What It Is

A hip ultrasound is a safe and painless test that uses sound waves to make images of the hip.

During the examination, an ultrasound machine sends sound waves into the hip area, and images are recorded on a computer. The black-and-white images show the internal structures of the hip, including the ball-shaped top of the thighbone (femoral head) and its socket (acetabulum) in the pelvic bone.

It can be performed on babies up to about 6 months of age.

Why It's Done

Doctors order a hip ultrasound when they suspect a problem called developmental dysplasia of the hip (DDH). DDH is a hip deformity that can occur before, during, or weeks to months after birth.

In a normal-functioning hip, the femoral head rests comfortably in its socket. In babies with DDH, the femoral head moves back and forth within the socket; in more serious cases, it may move out of the socket, but can be put back into place with pressure — this is called dislocation. In the most severe cases, it may not be possible to put the femoral head into the socket at all.

The likelihood of DDH increases in these situations:

• pregnancies in which the fetus is cramped in the uterus (due to a decrease in the amount of amniotic fluid, called oligohydramnios)
• abnormal position of the baby in the womb (breech position)
• babies with a family history of DDH

Also, DDH occurs more frequently in girls than boys and among first-born infants.

Doctors will consider all of these factors when deciding whether a baby's hips should be checked by ultrasound. In addition, a baby will be sent for ultrasound if the doctor finds an abnormality of the hip during a physical examination, such as:

• at birth, an inability to move the thigh outward at the hip as far as normally possible
• a hip "click" heard or felt by the doctor when moving the infant's thigh outward during a routine checkup
• differences in the lengths or appearances of the infant's legs

Preparation

Usually, you don't have to do anything special to prepare your baby for a hip ultrasound. You should tell the technician about any medications your baby is taking before the test begins.

Procedure

The hip ultrasound usually will be done in the radiology department of a hospital or in a radiology center. Parents usually can accompany their child to provide reassurance and support.

You'll be asked to partly undress your baby and to remove the diaper for the test. Your baby will be placed on a table on his or her back or side. The room is usually dark so the images can be seen clearly on the computer screen.

A technician (sonographer) trained in ultrasound imaging will spread a clear, gel on the skin of the hip. This gel helps with the transmission of the sound waves. The technician will then move a small wand (transducer) over the gel. The transducer emits high-frequency sound waves and a computer measures how the sound waves bounce back from the body. The computer changes those sound waves into images to be analyzed.

Sometimes a doctor will come in at the end of the test to meet your baby and take a few more pictures. The procedure usually takes about 20 minutes. Both hips are usually examined.

What to Expect

The hip ultrasound is painless. Your baby may feel a slight pressure on the hip as the transducer is moved, and the gel may feel wet or cold.

Babies might cry in the ultrasound room, especially if they're restrained, but this won't interfere with the procedure.

Getting the Results

A radiologist (a doctor who is specially trained in reading and interpreting X-ray and ultrasound images) will interpret the ultrasound results and then give the information to your doctor, who will go over the results with you.

Results are usually ready in 1-2 days. In most cases, results can't be given directly to the family at the time of the test.

Risks

No risks are associated with a hip ultrasound. Unlike X-rays, radiation isn't involved with this test.

Helping Your Infant

It might be helpful to feed your baby just before the ultrasound to make him or her more relaxed. If you're present during the test, comfort your baby with a calm and soothing voice or sing a favorite song. Make sure to stand where he or she can see your face.

If You Have Questions

If you have questions about the hip ultrasound, speak with your doctor. You can also talk to the technician before the exam.

Reviewed by: Yamini Durani, MD
Date reviewed: March 2012