What It Is
A knee X-ray is a safe and painless test that uses a small amount of radiation to take a picture of a person's knee. During the examination, an X-ray machine sends a beam of radiation through the knee, and an image is recorded on a computer or special film. This image shows parts of the bones of the knee, including the femur (the bone above the knee), the tibia and fibula (the lower leg bones), the patella (kneecap), and the soft tissues.
The X-ray image is black and white. Dense body parts that block the passage of the X-ray beam through the body, such as bones, appear white on the X-ray image. Softer body tissues, such as muscles, allow the X-ray beams to pass through them and appear darker.
X-rays are performed by an X-ray technician in the radiology department of a hospital, a freestanding radiology center, or a health care provider's office. Three different pictures are usually taken of the knee: one from the front (anteroposterior view or AP), one from the side (lateral view), and one of the kneecap when the knee is bent (sunrise view).
Why It's Done
A knee X-ray can help find the causes of common signs and symptoms such as pain, tenderness, swelling, or deformity of the knee. It can detect broken bones or a dislocated joint. After a broken bone has been set, the image can help determine whether the bone is in proper alignment and whether it has healed properly.
If knee surgery is required, an X-ray may be taken to plan for the surgery and, later, to see the results of the operation. Also, a knee X-ray can help to diagnose later stages of infection, as well as cysts, tumors, or other diseases in the bone.
Preparation
A knee X-ray doesn't require any special preparation. Your child may be asked to remove some clothing, jewelry, or any metal objects that might interfere with the image.
If your daughter is pregnant, it is important to tell the X-ray technician or her doctor. X-rays are usually avoided during pregnancy because there's a small chance the radiation may harm the developing baby. But if the X-ray is necessary, precautions can be taken to protect the fetus.