The diagnosis of osteoarthritis of the knee relies first and foremost on the clinical examination. osteoarthritis of the knee should be considered in older patients over the age of 50 years with knee pain, morning stiffness, and swelling. Imaging also plays an important role in osteoarthritis of the knee, as it can clarify the diagnosis of osteoarthritis, identify the site of involvement, and assess the stage of the disease. Imaging manifestations help to clarify the cause of osteoarthritis when symptoms appear and can provide information on the evolution of the disease during the treatment process. Standing anteroposterior images best demonstrate the degree of joint space narrowing and any underlying dynamic joint instability. It can also show marginal bony redundancy, tibial and patellar bone spurs, subchondral bone sclerosis, joint surfaces becoming flat, femoral condyles becoming square, and joint lines becoming angular. Although not considered useful for the analysis of osteoarthritis of the knee, the lateral view is useful for relatively reliable analysis of the joint space and for easy differentiation of the condylar pattern and tibial plateau; it is also useful for reliable and repeatable analysis of the patellofemoral joint, not only in terms of marginal redundancy and narrowing of the joint space, but also in terms of associated lesions, such as abnormalities of the involved patella. A tangential image of the patellofemoral joint with the knee flexed at 45 degrees shows the patellofemoral joint well and helps to analyze the degree of narrowing of the joint space and the condition of the bony bulge. At 30 degrees of knee flexion, the abnormalities of the affected patella can be understood, but the joint space is not well visualized. Sometimes it is necessary to take a special position of the knee, for example, an anterior image after 45 degrees of flexion or a long-legged image, to clarify the degree of deformity and to obtain information on the morphology of the femur and tibia in patients with a history of trauma or fracture.