Influence of Material, Design, and Loading on the Biomechanical Behavior of Femoral Stems: A Comparative FEM Study

The longevity and success of total hip arthroplasties (THA) depend on various factors, including material selection, design, and the activity level of the patient. However, the combined effect of these factors on implant performance is often overlooked. This study aims to address this gap by investigating finite element analysis (FEA) on three commercially available femoral stem designs made of titanium and cobalt-chromium alloys. Specifically, the influence of four neglected activity load cycles, namely stand-up, stairs-up, sit-down, and stairs-down, was examined. The assignment of materials was based on Hounsfield units (HU) obtained from CT scan images, ensuring accurate representation of hip geometry. Von-Mises stress distributions and their maximum values were analyzed, and a maximum stress ratio (MSR) parameter was introduced to quantitatively assess the risk of stress shielding. Our findings revealed that titanium exhibited lower MSR values overall, while the stem design variants demonstrated varying levels of MSR. Moreover, among the four loading scenarios, stairs up and stand up had the most and least criticality, respectively, and showed 52.6% and 38.5% percentage higher and lower than the mean stress values experienced by femoral stem. These findings have significant implications for clinicians in offering improved treatment and guiding patients who have undergone THA towards safer and longer-lasting replacements. Additionally, engineers can utilize these results to design and manufacture tailored implants for THA, enhancing overall implant performance.