大腿残肢步态过程的非线性有限元分析

目的利用三维有限元分析方法研究大腿截肢患者在行走过程中3个不同时相下残肢的生物力学特性,为建立完整的大腿接受腔测量、设计与评估系统提供研究基础。方法首先根据CT图像三维重建大腿截肢患者的骨骼、肌肉软组织和接受腔的三维几何模型;定义软组织为超弹性和线弹性材料属性,并相应建立两个有限元仿真模型;定义残端与接受腔之间的接触关系,约束残肢近端,对模型的远端施加膝关节载荷,模拟步态周期中足跟着地时期、站立相中期、脚尖离地3个时相下大腿残肢-接受腔系统所受载荷;计算分析接触界面上的应力,并对比分析超弹性和线弹性软组织力学特性对接触界面力学行为特性的影响。结果无论线弹性还是超弹性模型,3个时相下大腿残肢-接受腔界面的最大接触压力均在残肢末端达到最大值。超弹性模型3个时相下接触压力峰值分别为55.80、47.63和50.44 kPa;而线弹性模型接触压力的最大值都增加2倍以上,其值分别为149.86、118.55和139.68 kPa。同时通过分析接触面间的径向剪切应力和轴向剪切应力发现,3个时相下接触界面间的应力在残肢末端较集中,在足跟着地到脚尖离地过程中,有部分力通过接受腔后侧缘传递转向接受腔前缘传递。结论不同时相下残肢与接受腔接触界面的压力和剪切应力分布情况不同,在设计接受腔时需要充分考虑其受力特点。     

预应力下大腿残肢站立中期时相的有限元分析

目的研究大腿截肢患者在行走过程中站立中期时相下残肢的受力情况,为建立完整的大腿接受腔测量与评估系统提供基础。方法首先根据计算机断层扫描图像三维重建大腿截肢患者的骨骼、肌肉软组织和接受腔的三维模型,考虑步行中关节角度变化进行组装。然后,建立模拟步态周期中站立中期时相受力的有限元模型,对模型进行预应力影响下非线性大变形有限元分析。结果当考虑了步行中关节角度变化和预应力的影响以后,计算所得的接触法向界面压力值最大值均位于残肢的末端部位,为257.66 kPa,与实际测量患者步行中站立中期时相下最大应力258.90 kPa符合较好。结论考虑关节角度变化、预应力和摩擦的三维模型能够更为有效地模拟患者在步行中的受力情况。     

髋离断假肢接受腔-残肢站立期静态有限元分析

目的 利用有限元分析方法研究髋残肢在支撑阶段与髋离断假肢接受腔生机界面的力学特性,为优化、设计髋接受腔结构提供理论依据,为评估髋接受腔舒适度提供研究基础。方法 根据患者残肢CT扫描模型,采用逆向建模的方式,三维重建骨骼、软组织以及接受腔模型。利用有限元方法 研究站立状态下残肢-髋接受腔界面正应力及剪切应力的分布情况,并通过设计压力采集模块系统进行验证。结果 残肢与髋接受腔界面应力主要分布在腰部和残肢底部,位于残肢其余区域的界面应力则分布较为均匀。有限元计算结果和压力采集模块系统测量结果 有较好的符合。结论 为能较好实现髋接受腔功能传递性和安全舒适性,需要充分考虑残肢腰部和底部的受力以及残肢与接受腔的配合度。     

基于便携式步态测试仪的不同接受腔单侧大腿截肢者行走特点研究

目的 探讨穿戴坐骨包容接受腔与四边形接受腔大腿假肢的单侧大腿截肢者在日常生活中行走时的步态差异，为临床制定大腿假肢使用处方提供指导。方法 选取7位大腿截肢患者作为试验组，为患者分别适配四边形和坐骨包容接受腔大腿假肢。同时选取7位年龄、性别、身高和体质量相匹配的健康受试者作为对照组。所有受试者以舒适的步速在室外平路上行走240 m,应用便携式步态测试仪(intelligent device for energy expenditure and activity, IDEEA)采集步态数据，包括7个时空参数和4个加速度参数，通过IBM SPSS Statistics 23对数据进行处理。对比患者穿戴两种假肢与健康受试者之间、患者分别穿戴同种假肢时患侧与健侧之间、患者穿戴两种假肢时患侧之间、健侧之间的参数差异。结果 与健康受试者相比，患者分别穿戴两种假肢行走时，两种假肢健侧和患侧的站立时间和步态周期增大(P<0.05),步速、步频、跨步长减小(P<0.05);两种假肢患侧的摆动时间延长(P<0.05),地面冲击和足落地控制减小(P<0.05);四边形接受腔假肢双侧和坐...     

小腿假肢接受腔计算机三维模型的构建

背景:假肢接受腔作为截肢患者肢体残端和假肢之间载荷传递的惟一通道,是影响假肢适配性的重要部件。假肢接受腔的三维建模是接受腔实用性的关键,可以在测量时得到更准确的数据。目的:建立假肢接受腔计算机三维模型,为接受腔有限元分析提供数据基础,为加工制造接受腔提供可靠的参数。方法:选择1例32岁右侧小腿截肢的男性患者,髋关节各肌力正常,髋18°屈曲挛缩,其他关节活动度正常。根据患者CT和核磁共振扫描图像,采用Mimics10.0软件处理数据,构建假肢接受腔计算机三维模型,准确模拟残肢和接受腔的结构。结果与结论:建立的小腿残肢和接受腔计算机三维模型比较准确地反映了接受腔和残肢的几何特征和外部轮廓。假肢接受腔三维模型的建立有助于提高制作的成功率,从根本上改变传统依靠手工设计、测量、取型、修型等落后的生产模式。     

小腿残肢与接受腔的非线性有限元分析

目的研究残肢与接受腔生机界面力学特性及残端应力情况,为设计和优化小腿接受腔结构、提高其佩戴舒适性提供理论依据。方法针对释压稳定(compression-release stabilization,CRS)接受腔,采用有限元软件ABAQUS分析残肢与CRS接受腔界面应力分布情况,软组织采用非线性超弹性材料Mooney-Rivlin本构模型,得到静止站立中期残肢与CRS接受腔接触界面正应力和剪切应力分布情况,并相应建立髌韧带承重(patellar tendon bearing,PTB)小腿接受腔三维有限元模型,将两者结果进行比较。结果残肢与CRS接受腔界面应力主要分布在胫骨内侧、胫骨外侧和后肌群等承重区,与PTB接受腔模型主要受力区域相似,CRS接受腔残肢末端平均界面应力较PTB接受腔高19 kPa。结论 CRS接受腔具有较好的透气性且应力分布较合理,接受腔形状的不同可改变残肢与接受腔生机界面应力分布,优化其设计有助于提高假肢穿戴舒适性。     

假肢接受腔设计及界面应力的有限元分析

文题释义： Mimics 10.0软件：作为专业的三维图像处理软件,能将CT图像转化为残肢的三维模型,计算机生成的三维模型与患者的实际尺寸基本无差别。 有限元分析：是利用数学近似的方法对真实物理系统(几何和载荷工况)进行模拟的方法。 背景：残肢-接受腔界面生物力学特性不仅对假肢的适配性有着直接影响,而且也是对接受腔结构进行优化设计的基础。将数字化设计技术与康复工程结合在一起,将有效地提髙假肢接受腔的制作效率和质量。 目的：采用逆正向结合的建模方法,对小腿截肢患者进行定制式的接受腔模型设计,评估残肢与接受腔的界面应力,对接受腔进行迭代设计,优化后的模型采用3D打印制作,以改善传统手工制作接受腔方法。 方法：选择2例内蒙古自治区荣誉军人肢残康复中心的小腿截肢志愿者,根据患者残肢的CT扫描图像,采用Mimics进行图像处理,然后经过Geomagic和UG逆向得到残肢的几何模型。通过使用计算机辅助设计软件Fusion360,根据残肢各个部位的组织结构不同的承受能力作为修型原理对接受腔进行正向建模设计。选用Mooney-Revlin超弹性模型定义软组织的材料特性,对残肢-接受腔界面应力进行有限元分析,并根据结果反馈指导对接受腔进行迭代设计,对再次修型后的接受腔模型进行评估。3D打印制作出接受腔,并进行实验测量。 结果与结论：①对迭代设计后的接受腔与残肢界面的应力进行分析,得到残肢各区域的应力值均低于疼痛阈值,符合设计标准,能较好实现功能传递性和安全舒适性;②此2例患者穿戴3D打印制作的接受腔适配性、稳定性良好,步行对称性相比手工制作接受腔均有显著改善,满足残肢生物力学要求;③试验建立了完整的假肢接受腔的设计、评估及制造系统。 ORCID: 0000-0002-8570-9689(王晓辉) 中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程     

下肢假肢接受腔对残肢肌肉萎缩影响的数值研究

下肢截肢后残肢的肌肉萎缩对患者康复十分不利。为探明残肢肌肉萎缩的生物力学机制,本研究利用大腿截肢患者残肢的磁共振断层影像(MRI),建立了包含肌肉、骨骼以及主要血管的残肢有限元模型,研究分析了下肢假肢接受腔对残肢软组织及血管的生物力学影响。结果发现,旋股外侧动脉降支因挤压而发生的狭窄最为严重,股深动脉的狭窄则相对较小;旋股外侧静脉的降支、股静脉、股深静脉狭窄的程度依次降低,大隐静脉的狭窄程度较为严重。前侧肌群中应力应变最高;下侧肌群在股骨的末端处出现应力集中,并且其他生物力学指标在下侧区域中也相对较高。本研究在一定程度上揭示了接受腔对血管的挤压是导致肌肉萎缩的重要原因,这为进一步研究残肢肌肉的萎缩机制和采取有效的预防措施提供了理论参考。     

惯性载荷对截肢患者残肢/接受腔界面应力的影响研究

接受腔/残肢界面压力分布特征是假肢优化设计的基础,传统的有限元模型只限于静态分析,不符合实际情况。本文以小腿截肢患者为研究对象,建立了三维非线性有限元模型,给出了一个步态周期内残肢界面压力的变化规律,并对惯性载荷的影响进行了定量比较。结果表明:界面压力主要分布在髌韧带、胫骨内外侧和窝区,一个平地正常速度行走的步态周期内,站立相压力变化呈双峰蝶形,惯性载荷引起的平均压力幅值变化为8.4%;而在摆动相压力幅值变化高达20.1%,并且变化规律相反。行走过程中惯性载荷的影响不能忽略。     

基于机器视觉的残肢表面形状测量

传统的假肢阳模制造过程完全以手工操作为基础，不能满足需要。本文把微型计算机作为平台，利用计算机视觉对截肢者残肢的表面形状进行测量。初步测量结果表明这种方法具有不接触、速度快、精度较高、全自动的特点。从而为假肢接受腔的进一步计算机辅助设计和制造打下基础     

Development of a non-linear finite element modelling of the below-knee prosthetic socket interface

A non-linear finite element model has been established to predict the pressure and shear stress distribution at the limb-socket interface in below-knee amputees with consideration of the skin-liner interface friction and slip. In this model, the limb tissue and socket liner were respectively meshed into 954 and 450 three-dimensional eight-node isoparametric brick elements, based on measurements of an individual's amputated limb surface; the bone was meshed into three-dimensional six-node triangular prism elements, based on radiographic measurements of the individual's residual limb. The socket shell was assumed to be a rigid boundary. An important feature of this model is the use of 450 interface elements (ABAQUS INTER4) which mimic the interface friction condition. The results indicate that a maximum pressure of 226 kPa, shear stress of 53 kPa and less than 4 mm slip exist at the skin-liner interface when the full body weight of 800 N is applied to the limb. The results also show that the coefficient of friction is a very sensitive parameter in determining the interface pressures, shear stresses and slip. With the growth of coefficient of friction, the shear stresses will increase, while the pressure and slip will decrease.     

The quasi-static response of compliant prosthetic sockets for transtibial amputees using finite element methods

The finite element method (FEM) is a very powerful tool for analyzing the behavior of structures, especially when the geometry and mechanics are too complex to be modeled with analytical methods. This study focuses on the analysis of patellar tendon bearing prosthetic sockets with integrated compliant features designed to relieve contact pressure between the residual limb and socket. We developed a FEM model composed of a socket, liner and residual limb and analyzed it under quasi-static loading conditions derived from experimentally measured ground reaction forces. The geometry of the residual limb, liner and socket were acquired from computed tomography (CT) data of a transtibial amputee. Three different compliant designs were analyzed using FEM to assess the structural integrity of the sockets and their ability to relieve local pressure at the fibula head during normal walking. The compliant features consisted of thin-wall sections and two variations of spiral slots integrated within the socket wall. One version of the spiral slots produced the largest pressure relief, with an average reduction in local interface pressure during single-leg stance (20-80% of the stance phase) from 172 to 66.4 kPa or 65.8% compared to a baseline socket with no compliant features. These results suggest that the integration of local compliant features is an effective method to reduce local contact pressure and improve the functional performance of prosthetic sockets.     

Comparison of computational analysis with clinical measurement of stresses on below-knee residual limb in a prosthetic socket

Interface pressures and shear stresses between a below-knee residual limb and prosthetic socket predicted using finite element analyses were compared with experimental measurements. A three-dimensional nonlinear finite element model, based on actual residual geometry and incorporating PTB socket rectification and interfacial friction/slip conditions, was developed to predict the stress distribution. A system for measuring pressures and bi-axial shear stresses was used to measure the stresses in the PTB socket of a trans-tibial amputee. The FE-predicted results indicated that the peak pressure of 226 kPa occurred at the patellar tendon area and the peak shear stress of 50 kPa at the anterolateral tibia area. Quantitatively, FE-predicted pressures were 11%, on average, lower than those measured by triaxial transducers placed at all the measurement sites. Because friction/slip conditions between the residual limb and socket liner were taken into consideration by using interface elements in the FE model, the directions and magnitudes of shear stresses match well between the FE prediction and clinical measurements. The results suggest that the nonlinear mechanical properties of soft tissues and dynamic effects during gait should be addressed in future work.     

A finite element model to assess transtibial prosthetic sockets with elastomeric liners

People with transtibial amputation often experience skin breakdown due to the pressures and shear stresses that occur at the limb-socket interface. The purpose of this research was to create a transtibial finite element model (FEM) of a contemporary prosthesis that included complete socket geometry, two frictional interactions (limb-liner and liner-socket), and an elastomeric liner. Magnetic resonance imaging scans from three people with characteristic transtibial limb shapes (i.e., short-conical, long-conical, and cylindrical) were acquired and used to develop the models. Each model was evaluated with two loading profiles to identify locations of focused stresses during stance phase. The models identified five locations on the participants’ residual limbs where peak stresses matched locations of mechanically induced skin issues they experienced in the 9 months prior to being scanned. The peak contact pressure across all simulations was 98 kPa and the maximum resultant shear stress was 50 kPa, showing reasonable agreement with interface stress measurements reported in the literature. Future research could take advantage of the developed FEM to assess the influence of changes in limb volume or liner material properties on interface stress distributions.

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Graphical abstract Residual limb finite element model. Left: model components. Right: interface pressures during stance phase

     

Effects of liner stiffness for trans-tibial prosthesis: a finite element contact model

The socket liner plays a crucial role in redistribution of the interface stresses between the stump and the socket, so that the peak interface stress could be reduced. However, how the peak stress is affected by various liner stiffnesses is still unknown, especially when the phenomenon of the stump slide within the socket is considered. This study employed nonlinear contact finite element analyses to study the biomechanical reaction of the stump sliding with particular attention to the liner stiffness effects of the trans-tibial prosthesis. To validate the finite element outcomes, experimental measurements of the interface stresses and sliding distance were further executed. The results showed that the biomechanical response of the stump sliding are highly nonlinear. With a less stiff liner, the slide distance of the stump would increase with a larger contact area. However, this increase in the contact area would not ensure a reduction in the peak interface stress and this is due to the combined effects of the non-uniform shape of the socket and the various sliding distances generated by the different liner stiffnesses.     

Finite element modeling of the contact interface between trans-tibial residual limb and prosthetic socket

Finite element method has been identified as a useful tool to understand the load transfer mechanics between a residual limb and its prosthetic socket. This paper proposed a new practical approach in modeling the contact interface with consideration of the friction/slip conditions and pre-stresses applied on the limb within a rectified socket. The residual limb and socket were modeled as two separate structures and their interactions were simulated using automated contact methods. Some regions of the limb penetrated into the socket because of socket modification. In the first step of the simulation, the penetrated limb surface was moved onto the inner surface of the socket and the pre-stresses were predicted. In the subsequent loading step, pre-stresses were kept and loadings were applied at the knee joint to simulate the loading during the stance phase of gait. Comparisons were made between the model using the proposed approach and the model having an assumption that the shape of the limb and the socket were the same which ignored pre-stress. It was found that peak normal and shear stresses over the regions where socket undercuts were made reduced and the stress values over other regions raised in the model having the simplifying assumption.     

Comparison of adaptive neuro-fuzzy inference system (ANFIS) and Gaussian processes for machine learning (GPML) algorithms for the prediction of skin temperature in lower limb prostheses

Monitoring of the interface temperature at skin level in lower-limb prosthesis is notoriously complicated. This is due to the flexible nature of the interface liners used impeding the required consistent positioning of the temperature sensors during donning and doffing. Predicting the in-socket residual limb temperature by monitoring the temperature between socket and liner rather than skin and liner could be an important step in alleviating complaints on increased temperature and perspiration in prosthetic sockets. In this work, we propose to implement an adaptive neuro fuzzy inference strategy (ANFIS) to predict the in-socket residual limb temperature. ANFIS belongs to the family of fused neuro fuzzy system in which the fuzzy system is incorporated in a framework which is adaptive in nature. The proposed method is compared to our earlier work using Gaussian processes for machine learning. By comparing the predicted and actual data, results indicate that both the modeling techniques have comparable performance metrics and can be efficiently used for non-invasive temperature monitoring.     

小腿假肢接受腔的三维有限元分析

通过建立三维非线性有限元模型来分析小腿假肢接受腔与残肢之间的载荷分布。此模型基于残肢,骨头,软套和接受腔的三维几何形状,考虑界面摩擦滑动条件和软组织的大变形等非线性因素。模型可以预测不同外载下残肢和接受腔之间的压力,剪切力和相对滑动情况。并分析了不同的接受腔形状对载荷分布的影响。