Less Midterm Damage and Oxidation Are Seen in Retrieved Highly Crosslinked Ultrahigh-Molecular-Weight Polyethylene Tibial Inserts than in Direct Compression Molded Polyethylene Inserts
Highly crosslinked ultrahigh-molecular-weight polyethylene (XLPE) shows reduced wear in total hip arthroplasty compared to direct compression-molded polyethylene (compPE); however, minimal research evaluating polyethylene damage in XLPE tibial inserts in total knee arthroplasty exists.
We evaluated damage and material properties in retrieved XLPE components at midterm (≥ 2.5 years) follow-up.
We identified 19 XLPE tibial inserts with ≥ 30 months in vivo using our institutional review board–approved implant retrieval system; 19 compPE retrieved inserts were matched based on age at index surgery, body mass index, sex, and length of implantation. Articular surface damage was assessed using a subjective grading system. Swell ratio testing and Fourier-transform infrared spectroscopy were used to measure crosslink density (XLPE) and oxidation (XLPE, compPE), respectively, at loaded and unloaded surface and subsurface regions.
CompPE inserts had higher overall damage than XLPE inserts, specifically at the post of posterior-stabilized inserts. The XLPE inserts had lower crosslink density at the loaded surface (0.159 mol/dm3) than either unloaded region (0.183 mol/dm3). CompPE peak oxidation index (OI) was greater than XLPE peak OI in the loaded and unloaded surface regions (1.67 vs. 0.61 and 1.38 vs. 0.46, respectively).
Surface damage and oxidation are reduced in XLPE inserts compared to compPE at midterm follow-up. Peak OI greater than 1.0 in the compPE group suggests that mechanical-property degradation had occurred, a likely cause for increased damage. Longer-term retrievals will determine whether these trends continue. Based on midterm results, XLPE shows an advantage over compression molded PE in total knee arthroplasty.
KeywordsCrosslink density Oxidation analysis Polyethylene degradation Surface damage Total knee arthroplasty
We thank Christina Esposito, PhD, at Hospital for Special Surgery, for her role in helping to complete data collection for this research.
Compliance with Ethical Standards
Conflict of Interest
Alexandra Stavrakis, MD, and Lydia Weitzler, MS, declare that they have no conflicts of interest. Timothy Wright, PhD, reports receiving royalties from and owning stock in Exactech and having a research contract with Stryker, both related to this work; he also reports owning stock in OrthoBond, having a research contract with Lima, and acting as education committee member for the Knee Society, outside the current work. Douglas E. Padgett, MD, reports acting as a paid consultant to DJO Global and a board or committee member for the Hip Society and the Journal of Arthroplasty, outside the current work.
All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2013.
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