When using the current version of this test method on its rotating platform knee designs, DePuy experiences dislocation of the femur off the back of the bearing in the 1st few cycles of the dynamic test when using the A/P shear loading as specified in paragraph 7.5.1 (90% of the peak load to dislocate in the initial static test). In order to resolve this, we have had to use a lower shear load in that direction only. We obtained the lower load value by doing the static test of paragraph 7.5.1 multiple times on the same bearing. We find that the peak load drops with each successive cycle until it levels out. We then use 90% of that value for our 110,000 cycle dynamic test to avoid the femoral dislocation.
Citing ASTM Standards
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