Upon review of the existing literature and examination of the performances of current total knee implants, it must be determined whether there is a wear problem with the current implants. The investigators in these studies used monolithic components, and the polyethylene was actually attached to the metal at the manufacturing plant. This was a different implant compared to the implant most surgeons are using today, but some of the reports are not as good with the updated devices. With modular designs, wear on the articulating surface and the surface between the polyethylene and the tibia has been a concern. Wasielewski 5 and Parks 6 demonstrated the micromotion that is associated with modular components as they go through a range of motion.
Limited evidence is available on the wear of mobile-bearing knee implants.
Less wear may occur with the mobile-bearing designs because of improved conformity between the femur and the tibia surface which lowers contact stresses. If motion occurs between the tibial tray and the insert, it would be at an interface that is more wear-friendly with the polished surface of the tibial tray. When considering a newer mobile-bearing design system, surgeons should examine the bearing surface and the type of polyethylene used because oxidative degradation must be prevented. The foil package retains the hydrogen gas, which in combination with the vacuum increases hydrogen recombination. Oxidation is significantly reduced by a vacuum atmosphere, and it remains at minimum levels during the entire storage process or on the shelf-life of the implant.