There is much controversy over different options available for TKA. The success of the Total Condylar knee has been explained by its higher conformity and lower stress on the insert, making it easier to correct deformity [19].

One of the most important sources for wear after primary TKA is the type of tibial plate. Modularity may have some advantages like insert exchange in case of wear [20] or infection. During the surgical procedure it may also be easier to test the flexion and extension gaps, However, there are more important consequences. Backside wear is a very well known cause of wear in TKA, and different UHMWPE protrusions have been reported with different brands and capture mechanisms of the TKA tibial tray [21]. The number of clinical reports supporting the use of all polyehylene tibial plates is rising (Fig. 17.2). The risk of revision is lower for monoblock tibial constructs, particularly in younger patients [6]. Other authors do not report better results with metal-backed components [22, 23] and the lower cost of the monoblock component is also an important issue when choosing these implants.

Mobile-bearing TKAs are supposed to improve wear performance and subsequently decease the rates of aseptic loosening in the long-term; however, this is another topic of controversy. Recently, Van der Voort et al. have reported that revision rates are similar for both fixed- and mobile-bearing inserts; thus, the clinical results did not improve with mobile-bearing TKAs [24]. Increased implant conformity and less transmission of forces to bone interface have not been confirmed clinically. Radiological and radiostereommetric studies have shown similar radiolucency and osteolysis rates. Table 17.1 shows some randomized controlled trials for comparative studies between monoblock all-polyethylene tibial implants and metal backed components, and rotating platform and fixed-bearing tibial components. Finally, Kalisvaart et al. have reported similar results at 5 years for clinical outcome and durability in all three options for a single posterior-stabilized distal femoral implant in a randomized study involving 240 TKAs; to date the only revision for aseptic loosening was the metal-backed group [28].

Highly cross linked polyethylenes are widely used due to their lower rates of wear in total hip arthroplasty at 10 years [29]; however, their use is not as frequent in primary TKA. Type of sterilisation has been studied as a possible factor for loss of medial compartment thickness [30]. This loss was higher with gamma-in-air polyethylene than with other types of UHMWPE sterilized with gamma radiation in an inert gas or with a non-irradiation method. In retrieval analysis, Medel et al. has reported lower oxidation and oxidation potential for tibial inserts sterilized in inert gas compared to those sterilized with gamma radiation in air; although wear resistance was similar between both types, there was a lower delamination rate in the first decade of implantation for UHMWPE tibial inserts [31]. In vitro analyses report lower wear rates for highly cross-linked polyethylenes tested after aging [32]. Clinical studies with PS designs have shown good mid-term results and a lower incidence of radiolucent lines for these new tibial inserts [33]. The introduction of vitamin E to stabilized UHMWPE has produced better performance after aging and a reduction in wear rates [34].

Other options rather than the type of UHMWPE have been assessed. Oxidized zirconium is used for the femoral component due to the low-friction oxide that is observed after oxygen diffusion, and in vitro studies have confirmed higher wear resistance with oxidized zirconium compared with cobalt-chromium (Co-Cr) alloys [35]. Clinical results also suggest that it is a safe implant, although there is a lack of long-term and comparative studies [36]. Finally, short term clinical studies show no benefit for these implants or highly cross-linked polyethylene when compared to traditional Co-Cr femoral components on conventional UHMPEs [37].

Variability and the age and physical activity of patients who undergo a TKA determine the different options available to surgeons nowadays. Long-term results show no benefit for any particular design and emphasize the importance of wear and osteolyis rather than other short- or mid-term failures; excellent long term results suggest that all polyethylene monoblock tibial components may be adequate despite the possibility of non-modular trays. The sterilization method for UHMWPE is one of the most important factors in choosing a particular TKA. Although new highly cross-linked polyethylenes are safe in primary TKA, there is a lack of studies to confirm the superior in vitro results in patients.