基于X线片定制股骨柄假体的设计原理及方法

目的 介绍自编的基于X线片设计定制型股骨柄假体程序系统的设计原理及功能模块。方法 利用图像处理方法提取X线片上一些患者股骨解剖特征点（如小粗隆最高点、股骨头中心及转子间窝等）、2个规划的手术截骨位置点（大粗隆侧截骨边界位置点及截骨线最低点位置点）以及一些设计用关键位置点（如假体远端位置、假体颈干连接段最高点位置等）,以此预测患者股骨近端髓腔,并通过输入设计参数值（如颈干角、前倾角、预留的松质骨厚度、假体匹配段截面圆弧半径及假体过渡段高度等）设计出定制型股骨柄假体。并对设计出的定制股骨柄假体进行匹配区域多个截面的二维截面验证和三维的总体验证。结果 根据验证情况,调整设计参数重新生成股骨柄假体模型点云数据,使设计出的股骨柄假体与患者股骨腔相匹配,达到定制型假体设计要求。结论 介绍的程序系统可用于为患者设计定制型股骨柄假体,设计周期较短,成本较低,有利于促进定制型股骨柄假体在临床上的应用,进一步提高患者的生活质量。     

髋关节置换手术定制型髓腔锉的设计与加工

目的 介绍定制型髓腔锉的设计与加工方法。方法 根据相应的定制型股骨柄假体的三维模型设计髓腔锉,在计算机辅助设计（CAD）软件中,通过截除、拉伸及偏移面等操作构建出髓腔锉三维模型。采用计算机辅助制造（CAM）技术加工出定制型髓腔锉。采用本研究的CAD及CAM方法,分别为实验及临床试用设计加工了定制型髓腔锉。结果 实验及临床试用的定制型髓腔锉被用于切削相应的尸体股骨腔及患者股骨腔,植入定制型假体以后,通过分析发现假体与股骨腔匹配较好。结论 采用该研究方法设计加工定制型髓腔锉,将能够提高植入定制型股骨柄假体的成功率,将减少定制型股骨柄假体在患者股骨腔中松动的风险,能够促进股骨松质骨长入假体表面来固定假体。     

CAD/CAM/Robotic集成方法设计与制作生物型股骨柄假体

背景:生物型股骨柄假体无菌松动是全髋关节置换失败的主要因素,减少无菌松动的先决条件是增加股骨柄假体在股骨髓腔中的填充率。目的:得到定制式股骨柄假体在髓腔中的填充率,验证计算机辅助设计/计算机辅助制造/工业机器人加工(CAD/CAM/Robotic)集成方法和机器人磨削的有效性。方法:利用CT数据重建股骨髓腔三维模型,在此三维模型基础上设计股骨柄假体的柄体,依据标准直柄股骨柄假体近端模型设计股骨柄假体的其余部分。将设计的股骨柄假体模型导入CAD/CAM/Robotic集成系统生成机器人磨削轨迹,利用该轨迹对股骨柄假体进行磨削加工。将加工好的股骨柄假体与股骨髓腔匹配,分析股骨柄假体在髓腔中的填充率。结果与结论:实验结果表明,定制式股骨柄假体在髓腔中有良好的填充率,髓腔的解剖结构可以阻止股骨柄假体的扭转,获得股骨柄假体在髓腔中的稳定固定。     

基于X线片与模板的股骨柄假体生物力学评价

目的对4组与股骨匹配的股骨柄假体进行生物力学的评价,寻找与正常股骨上力学分布最为接近的股骨柄假体。方法在Matlab中导入股骨近端X线正位片及4组股骨-股骨柄假体模板的bmp格式的图像文件,分别提取股骨、带假体模板的股骨二维轮廓数据,利用ANSYS软件建立股骨、股骨-股骨柄几何模型及二维非线性有限元模型,负荷加载后对股骨近端的应力分布进行分析、比较。结果假体置入后股骨上的力学分布与正常股骨有较大的差异,但在4组股骨柄假体中,终有一种假体其在股骨上应力大小及分布情况与正常股骨最为接近,而这种假体相对于此股骨来说其生物力学性能为最优。结论通过基于X线片与模板的股骨柄假体生物力学的分析比较,可对股骨柄假体的生物力学性能作出评价,为假体的优化选择提供依据。     

标准截面形状定制型股骨柄假体设计

目的 介绍一种标准截面形状定制型股骨柄假体结构以及自行开发的设计方法。方法首先利用DICOM格式的患者股骨CT图像,重建患者股骨近端模型;根据重建出的患者股骨近端模型构建股骨柄假体匹配段矩形的截面边界,并在矩形截面边界内用简单的线条初步构建出假体的截面轮廓曲线;利用股骨近端模型对初步设计出的股骨柄假体进行验证,并通过调整设计参数使最终设计出的个性化股骨柄假体与患者股骨髓腔相匹配。结果 定制型人工髋关节股骨柄假体采用标准截面形状,便于快速设计出个性化假体,而且设计操作简单。参数化程序设计大大降低了个性化股骨柄假体的设计工作量。结论 标准截面形状定制型股骨柄假体的设计将有助于提高定制型人工髋关节置换手术的成功率,促进定制型股骨柄假体在临床上的应用,进一步提高患者的生活质量。     

扭转力传递的非骨水泥髋关节假体设计、制作及实验分析

背景:人体股骨髓腔具有扭转的解剖结构,如果股骨髓腔的扭转结构被复制到假体的柄体上,当假体插入髓腔并在假体上加载力时,假体将加载的力转换成股骨髓腔对柄体的扭转力并将该力传递到股骨近端。目的:优化股骨近端的力传递,避免假体近端应力遮挡。方法:利用人股骨标本的CT图片重建股骨髓腔的3D模型,将该3D模型作为柄体的设计模型。将定制式柄体模型与标准假体的近端模型拼合,形成定制式假体。采用机器人磨削技术制作定制式假体,并将定制式假体与标本股骨髓腔匹配。利用有限元仿真和实验方法分析假体上加载的力与假体近端扭转微动的关系。结果与结论:仿真和实验结果表明,股骨髓腔与柄体匹配的扭转结构,可有效地将假体上加载力以扭转力的形式传递到股骨近端,假体近端的扭转微动与柄体的微动相关,而柄体的微动可通过改变柄体与髓腔的匹配区大小得到控制。     

基于X线片三维重建股骨近端髓腔

本文提出利用X线片三维重建患者股骨近端髓腔,为患者设计定制型股骨柄.并根据80根股骨样本CT图像,构建了一个中国人股骨近端平均截面数据库.数据库的构建使利用X线片重建患者股骨近端髓腔成为可能.基于X线片三维重建股骨近端髓腔的软件已被开发出来,其中包括提取患者股骨腔数据以及构建出患者股骨近端髓腔数据库等.利用这个软件重建患者股骨近端髓腔较为方便,费时较少,同时可解决一些临床上无法用CT片重建患者股骨近端髓腔的问题.     

双锥面高抛光股骨柄治疗老年股骨颈骨折的临床应用

目的探讨抛光型股骨柄假体在老年股骨颈骨折假体置换中的应用。方法使用双锥面高抛光股骨柄假体固定治疗老年股骨颈骨折患者63例,股骨假体固定采用第二代骨水泥技术,分析其临床效果。结果术后随访3个月,根据髋关节X线片。所有患者均无髋关节脱位发生。双下肢长度差异为（3．1±1．2）mm。术后3个月髋关节Harris评分为（86±10）分。结论抛光型股骨柄假体通过其在假体设计和假体固定上的改进,可以比较好地解决老年人股骨颈骨折假体置换中所遇到的假体固定闲难等问题。     

国人生物固定型股骨柄假体几何设计系统方法

生物固定型股骨柄假体要达到取代病变骨组织、完成被替代部分的动力学功能的目的,就必须要求假体结构上满足两个特征,即:与股骨髓腔良好的结构相容性(假体与股骨良好的匹配、稳定密合)和与骨组织的生物力学相容性.目前,国产股骨柄基本上以仿制欧美柄型为主,因此,国人与西方人种之间股骨的解剖学统计差异直接影响到股骨柄的临床使用效果.本文从国人股骨几何解剖特征入手,详细阐述股骨柄分型的具体方法、股骨柄几何形状确定的一般原则,并运用CAD/CAE虚拟设计与分析系统以及生物力学试验等必要的评价来说明股骨柄假体几何设计的系统思路.     

Tri-Lock骨保留型股骨柄假体的设计特征与临床应用

背景：新一代Tri-Lock BPS型股骨柄假体在原有设计基础上得到进一步改进,目前尚少有报道总结其设计特征及手术技巧。 目的：总结Tri-Lock BPS型股骨柄假体的设计特征及其在全髋关节置换中的应用。 方法：选择Tri-Lock BPS柄行全髋关节置换的患者9例(10髋),其中股骨头坏死8例,创伤性关节炎1例。置换前后的髋关节功能和置换后股骨柄假体的生物学固定分别按Harris标准和Engh标准评定,置换后股骨柄假体的初始固定质量按Healy标准评定,分析透亮线、骨溶解的发生率,分别按Delee和Gruen分区描述髋臼和股骨侧的骨长入,按D’Antonio法测量股骨柄假体的下沉,股区痛则采用目测类比评分10分制评定。 结果与结论：10髋置换后X射线片显示股骨柄假体的初始固定均符合优良标准。凡手术满3个月的患者,髋关节功能(Harris评分)均可恢复至平均92分(85~96分),无主诉存在股区痛,无X射线显示的假体松动征。结果证实,Tri-Lock BPS型假体设计更符合人体解剖特征,髋关节功能恢复快,骨量保留多等优点。     

Investigation of stress shielding around the Stryker Omnifit and Exeter periprosthetic hip implants using an irreversible thermodynamic-based model

This study investigates stress shielding by predicting bone density around two different implants following total hip arthroplasty using a new thermodynamic-based model for bone remodeling. This model is based on chemical kinetics and irreversible thermodynamics in which bone is treated as a self-organizing system capable of exchanging matter, energy, and entropy with its surroundings. Unlike the previous works in which mechanical loading is regarded as the only stimulus for bone remodeling, this model establishes a coupling between mechanical loading and the chemical reactions involved in the process of bone remodeling. This model is incorporated into the finite element software ANSYS by means of a macro to investigate stress shielding around two different implants: Stryker Omnifit and Exeter periprosthetic hip stems. The results of the simulation showing bone density reductions of 17% in Gruen zone 1 and 27% in Gruen zones 7 around the Omnifit hip stem agree well with dual-energy X-ray absorptiometry (DEXA) measurements reported in the literature. On the other hand, the Exeter implant is found to result in more severe resorption in the proximal femur. This is consistent with clinical studies, which report a higher survivorship rate for HA-coated Omnifit hip stems.     

Design and manufacturing of customised femoral stems for the Indian population using rapid manufacturing: a finite element approach

Joint replacement surgeries in India primarily involve the use of conventional implants, also referred to as 'standard implants'. There has been a little awareness about the possibility of using customised implants for such surgeries. Although standard implants from various biomedical companies are easily available in the Indian market, they are expensive and rarely conform to patient's anatomy. Studies in the past have shown that there are anatomical variations in the hip joint for different ethnic backgrounds and geographical locations. This article evaluates the feasibility of using custom-manufactured hip implants and presents a comparison between the former and standard implant from stress reduction point of view. Two CAD models of femoral stems - one from standard sized hip implant available in the market and other from customised hip implant designed as per parameters from a radiograph (specific to the patient's anatomy) - are used for evaluation. Finite element analysis was carried out for a double-legged stance. The comparative study indicated lesser stresses in head and neck region of the customised femoral stems than the standard implant. The study suggests design feasibility of customised implants for the Indian population owing to reduction in stresses in the implant.     

Design and manufacturing of customised femoral stems for the Indian population using rapid manufacturing: a finite element approach

Joint replacement surgeries in India primarily involve the use of conventional implants, also referred to as ‘standard implants’. There has been a little awareness about the possibility of using customised implants for such surgeries. Although standard implants from various biomedical companies are easily available in the Indian market, they are expensive and rarely conform to patient’s anatomy. Studies in the past have shown that there are anatomical variations in the hip joint for different ethnic backgrounds and geographical locations.

This article evaluates the feasibility of using custom-manufactured hip implants and presents a comparison between the former and standard implant from stress reduction point of view.

Two CAD models of femoral stems – one from standard sized hip implant available in the market and other from customised hip implant designed as per parameters from a radiograph (specific to the patient’s anatomy) – are used for evaluation. Finite element analysis was carried out for a double-legged stance.

The comparative study indicated lesser stresses in head and neck region of the customised femoral stems than the standard implant.

The study suggests design feasibility of customised implants for the Indian population owing to reduction in stresses in the implant.     

Analysis of titanium induced CT artifacts in the development of biomechanical finite element models

X-ray computerized tomography (CT) is capable of providing detailed information about the geometry and mineral density of skeletal structures. Such accurate data are of great interest in studying the effects of orthopaedic implants on bone adaptive behaviour in vivo. Metallic implants, however, generate artifacts, typically seen as starburst streaking. These artifacts can degrade the capabilities of CT images to provide accurate information about the geometry and mineral density of bone structures. The aim of this work was to investigate the possibility of developing finite element models (FEM) of the human femur after hip joint arthroplasty using CT images acquired directly after surgery. The capability of modern CT scanners to accurately reconstruct the cross-section geometry of titanium alloy hip joint prosthetic stems was primarily investigated. A new measuring procedure dealing with the geometry of real stems was developed and its accuracy assessed. Secondly, the artifacts generated by a prosthetic stem on the radiological density of the bone were analysed, and their effects on the assessment of FEM material properties were evaluated. Results showed that CT images provide accurate information on metal stem geometry. An average error of 0.45 mm was estimated in the reconstruction of stem cross-section geometry. Concerning bone density estimation around the implant, it was observed that the effect of metal artifacts on tissue density becomes zero at a distance of 2 mm from the implant.     

一种自动优选标准型股骨柄的方法

髋关节置换手术中采用标准型假体时,术前只能大致选取假体,术中还要预备多个假体,往往手术时间增长。为了解决这一问题,本文提出一种利用计算机优选标准型髋关节假体的方法。从X线片中获取患者股骨解剖数据。利用这些解剖数据和股骨近端截面平均数据库三维重建患者股骨近端,重建出的股骨近端模型使优选标准假体成为可能。理论分析表明,该方法切实可行。     

Stiffness and strength tailoring of a hip prosthesis made of advanced composite materials

This work is concerned with the design of hip prostheses using advanced fiber reinforced composite materials. The major focus of the study is to evaluate how the stiffness and strength of composite hip prostheses can be affected by variations in ply orientation and stacking sequence for a selected manufacturing method. This investigation involved both analytical and experimental work. An analytical model was developed which consists of a stress analysis and a failure analysis. A finite element program was developed during the course of the investigation for analyzing stresses, strains, and deformations of composite stems with a simplified configuration. Failure and mode of failure were predicted by appropriately selected failure criteria. Experiments were also performed on T300/976 graphite/epoxy composites to verify the analysis and the computer calculations. Both testing and analysis accounted for the various combinations of in-plane and out-of-plane (torsion) loading that can act on the prosthetic hip. Simplified composite stems with a 120 layer thickness were fabricated and tested. An excellent agreement was found between the measured strain data and the numerical calculations. Using the program, parametric studies were performed. It was found that an optimal design of hip stems can be achieved by using advanced fiber-reinforced composite materials, but great care must be taken when selecting the appropriate ply orientation and stacking sequence for a chosen fabrication method.     

Stress and strain distribution in the intact canine femur: finite element analysis

Information regarding the stresses and strains in the canine femur during various activities is important for veterinary orthopaedic surgeons, engineers designing implants for dogs, and researchers of human orthopaedics who use dogs as models. Nevertheless, such information is currently unavailable. The objective of this study is to determine the stress and strain distribution in the canine femur during mid-stance, for two loading scenarios. Three-dimensional finite element models of the canine femur were created. Two loading cases were considered: the hip joint reaction force alone, and the hip joint reaction force with all muscle forces acting on the femur. Force directions and magnitudes were obtained from the literature. Analyses were performed with NASTRAN for Windows software. When all muscle forces were considered, stresses and strains were significantly reduced, peak compressive stresses were found to occur in the medial diaphysis, and peak tensile stresses occurred in the lateral diaphysis. While the canine femur seems to be loaded primarily in bending when only the hip joint reaction force is considered, the bending moment is significantly decreased when all muscle forces are considered as well. Further in vivo and in vitro experiments are needed to validate the results of the calculations described in this paper. It is expected that future studies will be carried out, in which the stress and strain distributions in femora with different types of implants and stems will be compared to those in the normal femur.     

A preliminary biomechanical study of a novel carbon-fibre hip implant versus standard metallic hip implants

Total hip arthroplasty is a widespread surgical approach for treating severe osteoarthritis of the human hip. Aseptic loosening of standard metallic hip implants due to stress shielding and bone loss has motivated the development of new materials for hip prostheses. Numerically, a three-dimensional finite element (FE) model that mimicked hip implants was used to compare a new hip stem to two commercially available implants. The hip implants simulated were a novel CF/PA12 carbon-fibre polyamide-based composite hip stem, the Exeter hip stem (Stryker, Mahwah, NJ, USA), and the Omnifit Eon (Stryker, Mahwah, NJ, USA). A virtual axial load of 3 kN was applied to the FE model. Strain and stress distributions were computed. Experimentally, the three hip stems had their distal portions rigidly mounted and had strain gauges placed along the surface at 3 medial and 3 lateral locations. Axial loads of 3 kN were applied. Measurements of axial stiffness and strain were taken and compared to FE analysis. The overall linear correlation between FE model versus experimental strains showed reasonable results for the lines-of-best-fit for the Composite (Pearson R(2)=0.69, slope=0.82), Exeter (Pearson R(2)=0.78, slope=0.59), and Omnifit (Pearson R(2)=0.66, slope=0.45), with some divergence for the most distal strain locations. From FE analysis, the von Mises stress range for the Composite stem was much lower than that in the Omnifit and Exeter implants by 200% and 45%, respectively. The preliminary experiments showed that the Composite stem stiffness (1982 N/mm) was lower than the metallic hip stem stiffnesses (Exeter, 2460 N/mm; Omnifit, 2543 N/mm). This is the first assessment of stress, strain, and stiffness of the CF/PA12 carbon-fibre hip stem compared to standard commercially-available devices.