The knee joint consists of three parts: the knee cap (patella), the femur (thigh bone), and the tibia (lower leg bone). A knee joint replacement is done when arthritic changes cause pain, swelling, and loss of knee function.

Arthritic changes occur inside the knee joint as well as behind the patella. The patella may need to be resurfaced for a successful joint replacement. This means a metal or plastic backing is added to the patella. This helps it ride smoothly over the other parts of the implant when the knee moves.

Not every patient needs patellar resurfacing. Doctors decide whether or not to do this when they look at the back of the patella during the operation. The doctor looks at the shape of the patella and the condition of the cartilage when making this decision.

Selective resurfacing refers to the fact that not all patients have the patella resurfaced, only those who need it based on the surgeon's exam.