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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The spherocentric knee, designed to allow triaxial rotation and provide intrinsic stability, includes desirable design features of metal on high density polyethelene bearing surfaces, metal support for all plastic components, metal-cement-bone interfacing for all fixation surfaces, sufficient strength to eliminate fatigue fracture of metallic components as a potential source of failure, cam deceleration for hyperextension control, and an inverted central plastic socket which minimizes wear. The system assures a low coefficient of friction and thereby minimizes loosening. This prosthesis has been used for surgical arthroplasty in 134 knees with gross instability or severe fixed deformity or both, in which optimal results would not have been anticipated with non-articulated resurfacing prostheses. The patients have been followed for an average of nearly 3 years (range one to 5 years). Results in terms of correction of deformity, improvement of stability, range of motion, pain relief and improved function, have been outstanding. Problems of infection, loosening and fracture of adjacent bone have been less than with other intrinsically stable prostheses (hinge prostheses) and are less than most reports of non-articulated resurfacing prostheses followed for a comparable time. There have been no failures within the prosthesis. Our loose prostheses represent failures that occurred between the prostheses and the bone. The spherocentric prosthesis is the prosthesis of choice for arthroplasty of a knee with severe preoperative deformity or severe instability or both in which optimal results would not be anticipated following insertion of a resurfacing type of prosthesis.
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PMID:Spherocentric knee arthroplasty. 53 60

Six cases have been described where an osteosynthesis was performed using the stem of a hinge knee joint in combination with methylmethacrylate and other osteosynthetic devices (screws, wires). Need for an osteosynthesis existed because of pseudarthrosis after supracondylar and high tibial osteotomies, intraoperative fracture for implantation of a total knee, reimplantation after deep infection, and fatigue fracture after a total knee. The advantage of the procedure lies in early mobilisation and weight bearing. We do not believe in reimplantation after an infected prosthesis. Instead, we recommend fusion after implant removal.
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PMID:[Osteosynthesis with hinge joints and methylmethacrylate (author's transl)]. 88 35

Hexsyn is the Goodyear Tire and Rubber Company tradename for a polyolefin rubber synthesized from 1-hexene with 3-5% methylhexadiene as the source of residual double bonds for vulcanization. Under license from Goodyear, this same polymer has been manufactured by Lord Corporation for the hinge portion of finger joint prostheses using the tradename Bion. This rubber is currently licensed to the University of Akron and to the Cleveland Clinic Foundation for use in biomedical applications, and is being used primarily for biocompatible and highly fatigue resistant rubber components in ventricular assist and artificial heart systems. Results are presented from the physical, mechanical, and biological characterization of Hexsyn. Procedures are described for the synthesis, compounding, and post-molding extraction for Hexsyn. The physical testing of Hexsyn reported includes determinations of its density at 23 and 37 degrees C, initial hardness and hardness after aging in oxygen, blood, pseudoextracellular fluid and polyethylene glycol 600, typical molecular weights determined by gel permeation chromatography/low angle laser light scattering and intrinsic viscosity, thermal analyses by differential scanning calorimetry of Hexsyn gum, and vulcanized Hexsyn after exposure to blood and blood/fatigue conditions. Also reported are results of differential thermal analyses, thermomechanical analyses of virgin and annealed samples, and thermogravimetric analyses conducted in helium and in air. Dynamic mechanical analyses of Hexsyn include Clash-Berg and Rheovibron tests. Swelling was conducted to determine lot-to-lot and sheet-to-sheet variation for quality control and also a number of solvents were used so that the polymer-solvent interaction parameters could be determined. The permeability of Hexsyn to water, water vapor, and a variety of gases is reported. The permeability by contact angle measurements, refractive index, residual solvent analyses, migration of blood components into Hexsyn, melt rheology by Monsanto Rheometer, resistance to acids, and typical mold shrinkage for Hexsyn are reported. Mechanical testing of Hexsyn includes tensile strength, elongation, and tensile stress (modulus) at 23 and 37 degrees C and after conditions including exposure to blood, pseudoextracellular fluid, polyethylene glycol, oxygen, 100% relative humidity, and fatigue testing. Stress/strain calibration curves, flexural rigidity after aging in blood, tension set, compression set, stress relaxation, and the effect of repeated cycling on the elastic modulus are presented along with the results of Pico abrasion, skid resistance tests on wet concrete.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Characterization of Hexsyn, a polyolefin rubber. 350 71

Bovine pericardium, stabilized with glutaraldehyde, is used widely in the construction of heart valve substitutes, but the design and construction of valve substitutes from this material are empirically based. Collagenous tissue can support tension, but experimental evidence indicates that flexure-induced compressive stresses can lead to fatigue failure. This study uses experimental results obtained from cyclic uniaxial load tests to predict the type and magnitude of operational stresses which occur in pericardial heterograft leaflets. Both Young's modulus and Poisson's ratio varied with uniaxial loading in pericardium, chemically modified free of tension. Leaflet stresses were analysed in using effective incremental representations of these parameters. In leaflets with unrestricted rotation at the point of attachment to the stent, the mid-plane tensions always exceeded the bending stresses, and no zones of leaflet compression were predicted. In contrast, with totally restricted leaflet rotation induced by clamping (possibly between a male and female frame) the bending stresses were greater than the mid-plane tensions at the hinge line and significant compressive stresses were predicted at this site. If elastic boundary conditions were introduced at the stent (possibly by wrapping the stent in pericardium) then the compressive stresses were reduced as the degree of elasticity was increased. Glutaraldehyde fixation of the pericardium under load produced a stiffer material; higher compressive stresses at the stent and significant increases in total stress were predicted for this tissue. The application of elevated pressure loading also increased the compressive and total stresses in the leaflet. Finally, it was shown that bicuspid leaflets were likely to experience higher stresses than tricuspid leaflets. This simple stress analysis should help valve designers of pericardial heterografts to identify those conditions which lead to tissue compression, high total stress, and ultimately material fatigue.
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PMID:Pericardial heterograft valves: an assessment of leaflet stresses and their implications for heart valve design. 368 98

This article provides a review of the progress that has been made on the biomechanical, functional performance and epidemiological investigations into the effectiveness of prophylactic knee braces (PKBs) since the position statement against their use was issued in 1987 by the American Academy of Orthopaedics and a review of this subject was last published in Sports Medicine in 1989 by Montgomery and Korziris. The evolution of the salient design features of three surrogate knee models are reviewed along with the results of PKB effectiveness and safety factor testing. While still too limited in scope to be totally realistic, major advances have been made in the sophistication of the present biomechanics laboratory testing conditions. The on-the-field functional performance effects of wearing a knee brace are not always manifest in all individuals. The efficacy of PKBs remains in question but recent studies have taught us enough to put their use into perspective. While they may play some role, PKBs probably represent the least important factor in influencing the likelihood that a medial collateral ligament (MCL) sprain will occur. On the other hand, there is no evidence that such braces put added valgus pressure on some knees, or that wearing a brace is associated with an increased frequency or severity of knee or ankle injury. All else being equal, from the biomechanical studies, we know that whilst some braces are better than others, currently available PKBs can provide 20 to 30% greater resistance to a lateral blow, with the possibility that the anterior cruciate ligament (ACL) is given even greater protection than the MCL. This appears to be true when the lateral blow is of sufficient magnitude to cause significant medial joint line opening, but is not as great at the very lowest levels of impact. Regardless of the material they are made of, the most effective PKBs are those sufficiently stiff to prevent an external blow at the joint line from causing brace hinge contact with the knee tissues. Based on the superior results of the custom-fit functional braces, the most important future design feature appears to be the sizing and fitting of the thigh and tibial cuffs. On the negative side, the presence of a brace may slow an athlete's straight-ahead sprint speed and cause early fatigue to its wearer. This effect appears to vary from one brace to another according to its weight, design features, and pressure from the leg and thigh straps. However, it appears that knee braces do have the potential to restrict performance of the athlete for high-speed running but the effect is related to several factors. The weight of the brace resultant friction of the hinges, completeness of fit, and tightness of straps appear to be important. The most measurable effects include: increased muscular relaxation pressures; increased energy expenditure; and a related increase in blood lactate levels, maximal torque output, oxygen consumption and heart rate. On the other hand, experienced brace wearers and larger, stronger individuals displayed fewer, or no effects of donning a brace. Improvements in the protectiveness of the PKB are likely to accompany improvements in the ability to contour the braces to fit each individual's leg in the equipment room without the added expense of the cast-moulding process. Further improvement may be realised by friction-free polycentric joints, as well as an attachment system that minimises thigh and calf soft tissue compression perhaps by incorporating the braces into the trousers of the uniform to provide suspension from the waist.
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PMID:Use of knee braces in sport. Current recommendations. 857 Oct 3

Two 29 mm St. Jude Medical valves, two 29 mm CarboMedics valves and two 29 mm Sorin Bicarbon valves were tested in a real time fatigue test rig. The test rig was run at 72 beats/min with a stroke volume of 70 ml for approximately one million cycles. Optical microscopy was used to investigate the valve surfaces. Possible deterioration of the surface finish was observed on the stops of the hinge recesses in the St. Jude Medical and CarboMedics valves. In the Sorin valves areas of the pyrolytic carbon coating was worn away adjacent to and on the valve stops.
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PMID:An initial investigation into the wear and damage within the pivots of three types of bileaflet mechanical heart valves. 880 63

This report discusses the Daphne prosthesis for the metacarpophalangeal joint on the basis of the mechanical, chemical and biological performance of the materials employed. The Daphne prosthesis is a mobile device. The main body is made of a new generation polymethylmetacrylate, while the hinge is made of AISI 316 L stainless steel. Biocompatibility tests were performed on the materials employed. Systemic toxicity, cytotoxicity and contact tests have given favourable results. Mechanical engineering tests have been used to investigate the performances and reliability of the selected materials. The polymethylmetacrylate used in Daphne behaves in a ductile fashion. No mechanical failures were encountered in fatigue tests after 10 million cycles.
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PMID:A new prosthesis for the metacarpophalangeal joint. Study of materials and biomechanics. 1019 Jun 8

The authors present a case of fatigue fracture of the proximal tibia with concurrent degenerative changes of the knee in a 53 year old patient with rheumatoid arthritis. The patient was treated surgically with a hinge-rotation prothesis. The procedure yielded pain relief, correction of the axis of the lower limb with progressive bone union.
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PMID:[Fatigue tibial fracture coexistent with severe degenerative changes of the knee in a patient with rheumatoid arthritis]. 1096 35

Eleven fractured Sutter metacarpophalangeal prostheses were obtained from the hands of three patients. All of the implants had fractured at the junction of the distal stem and the hinge. After visual examination, the fracture faces were prepared and viewed using a scanning electron microscope. These images indicated that fracture was initiated by abrasion on the dorsal aspect of the distal stem of the prostheses, close to the hinge. Crack propagation was shown to be due to a fatigue process. Once a crack started, its direction of travel could be followed, using topographical features common to engineering fracture analyses. Propagation was from radial to ulnar and from dorsal to palmar.
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PMID:Analysis of the mechanism of fracture of silicone metacarpophalangeal prostheses. 1893 33

Material failure is a rare complication in total knee arthroplasty (TKA). This case report shows a fatigue fracture of the hinge pin as a consequence of a postoperative persisting valgus deviation in a semi-constrained TKA.
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PMID:Fatigue fracture of the hinge pin in a semi-constrained total knee arthroplasty: a case report. 2056 55


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