Polyethylene Wear in Total Hip Arthroplasty for Suboptimal Acetabular Cup Positions and for Different Polyethylene Types: Experimental Evaluation of Wear Simulation by Finite Element Analysis Using Clinical Radiostereometric Measurements
We have examined the effects of optimal and sub-optimal cup position and different types of polyethylene on the simulated polyethylene wear. Finite Element (FE) Analysis was used, and ultra high molecular weight (UHMWPE), highly cross-linked (HCL), and E vitamin stabilized (E-poly) polyethylene were examined. We found structural stress parameters to be three times higher for a steep cup compared with a cup in optimal position. There were no differences in predicted polyethylene wear for the three examined polyethylene liners.
We further evaluated the in vivo polyethylene wear of total hip arthroplasties in 14 young patients with UHMWPE liners at mean follow-up of 5 years using model-based radiostereometric analysis (RSA). A three-dimensional estimation of polyethylene wear (femoral head penetration into the liner) located the main portion of wear in the posterior-superior part of the liner. The measured clinical wear was correlated to structural stress and strain parameters in an extended FE model of the metal-on-UHMWPE bearing coupling. All structural parameters with the extended simulation model were located in the posterior-superior part of the liner and measures were within 1 standard deviation of the clinically measured RSA wear. Stain parameters gave the best correlation.
KeywordsStrain Energy Density Polyethylene Wear Polyethylene Liner Volumetric Wear Radiostereometric Analysis
directional shear stress
- EGS models
elementary geometric shape models
root mean square error
total hip arthroplasty
ultra high molecular weight polyethylene
Von Mises stress
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