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X-Ray Exam: Leg Length

Reviewed by: Larissa Hirsch, MD
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What's an X-Ray?

An X-ray is a safe and painless test that uses a small amount of radiation to make an image of bones, organs, and other parts of the body.

The X-ray image is black and white. Dense body parts, such as bones, block the passage of the X-ray beam through the body. These look white on the X-ray image. Softer body tissues, such as the skin and muscles, allow the X-ray beams to pass through them. They look darker on the image.

X-rays are commonly done in doctors’ offices, radiology departments, imaging centers, and dentists’ offices.

What's a Leg Length X-Ray?

In a leg length X-ray, an X-ray machine sends a beam of radiation through the legs, and an image is recorded on special film or a computer. The image shows the soft tissues and the bones, which includes the femur, tibia, and fibula, letting doctors measure and compare the legs’ length.

An X-ray technician may take pictures of the legs while the child is:

  • standing:
    • of both legs at the same time
    • from the front
  • lying down:
    • of the hips
    • of the knees
    • of the ankles

Kids should stay still for 2–3 seconds while each X-ray is taken so the images are clear. If an image is blurred, the X-ray technician might take another one.

Why Are Leg Length X-Rays Done?

No one is perfectly symmetrical. But some kids have significant differences in the length of their legs, a condition known as leg length discrepancy. This can have several causes, as well as several symptoms. Some kids don't feel anything at all, while others might have knee, hip, or back pain. Some kids might limp or may get tired easily while walking.

Doctors do leg length X-rays to help with leg measurement. It's important to know the exact difference in leg length before doctors choose a treatment plan. These X-rays might be repeated over time to see if the difference gets greater or to see how well treatment is working.

What if I Have Questions?

If you have questions about the leg length X-ray or what the results mean, talk to your doctor.

Reviewed by: Larissa Hirsch, MD
Date reviewed: March 2022