Knee replacement. Computer artwork of the bones and ligaments surrounding an artificial (prosthetic) knee joint (blue-grey) that has been surgically implanted to replace the existing knee. The patella (knee cap) has been removed, and the upper and lower parts of the implant cemented and drilled into the existing bones (the tibia, bottom; and the femur, top), see lower two diagrams. The prosthetic knee joint is hinged to replicate the movement of a normal knee joint. Total knee replacements are used for conditions such as osteoarthritis.