Primary Stability Assessment of Patient-Specific Transfemoral Osseointegrated Implants During Static Load-Bearing Exercise: A Comparative Analysis

The long-term effectiveness of osseointegrated implants is heavily dependent on the short-term stability, primarily achieved immediately after surgery through a mechanical connection between the bone and the implant. The most common implant designs nowadays are straight and rely on screw or press-fit fixtures. Despite the promising results achieved by current transfemoral implants, the incidence of early failures and complications is still high. Starting from the hypothesis that a patient-specific approach could lead to better primary stability immediately post-surgery, this study aims to investigate the effect of implant design on primary stability. This was performed by analyzing two patient-specific implants, customized according to the medullary canal morphology, and a simple straight implant as the reference standard. To quantitatively assess the primary stability, a comparative computational analysis was conducted to examine the effective contact area, the relative micromotion, and the stress distribution at the interface between the bone and the implant stem during a static load-bearing exercise. The results showed that implants that follow the curvature of the residual femur provide lower micromotion values and a wider contact area, with a reduction of up to 30.4% and an increase of 10.8%, respectively, compared to the straight design, leading to a more homogeneous load distribution. Patient-specific prosthetic implants allow a more homogenous contact distribution that could lead to higher primary stability by reducing micromotion at the bone–implant interface concerning the straight profile, lowering the risk of loosening related to the short-term stability.