The patella rests inside a groove on top of the femur called the trochlear groove. After you bend and straighten your knee, the patella moves forwards and backwards inside this groove. A plastic button, or cover, is used to resurface the backside on the patella. This button will line up with a http://knee cap replacement https://www.theorthopaedicandpainpractice.com/knee-cap-replacement-understanding-the-basics-of-this-orthopaedic-surgery/