Assessing Implant Stability in Cementless Femoral Components with Different Interference Fits

Cementless total knee arthroplasty implants offer advantages over cemented implants, such as bone preservation and easier revision procedures. However, the optimal interference fit required to achieve a good press-fit fixation, essential for both primary and long-term stability, remains uncertain. This study uses finite element analysis to investigate the effects of two interference fits (350 µm and 700 µm) on micromotions, gap behavior, and plastic deformation at the bone-implant interface of a cementless femoral component under various loading conditions. Finite element models were developed using paired cadaveric femurs, incorporating microCT and optical scans. Micromotions were quantified as shear displacement, while gaps were quantified as normal displacement. Bone response was assessed by quantifying the volume of bone experiencing total equivalent plastic strain. The models showed moderate correlation with experimental results, predicting 35% of displacement variability. Although high interference fit implants slightly reduced micromotions and gaps, these differences were not statistically significant (p = 0.252 and p = 0.759, respectively). The high interference fit implants exhibited significantly greater plastic deformation (+15.7%, p = 0.031), particularly at the posterior femoral condyles. These findings suggest that while an increased interference fit does not enhance primary stability, it may lead to more plasticity in the bone, potentially leading to more damage. Thus, optimizing the interference fit is crucial to balance implant fixation and minimize bone damage.