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。     

Advanced Stellite alloys with improved metal-on-metal bearing for hip implants

Stellite 21 is a low-carbon Co–Cr–Mo alloy that has been used for hip implants for decades. The Stellite 21 implants can fail when the femoral head and the acetabular cup loosen because of limited metal-on-metal bearing. Two modified Stellite 21 alloys with better bearing capacities are proposed as replacements in this study: Cr-modified Stellite 21 with additional 10 wt.% Cr, and N-modified Stellite 21 with addition of 0.5 wt.% CrN. The wear and corrosion resistances of these alloys were investigated in simulated conditions experienced by hip implants in human bodies. The experimental results show that the proposed alloys all exhibit better wear resistance than the conventional hip implant material, but only Cr-modified Stellite 21 displays better corrosion resistance, thus this alloy should be considered for use in future hip implants.     

Effects of hip-loading input on simulated wear of Al2O3–PTFE materials

The objective of this study was to compare the effects of static, sinusoidal and physiological load-profiles on wear of Al₂O₃–PTFE materials. This was an accelerated wear model of clinical relevance. In nine experiments, the peak load-levels were varied from 1 to 4 kN in a hip simulator with multi-directional kinematics and with bovine serum used as the lubricant. Systematic wear differences were checked using three sizes of femoral heads in each experiment. The Paul load-profile used was found to be more aggressive than sinusoidal, raising the polytetrafluoroethylene (PTFE) wear-rates by 28%. The PTFE cups showed a very mild response to increased load magnitudes, only 11–20% increase evident in volumetric wear per 1 kN increase in load. One recommendation was that simulator wear-studies adopt a 0.25–2.5 kN Paul load-profile as their standard. An experiment with 0.84 kN constant-load also performed satisfactorily, with PTFE wear-rates actually higher than with the 1 kN sine and Paul load-profiles. Some wear anomalies were encountered due to the use of serum lubrication. Combinations of large head size, high load-magnitudes, the Paul load-profile and the high serum protein concentrations used in this study were at times contributing factors. Use of low-protein serum solution may be advisable for wear studies, not only to properly simulate the polymeric wear characteristics but also to minimize the degradation artifacts more prevalent in higher protein-concentrations.     

Shape optimization of uncemented hip prostheses

A computational model to obtain optimized geometries for the femoral component of hip prosthesis is presented. Using structural optimization techniques, the objective is to determine the shape of uncemented stems that maximize initial stability and improve performance. To accomplish this, the optimization problem is formulated by the minimization of the contact stresses and relative displacement on bone–stem interface. Design variables are geometric parameters that characterize selected cross sections. These parameters are subject to a set of linear geometric constraints in order to obtain clinically admissible geometries. Furthermore, a multiple load formulation is used to incorporate different daily life activities. Optimization results are useful to design new stems or, if integrated in an appropriate computer-aided design (CAD) system, to design custom-made hip prostheses. In the later case, the model is able to include personalized information such as patient's femur geometry and therefore personalized geometric constraints and optimization parameters.     

Double permanent magnet vibration power generator for smart hip prosthesis

Ever since the first studies about biomedical implantable devices, the problem of how to energize them has stood out as both important and notoriously difficult to solve. In order to extend the lifetime of implants, it is imperative to develop power generators that are autonomous, safe and maintenance-free. Energy harvesting is a natural way of meeting these requirements. First, the energy source is theoretically everlasting, a fact that helps to guarantee the autonomy. Second, the energy is obtained from the environment of the application itself, contributing to its safety. Finally, a properly designed energy harvesting system is very unlikely to ever require maintenance. This paper follows this line and describes an electromagnetic power transducer that harvests electrical energy from the human gait and stores it. An efficient power management module uses the stored energy to energize the telemetric system of a smart hip prosthesis implant, enabling the early detection of loosening, the target application of this work. The system is able to extract a total 1912.5 μJ of usable energy under normal walking conditions.     

Fatigue behaviour of fine-grained alumina hip-joint heads under normal walking conditions

In prosthetic applications, the reliability of implant materials over a period of thirty years is absolutely essential. Calculation of the lifetimes of alumina ceramic heads is generally made on the basis of experimental fatigue and slow crack growth tests using finite element analysis. This investigation is aimed at understanding the fatigue behaviour of fine-grained alumina heads of hip joints. The service conditions of cyclic stress experienced by hip joints during walking are used in evaluating the fatigue behaviour of alumina femoral heads. These femoral heads have successfully withstood 10⁷ cycles at a maximum walking stress of 17.2 kN, which is equivalent to a body weight of 400 kg. The femoral heads did not exhibit any sub-critical crack growth at the maximum walking load of 10kN, indicating the quasi-infinite performance life in patients up to a body weight of 250 kg. The details of proof testing designed for evaluating the performance of femoral heads over 40 years are also presented.     

Volumetric wear assessment of failed metal-on-metal hip resurfacing prostheses

Recent advancements in hip arthroplasty have allowed the operation to boast excellent results and high survivorship. However, failures do still occur and a major cause is complications arising from wear debris. It is essential therefore that debris is minimized by reducing wear at the bearing surface. One proposed method of achieving this wear reduction is through the use of metal-on-metal articulations. One of the latest manifestations of this biomaterial combination is in designs of hip resurfacing which are aimed at younger, more active patients who might wear out a conventional metal-on-polymer hip prosthesis. However, do these metal-on-metal hip resurfacings show less wear when implanted into patients?Using a co-ordinate measuring machine and a bespoke computer program, volumetric wear measurements for retrieved Articular Surface Replacements (ASR™, DePuy) metal-on-metal hip resurfacings were undertaken. Thirty-two femoral heads and twenty-two acetabular cups were measured. Acetabular cups exhibited mean volumetric wear of 29.00 mm³ (range 1.35-109.72 mm³) and a wear rate of 11.02 mm³/year (range 0.30-63.59 mm³/year). Femoral heads exhibited mean wear of 22.41 mm³ (range 0.72-134.22 mm³) and a wear rate of 8.72 mm³/year (range 0.21-31.91 mm³/year). In the 22 cases where both head and cup from the same prosthesis were available, mean total wear rates of 21.66 mm³/year (range 0.51-95.50 mm³/year) were observed. Compared with in many vitro tests, these are significantly higher than those expected in a well functioning metal-on-metal hip resurfacing prosthesis and are of concern.     

实验验证用股骨柄假体样件的加工

金属在CT图像上会产生伪影,在需要分析人工髋关节股骨柄假体样件与相应股骨腔匹配情况实验中,股骨柄假体样件不能采用金属材料。由于光敏树脂成形后具有一定硬度,光敏树脂材料的股骨柄假体样件能够植入相应股骨腔而不会发生变形。此外,树脂材料样件加工方便,加工成本较低。提出采用光敏树脂作为实验验证用股骨柄假体样件材料,并介绍了采用SLA快速成型方法加工股骨柄假体样件的方法。实验中,光敏树脂材料的股骨柄假体样件被植入股骨腔中并拍摄了CT图像。CT图像中光敏树脂材料股骨柄假体样件与股骨松质骨之间分界明显,采用边缘检测方法很容易从CT图像中检测出股骨柄假体样件轮廓曲线。这使股骨柄假体样件与相应股骨腔之间的匹配程度得以定量分析。上述结果表明,采用光敏树脂作为股骨柄假体样件材料来分析股骨柄假体样件与股骨腔的匹配程度切实可行,较好地解决了金属股骨柄假体样件不能用来分析在股骨腔中的匹配程度问题。     

Self-reported ache,pain, or numbness in hip and lower back and use of computers and cell phones amongst Finns aged 18–65

The aim of our work is to study persons who self-reported aches, pain, or numbness in the hip and lower back very often and their use of computers and cell phones via a questionnaire. The study was carried out as a cross-sectional study by posting a questionnaire to 15,000 working-age persons, and among all respondents (6121), 8.2% of them reported that they very often experienced pain, numbness, and aches in the hip/lower back. Thirty-eight percent of them used a desktop computer at work daily, and 79.0% used cell phones at leisure. As a group, they had more physical and mental symptoms than others. We found also significant differences in the use of different computers at work. In the future, it is important to take into account that persons' physical symptoms in the hip and lower back very often can be associated with other physical or mental symptoms and computer usage.Relevance to industryHip and lower back symptoms are quite common discomforts that affect the productivity and well-being of industrial workers. A large-scale questionnaire offers a good reference for evaluating the prevalence of the hip and lower back symptoms associated with other symptoms and usage of computers and cell phones.     

Interference effects on wind loads on low-rise hip roof buildings

The Natural wind in the wind tunnel was simulated at the University of Roorkee (India) on the basis of full/model-scale comparison. For this, the Texas Tech University (TTU) building model was fabricated on a geometric scale of 1:50 and tested in the simulated wind for comparison of the pressures with full-scale values. A hip roof building model (geometric scale 1:50) of plan dimensions 280 mm×140 mm×58 mm (eave height) with 30° roof slope was selected as the test building (T.B.) so as to examine interference with a similar building as well as three similar buildings placed on the upstream side at fifteen different locations (Fig. 2). A quadrant portion of the model roof was divided into ten different zones to see the effect of interference at critical roof positions. Significant effects have been observed.