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Improving Clinical Wear Rates

Polyethylene wear still remains the most common failure mechanism of total knee arthroplasty.^{15-19, 30-34} Factors that directly affect wear include high shear stresses transmitted between the tibia and femur during gait and low tibio-femoral contact areas. The ADVANCE® Knee System femoral implants were designed to maximize contact area with the polyethylene tibial components, thereby increasing the longevity of the implant by reducing contact stresses. By closely matching the femoral and tibial articular surface radii, contact areas were maximized in the ADVANCE® tibial inserts while still providing adequate internal/external rotational freedom.⁴² In contemporary designs, contact areas often decrease with increasing flexion because of the decreasing radius of femoral curvature. Because of the constant radius of the femoral component, contact areas with the ADVANCE® tibial inserts remain constant into deep flexion (Figure 10).^{42, 43}

Many contemporary designs with limited, decreasing contact areas incur extreme wear caused by internal stresses that exceed the mechanical properties of ultra-high molecular weight polyethylene (UHMWPE). To improve and maintain wear resistance, the ADVANCE® Knee System combines constant contact areas with state-of-the-art polyethylene components. These implants are produced with materials, manufacturing methods and sterilization processes that have clinically demonstrated the ability to maintain the inherent wear-resistance of polyethylene. The components are produced from compression-molded GUR1020 polymer which was chosen due to its mechanical properties and high-consolidation. After production, the implants are sterilized with ethylene oxide (EtO). Unlike gamma sterilization, EtO does not reduce the natural toughness of polyethylene or alter its physical properties.^18,31,32 The EtO sterilization process provides a safe, non-destructive sterilization method which has been successfully utilized in orthopaedics for more than twenty years.

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