Patients in this study require a replacement of a lower thighbone and knee joint. A new device, called the ComPreSs, will be used in this study to replace the lower thighbone. This new device has not yet been approved by the Food and Drug Administration (FDA). There is not enough data to assure that it is as good as other devices currently available. Taking part in this study will help provide data to the FDA. Other devices used to replace large pieces of bone and joints in the leg can result in damage to the bone over time. The bone damage can cause the device to come loose from the bone. This is a bad problem, and causes pain, and often more surgery is needed. This new device connects to the bone in a different way to prevent some of the problems seen with other devices. The new device protects the bone, and may help the replacement last longer. So far, the device has been used in over 50 patients on a selective basis.