Patients will be asked for a brief medical history so that we may determine if he/she can participate in the study. If the patient is going to have partial knee replacement, he/she will be randomly assigned to receive either a fixed-bearing (Vanguard M, Biomet, Warsaw, IN) or mobile-bearing (Oxford, Biomet, Warsaw, IN) partial knee replacement. Both implant systems are FDA approved and Dr. Christensen is equally skilled with both systems. The fixed-bearing partial knee replacement is made up of a polished metal piece that is cemented to the femur and a metal piece that is cemented to the tibia. The plastic portion of the fixed-bearing partial knee replacement is attached to the tibial metal tray and does not move. The mobile-bearing knee replacement also has a metal pieces cemented to the femur and tibia, but between the two metal pieces is a small plastic piece that moves as the knee bends and straightens. Patients will have an equal opportunity of receiving either implant system.