Introduction: Although there has been significant progress in the design of implants for osteosynthesis, the occurrence of failures in these medical devices are still frequent. These implants are prone to suffer from fretting corrosion due to micromotion that takes place between the screw heads and plate holes. Consequently, fretting corrosion has been the subject of research in order to understand its influence on the structural integrity of osteosynthesis implants. The aim of this paper is to correlate the surface finish characteristics of bone plate-screw systems with fretting corrosion. Methods: The surface finish (machined and polished) of five specimens taken from three commercial dynamic compression plates (DCP) were evaluated. For testing, the specimens were fixed with bone screws, immersed in a solution of 0.90% NaCl and subjected to a rocking motion with an amplitude of 1.70 mm and frequency of 1.0 Hz for 1.0 × 10 6 cycles, according to the ASTM F897 standard. Both, plate and screws were manufactured in Brazil with ASTM F138 stainless steel. Results: Flaws on the hole countersink area and on the screw thread of some specimens were identified stereoscopically. At the end of the test all the specimens showed evidence of fretting corrosion with an average metal loss of 4.80 mg/million cycles. Conclusion: An inadequate surface finish in some areas of the plates and screws may have favored the incidence of damage to the passive film, accelerating the fretting corrosion at the interfaces between the plate hole countersink and the screw head.
In the present work, the corrosion resistance of an ASTM A 387 G11 steel was evaluated under two conditions: an oxidizing atmosphere in a fluid catalytic cracking regenerator of a petroleum processing unit and a simulated atmosphere in the laboratory, at temperatures of 650 °C and 700 °C. The characterization of the phases present in the oxidized layer was carried out by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM) with X-ray energy dispersive analysis (EDS). Severe corrosion was observed after exposure to both the real and simulated conditions, with formation of several iron oxides (Fe2O3, Fe3O4 and FeO) in the product scale layer, as well as a slight inner oxidation and sulfidation of chromium in the substrate. Internal nitridation of the silicon and the manganese was observed only in the real condition, probably related to the long-term exposure inside the regenerator
The increasing lifetime of the population on a world-wide scale over the last decades has led to a significant growth in the use of surgical implants for replacement of bones and teeth in affected patients. Other factors, such as scientific-technological development and more frequent exposure of individuals to trauma risk, have also contributed to this general trend. Metallic materials designed for applications in surgical implants, no matter whether orthopedic or dental, must show a group of properties in which biocompatibility, mechanical strength, and resistance to degradation (by wear or corrosion) are of primary importance. In order to reach these aims, orthopedic materials must fulfill certain requirements, usually specified in standards. These requirements include chemical composition, microstructure, and even macrographic appearances. In the present work, three cases of implant failure are presented. These cases demonstrate the most frequent causes of premature failure in orthopedic implants: inadequate surgical procedures and processing/ design errors. Evaluation techniques, including optical and scanning electron microscopy (SEM), were used to evaluate macroscopic and microstructural aspects of the failed implants, and the chemical composition of each material was analyzed. These evaluations showed that design errors and improper surgical procedures of outright violation of standards were the cause of the failures.
Femoral stem fractures in total hip arthroplasty (THA) are a problem in clinical practice that results in great morbidity and high cost of revision hip surgery. Stem fractures are multifactorial events that are usually related to a combination of factors that increase the mechanical stress on the stem or decrease the mechanical strength of the implant. Failure analyses of hip prosthesis have identified that the presence of inadequate grain size may lead to implant failure. The aim of this article is to develop a rational to set specific sites to perform grain size measurements along stems used in THA as well as appropriate procedures to evaluate the heterogeneity of the microstructure related to the grain size distribution. In the present study, nonmodular femoral stems from three manufacturers with different wrought materials were chosen: stainless steel ISO 5832-1 (Manufacturer I), high nitrogen stainless steel ISO 5832-9 (Manufacturer II), and cobalt-chromium-molybdenum alloy ISO 5832-12 (Manufacturer III). The results of this study showed a great variability of grain size number depending on the cross section and fields evaluated. Therefore, the current technical standards for evaluating THA stems need to be modified. Analyses of grain sizes at different cross sections and inside each cross section of the stem is necessary to ensure the safety of hip stems.
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