Simulator Study of MOM using Steep-cup Flexion - A Clinically Relevant Incorporation of Intermittent Edge-loading

Background: Adverse-wear phenomenon in metal-on-metal (MOM) arthroplasty has been attributed to “edge-loading” of the CoCr cups. Simulator studies of steeply-inclined cups run in the ‘Anatomic-cup’ model represented many variations in design and test parameters with no coherent rationale. We created an algorithm to synthesize MOM test parameters and noted that wear areas typically averaged only 10-15% of cup surface. In contrast, retrievals showed wear areas extending to 60% of cup surface. We hypothesized that MOM wear studies run in the orbital hip simulator with the ‘Inverted-cup’ model would, (i) differentiate normal-loading versus edge-loading, (ii) demonstrate cup wear areas x3.8-times larger than on femoral heads, cover 30% of cup surface, and (iii) double the wear-rates measured in prior Anatomic-cup study.Methods: Edge-loading occurs when the cup rim is allowed to truncate the habitual wear area that provides optimal tribological conditions. A MOM algorithm was developed to synthesize relevant test parameters. The 60mm MOM bearings donated for this study were run in an orbital hip simulator using the Inverted-cup model. Tests #1 and #2 to one million cycles (1-Mc) duration assessed wear at peak cup inclinations 40° and 50°. Test #3 evaluated edge-loading with peak cup inclinations achieving 70° (5-Mc duration).Results: Wear areas in Inverted-cups averaged 1663mm2 in tests #1 and 2, were fully contained within cup rims, and covered 30% of cup surface as predicted by algorithm. Test-3 with 70° cup inclination produced the predicted edge-loading with volumetric wear-rates averaging 2mm3/Mc, approximately 5-fold greater wear than prior Anatomic-cup study.Discussion and Conclusions: Simulator studies of steep-cup mechanisms necessitate production of clinically-relevant wear-patterns such that the biomechanical and tribological functionality is respected. As an aid to steeply-inclined cup analyses, the MOM algorithm allowed integration of confounding test parameters. The algorithm successfully differentiated between “normal” and “edge loaded” cups and the MOM wear areas were as predicted for three cup inclinations. Also as predicted, wear-patterns in Inverted-cup model exactly reversed those of the Anatomic-cup model. Even with only intermittent edge-loading, Test-3 produced 5-fold greater wear than our prior Anatomic study.Clinical Significance: The Inverted-cup simulator model successfully mobilized the cup to produce larger wear areas that were more representative of those in-vivo and therefore reproduced more realistic test conditions for studies of edge-loaded cups.

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Can cobalt levels estimate in-vivo wear of metal-on-metal bearings used in hip arthroplasty?

Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine ◽

10.1243/09544119jeim270 ◽

2007 ◽

Vol 221 (8) ◽

pp. 929-942 ◽

Cited By ~ 10

Author(s):

M Khan ◽

J H Kuiper ◽

J B Richardson

Keyword(s):

Clinical Studies ◽

Wear Debris ◽

Metal Ion ◽

Large Diameter ◽

Small Diameter ◽

Wear Rates ◽

Hip Simulator ◽

Metal On Metal ◽

Metal Levels

High levels of cobalt and chromium ions are detected in the blood and urine of patients with metal-on-metal (MoM) hip replacement. These elements are released as a result of wear at the bearing surfaces. Wear rates depend on a multitude of factors, which include the bearing geometry, carbon content, manufacturing processes, lubrication, speed and direction of sliding of the surfaces, pattern of loading, and orientation of the components. In-vivo wear of MoM bearings cannot be reliably measured on X-rays because no distinction can be made between the bearing surfaces. Hip simulator studies have shown that wear rates are higher during the initial bedding-in phase and subsequently drop to very low levels. Accordingly, metal ion levels would be expected to decrease with the use of the bearing, measured as implantation time following surgery. However, several clinical studies have found that metal ion levels either gradually rise or fluctuate instead of decreasing to lower levels. Moreover, hip simulator studies predict that large-diameter bearings have lower wear rates than small-diameter bearings. In clinical studies, however, metal levels in patients with large-diameter bearings are unexpectedly higher than those in patients with small-diameter bearings. As a consequence, high cobalt ion levels in patients do not necessarily imply that their MoM bearings produce much wear debris at the time that their levels were measured; it may simply be due to accumulation of wear debris from the preceding time. Exercise-related cobalt rise may overcome this limitation and give a better assessment of the current wear status of a MoM bearing surface than a measure of cobalt levels only.

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Wear Simulation of Metal on Metal Hip Replacements: An Analytical Approach

Volume 4: Advanced Manufacturing Processes; Biomedical Engineering; Multiscale Mechanics of Biological Tissues; Sciences, Engineering and Education; Multiphysics; Emerging Technologies for Inspection ◽

10.1115/esda2012-82393 ◽

2012 ◽

Cited By ~ 1

Author(s):

Lorenza Mattei ◽

Francesca Di Puccio ◽

Enrico Ciulli

Keyword(s):

Hip Replacement ◽

Experimental Tests ◽

Wear Model ◽

Wear Rates ◽

Metal On Metal ◽

Hip Replacements ◽

Wear Law ◽

Implant Wear

Hip replacement failure is mainly attributable to the implant wear. Consequently preclinical wear evaluations are extremely important. As experimental tests are attractive but highly cost/time demanding, several predictive models have been proposed mainly based on finite element simulations and for metal on plastic (MoP) implants. The aim of this study is to develop a mathematical wear model of metal on metal prostheses, revision of the previous one for MoP implants, developed by the same authors. The model, based on the Archard wear law and on the Hertzian theory, was applied to compare a total (THR) and a resurfacing (RHR) hip replacement under both in vivo and in vitro gait conditions. The results were in agreement with the literature predicting wear rates significantly higher for the RHR than for the THR. The effect of the boundary conditions on wear rates/maps was also investigated and the model limitations discussed.

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Understanding the differences between the wear of metal-on-metal and ceramic-on-metal total hip replacements

Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine ◽

10.1243/09544119jeim363 ◽

2008 ◽

Vol 222 (3) ◽

pp. 285-296 ◽

Cited By ~ 20

Author(s):

C G Figueiredo-Pina ◽

Y Yan ◽

A Neville ◽

J Fisher

Keyword(s):

Open Circuit ◽

Long Term Results ◽

Cobalt Chromium ◽

Material Loss ◽

Hip Simulator ◽

Metal On Metal ◽

Hip Replacements ◽

Efficient Alternative

Hip simulator studies have been carried out extensively to understand and test artificial hip implants in vitro as an efficient alternative to obtaining long-term results in vivo. Recent studies have shown that a ceramic-on-metal material combination lowers the wear by up to 100 times in comparison with a typical metal-on-metal design. The reason for this reduction remains unclear and for this reason this study has undertaken simple tribometer tests to understand the fundamental material loss mechanisms in two material combinations: metal-on-metal and ceramic-on-ceramic. A simple-configuration reciprocating pin-on-plate wear study was performed under open-circuit potential (OCP) and with applied cathodic protection (CP) in a serum solution using two tribological couples: firstly, cobalt—chromium (Co—Cr) pins against Co—Cr plates; secondly, Co—Cr pins against alumina (Al2O3) plates. The pin and plate surfaces prior to and after testing were examined by profilometry and scanning electron microscopy. The results showed a marked reduction in wear when CP was applied, indicating that total material degradation under the OCP condition was attributed to corrosion processes. The substitution of the Co—Cr pin with an Al2O3 plate also resulted in a dramatic reduction in wear, probably due to the reduction in the corrosion—wear interactions between the tribological pair.

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STEROID METABOLISM IN THE PERFUSED HUMAN PLACENTA

Acta Endocrinologica ◽

10.1530/acta.0.0870181 ◽

1978 ◽

Vol 87 (1) ◽

pp. 181-191 ◽

Cited By ~ 6

Author(s):

Alfred S. Wolf ◽

Klaus A. Musch ◽

Werner Speidel ◽

Jürgen R. Strecker ◽

Christian Lauritzen

Keyword(s):

Venous Blood ◽

Placental Lactogen ◽

Dehydroepiandrosterone Sulphate ◽

Metabolic Capacity ◽

Loading Test ◽

Lower Range ◽

Group I ◽

High Concentrations ◽

Steroid Precursor

ABSTRACT A new model for the perfusion of human term-placentas has been developed for studies on the placental biogenesis of C-18 and C-19 steroids. For viability criteria, the glucose- and oxygen-consumption, regional perfusion control by dye-infusions or scanning after injection of 99Tc-labelled macroparticles, and the histological qualification were chosen. The recycled perfusate was investigated for the steroids oestrone (Oe1), oestradiol-17β (Oe2), oestriol (Oe3), 4-androstene-3,17-dione (A), testosterone (T), and human placental lactogen (HPL) by radioimmunoassay in controls and perfusions with the foetal steroid precursor dehydroepiandrosterone sulphate (DHA-S). In control perfusions, steroid hormones were found in constant ratios (Oe1:Oe2:Oe3:T:A = 30:1.5:100:0.35:1). Following the administration of 10 mg DHA-S for testing the metabolic capacity of the organ, high concentrations of Oe1 (90–720 ng/ml = 250–3970 % as compared to 100% pre-injection values) were found, shortly preceded by a rapid increase of A (66–1000 ng/ml = 100–16 000 %). A typical surge of T (5.3–147 ng/ml = 265–4640 %) preceded the normally slower increment of Oe2 (22–220 ng/ml = 1570–4330 %). The concentrations of Oe3 and HPL remained nearly unchanged. From different steroid patterns after DHA-S-load, two distinct responses of term-placentas could be differentiated: Group I (n=12) showed high concentrations of Oe1 (3200 ± 940 %), a small increase of T (1020 ± 500%), as well as low and delayed values of Oe2 (1660 ± 450%). In Group II (n = 5), values were high for T (3160 ± 1020%) and Oe2 (3300 ± 1110%), whereas Oe1 was found in a lower range (508 ± 302%). In contrast to in vivo findings in maternal venous blood after DHS-S injection to the mother, oestrone was found in perfusions as the main oestrogen fraction from DHA-S. Thus, the analysis of such metabolic differences might be of help in the interpretation of complex results from the DHA-S-loading test.

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Influence of Test Conditions on Sliding Wear Performance of High Velocity Air Fuel-Sprayed WC–CoCr Coatings

Materials ◽

10.3390/ma14113074 ◽

2021 ◽

Vol 14 (11) ◽

pp. 3074

Author(s):

Kaveh Torkashvand ◽

Vinod Krishna Selpol ◽

Mohit Gupta ◽

Shrikant Joshi

Keyword(s):

Wear Rate ◽

Test Performance ◽

Sliding Wear ◽

Normal Load ◽

Specific Wear Rate ◽

Wear Behaviour ◽

Wear Performance ◽

Test Conditions ◽

Test Parameters ◽

Sliding Distance

Sliding wear performance of thermal spray WC-based coatings has been widely studied. However, there is no systematic investigation on the influence of test conditions on wear behaviour of these coatings. In order to have a good understanding of the effect of test parameters on sliding wear test performance of HVAF-sprayed WC–CoCr coatings, ball-on-disc tests were conducted under varying test conditions, including different angular velocities, loads and sliding distances. Under normal load of 20 N and sliding distance of 5 km (used as ‘reference’ conditions), it was shown that, despite changes in angular velocity (from 1333 rpm up to 2400 rpm), specific wear rate values experienced no major variation. No major change was observed in specific wear rate values even upon increasing the load from 20 N to 40 N and sliding distance from 5 km to 10 km, and no significant change was noted in the prevailing wear mechanism, either. Results suggest that no dramatic changes in applicable wear regime occur over the window of test parameters investigated. Consequently, the findings of this study inspire confidence in utilizing test conditions within the above range to rank different WC-based coatings.

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Simple isolation method for the bulk isolation of wear particles from metal on metal bearing surfaces generated in a hip simulator test

Journal of Materials Science Materials in Medicine ◽

10.1007/s10856-012-4573-y ◽

2012 ◽

Vol 23 (4) ◽

pp. 891-901 ◽

Cited By ~ 12

Author(s):

Fang Lu ◽

Matt Royle ◽

Ferdinand V. Lali ◽

Alister J. Hart ◽

Simon Collins ◽

...

Keyword(s):

Wear Particles ◽

Isolation Method ◽

Hip Simulator ◽

Metal On Metal ◽

Simulator Test

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Individual motion patterns during gait and sit-to-stand contribute to edge-loading risk in metal-on-metal hip resurfacing

Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine ◽

10.1177/0954411913483639 ◽

2013 ◽

Vol 227 (7) ◽

pp. 799-810 ◽

Cited By ~ 33

Author(s):

Stephen J Mellon ◽

George Grammatopoulos ◽

Michael S Andersen ◽

Elise C Pegg ◽

Hemant G Pandit ◽

...

Keyword(s):

Hip Resurfacing ◽

Motion Patterns ◽

Sit To Stand ◽

Metal On Metal ◽

Edge Loading

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Influence of loading rate on the capacity of a model pile in clay

Canadian Geotechnical Journal ◽

10.1139/t95-036 ◽

1995 ◽

Vol 32 (2) ◽

pp. 364-368 ◽

Cited By ~ 5

Author(s):

Robert G. Horvath

Keyword(s):

Loading Rate ◽

Axial Loading ◽

Displacement Transducer ◽

Test Methods ◽

Point Load ◽

Test Results ◽

Loading Test ◽

Normal Loading ◽

Model Pile ◽

Rate Of Loading

Loading tests were carried out on a model pile embedded in clay to examine the influence of rate of loading on the capacity of the pile. The pile was loaded to failure using constant rate of penetration (CRP), quick maintained loading (QML), and quick continuous loading (QCL) methods of loading. The QCL test models the Statnamic loading test, which has been recently developed in Canada. The CRP tests were used as a reference, and the results were normalized using the CRP test results. The durations of the QML and QCL tests varied from approximately 0.1 s to 17 min, which are significantly faster than normal loading rates. Applied loads and point load were measured using load cells, and top displacement was measured using a displacement transducer. The test results showed an increase in pile capacity with increased rate of loading. Damping was found to be significant for the QCL tests (duration = 0.1 s) and negligible for the QML tests (duration ≥ 10 s). Correcting the results of the QCL tests for damping, using the equilibrium point method developed for Statnamic testing, greatly improved the correlation of the QCL and QML test results. Key words : model piles, axial loading, loading rate, clay, laboratory study, test methods.

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