Highly crosslinked polyethylene improves wear but not surface damage in retrieved acetabular liners.

Abstract

Highly crosslinked polyethylene (XLPE) is believed to demonstrate better wear resistance than conventional polyethylene (CPE) in total hip arthroplasty. The purpose of this study was to compare visual damage scores and micro-CT measurements of penetration, a surrogate for wear, between matched retrieved XLPE and CPE acetabular liners. Thirteen XLPE acetabular liners were matched in terms of implant design (all were of the same design), patient age, sex, liner dimensions, duration of implantation, and reason for revision to a group of CPE liners that were retrieved in the same time period. Penetration resulting from the combination of wear and creep in the two groups of liners was measured with micro-CT. Surface damage was scored by two blinded observers using a surface damage system that considers the seven common damage modes: pitting, scratching, burnishing, abrasions, impingement, embedded debris, and delamination, and wear patterns were documented. There was no difference (p=0.32) in total damage score between the XLPE group (14±4) and the CPE group (15±5). However, there was three times greater penetration (odds ratio, 3.1; confidence interval, 2.3-5.1; p<0.001) in the CPE group (0.18±0.09 mm/year) than in the XLPE group (0.05±0.07 mm/year). There was less volumetric loss in XLPE (82±SD 134 mm3) versus the CPE group (350±SD 342 mm3; p=0.017). XLPE liners undergo less penetration as a result of creep and wear than CPE liners based on quantitative measurements provided by micro-CT, which was not apparent using damage scoring alone. This demonstrates the use of three-dimensional imaging techniques such as micro-CT for quantifying wear in retrieval studies. In this study, XLPE had less wear but similar damage scores than CPE, allaying concerns that the beneficial wear properties of XLPE might come with a tradeoff arising from the increased brittleness of that material.