Caption: MODEL RELEASED. Total knee replacement surgery. Image 2 of 14. Close-up of a surgeon performing an operation to completely replace the worn knee joint (white, centre) of a patient suffering from severe osteoarthritis of the knee. Osteoarthritis causes the cartilage surface of the bones to wear down. This means that the bones of the joint rub against each other causing them to become rough and painful. This surgery is replacing the worn knee with a Zimmer Nexgen Legacy Posterior Stabilized (LPS) prosthetic knee. There isn't usually this much blood during surgical procedures but the patient has arterial disease, so the usual tourniquet couldn't be used to stop the bleeding.