Personalized External Knee Prosthesis Design Using Instantaneous Center of Rotation for Improved Gait Emulation

: The need to improve gait emulation in patients with transfemoral amputation has led to the development of customized prosthetic mechanisms. This study focuses on the design and validation of an external knee joint prosthesis mechanism, based on the trajectory of the Instantaneous Center of Rotation (ICR) of a healthy knee. The goal is to design a mechanism that closely follows the evolution of the ICR path, improving stability and reducing the user's muscle effort. An exploratory methodology was applied, using computer-aided design (CAD), kinematic simulations, and rapid prototyping with 3D printing. Several four-bar and six-bar mechanism configurations were evaluated by determining their ICR trajectories and comparing them to a reference model obtained in the lab from a specific patient, using MATLAB and Fréchet distance as the error metric. The results showed that the optimized four-bar mechanism, with the addition of gears, achieved the highest accuracy in matching the ICR trajectory, with a minimum error of 5 mm. Functional tests confirmed the effectiveness of the design in terms of stability and voluntary control during walking. It is concluded that optimizing the mechanism design based on the ICR significantly improves functionality and supports its clinical implementation and impact on users’ quality of life.