Knee osteoarthritis and total knee replacement. X-rays of the knees of a 55-year-old patient with advanced osteoarthritis (OA) of the knee. 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's osteoarthritis has caused severe narrowing of the patellofemoral joint space in the right knee (right), which causes bone on bone contact when the knee is bent. The patient has had a total knee replacement on their left knee (left). Prosthetic knee joints (white) are used to replace joints affected by injury or conditions such as osteoarthritis, and here, this operation has dramatically improved the patient's left knee joint mobility.