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.