Various parts of the knee can be replaced: the most common are the inside half of the knee or the joint between the kneecap and the knee (the patellofemoral replacement). This can have the advantage of preserivng more normal knee movements and more normal feeling of the knee. One obvious disadvantage is that the rest of the knee may wear out and it may need revising.
These operations are technically demanding and have high rates of failure if done badly so careful pateint selection, planning and surgical technique are vital to their success. It may be necessary to do scans preoperatively to assess the whole knee before deciding if these are the best option for you.