Finite element analysis of femoral components paper III – hip joints

Finite element analysis of the hip implant is conducted in this paper for representative femoral cross-section geometries and development of stress in the presence of bone cement is elucidated. Differences in cement stresses generated by varying implant cross-sections were compared with conventional features derived from representative implants. The analysis was performed under idealized implant assemblies by constraining the implant movement in the assembly. The cross-sections and implant geometries used are generic and intended to be representative of available geometries. This paper is a part of student research projects, prepared from a series of activities in biomedical implant research currently underway at Ohio Northern and Arkansas Tech Universities.     

Motion study of the hip joint in extreme postures

Many causes can be at the origin of hip osteoarthritis (e.g., cam/pincer impingements), but the exact pathogenesis for idiopathic osteoarthritis has not yet been clearly delineated. The aim of the present work is to analyze the consequences of repetitive extreme hip motion on the labrum cartilage. Our hypothesis is that extreme movements can induce excessive labral deformations and lead to early arthritis. To verify this hypothesis, an optical motion capture system is used to estimate the kinematics of patient-specific hip joint, while soft tissue artifacts are reduced with an effective correction method. Subsequently, a physical simulation system is used during motion to compute accurate labral deformations and to assess the global pressure of the labrum, as well as any local pressure excess that may be physiologically damageable. Results show that peak contact pressures occur at extreme hip flexion/abduction and that the pressure distribution corresponds with radiologically observed damage zones in the labrum.

应用陶瓷型人工髋关节治疗中青年髋关节伤病

目的比较陶瓷型与生物固定型人工髋关节治疗中青年髋关节创病的中短期应用结果，以探讨陶瓷型人工髋关节假体的临床应用价值。方法对人工全髋关节置换术132例164髋进行随访，其中生物固定型超高分子聚乙烯-钻铬钼合金全髋假体97例99髋，陶瓷-陶瓷非骨水泥型假体35例35髋，应用Harris评分进行功能评价，应用Gruen股骨分区与髋臼Delee—charnly分区方法进行影像学评价。结果Harris功能评分两组患者之间未见显著性差异，但是影象学上，超高分子聚乙烯-钻铬钼合金假体的松动范围或程度要大于陶瓷假体。结论对于年轻患者，陶瓷-陶瓷假体中短期效果良好，影象学松动率明显低于超高分子聚乙烯-钻铬钼合金假体。但是由于其价格昂贵，使用范围受到限制，而且远期结果有待于临床观察。     

An investigation on the dosimetric impact of hip prosthesis in radiotherapy

The objectives of this study are to evaluate the dosimetric impact of hip prosthesis using ELEKTA linac X-rays and compare the dose perturbations of metallic and nonmetallic hip prostheses. The local dose distributions of typical hip prostheses were calculated for 4, 8, and 15 MV beams by Geant4. Three prosthesis materials were selected in calculation to reveal the relation between material type and local dose perturbations of prostheses. Furthermore,the effect of nominal energy on prosthesis perturbation was also discussed and analyzed. Taking the calculated dose to the hip joint as reference, considerable differences were observed between prostheses and hip joints. In the prosthesis shadow region, the relative dose decreasing was up to 36, 21, and 16 % for the Co–Cr–Mo alloy, titanium alloy, and ceramic prostheses, respectively. In backscattering region, the relative dose increasing was about1–7 %. Overall, the results show that the dose perturbation effect of prostheses was mainly determined by material type, nominal energy, and density. Among these typical hip prostheses, ceramic prosthesis introduces the lowest dose perturbations.     

Effect of Radial Clearance on Wear and Contact Pressure of Hard-on-Hard Hip Prostheses Using Finite Element Concepts

Wear of the bearing surface increases the revision rate of artificial hip replacements and is influenced by the radial clearances between the acetabulum cup and the femoral head. The objective of this article is to determine the effect of various radial clearance values over the contact pressure and wear of the hard-on-hard—that is, polycrystalline diamond (PCD)—hip prostheses using finite element concepts for normal walking conditions. The wear of the hip bearing surface is determined by considering the contact pressures obtained from the hip gait instants of normal walking activity and sliding distance determined from the three-dimensional hip gait motions. The radial clearance value of 0.05 mm showed less volumetric wear rate when compared with other radial clearance values. Overall, it is recommended that the low radial clearance between the contacting pair is suitable for PCD-on-PCD hip prostheses.     

基于区域特征的步态识别研究

步态识别主要是以人走路的姿势来识别其身份。为了能准确快速地识别,本文依据步态的周期性,以一个步态序列中的6帧特殊图像来描述步态的变化,再提取步态髋关节以下部分作为研究对象,确定髋关节以下部分的质心,以质心为原点,建立坐标系。将髋关节以下的部分划分成36个小区域,以周期变化的区域面积作为特征,描述步态的周期变化。这样既可以较全面地描述一个步态的信息,又降低了维数,减小计算量。同时引入最近邻分类器进行分类。实验证明,该算法不仅能得到较好的识别率,并且计算速率快。     

骨科髋膝关节置换术临床路径实施体会

目的总结临床路径在骨科髋膝关节置换术中的实施体会。方法选取我院2009年11月至2010年12月收治的102例实施髋膝关节置换术的患者,按入院的先后顺序随机分为对照组和实验组,对照组仅采用传统模式,实验组在传统模式基础上实施临床路径。统计2组在住院天数、医疗费用、术后首次下床时间、术后首次功能锻炼时间、并发症发生情况以及患者满意度方面的相关数据,并比较其差异。结果所有方面的数据显示,实施临床路径的实验组明显比对照组有优势。结论骨科髋膝关节置换术实施临床路径的效果显著,值得在临床中加以推广应用。     

Monte Carlo characterization of materials for prosthetic implants and dosimetric validation of Pinnacle TPS

In external beam radiotherapy the calculation of dose distribution for patients with hip prostheses is critical. Metallic implants not only degrade the image quality but also perturb the dose distribution. Conventional treatment planning systems do not accurately account for high-Z prosthetic implants heterogeneities, especially at interfaces. The materials studied in this work have been chosen on the basis of a statistical investigation on the hip prostheses implanted in 70 medical centres. The first aim of this study is a systematic characterization of materials used for hip prostheses, and it has been provided by BEAMnrc Monte Carlo code. The second aim is to evaluate the capabilities of a specific treatment planning system, Pinnacle³, when dealing with dose calculations in presence of metals, also close to the regions of high-Z gradients. In both cases it has been carried out an accurate comparison versus experimental measurements for two clinical photon beam energies (6 MV and 18 MV) and for two experimental sets-up: metallic cylinders inserted in a water phantom and in a specifically built PMMA slab. Our results show an agreement within 2% between experiments and MC simulations. TPS calculations agree with experiments within 3%.     

Optimal design of customised hip prosthesis using fiber reinforced polymer composites

The need for new materials in orthopaedic surgery arises from the recognition of the stress-shielding effect of bone by high-modulus implants presently made of engineering alloys. A lower modulus implant material will result in the construction of a more biomechanically compatible prosthesis. In this respect, composite materials are gaining importance because they offer the potential for implants with tailor-made stiffness in contrast to metals. In the present study, the bending stiffness of composite prosthesis is matched with that of bone in both the longitudinal and radial directions by choosing optimal carbon fiber reinforced polyether ether ketone (PEEK) matrix lay-up. A numerical optimization algorithm is developed to deduce the optimal composite femoral prosthesis lay-up that matches the stiffness properties of the femoral bone in both the transverse and longitudinal directions. Effective bending moments and compressive forces acting on the hip joint are considered in the design of the optimal length and diameter of the prosthesis. The optimization algorithm was implemented, by using MATLAB(R)™ for designing the composite prosthesis to a patient’s specific requirement. Finally the efficiency of the composite stem is compared with that of metallic alloy stems in terms of stress shielding using a finite element program.     

人工髋关节假体的加工方案及夹具设计

本文提出一种加工人工髋关节假体这一特殊零件的加工工艺方案，设计了相应的夹具及装夹方案。使用该方案及夹具，可以保证获得准确的假体颈、干夹角以及其它颈、干相对位置要求；并能在普通车床加工出颈部圆锥段和圆柱段。或在数控车床上加工出假体关节球头。利用所设计的专用夹具，在ＭＡＨＯ数控加工中心ＭＨ６００Ｃ上加工出假体干上与股骨髓腔匹配段的假体轮廓段，之后再用普通车床加工出假体干的圆柱段部分。本文设计的加工方案与夹具的特点是工装简单，定位可靠、装夹方便，尤其是粗、精加工各工序都能保证颈、干轴线间的相对位置。