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

The measured tensile and fatigue strengths of wrought and heat-treated cobalt chromium-molybdenum-carbon alloys such as HS21 were found to be more than twice those of as cast alloys of the same composition. The resistance of wrought HS21 to crevice corrosion at metal-Teflon contacts in isotonic salt solution at 37 degrees C was found to be considerably greater than that of cast HS21, wrought HS25, wrought MP35, or 316L stainless steel which are currently used for surgical implants. The increased crevice corrosion resistance and mechanical strength of wrought HS21 as compared to as cast HS21 was attributed to greater chemical and structural homogeneity as well as to finer grain size and distribution of secondary phases. Fabrication of shaped implants from wrought HS21 is possible by techniques currently used for the fabrication of industrial parts from other wrought cobalt-chromium base alloys.
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PMID:Cast vs. wrought cobalt-chromium surgical implant alloys. 117 76

The clinical and metallurigical characteristics of five cast cobalt-chromium-molybdenum alloy femoral hip prostheses which failed in vivo were evaluated. The devices included: two of the Howmedica Muller-Charnley design, two of the Howmedica Charnley design, and one of the Zimmer Aufranc-Turner design. Fractographic analyses demonstrated that the five devices had failed by fatigue which originated on the lateral aspect. Failure occurred after an average in vivo time of 80.4 months (approximately 6.7 years). Only two of the devices had Rockwell hardness values that were within the ASTM specifications for the alloy. Upon metallurgical examination, moderate to severe levels of gas porosity, interdendritic shrinkage, and nonmetallic inclusions were found in all of the devices. As expected, extremely large grain sizes also were observed in the devices examined. These results indicate that the metallurgical flaws and defects associated with the cast cobalt-chromium-molybdenum alloys used in these devices may preclude successful longterm performance and warrant manufacturer's attention.
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PMID:Metallurgical analysis of five failed cast cobalt-chromium-molybdenum alloy hip prostheses. 382 Jan 19

Special instruments have been perfected for the laser microsurgery. Those instruments must not exceed 18 centimeters in length in order to reduce the possibility of infection through the middle part (microslad) tied up to the microscope. The instruments must be blackened to reduce the casual reflection of the laser ray over the intra-abdominal structures. Molybdenum mirrors with specifically outlined angles to reflect laser rays towards the inaccessible spots and also to strike the aimed tissue at the right place, have been perfected. In the same way, quartz straight and angular rods stronger to the laser fatigue than the pyrex are necessary to absorb laser energy during the vaporization and the excision of intra-pelvic adhesions. Thanks to these adapted instruments, the micro surgeon gynecologist will be able to practise his laser surgery with more safety, less eyestrain and less difficulties.
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PMID:[Instruments necessary for safe laser microsurgery]. 396 76

The behavior of the ASTM F1058 wrought cobalt-chromium-nickel-molybdenum-iron alloy (commonly referred to as Elgiloy or Phynox) is evaluated in terms of mechanical properties, magnetic resonance imaging, corrosion resistance, and biocompatibility. The data found in the literature, the experimental corrosion and biocompatibility results presented in this article, and its long track record as an implant material demonstrate that the cobalt superalloy is an appropriate material for permanent surgical implants that require high yield strength and fatigue resistance combined with high elastic modulus, and that it can be safely imaged with magnetic resonance.
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PMID:Assessment of wrought ASTM F1058 cobalt alloy properties for permanent surgical implants. 928 68

Ten patients who had had a total hip replacement with a forged cobalt-chromium-molybdenum femoral prosthesis (Precoat or Precoat Plus) inserted with cement were seen with a fatigue fracture of the stem an average of fifty months (range, nineteen to seventy-four months) postoperatively. The average age of the patients was sixty-one years (range, forty-three to seventy-three years), and the average weight was ninety-six kilograms (range, seventy to 130 kilograms). Eight patients had had a primary total hip replacement, and two had had a revision; all of the acetabular components had been inserted without cement. Radiographs that had been made before the fracture were available for four of the eight hips that had had a primary replacement; all four had radiographic evidence of debonding of the cement mantle from the proximal end of the stem. This probably caused exaggerated cantilever bending stresses on the proximal aspect of the stem as the distal end of the stem was well fixed. The radiographs of both hips that had had a revision demonstrated a non-union of the greater trochanter, which had resulted in separation at the cement-bone interface at the proximal portion of the femur before the fracture. Scanning electron micrographs of five of the ten fractured prostheses demonstrated a fatigue fracture that began near the anterolateral corner of the prosthesis, through characters that had been etched on the implant with a laser. Metallurgical analysis indicated subsurface voids or inclusions, or both, immediately under the region that had been etched. This finding is consistent with thermal changes to the microstructure of the alloy that probably caused a focal reduction in the material strength. A high proportion (seven) of the ten stems had a poor cement mantle. Also, of the seven small stems that were used, six had been implanted in patients who weighed more than eighty kilograms, so there was relative undersizing of the prostheses. Early debonding of the proximal end of a Precoat femoral prosthesis from the cement mantle may occur as a result of a thin cement mantle, leading to loosening and possibly to early fatigue fracture of the stem if the distal portion of the stem remains solidly fixed in the distal portion of the cement column. On the basis of our experience, we recommend that patients who have radiographic evidence of a debonded Precoat femoral component should be informed of the risk of fatigue fracture of the stem and be followed closely even though there may be no symptoms of loosening of the femoral component.
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PMID:Fatigue fracture of a forged cobalt-chromium-molybdenum femoral component inserted with cement. A report of ten cases. 940 98

The possibilities of using different material combinations for the replacement of knee joint endoprostheses are very limited. Therefore, cobalt-chromium-molybdenum alloys are currently being used for femoral components and ultra-high molecular weight polyethylene for tribologically stressed tibial components. Titanium alloys can be considered for the tibial component only. For tribological reasons, it is not possible to use a femoral component made of titanium unless it has a corresponding coating. As far as the design is concerned, problems arise from the fact that, on the one hand, there is a demand for the smallest possible size or resection height. On the other hand, however, the forces and strains are rather high and therefore a certain material thickness is necessary in order to avoid fatigue fracture. Regarding polyethylene, the same known principle must be taken into consideration here--not to avoid using the so-called floating design, i.e., the polyethylene components should always have a supporting limitation, or cold flow might occur. The tribological behaviour of polyethylene is restricted in cases of constrained tibia plateaus in so far as the linear or punctual contact of the initial run-in phase leads to correspondingly high surface pressure consequently overstressing the polyethylene. In order to improve this, mobile meniscal bearings are used and the surface pressures achieved here can be endured by the polyethylene even over a long-term. The extent to which the new so-called cross-linked polyethylene can be used in knee joint endoprosthetics is currently being tested, and the simulator results in this respect have been promising so far.
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PMID:[Knee endoprosthesis: selection and requirements of materials]. 1101 16

A comprehensive failure analysis was performed on 6 femoral components and 1 tibial component that fractured in service. All were Whiteside Ortholoc II total knee arthroplasty components, manufactured from cast cobalt-chromium-molybdenum alloy and porous coated. Fracture surface analysis revealed fatigue-induced failure in all cases. Most fractures occurred at regions of high stress concentration, such as sharp corners, sintered beads, and thin sections. Metallurgical examination showed significant variation in grain size, interdendritic carbides, and hardness between samples. In some cases, continuous carbide networks and voids were prominent at the bead-substrate interface. Patient weight and surgical placement were identified as contributory factors in component failure. Limitations of cast cobalt-chromium-molybdenum alloy in weight-bearing applications must be emphasized, particularly when important determinants, such as design, metallurgy, and specific clinical factors, are less than optimal.
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PMID:Fractured Whiteside Ortholoc II knee components. 1160 12

Fracture of dental implants is a rare phenomenon with severe clinical results. In this article, the literature is reviewed and various causative factors that may lead to fracture are presented. Galvanic activity has not been mentioned before as a possible cause for implant fracture, yet, it can occur at the level of contact with the superstructure. This is illustrated by the case of a titanium implant restored with a non-precious porcelain-fused-to-metal cemented crown that fractured 4 years after loading. The radiographs show alveolar bone resorption around the fixture. Metallurgical analysis of the implant indicated that the fracture was caused by metal fatigue and that the crown metal, a nickel-chromium-molybdenum alloy, exhibited corrosion. These findings suggest a new explanation for implant fractures; cytotoxic nickel ions, leaching from the base metal alloy may cause bone resorption. This in turn leads to increased mobility, facilitating washout of the luting cement. Contact of the base metal with titanium in the presence of oral fluids produces galvanic currents that hasten corrosion and leaching out of nickel ions, thus leading to further bone resorption. Loss of bone support allows lateral bending moments that cause metal fatigue, eventually leading to fracture. Therefore, good treatment planning and appropriate case selection might have prevented this fracture. Furthermore, the use of nonprecious metal alloy for the crown's infrastructure had further contribution to the chain of events that led to the implant's fracture.
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PMID:Fracture of dental implants: literature review and report of a case. 1207 95

Wear debris generated from total joint arthroplasty may elicit a granulomatous and inflammatory response and has also been implicated in the development of osteolysis. Technical difficulty in retrieval and isolation of wear material from tissues has hindered the study of their physicochemical properties. The purpose of this study was to retrieve and analyze metallic wear debris from periprosthetic tissue obtained during revision arthroplasty. Tissue from six osteoarthritic patients was obtained during revision arthroplasty. The tissue was minced and then heated in a sodium dodecyl sulfate solution. Undigested tissue was incubated sequentially with papain and pepsin solutions. Metallic wear debris retrieved from the digestion procedure was analyzed by scanning electron microscopy. Wear fragments were seen as irregularly shaped flakes, splinters and polyhedral structures ranging from 1 to 100 microns in size. These structures appeared to be free from non-metallic surface-adherent material. Energy dispersion spectroscopy verified the presence of cobalt, chrome and molybdenum which comprised the implant alloy. Fatigue lines were observed on the surface suggesting brittle wear. Our technique for isolating metallic fragments facilitates the retrieval and preparation of wear debris for analysis of physicochemical properties and how wear debris interacts with cellular elements in surrounding tissue.
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PMID:Extraction and characterization of metallic wear debris from total joint arthroplasty. 1748 65

A processing technology has been developed that can be applied to many different fine wire medical alloys to improve their fatigue properties. This technology has been used to process a low inclusion alloy, 35 cobalt-35 nitinol-20 chromium-10 Molybdenum (ASTM F562 chemistry), hereinafter referred to as System A. After processing, this ultra fine microstructure exhibited relatively high yield strength, good axial ductility and a fatigue limit of 1 GPa at a fatigue lifetime that exceeded 100 million cycles, as reported here.
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PMID:Nanocrystalline material with gigacycle fatigue life. 1807 28


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