• Performance of three functional tests on a force platform [ Time Frame: Baseline (preoperative), 6 weeks, 3 months, and 1 year postoperative ]
  
• Knee Society Scores [ Time Frame: Baseline (preoperative), and 6 weeks, 3 months, and one year after surgery ]
  
• Patient Satisfaction [ Time Frame: 6 weeks, 3 months, and one year after surgery ]
  
• Any postoperative complications [ Time Frame: 6 weeks, 3 months, and one year after surgery ]
  

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.

If the patient is having total knee replacement, the surgery will be the same as if he/she did not participate in the study, except that we will collect information from the patient during office visits and will ask the patient to perform the functional tests. If the participant is one of the healthy volunteers, he/she will not have knee surgery and will only be asked to perform the functional tests.

Information collected during office visits:

A member of our research team will ask the patient a series of questions about the knee. Patients will be asked to answer this series of questions a total of 4 times over the course of 1 year. Also, we will record how well the patient can bend and straighten the knee at these 4 office visits. We will have patients rate the pain in their knee and ask if they are satisfied with the surgery. If patients have any complications, those will also be recorded. Patients will have X-rays taken of your knee at your follow-up visits. This is the normal routine following knee replacement. The X-rays will be read by the surgeon to help determine the success of the surgery.

We will also ask patients to perform 3 functional tests at each of these office visits. These 3 tests will be performed on a raised platform that is approximately 2 inches above the floor. For the first test, the patient will be asked to stand still with knees straight for two seconds, and then be asked to stand still with knees bent to 45 degrees for two seconds. For the second test, the patient will be asked to stand up from a seated position. For the third test, the patient will be asked to step up onto a four-inch wooden box and then step back down onto the platform. Prior to testing, the patient will be allowed to practice each of these tests as many times as necessary until he/she feels comfortable. During testing, an investigator will help make sure that the patient is able to safely and properly perform 3 repetitions of each test. We will not ask patients to perform one or more of the functional tests if they are unable to perform the test without constant use of their arms for support.