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20 Cards in this Set
- Front
- Back
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What is the coefficient for friction for a native hip? What is the primary lubrication method?
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0.002 to 0.04
Elastohydrodynamic lubrication (surface deforms slightly) |
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Hard-on-soft bearings generate particles of what size? Hard-on-soft bearings are primarily lubricated by what method? What head sizes tend to generate the least volumetric wear?
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0.2 to 7 um
Boundary lubrication (contact between high points on surfaces) Smaller head minimizes volumetric wear |
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Hard-on-hard bearings generate particles of what size? Hard-on-hard bearings are primarily lubricated by what method? What head sizes tend to generate the least volumetric wear?
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<0.12um
Mixed lubrication (boundary and hydrodynamic) Larger head minimizes volumetric wear |
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Compare the annual wear rates of ultra high molecular weight polyethylene (UHMWPE), metal-metal, and ceramic-ceramic?
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UHMWPE: 100 um/year
Metal-metal: 5um/year Ceramic-ceramic: 2.5 um year |
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What type of wear is particularly problematic for polyethylene-titanium articulations?
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Volumetric wear
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What manufacturing process for polyethylene is generally most favored?
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Direct compression molding
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What manufacturing process is viewed least favorably?
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Heat processing
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What is the optimal crystallinity for PE?
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50%
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Has the addition of calcium stearate to PE been helpful or detrimental in terms of wear?
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Detrimental
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At what doses is highly cross-linked PE irradiated?
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5 to 15 megarads
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Polyethylene irradiation leads to the development of what structures?
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Free radicals
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If free radicals cross-link in an oxygen-free environment, what are the upside and downside?
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Upside: decreased wear rates
Downside: decreased mechanical properties |
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If free radicals cause chain scission, what is the possible negative clinical consequence?
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Delamination
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How are residual free radicals removed?
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Heat annealing
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What is the most common cause of polyethylene wear?
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Third-body wear
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What is the problem with titanium bearing surfaces? This is also referred to as what?
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Easily scratched
Notch sensitivity |
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The premature development of osteolysis in metal-on-metal THA may suggest what condition?
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Smaller
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Is alumina or Zirconia the preferred ceramic? Why?
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Alumina
Zirconia undergoes phase change to tetragonal configuration |
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When revising a ceramic THA, what procedure must also be performed?
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Synovectomy
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What three factors are predictive of worse outcomes in ceramic revisions?
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Retained acetabular component
Young patient Stainless steel head used |
