程度减小可导致终板-椎间盘界面应变减小，椎间盘刚度及髓核内压增加，椎间盘膨出、纤维环纤维张应力、纤维环基质应力、腰椎后部结构应力以及关节突接触力减小。 结论：终板凹陷程度的减小增强了椎间盘对椎体的保护作用；同时可通过影响终板的形变减少对椎间盘的营养传递。     

颈椎单侧半椎板及不同程度小关节切除术后生物力学变化的有限元分析

目的在人体颈椎有限元模型上观察单侧半椎板及不同程度同侧小关节切除术后颈椎生物力学的改变。方法构建人体正常颈椎C2-T1节段的三维有限元模型,并在此模型的上模拟C4-6半椎板切除及不同程度(25%,50%,75%)同侧C4-5小关节切除术。将T1椎体下端固定作为边界条件,采用3种加载模式于C2椎体上表面施加1.5 N·m的加载并使其产生前屈、后伸、侧屈和旋转运动。计算得到并比较不同手术模型的椎体节段间活动度及相应状态下韧带的拉力变化,小关节、终板和椎间盘的压力变化。结果在屈伸、侧弯和旋转状态下各手术模型节段间活动度的变化主要在C4-5节段,活动度随着小关节切除范围的增加而增加,在小关节切除范围大于50%时增加显著;三种运动状态下终板、纤维环和左侧小关节最大应力以及左侧关节囊韧带最大拉力的变化主要发生在C4-5节段,最大应力和最大拉力的增加随着小关节切除范围的增加而增加,在切除范围大于50%时增加显著。结论单侧半椎板切除时,如同时伴小关节切除,术后即刻会降低小关节切除节段的稳定性,切除超过50%时降低显著。单侧半椎板切除合并小关节切除术后会增加小关节切除节段的手术侧关节囊韧带拉力,小关节应力、椎间盘纤维环和终板的应力,破坏超过50%时增加明显。     

轴向载荷对双节段颈椎人工椎间盘置换邻下位关节突关节压力影响

【摘 要】 目的 探讨轴向载荷对双节段颈椎人工椎间盘置换和前路椎间融合内固定对邻下位节段关节突关节内压力的影响,为双节段人工颈椎间盘置换的临床运用提供生物力学依据。 方法 取11具新鲜完整的成人下颈段标本,按实验先后分别制成C4/5、C5/6椎间盘完整、椎间盘置换、椎间融合三个模型组,在标本上施加轴向分级载荷,将微型阻电式压力传感器置入C5/6、C6/7关节突关节内,测量合组各分级载荷下C5/6、C6/7关节突关节内的压力。 结果 1.在轴向加载下,下位节段关节突关节内的压力随着施加载荷的增大而增大。 2. C4/5、C5/6双节段人工椎间盘置换组与椎间盘完整组相比下位置换节段和邻近下位节段关节突关节内的压力变化相近,无显著性差异 (P>0.05)。3. C4/5、C5/6椎间融合组与人工椎间盘置换组、椎间盘完整组相比邻近下位节段关节突关节内的压力高,有显著性差异(P<0.05)。 结论 1. 颈椎双节段人工椎间盘置换后置换下位节段和邻近下位节段关节突关节内压力与完整标本相近,提示颈椎双节段人工椎间盘置换能够重建颈椎生物力学性能。2. 颈椎双节段椎间盘摘除融合内固定后邻近下位关节突关节压力增加,可能是多节段颈椎融合术后邻近节段发生退变或退变加速的原因之一     

腰椎运动节段流固耦合有限元模型的建立与验证*

背景：传统的脊柱生物力学体外实验难以取得椎间盘液体相关的力学性能数据,国外可见多孔弹性有限元模型用于腰椎的固液二相性的研究,然而国内罕见相关报道。 目的：利用ANSYS12.1有限元分析软件,建立腰椎运动节段流固耦合有限元模型,旨在推动有限元分析技术在脊柱生物力学方面的广泛应用。 方法：对1名健康男性志愿者进行L4~5运动节段的螺旋CT扫描成像,利用医学图像处理软件Mimics10.01对其进行预处理,再利用逆向工程软件Geomagic9.0对模型进行NURBS曲面重构,然后导入有限元软件ANSYS12.1重建椎体皮质骨、松质骨、纤维环和髓核等结构,最后通过划分网格、定义材料属性、定义接触、加载求解等操作建立了腰椎运动节段流固耦合三维有限元模型,并将椎间盘高度随时间变化的数据与文献数据进行比较,以验证模型的有效性。 结果与结论：建立了L4~5运动节段的流固耦合有限元模型,模型的总节点数210 718个,总单元数85 973个。将本模型所测得的椎间盘高度数据与文献数据进行比较,结果基本一致。腰椎流固耦合有限元模型更加符合人体的生物力学特点。     

前屈后伸载荷下颈椎间孔的孔径变化：Bryan颈人工椎间盘置换与颈椎钢板植骨内固定的比较

背景：诸多针对脊椎椎体间固定融合后相邻节段应力变化的生物力学测试结果并不尽相同,载荷控制与位移控制试验模式下所反映出的相邻节段应力状况其结果也相差甚远。 目的：分析椎间盘完整、椎间盘切除、Bryan颈人工椎间盘置换和前路颈椎植骨融合钢板内固定后,成人尸体颈椎标本分别在前屈后伸载荷下C5/6椎间孔孔径和面积的变化情况。 方法：分别测量C5/6椎间盘完整、椎间盘髓核摘除、Bryan颈人工椎间盘置换和前路钢板植骨内固定4种状态下以0.25,0.50,0.75,1.00,1.25,1.50 N•m的分级载荷加载于标本的前屈后伸状态时C5/6椎间孔孔径和面积的变化情况。 结果与结论：前屈后伸各级加载时,C5/6椎间孔上下径、上前后径、下前后径和面积椎间盘完整组、Bryan颈人工置换组和钢板植骨内固定组高于椎间盘髓核摘除组,差异有显著性意义(P < 0.05),Bryan颈人工置换组高于钢板植骨内固定组,差异有显著性意义(P < 0.05),可见颈椎间盘髓核摘除后C5/6椎间孔有效空间明显减少。     

人工颈椎间盘置换的生物力学系统评价

目的：评价人工颈椎间盘置换对颈椎运动范围及临近节段生物力学的影响。 方法：以计算机检索方法检索中国期刊全文数据库中(CNKI：2005/2009)关于人工颈椎间盘置换治疗颈椎病的临床随访、对照实验，检索词为“人工颈椎间盘置换、生物力学”。检索后对每项研究的资料结果进行提取、分析。 结果：共有21项实验469例颈动脉狭窄患者符合纳入标准，分析结果显示人工颈椎间盘置换后脊髓功能JOA 评分较置换前明显升高，置换节段稳定并部分恢复了颈椎正常的活动范围。而且与颈前路减压植骨融合术相比，人工颈椎间盘置换未增加临近节段的关节活动范围和应力负荷，阻止或降低了临近节段的退变及颈椎活动范围减小的发生率，随访时影像学均未见假体移位、脱落、下沉等并发症发生。 结论：人工颈椎间盘置换使颈椎运动范围得到一定保持，颈椎稳定性好，置换后对邻近节段影响较小，阻止了相邻节段的退变加速，是颈椎病治疗方面一种具有良好发展前景的治疗方法。但由于其临床应用时间短，其潜在的异位骨化、假体下沉、脱出等问题题仍有待于长期临床观察。     

Diagnostic Difficulties and Treatment Implications

Summary: Differentiation between types of epileptic seizures has been aided in recent years by the introduction of intensive neurodiagnostic techniques and the development of increasingly detailed classification systems. Paradoxically, these developments have not simplified the task of matching the appropriate antiepileptic drug to a particular seizure type. It is reasonable to assume that anticonvulsant drugs will have different effects on different types of seizures, but faulty, circular reasoning can enter the picture if one also assumes that responses of seizures to different drugs signify different seizure types. There are several examples of differential diagnoses that can fall prey to this problem, including the diagnosis between partial seizures with secondary generalization and generalized tonic-clonic seizures, and the diagnosis between complex partial seizures and absence seizures with automatisms, among others. Considerations of etiology in future classification systems can further complicate the problem: should one then choose an anticonvulsant drug on the basis of individual seizure type or on the basis of the type of epilepsy? Ramifications of this issue extend even to the drug approval process. Official sanction is not given for use of a drug for a seizure type not included in the original efficacy studies, even if later scientific evidence shows that seizure type to be related to a type that is included. New trials must be undertaken. These problems arise from how we choose to classify seizures.     

Cognitive Dysfunction Associated with Antiepileptic Drug Therapy

Summary: Epilepsy is frequently associated with cognitive dysfunction. However, the reasons for this correlation are unclear. Possible influential factors include patient age; duration, frequency, etiology, and type of seizures; hereditary factors; psychosocial issues; and antiepileptic drug (AED) therapy. Whereas many of these factors are beyond the physician's control, AED therapy is one element that can be addressed in treatment decisions by recognizing the potential cognitive effects of particular AEDs. For example, phenobarbital impairs memory and concentration; phenytoin affects attention, problem solving ability, and performance of visuomotor tasks. In contrast, carbamazepine may affect concentration, while valproate would appear to have minimal effects on cognition. Moreover, cognitive effects of AEDs are amplified with coadministration of multiple anticonvulsants (polytherapy). A review of studies on the cognitive effects of monotherapy with AEDs, as opposed to those of polytherapy, provides evidence that drug-related cognitive dysfunction can be reversed if patients are switched to a simpler therapeutic regimen. Future research should be directed toward developing reliable measures for assessing and monitoring cognition, and understanding the particular cognitive side effects of each AED. Physicians also need to revise their opinions about which side effects are "tolerable" for epileptic patients.     

Epilepsy and anomalies of neuronal migration: MRI and clinical aspects

Neuronal migration disorders are the result of disturbed brain development. In such disorders, neurons are abnormally located. In diagnosing these conditions, magnetic resonance imaging is superior to any other imaging technique. This enables us to improve our knowledge of the clinical correlates of neuronal migration. With reference to migrational disorder, a retrospective study of all 303 patients with epileptic seizures referred for magnetic resonance imaging during a 3-year period was performed, 13 patients (aged 12-41, mean age 27) were identified. They represent 4.3% of the entire study group. Of the patients with known epilepsy, 6.7% and of the mentally retarded, 13.7% had migrational disorders. Four patients had schizencephaly as the dominant finding, one was classified as hemimegalencephaly, 2 had isolated heterotopias, and 6 had localized pachy- and/or poly-microgyria. The clinical pictures are complex. Ectopias of grey matter are recognised foci of epilepsy, but from an epileptological and a clinical viewpoint little attention has been given to these disorders. The present study shows that malmigration is not rare in epilepsy patients, especially not in the mentally retarded.     

Carbamazepine Efficacy in Adults With Partial and Generalized Tonic-Clonic Seizures

Summary: Carbamazepine and phenytoin are drugs of choice in initial monotherapy for adult partial and secondarily generalized tonic-clonic seizures. These designations reflect the results of the Veterans Administration Epilepsy Cooperative Study Group of 1985. An earlier comparative study of carbamazepine and phenytoin by Ramsay and associates found both drugs equally effective in controlling new-onset seizures. Among the advantages of carbamazepine is that it causes relatively few cognitive and dysmorphic side effects. Its disadvantages are its unavailability in parenteral formulation and its metabolic autoinduction. The latter must be compensated for by planned dosage increases to maintain therapeutic plasma steady-state levels during the first 2 or 3 months of treatment. Carbamazepine is judged a drug of choice in the treatment of these secondarily generalized tonic-clonic seizures, and the drug of choice in children, adolescents, and women susceptible to the dysmorphic side effects associated with other anticonvulsant agents.     

Etiologic and Preventive Aspects of Epilepsy in the Child–Bridging the Gap Between Laboratory and Clinic

Summary: Four broad categories of basic phenomena are pertinent to developing ways to prevent epilepsy. These include mechanisms of epileptogenesis, ictal initiation and temporary entrainment by the seizure discharge of normally functioning brain, seizure propagation, and control mechanisms that function both to restrain the cascade of epileptic events culminating in a seizure and to arrest the epileptic event and restore the interictal state. In newborns and children, hypoxia-ischemia is a major factor leading to epileptogenesis, and several schemes are proposed to classify, quantify, and prevent hypoxic-ischemic encephalopathy. Control mechanisms must be better understood in order to develop prophylactic recommendations for epilepsy, and an experimental model of "kindling antagonism" may increase our understanding of these. Programs of prevention of seizures in children will evolve only if basic researchers and clinicians work productively together to develop an adequate understanding of factors important in epileptogenesis and antiepileptogenic control mechanisms.     

Classification of methods in transcranial Electrical Stimulation (tES) and evolving strategy from historical approaches to contemporary innovations

Transcranial Electrical Stimulation (tES) encompasses all methods of non-invasive current application to the brain used in research and clinical practice. We present the first comprehensive and technical review, explaining the evolution of tES in both terminology and dosage over the past 100 years of research to present day. Current transcranial Pulsed Current Stimulation (tPCS) approaches such as Cranial Electrotherapy Stimulation (CES) descended from Electrosleep (ES) through Cranial Electro-stimulation Therapy (CET), Transcerebral Electrotherapy (TCET), and NeuroElectric Therapy (NET) while others like Transcutaneous Cranial Electrical Stimulation (TCES) descended from Electroanesthesia (EA) through Limoge, and Interferential Stimulation. Prior to a contemporary resurgence in interest, variations of transcranial Direct Current Stimulation were explored intermittently, including Polarizing current, Galvanic Vestibular Stimulation (GVS), and Transcranial Micropolarization. The development of these approaches alongside Electroconvulsive Therapy (ECT) and pharmacological developments are considered. Both the roots and unique features of contemporary approaches such as transcranial Alternating Current Stimulation (tACS) and transcranial Random Noise Stimulation (tRNS) are discussed. Trends and incremental developments in electrode montage and waveform spanning decades are presented leading to the present day. Commercial devices, seminal conferences, and regulatory decisions are noted. We conclude with six rules on how increasing medical and technological sophistication may now be leveraged for broader success and adoption of tES.     

Predisposing and Causative Factors in Childhood Epilepsy

Summary: We review information from large studies of defined populations, examining the role of known factors and especially of prenatal and perinatal factors in contributing to nonfebrile seizure disorders of early childhood. We depend especially, but not exclusively, on the recently completed analyses from the Collaborative Perinatal Project of the National Institute of Neurological and Communicative Disorders and Stroke, the NCPP. About 4% of children in the NCPP who had at least one non-febrile nonsymptomatic seizure by the age of 7 years had a previous seizure during acute neurologic illness, such as meningitis or during the acute illness after trauma. Many such seizures should potentially be preventable. Of children with seizures, 10% had had a neonatal seizure and 13% had had a febrile seizure. Among the hundreds of prenatal and perinatal factors explored as predictors of childhood seizure disorders, the principal predictors identified were congenital malformations of the fetus, cerebral and noncerebral; family history of certain neurologic disorders; and neonatal seizures. In agreement with the British National Child Development Study, labor and delivery factors in the NCPP appeared to contribute very little to childhood seizure disorders. Maldevelopment, rather than damage at birth to an initially intact nervous system, appeared to be the more common mechanism. Most seizure disorders of early childhood remained unexplained by the large set of prenatal and perinatal characteristics examined.     

Treatment Considerations in Anticonvulsant Monotherapy

Summary: The long-standing practice of polypharmacy in treating epilepsy is giving way to use of monotherapy. Monotherapy can improve seizure control as well as reduce the risk of serious idiosyncratic reactions, dose-related side effects, and complex drug interactions. Monotherapy also offers improved compliance and cost-effectiveness. The basis of monotherapy is accurate diagnosis and assessment of the patient's seizure type(s), followed by selection of a single appropriate anticonvulsant drug. Many patients currently treated with multiple anticonvulsants can be successfully converted to monotherapy with a carefully monitored program in which troublesome and redundant drugs are gradually withdrawn from the therapeutic regimen.     

Anticonvulsant Drugs and Cognitive Function: A Review of the Literature

Summary: Alterations of cognitive function are separate from disturbances of behavior seen in association with epilepsy. The nature of the cognitive disability may to a certain extent depend on the seizure type. Partial seizures, mainly derived from a temporal lobe focus, impair memory tasks, while generalized seizures seem to have more effect on attentional abilities. A number of studies, reviewed in this paper, suggest that anticonvulsant drugs further impair cognitive function. Maximal impairments are seen in patients receiving polytherapy: rationalization of polytherapy improves cognitive abilities. Studies in children and adults have allowed differentiation of the effects of various commonly used antiepileptic agents. Maximal cognitive deficits are seen with. phenytoin, while phenobarbital and sodium valproate induce moderate disturbances, and carbamazepine seems relatively free from such toxicity. Further research is needed on the interrelationship between types of seizure disorders, types of anticonvulsant medications, and cognitive function.     

Dextromethorphan: Cellular Effects Reducing Neuronal Hyperactivity

Summary: Dextromethorphan is a dextrorotary morphinan without affinity for opioid receptors, commonly used as an antitussive medication. During the past 5 years, interest in the compound and its demethylated derivative, dextrorphan, has been revived because additional neuroprotective and an-tiepileptic properties were found in in vitro studies, animal experiments, and a few clinical cases. Both morphinans are able to inhibit N -methyl-D-aspartate (NMDA) receptor channels and voltage-operated calcium and sodium channels with different potencies. The inhibition of the NMDA receptor is believed to be the predominant mechanism of action responsible for the anticonvulsant and neuroprotective properties of the compounds.