The size of the polyethylene particle has been demonstrated to influence osteolysis; the smaller particles are thought to be more biologically active due to their ease of being phagocytosed [85]. Highly cross-linked polyethylene (XLPE) has been used in total hip arthroplasty for over 10 years and has proved in vivo to show less wear than conventional UHMPWE because it is thought to yield less wear particles [34, 86–90]. In vitro studies for TKA have demonstrated a reduction in wear of XLPE [91]. Iwakiri et al. compared XLPE and conventional polyethylene in small numbers retrospectively and showed a reduction in wear particles for XLPE, but this was not confirmed by Hinarejos et al. who found no significant reduction in wear particle concentration of synovial fluid from TKAs using XLPE when compared to conventional polyethylene [92, 93]. The size of the particle was not significantly different either, but their follow-up was only 1 year, and longer-term studies may demonstrate more significant advantages. Highly cross-linked polyethylene has also shown reduced fracture strength (Huot JC 2011), so coupled with the arguments above, its use is not widespread as yet [94, 95].

In TKA, surgeons have the choice of an all-polyethylene tibial component or a modular unit using a polyethylene liner (or bearing) mounted on a metal tray. Historically, the total condylar TKA used an all-polyethylene component for which excellent long-term survival rates have been reported [96, 97]. Metal-backed tibial designs originated when biomechanical studies demonstrated that they improved the distribution of forces between the implant and cement [98, 99].

The modularity that metal-backed tibial components allowed, as well as the possibilities for isolated liner exchange in revision procedures, fuelled their popularity. Disadvantages of metal-backed components include backside wear, osteolysis and micromotion [100–102]. Convincing arguments in favour of all-polyethylene components still exist. It is less expensive than its metal-backed counterpart, and studies have shown equal results in terms of function, range of motion, primary stability and long-term implant survival [103–108].

An analysis of over 27,000 TKAs by Gudnason et al. revealed that all-polyethylene tibial components had marginally better 10-year survival compared with metal-backed components, and this was attributed to an increased risk of infection with metal-backed designs [109]. This is a reproducible finding in the literature [110–114]. Some studies have shown a lower migration for all-polyethylene components using radiostereometric analysis, which is accurate for in vivo migration, which in turn is correlated to later aseptic loosening [115, 116]. There are subtle differences in the surgical technique which should not influence choice, but the surgeon of the future will undoubtedly have financial pressures to factor in to the decision-making process when choosing the tibial component for TKA; pleasingly modern polyethylene (oxygen-free gamma irradiated, thermal treated) has ensured that both components enjoy low wear rates and therefore associated osteolysis.

If one is faced with failure of a modular TKA as a result of wear, osteolysis and loosening and components are well fixed and well aligned, then isolated liner exchange is a valid treatment. Although there has been doubt cast on the benefits, studies against isolated exchange may have included diagnoses such as stiffness, instability and synovitis which have different re-revision rates compared to rates for osteolysis and wear, and quality of polyethylene has not been mentioned in the setting of RTKA [117–120]. In conclusion, isolated polyethylene exchange when components are well aligned, well fixed and without backside wear can be successfully used to treat patients undergoing revision for wear or osteolysis as long as the replacement polyethylene quality is good.

Increasing numbers and a progressively younger patient population have stimulated the debate of cemented or cementless fixation in TKA. Young patients expect their activity levels to be higher post-operatively, and because of longer life expectancy, this patient group is more interested in 30-year survival rates of an implant than its 10- or 20-year survival rate. Therefore, preservation of the bone and good function and longevity are the established aims in TKA, and uncemented fixation is well tested and works well in several areas [121]. The bone-implant interface is physiologic and as a living interface it responds to stress in a physiologic way; thus, the attraction of cementless fixation is obvious. Despite success in total hip arthroplasty, uncemented fixation in TKA has not enjoyed similar results because several initial press-fit designs failed and many did not show superiority over cemented fixation [66, 122]. The meta-analysis by Wang et al. excluded the technical failures at an early stage as bias and, using comparative analysis of registers, demonstrated that uncemented TKA performed equally well with cemented TKA [123]. This contraindicated the findings from the study by Gandhi et al., but early technical failures were not excluded and follow-up was only at a mean of 2 years [124]. The other presumed advantage of cementless fixation is reduced operative time and several studies have shown that the absence of antibiotic impregnated cement does not influence the incidence of infection after TKA [125, 126]. The largest obstacle to comparison studies is the low numbers of uncemented cases performed worldwide but also the heterogeneity of the implants used for comparison within the uncemented group, as well as the great variation in surgical technique, ligament balancing and patellofemoral resurfacing options within study populations. On a background of multiple published case series of cemented TKA reporting survivorship for mechanical failure of 90–97 % at 10–15-year [96, 127–129] and between 85 and 98 % at 15–20-year follow-up [1, 2, 26, 130–134], as well as more recent concern that cementless fixation may be more sensitive to malalignment, especially on the tibial side since shear forces caused by varus or valgus tibial base plate positioning will alter the compressive forces distributed across the implant-bone interface, the enthusiasm for cementless TKA has always stuttered.

Cemented fixation in TKA is still the gold standard, evidenced by worldwide registry data that demonstrates more usage than cementless implants; this is despite the hydroxyapatite coating of components and newer developments such as trabecular metal which may infer favourable characteristics of bony ingrowth and maintenance of bone density [135, 136].