基牙牙周膜厚度不同时固定桥应力分布的研究

目的：研究固定桥基牙牙周膜厚度不同对双端固定桥应力分布的影响。方法：采用螺旋CT扫描获取健康人下颌骨、牙齿及牙周支持组织的二维图像，通过图像合成软件建立三维数字模型，并应用三维有限元分析软件生成下颌后牙固定桥的三维有限元分析模型。在相同垂直载荷和水平载荷情况下，分析基牙牙周膜厚度不同时固定桥的应力分布。结果：当基牙牙周膜厚度小于0．1mm时固定桥基牙与牙槽骨表面应力大小相当；当基牙牙周膜厚度大于0．1mm小于0．4mm时固定桥牙槽骨表面应力随牙周膜厚度增大而减小但非线性关系；基牙牙周膜厚度大于0．4mm时固定桥牙槽骨表面应力不随牙周膜厚度增加而变化。结论：下颌后牙固定桥的应力分布与基牙牙周膜厚度在一定范围内具有相关性，表现为缓冲作用。     

固定桥基牙牙周膜厚度不同时牙周膜内的应力分析

目的：研究固定桥基牙牙周膜厚度不同时牙周膜内的应力分布，为临床工作提供理论依据。方法：采用螺旋CT扫描获取健康人下颌骨、牙齿及牙周支持组织的二维图像，通过图像合成软件建立三维数字模型，并应用三维有限元分析软件生成下颌后牙固定桥的三维有限元分析模型。在相同垂直载荷和水平载荷情况下，分析固定桥基牙牙周膜厚度不同时牙周膜内的应力分布。结果：当固定桥基牙牙周膜厚度小于0.1mm时，牙周膜内应力最大值无变化；当固定桥基牙牙周膜厚度大于0.1mm小于0.4mm时，牙周膜内应力最大值随牙周膜厚度增加而增大但非线性关系；当固定桥基牙牙周膜厚度大于0．4mm时，牙周膜内应力最大值不随牙周膜厚度增加而增大。结论：固定桥基牙牙周膜厚度在一定范围内影响牙周膜内的应力分布。     

静载荷作用下骨盆三维有限元分析及其生物力学意义

目的：探讨骨盆受到静力载荷作用后的力学行为特征，为临床分析及判断骨盆力学分布、静载荷影响提供力学基础。方法：实验于2002—01／2004—04在第二军医大学长海医院骨科实验室和同济大学牛命科学与技术学院生物力学实验室完成采用计算机仿真模拟方法，将所构建骨盆三维实体模犁导入三维有限元分析软件ANSYS7．0，分别计算单侧髂前上棘和单侧髂骨正后方静载荷作用下骨盆的力学行为表现，静载荷为8000N，分析主直力值，应力分布情况以及主应力方向上骨盆单元的位移。结果：单侧髂前上棘侧方加载下，应力沿着受力点与骶髂关节连线方向传导，没有应力沿着髋臼或者耻骨、坐骨传导；单侧髂骨后方静载荷加载时．应力沿着髂骨纵行方向、髂骨与骶髂关节部位连线方向、同侧耻骨上支传导。结论：分析静载荷作用下骨盆各部位应力分布以及骨盆各个单元在应力作用下的位移变化．有助于临床上进行骨盆损伤内固定力点的选择。     

静载荷作用下骨盆三维有限元分析及其生物力学意义

目的:探讨骨盆受到静力载荷作用后的力学行为特征,为临床分析及判断骨盆力学分布、静载荷影响提供力学基础。方法:实验于2002-01/2004-04在第二军医大学长海医院骨科实验室和同济大学生命科学与技术学院生物力学实验室完成。采用计算机仿真模拟方法,将所构建骨盆三维实体模型导入三维有限元分析软件ANSYS7.0,分别计算单侧髂前上棘和单侧髂骨正后方静载荷作用下骨盆的力学行为表现,静载荷为8000N,分析主应力值、应力分布情况以及主应力方向上骨盆单元的位移。结果:单侧髂前上棘侧方加载下,应力沿着受力点与骶髂关节连线方向传导,没有应力沿着髋臼或者耻骨、坐骨传导;单侧髂骨后方静载荷加载时,应力沿着髂骨纵行方向、髂骨与骶髂关节部位连线方向、同侧耻骨上支传导。结论:分析静载荷作用下骨盆各部位应力分布以及骨盆各个单元在应力作用下的位移变化,有助于临床上进行骨盆损伤内固定力点的选择以及进一步明确骨盆内在应力值分布。     

无髓牙为基牙作固定桥修复的临床疗效观察

修复门诊医生对患者牙列中单个牙或少数牙缺失,多采用固定桥修复,而选作的基牙中多有因各种原因已进行牙髓治疗的无髓基牙。为进一步了解无髓基牙修复治疗后的临床疗效,笔者对本科60例无髓牙选作桥基牙的病例,进行了0.5~3年的跟踪随访,并进行近远期疗效观察,现报道如下。     

根桩做单端固定桥基牙失败原因的分析

目的 对根桩做单端固定桥的桥基牙失败病例进行分析，寻找失败的原因。方法 通过18例单端固定桥修复后3～6个月脱位，3例牙根折裂的单端固定义齿行力学分析。结果 作进一步分析脱位原因与受咬合力、桥体的设计死髓牙的机械感受器的敏感度等有关。结论 为单端固定义齿基牙(桩)受力复杂，临床设计一定要慎重。用根桩作单端固定义齿的基牙，其对骀牙为天然牙，这种设计不可取。     

垂直载荷作用下骨盆的三维有限元分析

背景：目前对骨盆的力学分析还处于极其粗糙阶段，而有限元法因其具有不受样本量限制，实验误差小，重复性好等优点，正日益成为骨盆生物力学研究的重要手段。 目的：建立正常骨盆的三维有限元模型，分析骨盆在垂直载荷作用下的应力／应变和位移分布。 设计、时间及地点：三维有限元分析，单一样本观察。于200703／09在南方医科大学生物力学实验室完成。 材料：健康成年男性志愿者1例进行PET—CT扫描，层厚1FfLrn，得N-维原始图像以DICOM格式输出。 方法：应用Mimics、Freeform、ANSYS等软件进行三维重建，并建立正常骨盆的有限元模型。模拟人体双腿直立位的生理姿势，对模型施加500N轴向载荷。具体方式为约束双侧靛臼，向骶骨椎体上表面垂直加压，压力均匀分布于各个结点。 主要观察指标：计算该加载方式下骨盆的应力、应变及位移的分布情况。 结果：垂直加载500N载荷于骶骨上表面时，应力经两侧骶骨翼、骶髂关节，斜向下方经过坐骨大切迹附近，髂骨中央弓状线，传导至两侧髋臼。骨盆前环即耻骨支和耻骨联合受力较小。应变集中在两侧骶髂关节，绝对值很小，前方的耻骨联合处应变极小，呵忽略不计。位移以骶骨背侧的骶正中嵴处最大。 结论：正常骨盆是一个非常稳定的力学结构。过大的垂直应力容易引起骶骨或骶髂关节受损导致骨盆的垂直稳定性下降；恢复骶骨至髋臼的连续性对应力传导非常重要。     

有限元分析在腰椎生物力学研究中的应用

三维有限元分析方法作为脊柱生物力学研究方法之一,随着人们对脊柱力学特性的认识,有限元分析软件在国内外不断开发与应用,不但促进了有限元技术的发展,而且推动着脊柱生物力学研究更深入发展.文章介绍了有限元的概念及其原理,总结了有限元分析法在腰椎生理和病理情况下生物力学分析中的应用,概述了不同术式、内固定器械对脊柱生物力学的影响,系统的概述了有限元法在腰椎融合方面的研究,包括不同术式对椎间融合器cage的生物力学特点及其置入后对融合节段生物力学的影响,动力性融合、人工椎间盘置入对脊柱生物力学的影响,探讨了应用有限元法分析骨质疏松性腰椎椎体的应力分布、骨折发生机制,分析了肌肉在有限元分析中的作用及意义,展望了有限元法在脊柱生物力学研究中的应用前景.     

垂直载荷下的下腰椎生物力学实验

背景：关节突关节之间的峡部缺损或椎间盘退变是腰椎滑脱的主要原因,而腰椎轴向压力是造成腰椎滑脱的重要因素。目的：观察轴向载荷下L5～S1上关节突与下关节突之间的峡部、椎间盘和髂腰韧带的应变和表面应力情况。设计、时间及地点：单一样本重复测量的生物力学实验,于2005-12/2006-06在河北省生物力学实验室完成。材料：自愿捐献成人男性防腐标本8具,截取L1至髋关节,去除椎旁肌肉,保留所有韧带、椎间盘、关节囊。方法：依次对完整标本、椎间盘切断标本及峡部切断标本,用CSS-44020生物力学实验机以5N/s的速度轴向加载至500N维持60s。主要观察指标：L5峡部贴应变片,用应变仪测量L5～S1峡部、椎间盘和髂腰韧带应变。结果：正常标本轴向压缩实验,70.7%的应力分布于峡部,分布在椎间盘应力为26.5%,而髂腰韧带则有2.8%应力分布。切断椎间盘的标本,峡部应力增加一倍,由正常标本的41.010kPa增加到83.051kPa,而髂腰韧带应力变化不大。切断峡部的标本,峡部应力为0,椎间盘向前的剪切应力由15.381kPa增加至20.643kPa,髂腰韧带的应力也有增加。结论：峡部和椎间盘是防止椎体滑脱的重要结构。在直立状态轴向载荷下峡部作用大于椎间盘。     

肱骨三维有限元分析及其记忆生物力学意义

目的：分析肱骨不同载荷加载下应力分布，探讨其相关的记忆生物力学意义。方法：选择湿肱骨标本行CT成像，大型有限元分析软件ANSYS5．6建立肱骨三维模型以及天鹅记忆加压接骨器(shape memory conector,SMC)固定模型。同时进行相应力学分析。结果：当纵向加压的压力P=300N时，Z方向的正应力为-4．0～-4．5MPa，断面区域的压应力为0～0．2MPa。结论：SMC固定肱骨后三维有限元的分析，可以为肱骨骨折后内固定的力学研究提供新思路。     

Biomechanical evaluation of double bundle augmentation of posterior cruciate ligament using finite element analysis

Background

Posterior cruciate ligament injuries commonly occur during sports activities or motor vehicle accidents. However, there is no previous comparison study of single bundle reconstruction, double bundle reconstruction, and double bundle augmentation with respect to biomechanical characteristics such as stability and ligament stress.

Methods

A three-dimensional finite element model of a lower extremity including femur, tibia, cartilage, meniscus, collagen fibers, and four major ligaments was developed and validated. In addition to the intact, posterior cruciate ligament injured, single bundle reconstruction, double bundle reconstruction, and double bundle augmentation models were developed. Then, the posterior and rotational tibial translations as well as the ligament stresses were predicted for 89 N posterior force and 3 Nm internal torque, respectively, in the normal (no secondary deficiency) and the secondary deficiency cases using finite element analysis.

Findings

The posterior stability and ligament stresses following double bundle augmentation were superior to those of single and double bundle reconstructions, especially after secondary deficiency in the reconstructed grafts, despite little difference in posterior stability between double bundle reconstruction and augmentation in the normal case. Similarly, the double bundle augmentation had the greatest rotational stability while there was little advantage in ligament stress compared to those of the other reconstruction method.

Interpretation

Double bundle augmentation has advantages with regard to posterior and rotational stabilities as well as ligament stress in comparison with other reconstruction methods, especially following secondary deficiencies in the reconstructed grafts.     

Biomechanical model of a high risk impending pathologic fracture of the femur: Lesion creation based on clinically implemented scoring systems

Background

Multiple classifications combine objective and subjective measures to predict fracture risk through a metastatic lesion. In our literature review, no studies have attempted to validate this predicted fracture risk from a biomechanical perspective. The study goal was to evaluate proximal femur strength after creating osteolytic defects. We report a standardized technique to re-create a metastatic lesion.

Methods

Eight femoral matched pairs were procured and a standardized technique was used to create an osteolytic femoral neck defect in one femur with the contralateral specimen serving as the control. Femurs were loaded to failure in a material testing machine at 2 mm/s. Failure load (N) and location of failure were documented. 3D finite element (FE) femur models with and without the lesions were developed to predict von Mises stresses in the femoral neck and compare between the two models.

Findings

Femurs containing the osteolytic defect failed at significantly lower loads than the intact specimens in a reproducible manner (intact: 10.69 kN (3.09 SD); lesion: 5.56 kN (2.03 SD), p < 0.001). The average reduction in failure load was 48%, and the fracture pattern was consistent in all specimens. FE model comparison similarly predicted significantly higher von Mises stress at the lesion.

Interpretation

Our methods and pathologic fracture model represent the clinical parameters of metastatic bone disease and suggest a significant reduction in structural integrity of the lesion-containing femur. Prophylactic surgical fixation may be warranted clinically to reduce the risk of pathologic fracture. Our model technique is reproducible and may be used in future studies.     

Biomechanical response of the passive human knee joint under anterior-posterior forces

Objective. To investigate the detailed biomechanics of the passive tibiofemoral knee joints in full extension under anterior/ posterior drawer forces of up to 400 N.

Design. A nonlinear three-dimensional finite element model of the entire human tibiofemoral joint consisting of bony structures, their articular cartilage layers, menisci, and four principal ligaments was utilized.

Background. The mechanics of the knee joint, specially under drawer forces, have extensively been investigated. Despite all these works, the detailed joint biomechanics, specially the role of boundary conditions, load transmission through menisci/ articular cartilage layers, and coupling between menisci and cruciate ligaments are not yet quantified.

Method. Nonlinear elastostatic analyses were carried out considering the tibiofemoral joint at full extension under anterior and posterior loads of up to 400 N applied either to the tibial or the femoral shaft. Cases with various boundary conditions, cruciate ligament deficiency (anterior or posterior), and total unilateral meniscectomy (medial or lateral) were analysed.

Results. In addition to the total primary anterior-posterior motion of about 9 mm at ± 400 N, significant coupled external tibial rotations of about 9 ° and 10 ° were computed under 400 N femoral posterior and anterior forces, respectively. The response was influenced by the manner of loading and boundary conditions. The anterior cruciate ligament and posterior cruciate ligament were the primary restraints to femoral posterior and anterior drawer forces, respectively. Section of either of these ligaments drastically increased the joint anterior-posterior motion. In the absence of cruciates, the collaterals became the primary restraints in both anterior-posterior forces. In this case, the tibial plateaus, specially the medial one in the anterior cruciate ligament-deficient joint, experienced much larger compressive forces. In addition to causing an increase in joint primary anterior-posterior laxity and anterior cruciate ligament forces, medial meniscectomy substantially increased coupled tibial external rotation, forces on the lateral plateau, and stresses in the articular cartilage of the lateral plateau.     

Biomechanical analysis of two-step traction therapy in the lumbar spine

Traction therapy is one of the most common conservative treatments for low back pain. However, the effects of traction therapy on lumbar spine biomechanics are not well known. We investigated biomechanical effects of two-step traction therapy, which consists of global axial traction and local decompression, on the lumbar spine using a validated three-dimensional finite element model of the lumbar spine. One-third of body weight was applied on the center of the L1 vertebra toward the superior direction for the first axial traction. Anterior translation of the L4 vertebra was considered as the second local decompression. The lordosis angle between the superior planes of the L1 vertebra and sacrum was 44.6° at baseline, 35.2° with global axial traction, and 46.4° with local decompression. The fibers of annulus fibrosus in the posterior region, and intertransverse and posterior longitudinal ligaments experienced stress primarily during global axial traction, these stresses decreased during local decompression. A combination of global axial traction and local decompression would be helpful for reducing tensile stress on the fibers of the annulus fibrosus and ligaments, and intradiscal pressure in traction therapy. This study could be used to develop a safer and more effective type of traction therapy.     

Biomechanical analysis of posterior cruciate ligament retaining high-flexion total knee arthroplasty

Background

High-flexion knee replacements have been developed to accommodate a large range of flexion (>120°) after total knee arthroplasty. Both posterior cruciate ligament retaining and sacrificing high-flexion knee designs have been marketed. The main objective of this study was to evaluate the biomechanical performance of a cruciate-retaining high-flexion knee replacement. Furthermore, the mechanical behaviour of this high-flexion knee replacement was compared to both a cruciate-retaining conventional and a posterior-stabilized high-flexion knee replacement.

Methods

A finite element prosthetic knee model was developed to analyze the mechanical performance of the knee designs evaluated in this study. Polyethylene stresses and the amount of femoral rollback were studied during a squatting movement (flexion ? 150°).

Findings

During deep knee flexion, the cruciate-retaining high-flexion design demonstrated a lower peak tibio-femoral contact stress (74.7 MPa) than the cruciate-retaining conventional design (96.5 MPa). The posterior-stabilized high-flexion design showed the lowest peak tibio-femoral contact stress at the condylar articulation (54.2 MPa), although the post was loaded higher (77.4 MPa). The knee designs analyzed in this study produced a similar amount of femoral rollback during normal knee flexion (flexion ? 120°), whereas the cruciate-retaining designs showed a paradoxical anterior movement of the femoral condyles during high-flexion (flexion > 120°).

Interpretation

The current study demonstrates a cruciate-retaining high-flexion knee replacement produces a lower prosthetic load than a conventional cruciate-retaining replacement during deep knee flexion. Compared to a posterior-stabilized high-flexion design, the cruciate-retaining high-flexion design demonstrated an equivalent prosthetic loading along with an inferior amount of femoral rollback in the high-flexion range. Posterior cruciate ligament balancing is an important surgical aim for high-flexion knee arthroplasty.     

Biomechanical evaluation of a newly devised model for the elongation-type anterior cruciate ligament injury with partial laceration and permanent elongation

Objective. To biomechanically evaluate a newly devised model for the elongation-type anterior cruciate ligament injury with partial laceration and permanent elongation.

Design. Thirty-six rabbits were randomly divided into 4 groups of 9 animals each, after a quantitative injury was given to the right anterior cruciate ligament. The 4 groups were sacrificed at 0, 6, 12, and 24 weeks after surgery, respectively. Biomechanical and histological evaluations were performed at each period.

Background. No adequate animal models have been established for the elongation-type anterior cruciate ligament injury in which the mid-substance is permanently elongated with partial laceration.

Methods. The anteromedial and posterolateral half of the anterior cruciate ligament was transected at the proximal and distal one-third levels, respectively. Then, the anterior cruciate ligament was stretched by applying an anterior drawer force to the tibia at 90 degrees of knee flexion.

Results. The treatment significantly increased the anterior translation of the knee into approximately 150–250% at each period after surgery. The maximum load and the stiffness of the femur–anterior cruciate ligament–tibia complex significantly decreased to 30% or less immediately after surgery, and then gradually increased to 50% at 12 weeks.

Conclusions. In this model, this quantitative treatment created serious injuries with partial laceration and permanent elongation in the anterior cruciate ligament to similar degrees. Also, incomplete tissue healing occurred in the anterior cruciate ligament to similar degrees after the treatment.Relevance

This model will be useful to study new therapeutic methods for the elongation-type anterior cruciate ligament injury.     

Biomechanical comparison of traditional and minimally invasive intradural tumor exposures using finite element analysis

Background

Minimally invasive approaches to intradural pathology have evolved in part in an effort to reduce approach related destabilization of the spine. No biomechanical data exist however evaluating the effects of traditional and minimally invasive exposures.

Methods

A finite element model of the lumbar spine was generated, and a simulated open laminectomy and a modified hemilaminectomy at L4 were performed. Forces were applied to assess changes in flexion, extension, axial rotation, and lateral bending.

Findings

Open laminectomy produced much greater changes in extension, flexion, and axial rotation than the modified hemilaminectomy from the intact. Lateral bending was similarly unaffected for both exposures.

Interpretation

The results suggest that a minimally invasive hemilaminar exposure preserves the structural integrity of the lumbar spine and minimizes alterations to segmental motion postoperatively.     

Comparison of four reconstruction methods after total sacrectomy: A finite element study

Background

After total sacrectomy, it is mandatory to reconstruct the continuity between the lumbar spine and the pelvis. Only few biomechanical analyses exist which compare different reconstructions. Therefore, the aim of this study was to compare the lumbo-pelvic motion and the relative risk of implant breakage for four different reconstructions after total sacrectomy.

Method

Finite element analyses were performed for four general different reconstructions after total sacrectomy: sacral-rod reconstruction, four-rod reconstruction, bilateral fibular flaps reconstruction, and improved compound reconstruction. The rotations between L5 vertebra and ilium, the L5 shift-down displacement, and the maximum von Mises stress in the implants were calculated and evaluated for flexion, extension, lateral bending and axial rotation.

Findings

The decreasing order of the rotations between L5 vertebra and ilium as well as of the L5 shift-down displacement for the studied reconstruction methods was four-rod reconstruction > sacral-rod reconstruction > bilateral fibular flaps reconstruction > improved compound reconstruction. The decreasing order of the maximum von Mises stress in the implants was sacral-rod reconstruction > four-rod reconstruction > bilateral fibular flaps reconstruction > improved compound reconstruction.

Interpretation

From the mechanical point of view, improved compound reconstruction is superior to the other methods studied here as it shows the highest stability and the lowest maximum von Mises stress. However, clinical aspects must also be regarded when choosing a reconstruction method for a specific patient.     

减阻牵张成骨远移尖牙的三维有限元分析

背景：牙周膜牵张成骨通过力作用于牙周膜,带动牙齿移动;牙槽骨牵张成骨是通过整个骨盘的位移,达到牙齿移动的效果。目的：建立基于健康成人的、3种不同状态下的上下颌三维有限元模型,采用三维有限元方法对比研究3种模型在力的加载下应力分布和瞬时位移情况。方法：模型1通过多种软件结合建立常规状态下、模型2建立牙周膜减阻牵张成骨后、模型3建立牙槽骨减阻牵张成骨后移动尖牙的三维有限元模型,分别模拟力的加载。结果与结论：3种模型的最大瞬时位移均发生在尖牙近中牙冠上1/3处,其值模型＜模型3＜模型1;最大等效应力均位于上颌尖牙远中侧牙槽嵴处,其值模型2＜模型1＜模型3。说明牙槽骨和牙周膜减阻牵张成骨均能有效减小牙移动阻力,增加尖牙瞬时位移,且去除尖牙远中骨质效果更为显著。两种方法成功避免了支抗丧失,但尖牙存在远中倾斜趋势,临床工作中应采取相应措施加以控制。     

Biomechanical analysis of total elbow replacement with unlinked iBP prosthesis: an in vitro and finite element analysis

Background

Numerous models of elbow prostheses are being used and can be divided into two categories: one being a semi-constrained, linked type; and the other being non-constrained, unlinked type. Recent reports of National Elbow Arthroplasty Registers reveal no significant differences in the survival rates between linked and unlinked prosthesis brands, and the main cause appointed for revision for both types is loosening. Some previous biomechanical studies confirm the presence of abnormal bone stresses for the linked type, which can be associated with the risk of loosening. However for the unlinked type, biomechanical studies are not available that corroborate a loosening risk. It seems, that issue has not yet been fully answered and requires further analysis.

Methods

Cortex strains adjacent to the elbow joint were measured with strain gauges in synthetic humeri and ulnae, before and after replacement. To assess cancellous bone strains and cement stresses around the implant finite element models validated relative to measured strains were used.

Findings

Bone strains adjacent to the implant tip increased several times in the humerus and ulna. At the epiphyseal regions a generalised cancellous bone strain reduction was observed for both humerus and ulna relatively to the intact bones.

Interpretation

The unlinked elbow prostheses can be associated with the risk of bone fatigue failure by overload, particularly in the ulna, and bone resorption by stress-shielding at the epiphyseal regions. The identical structural behaviour relative to linked prostheses associated with the same loosening risks corroborates the results of recent arthroplasty published register reports.