Even with the advances in material selection, processing, and articular geometry for knee prostheses, there is still a need for in vitro evaluation of these components. The high occurrence of revision surgeries for failed prosthetics suggests that the component designs can still be improved. While historically the typical total knee recipient was an elderly woman, components are being implanted in younger patients who wish to lead more active lives with their new artificial knees. Therefore, the testing of new prostheses must be more rigorous and demanding than done previously. For these reasons a new five-axis electro-hydraulic knee simulator was constructed.