Finite Element Assessment of an Implant-Integrated Transfemoral Prosthesis: Reducing Stump–Socket Stress, Pressure and Shear During Walking and Stair Negotiation

Background/Objectives: Lower-limb amputation presents biomechanical challenges at the residual limb–prosthetic socket interface, where uneven load transfer may generate localized stress concentrations. This study investigates the biomechanical behavior of a patient-specific transfemoral residual limb–prosthesis system with and without a structural implant positioned at the distal femur. Methods: Finite element simulations were performed for three activities: normal walking, stair descent, and stair ascent. Von Mises stress, contact pressure (CPRESS), and longitudinal shear stress (CSHEAR1) were evaluated in the residual limb and prosthetic components. Results: During normal walking, stair descent, and stair ascent, the implant reduced the maximum von Mises stress in the residual limb by 62.9%, 55.1%, and 80.2%, respectively. The maximum longitudinal shear stress in the residual limb decreased by 28.6%, 28.0%, and 41.5%, respectively. During stair descent, the maximum contact pressure at the residual limb interface decreased by 79.4%, from 173 to 35.6 kPa, while during stair ascent it decreased by 38.6%, from 95.5 to 58.6 kPa. The maximum contact pressure on the prosthetic liner decreased by 43.0% during stair descent and 33.7% during stair ascent. Similarly, the maximum longitudinal shear stress on the socket decreased by 43.3% and 33.3%, respectively. However, slight increases in some peak contact and shear stress values were observed during normal walking. These findings indicate that the biomechanical effects of the implant depend on the activity and the parameter evaluated. Conclusions: Although the numerical results demonstrate reductions in several peak stress and pressure values, clinical benefits cannot be established from the simulations alone.