A method of implanting a lateral unicondylar knee prosthesis in a lateral articulating portion of a femur having a lateral condyle for engagement with a tibia, the method including the steps of: bending a patients knee such that the knee is not in full extension making an incision through the skin, muscle, and other soft tissue until the damaged bone surfaces are exposed resecting an end portion of the lateral tibia resecting an end portion of the lateral femoral condyle attaching a tibial prosthetic component to the resected end portion of the tibia attaching a lateral femoral condyle prosthetic component to the resected end portion of the lateral femoral condyle determining the thickness of a mobile bearing member with the knee in full extension and inserting the mobile bearing member between the tibial prosthetic component and the femoral prosthetic component.
