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At least 73 records · Page 4Linked to original sources
PubMed1991

[Basic study of cementless hip prosthesis design--analysis of the proximal femur in Japanese patients with osteoarthritis of the hip].

By CT scan, the author analyzed morphologically the proximal medullary canal of the femur in 52 cases of osteoarthritis of the hip. The purpose is to determine the stem shape of an artificial hip joint suitable for Japanese patients. The results were as follows: 1) The femoral head diameter indicated positive correlation with the height, the femoral length, the femoral shaft transverse diameter, and the medullary canal diameter. The proportionality of the femur was found in Japanese patients with osteoarthritis. 2) The femoral head offset indicated no correlation with any results obtained by various measurement. 3) The medullary canal diameter of the diaphysial portion as well as the ratio of the medullary canal to the femur increased with age. 4) The taper angle*, 3.8 degree on the average was positively correlated only with the medullary canal diameter. *"Taper angle" indicates the degree of tapering of the medullary canal.

Adolescent↗
PubMed1996

The Rotaglide total knee arthroplasty. Prosthesis design and early results.

The Rotaglide knee (Cozim Medical, UK) is a three-part knee containing a mobile polyethylene meniscal platform, imparting reduced loosening forces to the tibia. The femoral component design provides a high degree of congruency throughout the range of motion from 0 degree to 110 degrees, and both femoral and tibial components ensure minimal bone removal. The system is versatile, including a large number of component options, and it may be used in both primary and revision arthroplasties. The first results in 170 cemented knees (161 patients) with 2- to 5-year follow-up periods (average, 3.1 years) were very encouraging (excellent or good in 95% of knees, based on the British Orthopaedic Association knee assessment system). Poor results were seen only in revision cases. There have been no mechanical implant failures and no platform bearing dislocations, and the platforms continue to move as documented by postoperative roentgenograms, which show the metal markers of the platforms moving anteriorly in flexion and posteriorly in extension.

Aged↗
PubMed1994

A model of myelinated nerve fibres for electrical prosthesis design.

Starting with the spatially extended non-linear node model (Reilly et al., 1985), which incorporates Frankenhaeuser-Huxley non-linearities at each of several nodes in a row, a model is developed to describe many aspects of the behaviour of mammalian nerve fibres in a quantitative way. By taking into account the effects of temperature and by introducing a realistic nerve morphology, a good fit is obtained between the shape, duration and conduction velocity of simulated and in vivo action potentials in mammals. The resulting model correctly predicts the influence of physiological variations of body temperature on various aspects of nerve behaviour. It is shown that the absolute refractory period predicted by the model is within physiological ranges. Both in vivo and in the model, the spike amplitude and the spike conduction velocity are reduced in the relative refractory period. It is concluded that single-node models (although widely used) cannot replace this multiple nonlinear node model, as the stimulus repetition rates that can be followed by the simulated nerve fibre are limited by impulse conduction properties, rather than by the frequency following behaviour of a single node.

Action Potentials↗
PubMed2002

Combining biometric and symbolic models for customized, automated prosthesis design.

In a previous paper [Artif. Intell. Med. 5 (1993) 431] we described RaPiD, a knowledge-based system for designing dental prostheses. The present paper discusses how RaPiD has been extended using techniques from computer vision and logic grammars. The first employs point distribution and active shape models (ASMs) to determine dentition from images of casts of patient's jaws. This enables a design to be customized to, and visualised against, an image of a patient's dentition. The second is based on the notion of a path grammar, a form of logic grammar, to generate a path linking an ordered sequence of subcomponents. The shape of an important and complex prosthesis component can be automatically seeded in this fashion. Combining these models now substantially automates the design process, beginning with a photograph of a dental cast and ending with an annotated and validated design diagram ready to guide manufacture.

Anthropometry↗
PubMed1998

Composite hip prosthesis design. II. Simulation.

An investigation was performed to study the mechanical performance of fiber-reinforced composite hip prostheses. In Part I of the study, a three-dimensional finite element code was developed for analyzing a composite hip prosthesis in a femur. The material properties of the composite were treated as anisotropic and inhomogeneous while the properties of the femoral bone were treated as anisotropic and homogeneous. All the materials were assumed to behave linear-elastically. Thermoplastic graphite/PEEK material was selected for the study. No slippage was assumed at the interface between the implant and the surrounding femoral bone. In Part II, numerical simulations were performed using the code to study the performance of a composite prosthesis in the femur. The stress/strain distributions, micromotions, and strain energy density of the surrounding femoral bone were evaluated and found to be related to initial fixation and long-term stability of the prosthesis in the femur. Numerous fiber orientations were studied, and the results of the calculations were compared with those generated from a prosthesis made of cobalt chrome and Ti-6Al-4V titanium alloys. Based on the analysis, it was shown that compared to conventional metallic implants more favorable stresses and deformations could be generated in the femur using composite implants. In addition, by changing fiber orientations according to femoral loads, a composite implant could be designed specifically for the left or the right femur.

Computer Simulation↗
PubMed2003

Split-frame implant prosthesis designed to compensate for mandibular flexure: a clinical report.

When an edentulous mandible is restored with 4 or more implants connected by a metal bar and retained with screws, mandibular flexure may cause screw loosening and unnecessary stresses and strains on the prosthesis and implants. Separating the prosthesis at the midline can relieve these stresses and strains. This article describes the separation of a hybrid mandibular denture at the midline.

Dental Alloys↗
PubMed2004

Analysis of influence of lip line and lip support in esthetics and selection of maxillary implant-supported prosthesis design.

The lip line and lip support influence esthetics and selection of implant-supported prosthetic designs for maxillary edentulous patients. This article describes a procedure to analyze the influence of lip line and lip support on the esthetics of an existing maxillary complete denture, revealing potential limitations when planning a fixed implant-supported prosthesis.

Dental Prosthesis, Implant-Supported↗
PubMed1982

Wear-screening and joint simulation studies vs. materials selection and prosthesis design.

Satisfactory friction and wear performance of orthomedic biomaterials is an essential criterion for both hemiarthroplasty and total joint replacements. This report will chart the clinical historical experience of candidate biomaterials with their wear resistance and compare/contrast these data to experimental test predictions. The latter review will encompass publications dealing with both joint simulators and the more basic friction and wear screening devices. Special consideration will be given to the adequacy of the test protocol, the design of the experimental machines, and the accuracy of the measurement techniques. The discussion will then center on clinical reality vs. experimental adequacy and summarize current developments.

Bone and Bones↗
PubMed1998

Composite hip prosthesis design. I. Analysis.

An investigation was performed to study the mechanical performance of fiber-reinforced composite hip prostheses in a femur. The main objective of the study was to evaluate the effect of fiber orientation of a composite femoral implant on the response of the surrounding femoral bone. A three-dimensional finite element analysis was developed for analyzing a composite implant in the femur. A three-dimensional composite element was proposed to take into account ply drop-off due to a change of cross-section of the composite implant. The element could accommodate multidirectional layers and tapered composites. The material properties of the composite were treated as anisotropic and inhomogeneous while the properties of femoral bone were treated as anisotropic and homogenous. All the materials were assumed to behave linear-elastically. The thermoplastic graphite/PEEK material system was selected for the study. In this presentation, as the first part of the study, the development of the finite element analysis will be described. Numerical calculations were generated and compared with existing data and numerical results available from studies related to metal hip prostheses in the literature. Experiments on the composite hip implants were also conducted for further verification of the analysis and the computer simulations. In Part II, using the finite element code, an extensive study was performed to evaluate the stress/strain distributions, micromotions, and strain-energy density of the surrounding femoral bone, which have been related to initial fixation and long-term stability of the prosthesis in a femoral bone. Numerous fiber orientations were studied, and results of the calculations were compared with those generated by the prosthesis made of cobalt alloy and titanium alloy.

Hip Prosthesis↗
PubMed1996

New polyurethane heart valve prosthesis: design, manufacture and evaluation.

In light of the thrombogenicity of mechanical valves and the limited durability of bioprosthetic valves, alternative designs and materials are being considered for prosthetic heart valves. A new tri-leaflet valve, made entirely from polyurethane, has been developed. The valve comprises three thin polyurethane leaflets (approximately 100 microns thick) suspended from the inside of a flexible polyurethane frame. The closed leaflet geometry is elliptical in the radial direction and hyperbolic in the circumferential direction. Valve leaflets are formed and integrated with their support frame in a single dip coating operation. The dipping process consistently gives rise to tolerably uniform leaflet thickness distributions. In hydrodynamic tests, the polyurethane valve exhibits pressure gradients similar to those for a bioprosthetic valve (St Jude Bioimplant), and levels of regurgitation and leakage are considerably less than those for either a bi-leaflet mechanical valve (St Jude Medical) or the bioprosthetic valve. Six out of six consecutively manufactured polyurethane valves have exceeded the equivalent of 10 years function without failure in accelerated fatigue tests. The only failure to date occurred after the equivalent of approximately 12 years cycling, and three valves have reached 527 million cycles (approximately 13 years equivalent). The simplicity of valve manufacture, combined with promising results from in vitro testing, indicate that further evaluation is warranted.

Biocompatible Materials↗