Pre-clinical evaluation of fretting-corrosion at stem-head and stem-cement interfaces of hip implants using in vitro and in silico models.

Prior to clinical use, the corrosion resistance of new prosthesis system must be verified. The fretting-corrosion mechanisms of total hip arthroplasty (THA) implants generate metal debris and ions that can increase the incidence of adverse tissue reactions. For cemented stems, there are at least two interfaces that can be damaged by fretting-corrosion: stem-head and stem-cement. This investigation aimed to evaluate, through in vitro and in silico analyses, fretting-corrosion at the stem-head and stem-cement interfaces, to determine which surface is most affected in pre-clinical testing and identify the causes associated with the observed behavior. Unimodular stems and femoral heads of three different groups were evaluated, defined according to the head/stem material as group I (SS/SS), group II (CoCr/SS), and group III (CoCr/CoCr). Seven pairs of stems and heads per group were tested: three pairs were subjected to material characterization, three pairs to in vitro fretting-corrosion testing, and one pair to geometric modeling in the in silico analysis. The absolute area of the stem body degraded was more than three times higher compared with the trunnion, for all groups. These results were corroborated by the in silico analysis results, which revealed that the average micromotion at the stem-cement interface (9.65-15.66 µm) was higher than that at the stem-head interface (0.55-1.08 µm). In conclusion, the degradation of the stem-cement interface is predominant in the pre-clinical set, indicating the need to consider the fretting-corrosion at the stem-cement interface during pre-clinical implant evaluations.

Influence of acupuncture needle physical-chemical properties on needling quality.

OBJECTIVES: This study analyzed the physical-chemical properties of three different brands of acupuncture needle, classified by acupuncturists as high (A), medium (B) and low (C) quality. METHODS: Experienced acupuncturists, rated, in terms of perceived needling quality, three acupuncture needle brands as high (A), medium (B) and low (C) quality. Next, scanning electron microscopy (SEM) images of the tip and surface finish of the needles of each brand were analyzed. A mechanical test was developed and performed to evaluate the compressive force required to insert the needles through a smooth surface (silicon). In addition, X-ray fluorescence spectroscopy (XRF) and dispersive energy spectroscopy (DES) were conducted to analyze the material composition of the needles and presence of oxidation. RESULTS: SEM images revealed that needle brands A and B presented a sharper tip and a more regular surface finish in comparison to brand C. In the insertion test, needle brands A and B had similar performance characteristics, with A requiring less force to penetrate the silicon device when compared to B, while C failed to penetrate the silicon and complete the test. The XRF analysis did not reveal any differences in material composition between the three brands. However, brand C exhibited particles embedded on the needle surface and DES confirmed oxidation. CONCLUSION: This study demonstrates that perceived needling quality by acupuncturists can be correlated with physical-chemical properties of the needles, especially those related to finishing quality of the tip and the surface of the needles.

Retrieval analysis of neck fracture on uni-modular total hip arthroplasty stems: The contributions of material processing and stem design.

Total hip arthroplasty stem fracture is an important contributor to morbidity rate and increases the cost of revision surgery. Failure is usually caused by issues related to overload, inadequate stem support, inappropriate stem design or dimensions and material processing. In this study, the role of the relationship between material characterization and biomechanical performance in the fracture of retrieved stems was explored. The stems were manufactured with forged stainless steel, had the same length, 12/14 trunnion, and 28-mm head. These stems were evaluated by macroscopic and microscopic examination to identify the causes of premature failure. Each stem was sectioned into four regions, and the cross-sections were used for the microhardness and grain size analysis. Finite element analysis (FEA) was carried out, considering the stem positioned at the femur, a musculoskeletal model, and biomechanical loading. All stems had fractured through a fatigue mechanism, mainly a unidirectional bending loading condition, with crack nucleation on the lateral side and propagation on the medial side. The numerical analysis revealed maximum mechanical stress on the lateral side of the stem neck, but this was below the yield stress calculated via the hardness. The use of a shorter head neck length could reduce the maximum mechanical stress at the neck. At a cross-section near the plane of the stem fracture, the hardness was lower than that normally reported by the ASM, and there were heterogonous and coarse grain sizes on the lateral side. The main cause of failure of the two stems analyzed was a combination of low hardness and coarse grain size, due to inappropriate materials processing, worsen by a high level of stress on the lateral side of the neck due to the large stem-head offset selected by the orthopedic surgeon.

Does the Anchor Eye Alignment Affect the Performance of the Rotator Cuff Repair? A Biomechanical Study.

PURPOSE: To investigate the metal screw-in anchor failure mode and load to failure for 2 different eyelet alignments after anchor insertion in ovine humeri. METHODS: Sixteen ovine humeri were dissected, and a 5-mm metal anchor with 2 nonabsorbable polyblend polyethylene sutures was inserted into them in the proximal position of the greater tuberosity. The alignment of the anchors after insertion was adjusted to make 2 test groups, each with 8 specimens: In group 1, the anchor eyelets were malpositioned, whereas in group 2, the anchor eyelets were aligned according to the manufacturer's instructions. After insertion, cyclic tests from 10 N to 180 N were performed with a frequency of 1 Hz for 200 cycles; specimens were then loaded to failure to evaluate the maximum load of the system and observe the associated failure mode. RESULTS: The mean ultimate failure load in group 2 was not significantly different from that in group 1 (P = .472). CONCLUSIONS: For metallic screw-in suture anchors, the alignment of the eyelet does not change the failure mode and the load to failure after cyclic loading of the bone-anchor-suture system in ovine humeri. CLINICAL RELEVANCE: Our results indicate that on the basis of this anchor model, the position of the eyelet in the greater tuberosity does not interfere directly with the biomechanical performance of the system.

Evaluation of Surface Finish and Dimensional Control of Tribological Metal-Ultra High Molecular Weight Polyethylene Pair of Commercially Available Hip Implants.

BACKGROUND: Dimensional control and surface finish of the femoral head and acetabular liner are critical factors in the manufacturing process due to the risk of increased polyethylene wear, which is the primary cause of aseptic failure of a metal/polymer hip prosthesis. The aim of this study is to perform a dimensional and surface finish analysis to evaluate the reproduction and accuracy of the manufacturing processes of metal femoral heads and ultra high molecular weight polyethylene acetabular liners. METHODS: Four femoral heads and acetabular liners from 5 manufacturers were evaluated. The methods of evaluation followed the standards ISO 7206-2:2011 and ISO 21535:2010. RESULTS: The diameter, sphericity, and roughness of the femoral heads from all the manufacturers were in accordance with the standard requirements. Only the sphericity showed a lack of repeatability among the manufacturers. The variability in sphericity was high among some manufacturers and low in others. The diameters of the acetabular liners of 2 manufacturers were not in accordance with the standard requirements. The repeatability of sphericity, thickness, and roughness of the acetabular liners were heterogeneous among the manufacturers, which means that some manufacturers need to improve quality control. CONCLUSION: Our results showed a good dimensional and surface finish control of the manufacturing processes of the femoral heads. However, the same control was not shown during the manufacturing of the acetabular liners although all samples had a thickness and sphericity in accordance with the standard. A better quality control of the manufacturing process of ultra high molecular weight polyethylene acetabular liners should be made to improve the dimensional parameters of the acetabular liners and the tribological pair.

Scanning Electron Microscopy and Energy-Dispersive X-Ray Spectroscopy as a Valuable Tool to Investigate the Ultra-High-Molecular-Weight Polyethylene Wear Mechanisms and Debris in Hip Implants.

BACKGROUND: The use of scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS) was investigated to understand the wear mechanisms from a metal-on-polyethylene bearing couple. Morphological features of femoral head acetabular liner, and isolated particles resulting from hip wear testing were evaluated. EDS was proposed to investigate the polymeric nature of the particles isolated from the wear testing. METHODS: In this work, 28-mm conventional ultra-high-molecular-weight polyethylene acetabular liners paired with metallic heads were tested in a hip wear simulator over 2 million cycles. SEM-EDS was employed to investigate wear mechanisms on hip implant components and associated wear debris. RESULTS: SEM showed worn surfaces for both hip components, and a significant volume of ultra-high-molecular-weight polyethylene wear particles resulting from hip wear testing. Particles were classified into 3 groups, which were then correlated to wear mechanisms. Group I had particles with smooth surfaces, group II consisted of particles with rough surfaces, and group III comprised aggregate-like particles. Group I EDS revealed that particles from groups I and II had a high C/O ratio raising a concern about the particle source. On the other hand, particles from group III had a low C/O ratio, supporting the hypothesis that they resulted from the wear of acetabular liner. Most of particles identified in group III were in the biologically active size range (0.3 to 20 µm). CONCLUSION: The use of optical and electron microscopy enabled the morphological characterization of worn surfaces and wear debris, while EDS was essential to elucidate the chemical composition of isolated debris.

Obtención de embriones por maduración y fertilización in vitro de oocitos bovinos / Obtaining of embryos by maturationand fertilization in vitro of oocitos bovine

El objetivo del presente estudio fue obtener embriones bovinos in vitro, partiendo de oocitos recuperados de ovarios de vacas de matadero, procedentes del altiplano de La Paz y de los llanos del Beni, que fueron madurados in vitro. Los valores de maduración in vitro, tamaño y peso de ovarios; número total y clase de oocitos por ovario, obtenidos de vacas del altiplano y La Paz, se evaluaron a través de diseño de bloques completamente al azar: mientras que en análisis de fertilización de oocitos in vitro, se empleó diseño completamente al azar. La maduración de oocitos bovinos in vitro, se llevó a cabo en medio TCM-99 a 39§C Y 5 por ciento de CO2. Para las vacas del Beni se procesaron 2698 oocitos, obteniéndose 967 (36 por ciento) oocitos en metafase II, significativamente mayor a 662 (24 por ciento) oocitos en metafase II, obtenidos, de 2756 oocitos de vacas de La Paz. La fertilización in vitro, se efectuó en medio Talp a 39§C y 5 por ciento de CO2. Para las vacas del Beni se analizaron 956 oocitos, obteniéndose 213 (19.6 por ciento) embriones, significativamente superior a los obtenidos de las vacas de La Paz, en los que se evaluaron 973 oocitos y se obtuvieron 162 (16.2 por ciento) embriones

Evaluación de un efecto anticonceptivo de la Persea americana en un modelo experimental en ratas / Evaluation of an effect contraceptive of the pesea American in an experimental model in rats

Con el propósito de explorar nuevos productos para el control de la fecundidad a partir de la flora medicinal nativa, se desarrolló un Modelo Experimental en ratas para evaluar un efecto anticonceptivo post-coital (antiimplantación de embriones), del extracto acuoso total de las semillas de la Persea americana (palta). Para este estudio se utilizaron ratas hembras de la cepa Sprague Dawly, en las cuales el Ciclo Estral fue controlado diariamente mediante frotis vaginales. Se estandarizó el procedimiento de evaluación de la no implantación en el útero de ratas control de preñez, explorando el número de cuerpos lúteos y el número de implantaciones, y se desarrolló el Test de Antiimplantación en el útero de ratas tratadas con la P. americana para evaluar el efecto anticonceptivo. Una primera experiencia mostró una actividad de antiimplantación embrionaria con promedios de 13 por ciento, 24 por ciento, 44 por ciento y 45 por ciento a dosis de 0.001, 0.01, 0.1 y 1 g/Kg de peso, respectivamente. Los controles positivos de preñez, en los cuales solamente se administró el vehículo, mostraron promedios de 23 por ciento de no implantaciones. En una segunda experiencia con las mismas dosis, en la que se hicieron ajuste en las condiciones de habitat, se mostró una actividad de antiimplantación con promedios de 11 por ciento, 18 por ciento, 27 por ciento y 37 por ciento, respectivamente; los controles positivos de preñez mostraron un promedio de 8 por ciento de ausencia de implantaciones. Se discute las posibilidades de este Modelo para la exploración y estudio de otros productos con actividad anticonceptiva, así como las perspectivas de la Persea americana en este propósito