He's right. There is no such thing as a patellar replacement. Let me explain to you why. The patella is what we call a sesamoid bone, meaning it's a small bone that grows inside a tendon or ligament where there is pressure from a bone it's riding over. We don't just have them in the knees but also in the great toe and sometimes even the thumb! In the knee, these bones grow within the ligaments - the quads above and the patellar tendon below - and the position of it is maintained by the tension of those ligaments. They also have a small area of articular cartilage on the back If the patellar is fractured, it can often be repaired using a tension band wiring like this But if it is not salvageable, then the only remedy is for it to be removed and the two tendons stitched firmly together but this inevitably shortens the length of the quads so kneeling can be difficult.