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

Arthrodesis of the lumbosacral spine, although satisfactory for a majority of patients, has long term sequelae in 30% of patients. This is particularly true for adjacent segment degeneration. Numerous attempts at providing a mobile motion segment have been made in the past. The current status of the development of dynamic intervertebral prosthesis, including biomechanical and clinical data have been presented. The relevant material properties of plastics, ceramics, and metal are presented with the conclusion that metals currently present with the greatest longevity without undue fatigue and wear as many as 100,000,000 cycles (40 years use) as an alternative to spinal fusion. An analysis of the kinematics of the motion segment have resulted, together with the material properties in the development of a dynamic intervertebral disc for use in the lumbar spine. The disc resembles a normal motion segment. In motion stiffness and center of rotation, wear debris development in 1/300 equivalent to that of a total hip prosthesis for the same given time. Safety features include immediate screw fixation to prevent displacement, a wedge elastic (spring) shape, and a bony porous ingrowth surface. The prosthesis is constructed of cobalt chromium and titanium with minimal corrosive properties on long term testing.
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PMID:Intervertebral disc replacement. Experimental study. 913 73

This study investigated the resistance to deflection fatigue and surface hardness of grade 2 titanium bar samples to a portion of which a layer of cobalt-chromium alloy was cast under standard dental laboratory conditions. The uncovered part of the titanium bar was deflected, and the number of loading cycles required to cause a fatigue fracture in the titanium bar was recorded. The Vickers hardness of the titanium bar was measured, and the fracture surface was examined by scanning electron microscope and energy-dispersive spectroscopy. The number of loading cycles was considerably lower in bars with the cobalt-chromium surface cast (83 vs. 13.770 cycles) (P < .001), while the surface hardness of the titanium bar with the cobalt-chromium surface cast was higher than that without the surface cast (Vickers hardness number 329 vs. 178) (P < .001). These findings suggest that the cobalt-chromium surface cast dramatically affects the fatigue resistance of pure titanium, which should be considered when novel implant-supported prostheses made from premanufactured titanium parts are planned.
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PMID:Effects of cobalt-chromium alloy surface casting on resistance to deflection fatigue and surface hardness of titanium. 917 90

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 performance of any material in the human body is controlled by two sets of characteristics: biofunctionality and biocompatibility. With the wide range of materials available in the mid-1990s, it is relatively easy to satisfy the requirements for mechanical and physical functionality of implantable devices. Therefore, the selection of materials for medical applications is usually based on considerations of biocompatibility. When metals and alloys are considered, the susceptibility of the material to corrosion and the effect the corrosion has on the tissue are the central aspects of biocompatibility. Corrosion resistance of the currently used 316L stainless steel, cobalt-chromium, and titanium-based implant alloys relies on their passivation by a thin surface layer of oxide. Stainless steel is the least corrosion resistant, and it is used for temporary implants only. The titanium and Co-Cr alloys do not corrode in the body; however, metal ions slowly diffuse through the oxide layer and accumulate in the tissue. When a metal implant is placed in the human body, it becomes surrounded by a layer of fibrous tissue of a thickness that is proportional to the amount and toxicity of the dissolution products and to the amount of motion between the implant and the adjacent tissues. Pure titanium may elicit a minimal fibrous encapsulation under some conditions, whereas the proliferation of a fibrous layer as much as 2 mm thick is encountered with the use of stainless steel implants. Superior fracture and fatigue resistance have made metals the materials of choice for traditional load-bearing applications. In this review, the functionality of currently used metals and alloys is discussed with respect to stenting applications. In addition, the "shape memory" and "pseudo-elasticity" properties of Nitinol-an alloy that is being considered for the manufacturing of urologic stents-are described.
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PMID:Characteristics of metals used in implants. 944 Aug 45

Bone cement is commonly used to affix femoral implants to the bone during total hip reconstruction. Previous studies suggest that the expected life of a cemented femoral implant may depend on the thickness of the cement mantle surrounding the implant and the implant geometry. The purpose of this study was to determine whether different cement-mantle thicknesses and femoral stem sizes affected strain patterns in the bone cement around cemented femoral stems. Two different sizes of cobalt-chromium stems were cemented into composite femora with varying cement-mantle thickness. Strain gages were embedded in the cement mantle and the implanted stems were loaded axially and under conditions simulating walking and standing. An increase in stem size with the same cement-mantle thickness (approximately 2.2 mm) caused a 65% decrease in proximal medial cement strains. Increasing cement mantle thickness from 2.4 to 3.7 mm caused substantial strain reductions in the distal cement (40-49%). We conclude that increased cement-mantle thickness around femoral stems may increase the fatigue life of a bone-implant system by reducing peak strains within the cement.
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PMID:Cement-mantle thickness affects cement strains in total hip replacement. 945 87

Pure elemental titanium was alloyed with cobalt and chromium in dilutions of 4%, 5%, and 6% to evaluate the suitability of the resulting alloy for removable partial denture frameworks. The physical properties of the Co-Cr-Ti alloy were compared to the properties of a commercial pure titanium and Vitallium. Clasp replicas were cast in Co-Cr-Ti and Vitallium and subjected to cyclic deflection. Representative specimens from the fatigue failure tests were then evaluated using scanning electron microscopy and analyzed for elemental content. The 5% titanium dilution of cobalt-chromium proved to have the best physical properties and was used for comparison with the pure titanium and Vitallium. The Co-Cr-5% Ti had significantly better physical properties than pure titanium and a greater flexure fatigue limit than the Vitallium alloy.
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PMID:Cobalt-chromium-titanium alloy for removable partial dentures. 948 40

In this study fatigue resistance of experimentally prepared titanium-nickel (50.8% nickel and 49.2% titanium) cast clasps was evaluated in a simulated clinical situation. The change in force required to remove the titanium-nickel clasps was recorded under a repeated placement-and-removal test on steel model abutment teeth. Commercially-pure titanium, cobalt-chromium alloy, and gold-silver-palladium-copper alloy clasps were also tested for comparison. The tips of the clasps were located in the 0.25- and 0.50-mm undercut areas of the abutments. No significant changes in the retentive force were found in titanium-nickel clasps in the 1,010 repeated cycles, whereas the other three types of clasp revealed a significant decrease in the force required for removal during the test procedures (repeated analysis of variance P < 0.001). The results suggest that the cast titanium-nickel clasp may be suitable in removable prosthodontic constructions because of its significantly less permanent deformation during service. This report also discusses clinical applicability and some current problems with this new application.
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PMID:Fatigue resistance of titanium-nickel alloy cast clasps. 949 76

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

Femoral component fracture is a rare but well-documented complication after total hip arthroplasty. Historically, most stem fractures have occurred at the middle third of the implant, where proximal stem loosening and solid distal stem fixation result in cantilever bending and eventual fatigue failure. In contrast, we report 2 early fatigue failures of well-positioned, well-fixed, cemented, forged, cobalt-chromium femoral components at the neck-shoulder junction. A contributing factor to the implant failures was heavy laser etching in a region of the implant subjected to high stresses, leading to decreased fatigue resistance and subsequent fracture.
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PMID:Early fatigue failures of cemented, forged, cobalt-chromium femoral stems at the neck-shoulder junction. 1122 1


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