Total knee replacement. X-rays of the components of a prosthetic knee implant (white) used to replace the left knee joint of a 55-year-old female patient with advanced osteoarthritis (OA) of the knee. The patient's right knee is shown in 2 different positions - bent (left) and straight (right). Osteoarthritis is a disease resulting from the breakdown of joint cartilage (connective tissue) and the underlying bone. It often affects the large weight-bearing joints, such as the hips and knees, and causes joint pain and stiffness. Here, the patient has had a total knee replacement. Prosthetic knee joints are used to replace joints affected by injury or conditions such as osteoarthritis. The prosthetic joint dramatically improves the patient's knee joint mobility, however the artificial components can become loose over time.