"Total knee replacement (TKR) is one of the most expensive prosthetic surgery, causing large costs to European countries. In Europe, an average of 107 knee prostheses per 100.000 inhabitants was needed in 2008, generating the need of 335.000 knee prostheses. This number is increasing in European countries, being estimated that the global number will double each year. Considering an average cost of 10.000 euros/surgery in the EuroArea, it is then estimated a global cost of around 3883 M euros per year. In the US the situation is even more dramatic: an average of 500.000 knee prostheses are used each year. Most of knee prostheses are designed and fabricated according to high quality standards and several research groups world-wide are actively working in the subject, mainly in US and Japan. However, knee prostheses are usually affected by several factors, causing their loosening or fracture and then, shortening their long-term lifespan. This project address the enhancement of these designs by analyzing in deep biomechanical factors as fatigue, wear, bone loss of density, etc. Finite Element Analysis (FEA) will be used to study the behavior and performance of existing designs, including nonlinear stress analysis and stress-shielding effect. Comparative analyses will be performed to assess the behavior of different prostheses geometries thus allowing to make relevant changes both in geometry and prosthesis alignment, driven by the stresses gradients around the interface bone-prosthesis. It is well known that small variations in the prosthesis geometry can lead to increment/decrement of wear and thus to a reduction/increase of the prosthesis lifespan. As well, the prosthesis stem geometry is crucial for the coupling boneprosthesis,because the interface stresses can generate bone reabsorption. The main goal is to propose new geometries for the kneeprostheses to improve their performance and the enlargement of their long-term lifespan."