An X-ray of the knee is a safe and painless test to visualise the knee joint using small amount of radiation. The knee joint includes the lower end of the upper leg bone (femur), the upper end of the lower leg bones (the tibia and fibula), the kneecap (patella), and the soft tissues (skin and muscles) surrounding it. The image is recorded on a special X-ray film. The X-ray image is black and white. Dense structures such as the bones, appear white and softer body tissues, such as the skin and muscles appear darker. The actual exposure time to radiation is usually less than a second, although the overall test may take 15-20 minutes.