The patella rests in a groove on top of the femur called the trochlear groove. When you bend and straighten your knee, the patella moves back and forth inside this groove. Surgical treatment to exchange a worn-out knee joint is quite common. The results are frequently very good and a lot better http://knee cap replacement https://www.theorthopaedicandpainpractice.com/knee-cap-replacement-understanding-the-basics-of-this-orthopaedic-surgery/