How Does a Leg Length X-Ray Work?

Overview

What’s a Leg Length X-Ray and What Does It Show?

A leg length X-ray is a safe, painless test that uses a small amount of radiation to take pictures of the insides of the legs. It helps doctors measure and compare leg lengths to look for leg length discrepancy (a condition where one leg is shorter than the other).

The bones that a leg length X-ray shows include:

•  the femur (FEE-mur), or thighbone
• two bones in the lower leg: the tibia (TIH-bee-uh), or shinbone, and the fibula (FIH-byuh-luh)

Before starting any treatment plan for a leg length discrepancy, it's important to know the exact difference in leg length. Doctors might do more leg X-rays over time to see if one leg gets longer or to check how well treatment is working.

Top Things to Know

• A leg length X-ray is a quick and pain-free test that makes images of the inside of the legs.
• The X-ray helps show if there’s leg length discrepancy (the legs are different lengths).
• The test uses a very small amount of radiation, which is safe for kids.
• Your child will need to stay still for a few seconds so the images come out clear.

What to Expect

How Does a Leg Length X-Ray Work?

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 X-ray film or a computer screen.

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

What Happens Before a Leg Length X-Ray?

To get ready for a leg length X-ray, kids may be asked to remove clothing from the waist down and change into a hospital gown because buttons, zippers, and clasps might affect the image. The test often happens in a special room that has a table and an X-ray machine. A parent can usually stay in the room. Tell the X-ray technician if you’re pregnant because developing babies are more sensitive to radiation.

If your child is in the hospital, sometimes a portable X-ray machine can be brought to the bedside.

You can help your child prepare by explaining the test in simple terms. Say that it’s important to hold still to get the best images.

What Happens During a Leg Length X-Ray?

Leg length X-rays take just a few minutes. When your child is standing, the technician may take several X-rays of both legs so that the bones in each leg can be compared . Sometimes images are taken with wooden blocks placed under the shorter leg. This can show if the hips are even and if the spine straightens out. When your child is lying down on the table, X-rays may be taken of the hips, knees, and ankles.

After getting your child into the right position, an X-ray technician goes into the next room to take the images. Kids should stay still for 2–3 seconds while each X-ray is taken so the pictures are clear. If an image is blurred, the technician might take another one. Older kids may be asked to hold their breath for a few seconds to help keep them from moving.

If your child has an injury and can't stay in the right position, the technician can help find a position that feels better.

What Happens After a Leg Length X-Ray?

A radiologist (a doctor trained in reading and understanding X-rays) will look at the images and help figure out what the results mean. This person will send a report to your doctor, who will explain what the X-rays show.

What Else Should I Know?

In general, leg length X-rays are very safe. There can be some risk to the body with radiation, but the amount in leg length X-rays is so small that it’s not thought to be dangerous. X-ray technicians use the least radiation needed to get the best images.

Based on the results of the leg length X-ray, your child may need a follow-up appointment with the doctor or get more X-rays or other imaging tests.

If you have questions about the leg length X-ray or what the results mean, speak with your doctor. You can also talk to the X-ray technician before the test.