Why would you have all your knee replaced if you only have arthritis in part of the joint, a partial knee replacement is possible, and more likely to give you better functional results ??

Any of the 3 main parts of the knee joint can be selectively replaced. Most commonly this is the inside (medial) part of the knee, followed by the patellofemoral joint (kneecap), and least commonly the outside (lateral) aspect of the joint.