CORR Insights(®): Surface Damage Is Not Reduced With Highly Crosslinked Polyethylene Tibial Inserts at Short-term.

Abstract

L iu and colleagues compared retrieved tibial components from TKA prostheses that incorporated either conventional polyethylene (sterilized with ethylene oxide or gamma in low oxygen) or highly crosslinked polyethylenes (XLPEs). They found only minor differences in the types and amounts of surface damage, but slightly more thinning (penetration) on the XLPE polyethylene components. There are several reasons why the long-term clinical advantages that the XLPE polyethylenes were designed to provide would not be evident as a substantial reduction in these shortterm surface damage scores. Historically, the two main weaknesses of conventional polyethylene were wear on a submicron scale, which produced billions of particles that were the primary drivers of periprosthetic osteolysis, and (for those implants sterilized with gamma radiation) oxidative degradation that markedly weakened the polyethylene, potentially leading to fatigue wear and/or component fracture. Wear on the submicron scale results in polishing (burnishing) of the surface and thinning of the polyethylene component [5]. However, as Liu et al. note, thinning during the first few years in vivo is due primarily to creep deformation, which does not involve wear [7] and the initial (creep) thinning of an XLPE tibial plateau is expected to be comparable to, or slightly greater than, that of a conventional polyethylene plateau. Consequently, based the wear rates measured in knee simulator studies [3, 6, 9], the portion of the total thinning after 44 months or less in vivo that is due to debris-producing wear would likely be too small with either type of polyethylene for the difference between the two to be measured using the methods of Liu et al. The authors of the current study also report no delamination damage with XLPE or conventional polyethylene. Delamination can result from substantial oxidative degradation [8] and has been observed with XLPE tibial plateaus that were sequentially annealed (rather than remelted) [4]. This CORR Insights is a commentary on the article ‘‘Surface Damage Is Not Reduced With Highly Crosslinked Polyethylene Tibial Inserts at Short-term’’ by Liu and colleagues available at: DOI:10.1007/s11999-0154344-4. One of the authors (HAM) certifies that he has received or may receive patent arrangement benefits from DePuy Orthopaedics Inc, (Warsaw, IN, USA), and grants and personal fees from Depuy Orthopaedics Inc, outside the submitted work. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request. The opinions expressed are those of the writer, and do not reflect the opinion or policy of CORR or The Association of Bone and Joint Surgeons. This CORR Insights comment refers to the article available at DOI:10.1007/s11999-0154344-4. H. A. McKellop PhD (&) UCLA & OIC Department of Orthopaedic Surgery, Orthopaedic Institute for Children, 403 West Adams Blvd, Los Angeles, CA 90007-2664, USA e-mail: HMcKellop@mednet.ucla.edu