Wear of composite ceramics in mixed-material combinations in total hip replacement under adverse edge loading conditions

Further development of ceramic materials for total hip replacement aim to increase fracture toughness and further reduce the incidence of bearing fracture. Edge loading due to translational mal positioning (microseparation) has replicated stripe wear, wear rates, and bimodal wear debris observed on retrievals. This method has replicated the fracture of early zirconia ceramic-on-ceramic bearings. This has shown the necessity of introducing microseparation conditions to the gait cycle when assessing the tribological performance of new hip replacement bearings. Two novel ceramic matrix composite materials, zirconia-toughened alumina (ZTA) and alumina-toughened zirconia (ATZ), were developed by Mathys Orthop€adie GmbH. In this study, ATZon- ATZ and ZTA-on-ZTA bearing combinations were tested and compared with alumina-on-alumina (Al2O3-on-Al2O3) bearings under adverse microseparation and edge loading conditions using the Leeds II physiological anatomical hip joint simulator. The wear rate (695% confidence limit) of ZTA-on-ZTA was 0.1460.10 mm3/million cycles and that of ATZ-on-ATZ was 0.0660.004 mm3/million cycles compared with a wear rate of 0.7461.73 mm3/million cycles for Al2O3- on-Al2O3 bearings. Stripe wear was evident on all bearing combinations; however, the stripe formed on the ATZ and ZTA femoral heads was thinner and shallower that that formed on the Al2O3 heads. Posttest phase composition measurements for both ATZ and ZTA materials showed no significant change in the monoclinic zirconia content. ATZon- ATZ and ZTA-on-ZTA showed superior wear resistance properties when compared with Al2O3-on-Al2O3 under adverse edge loading conditions. VC 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 00B: 000–000, 2013

Contact mechanics of modular metal-on-polyethylene total hip replacement under adverse edge loading conditions

Edge loading can negatively impact the biomechanics and long-term performance of hip replacements. Although edge loading has been widely investigated for hard-on-hard articulations, limited work has been conducted for hard-on-soft combinations. The aim of the present study was to investigate edge loading and its effect on the contact mechanics of a modular metal-on-polyethylene (MoP) total hip replacement (THR). A three-dimensional finite element model was developed based on a modular MoP bearing. Different cup inclination angles and head lateral microseparation were modelled and their effect on the contact mechanics of the modular MoP hip replacement were examined. The results showed that lateral microseparation caused loading of the head on the rim of the cup, which produced substantial increases in the maximum von Mises stress in the polyethylene liner and the maximum contact pressure on both the articulating surface and backside surface of the liner. Plastic deformation of the liner was observed under both standard conditions and microseparation conditions, however, the maximum equivalent plastic strain in the liner under microseparation conditions of 2000 µm was predicted to be approximately six times that under standard conditions. The study has indicated that correct positioning the components to avoid edge loading is likely to be important clinically even for hard-on-soft bearings for THR

Effect of Impact Assembly on the Interface Deformation and Fretting Corrosion of Modular Hip Tapers: an in Vitro Study

Wear and corrosion at the modular head–neck junction has been recognised to be a potential clinical concern, with multiple reports on adverse local tissue reactions and subsequent early failure of metal‐on‐metal hip replacements. Furthermore, reports on head–neck taper corrosion are also being described with conventional metal‐on‐polyethylene bearings. Manufacturing tolerances, surgical technique, non‐axial alignment, material combination, high frictional torque and high bending moment have all been implicated in the failure process. There is limited guidance on the force of impaction with which surgeons should assemble modular hip prostheses. This study aims to investigate the effect of impaction force on the deformation and corrosion of modular tapers. Short neck tapers with high surface roughness (average Rz = 16.58 μm, Ra = 4.14μm) and long neck tapers with low surface roughness (average Rz = 3.82 μm, Ra = 0.81μm), were assembled with CoCrMo alloy heads (smooth finish) under controlled conditions with 2, 4 or 8 kN of impaction force. Material combinations tested included CoCrMo‐head/CoCrMo‐neck and CoCrMo‐head/Ti‐6Al‐4V‐neck. Assessment of surface deformation before and after impaction was made using surface profilometry. Measurement of fretting current during sinusoidal cyclic loading evaluated mechanically assisted corrosion for each assembly load during short‐term cyclic loading (1000‐cycles) and long‐term cyclic loading (5 million‐cycles). Deformation on head and neck tapers increased with assembly load. Fretting currents during short term simulation testing showed significantly lower currents (p < 0.05), in 8 kN assemblies when compared to 2 and 4 kN, especially for the short‐rough tapers. Long‐term simulator testing demonstrated a progressive reduction in fretting corrosion for samples impacted with 4 and 8 kN; however, this reduction was greater for samples impacted at 8 kN even at the start of testing. Based on our results, surgeons could minimise mechanically assisted crevice corrosion by using higher impact loads when assembling the head to the stem in total hip arthroplasty

A review of squeaking in ceramic total hip prostheses

The occurrence of audible squeaking in some patients with ceramic-on-ceramic (CoC) hip prostheses is a cause for concern. Considering multifactor contributing to this phenomenon, many studies have been conducted over the last decade. Great efforts have been put on understanding the mechanics of the hip squeaking to gain a deep insight into factors resulting in sound emission from hip articulation. Disruption of fluid-film lubrication and friction were reported as main potential causes of hip squeaking, while patient and surgical factors as well as design and material of hip implants were identified as affecting factors. This review article therefore summarised the recent available literature on this subject to provide a platform for future developments. Moreover, high wear rates and ceramic liner fracture as viable consequences of hip squeaking were discussed.The first author gratefully acknowledges Macquarie University for International Macquarie University Research Excellence Scholarship (iMQRES)-No. 2010017. The second author would like to thank to the Portuguese Foundation for Science and Technology through the project UID/EEA/04436/2013

In vitro wear of metal on metal hip replacements: a multifactorial problem

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

In vitro wear of metal on metal hip replacements: a multifactorial problem

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Efficiency of Some Selective Herbicides in Canola (Brassica napus L.) Cultivation and Their Interaction with Biofarm Biological Fertilizer

To evaluate the effect of herbicides and biofarm (Pseudomonas spp.) as biological fertilizer on weeds and yield components of canola, a factorial experiment based on randomized complete block design with three replications was conducted at Agricultural Research Center of East Azarbaijan in 2009. The treatment factors consisted of herbicide (factor A) at 4 levels (application of trifloralin, Treflan, at 2.5 l/ha as pre-planting, chlopyralid, Lontrel, at 0.8 l/ha when canola plants were at 2-4 leaf stage, metazachlor+quinmerac, Butizan star, at 2.5 l/ha at cotyledonous stage of canola, and not controlling the weeds as check. Biological fertilizer (factor B) at 2 levels, using or not using the biofarm. Wild mustard (Sinapis arvvensis) and tansy mustard (Descurainia sophia), being in same family with canola, were the dominant weeds in the field. Traits like number of species and biomass of weeds, biomass and yield of the crop were recorded to evaluate the effects of the treatments. The statistical analysis indicated that Botizan star and Treflan, compared with control, significantly reduced the number and biomass of wild mustard. In spite of non significant effect of the herbicide on number of tansy mustard and total weed, Botizan star and Treflan significantly reduced their biomasses. Application of biofarm and its interaction with herbicides did not influence the evaluated traits significantly. The herbicides, also, did not have significant effect on biomass and yield of the crop