Primary fixation of the cementless femoral component is essential for bone ingrowth on and into the implant surface, which occurs a few weeks to months after total knee arthroplasty (TKA) procedure (Hofmann et al., 1997). This primary fixation is established by the compressive and shearing forces that are generated during the implantation of the press-fit components. Apart from the frictional properties of the implant surface, the primary fixation depends on the design and material of the femoral component. When introducing a new implant material for TKA designs, it is therefore important to study its effect on the primary fixation.

While cobalt-chrome (CoCr) alloy currently is the default material for cementless femoral TKA components, polyetheretherketone (PEEK-OPTIMATM) is of interest as the material has several potential advantages. One of the advantages of PEEK is that it can be used in patients with metal hypersensitivity. Moreover, the use of a non-metal TKA allows for easier analysis of the peri-prosthetic tissue with modalities such as MRI and CT in case of implant failure as metal artefacts will be avoided (Nishio et al., 2023). From a mechanical perspective, the stiffness of PEEK (3.7 GPa) closer resembles the stiffness of human bone that is replaced during the surgery compared to CoCr (210 GPa). Therefore, the potential peri-prosthetic stress-shielding may be reduced (de Ruiter et al., 2017, Rankin et al., 2016).

To study the effect of PEEK as an implant material on the primary fixation, finite element (FE) studies can be adopted to simulate micromotions at the implant – bone interface, which can be used to evaluate the ingrowth potential of press-fit implants. Previous FE studies on the cementless PEEK femoral component mainly focused on the analysis of a single femoral model with parametric variations (Post et al., 2022), while in clinical practice the outcome depends on patient factors such as age, gender and body weight index (BMI). For instance, several studies have investigated the influence of BMI on the outcomes of TKA (Başdelioğlu, 2020, Daniilidis et al., 2016, Wan et al., 2023). While there has been controversy on whether or not a high BMI negatively affects the primary fixation, a recent study has shown that a high BMI causes larger micromotions in reconstructions with metal implants (Wan et al., 2023). However, the influence of a high BMI on the primary fixation of a cementless PEEK femoral component is currently unknown. By adopting a population-based approach more insight can be gained into potential risk factors in patient populations.

Therefore, the research questions of this study were 1) What is the effect of simulated implant material change (PEEK vs. CoCr) on femoral micromotions within a population? 2) Is the primary fixation of a cementless femoral component influenced by patient characteristics (gender, age and BMI), and is there a difference in response as quantified by micromotions between PEEK and CoCr material?