Rapid Sintering and Synthesis of Nanocrystalline Ta-ZrO2 Composite

ZrO₂ is a promising candidate for knee and hip joint replacements due to its excellent combination of low density, corrosion resistance and biocompatibility. Nevertheless, a low fracture toughness of pure ZrO₂ at room temperature limits its wider application in the industry. One of the most obvious ways to solve the problem is to add a reinforcing phase, to produce a nanocrystalline composite material. Nanomaterials have been widely studied in recent years because they can improve hardness and fracture toughness. To produce nanocrystalline materials, the pulsed current activated sintering method has the advantage of simultaneously applying mechanical pressure and pulsed current during sintering. As a result, nanocrystalline materials can be produced within a very short time. Ta and ZrO₂ nanopowders were mechanically synthesized from Ta₂O₅ and 2.5Zr powders according to the reaction (Ta₂O₅ + 5/2Zr → 2Ta + 5/2ZrO₂). The synthesized powders were then sintered using pulsed current activated heating under 80 MPa uniaxial pressure within two minutes. Hardness and fracture toughness were measured using a Vickers hardness tester. The average hardness and fracture toughness of the nanocrystalline 2Ta-5/2ZrO₂ composite sintered at 1350 ^oC were 1008 kg/mm² and 10 MPa·m^1/2, respectively. Both the hardness and fracture toughness of the composite were higher than monolithic ZrO₂. The microstructure and phase of the composite was also investigated by FE-SEM and XRD.

Korean epidemiology and trends in hip joint replacements

This study aimed to analyze the epidemiologic characteristics of patients who underwent hip arthroplasty using the Korean nationwide database and investigate the recent trends in implant fixation methods and bearing surface selection. We aimed to compare clinical characteristics and differences with the results from the registry of other western countries. We analyzed the data collected by the Health Insurance Review and Assessment Service database of Korea from 2007 to 2011 and the Main Surgery Statistical Yearbook from 2014 to 2018, published by the National Health Insurance Service. The number and rate of patients who underwent hip joint arthroplasty per 10,000 persons have been steadily increasing since 2007. There was a big difference in mean age and preoperative diagnosis of patients between the bipolar hemiarthroplasty and total hip arthroplasty groups. Most patients underwent surgery using a cementless biological fixation method, and the cemented fixation method was selectively used for a small portion of old aged osteoporotic patients. In relation to the use of bearing surfaces, the registry data showed that ceramic-ceramic bearings were used at an overwhelmingly high rate (81%) in Korea compared to other countries. The reason was attributable to various factors, such as patient’s age or economic status, differences in the health insurance system between countries, and recently reported complications, such as ceramic fracture or noise.

Comparison of Different Locking Mechanisms in Total Hip Arthroplasty: Relative Motion between Cup and Inlay

The resulting inflammatory reaction to polyethylene (PE) wear debris, which may result in osteolysis, is still considered to be a main reason for aseptic loosening. In addition to the primary wear in hip joint replacements caused by head-insert articulation, relative motions between the PE liner and the metal cup may cause additional wear. In order to limit this motion, various locking mechanisms were used. We investigated three different locking mechanisms (Aesculap, DePuy, and Zimmer Biomet) to address the resulting relative motion between the acetabular cup and PE liner and the maximum disassembly force. A standardized setting with increasing load levels was used in combination with optically based three-dimensional measurements. In addition the maximum disassembly forces were evaluated according to the ASTM F1820-13 standard. Our data showed significant differences between the groups, with a maximum relative motion at the maximum load level (3.5 kN) of 86.5 ± 32.7 µm. The maximum axial disassembly force was 473.8 ± 94.6 N. The in vitro study showed that various locking mechanisms may influence cup-inlay stability.