At the recent American Academy of Orthopaedic Surgeons annual meeting in Las Vegas Nevada, a research project from the Orthopedic Research Laboratories in Cleveland, Ohio, reviewed use of a new device (KNEE SIM) to evaluate the effect of various total knee designs on range of motion and function. The goal of knee replacement design is to develop and implant that closely approximates the feel and function of a healthy unoperated knee. In the past such design objectives have seemed unobtainable. More recently knee replacement designs have improved to where they more closely replicate the function of a normal healthy knee. This hopefully will lead to a “normal feeling” knee replacement, particularly as we increase the number of knee replacement in younger healthier individuals secondary to the increasing need for knee replacement in the middle aged population. Knee motion is a combination of rolling, sliding, and rotation, which is directed by the intact ligaments of a normal knee. In knee replacement, often the anterior cruciate and posterior cruciate ligament are removed, therefore, what guides the motion of the two joint surfaces is the geometry of the implant as it articulates against the opposite side. This motion is further influenced by the integrity of the muscles and remaining collateral ligaments. Developers are using exciting new tools, like the KNEE SIM, to help evaluate potential deigns and modify them to enhance knee motion and function.