Important differences exist in both the materials and geometric forms of tibial bearings across total knee implant systems on the market. The extent of crosslinking, sterilization methods, mechanical/thermal treatment methods used for management of free radicals, the amount of incorporated antioxidants, and the methods for incorporation of antioxidants, are some of the material variables, which may affect bearing clinical performance. Despite initial concerns about increased fatigue damage and failure with crosslinked ultra high molecular weight polyethylene developed to reduce the incidence of osteolysis, their utilization now constitutes close to 50% of tibial bearings in primary operations. This is based on long-term clinical data, which show equivalent or better performance in revisions due to aseptic loosening compared with conventional materials. Similarly, bearing conformity, modularity and mobility, are important geometric elements influencing polyethylene wear and failure. With regard to conformity, conventional wisdom has favored more conforming designs. However, growing body of evidence suggests potential for improved wear performance with less conforming designs enabled by modern polyethylene processing techniques. Long-term clinical data show excellent outcomes for all-polyethylene bearings, which may assume an enhanced role in total knee replacement in the future. In contrast, modern fixed-bearing designs seem to outperform mobile-bearing designs in the long run. Consequently, the use of the mobile bearings has declined over time, and currently they account for about 7% of primary knee replacements.
*Harris Orthopaedics Laboratory, Department of Orthopaedic Surgery, Massachusetts General Hospital
†Department of Orthopaedic Surgery, Harvard Medical School, Boston, MA
K.M.V. receives royalties from Stryker Corp., and is a consultant for CeramTec GmbH. K.M.V. has stock ownership in Orthopaedic Technology Group. E.O. receives royalties from Zimmer Biomet, Stryker Corp., Corin Group, Renovis Surgical Inc., Aston Medical, and ConforMIS Inc. O.K.M. receives royalties from Zimmer Biomet, Stryker Corp., Corin Group, Renovis Surgical Inc., Aston Medical, and ConforMIS Inc. O.K.M. is a consultant for Zimmer Biomet Inc., receives research support from Zimmer Biomet and DePuy, and has stock ownership in Orthopaedic Technology Group. A.A.F. is a consultant for and receives royalties from Zimmer Biomet. A.A.F. has stock ownership in ArthroSurface Inc. and Orthopedic Technology Group.
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