What is Ultrasound Imaging of the Hip?

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Ultrasound images of the hip provide pictures of muscles, tendons, ligaments, joints and soft tissues of the hip. In infants, the hip (which has a ball and cup configuration) is composed mainly of cartilage and is easily recognized on ultrasound.

Ultrasound imaging, also called ultrasound scanning or sonography, involves the use of a small transducer (probe) and ultrasound gel to expose the body to high-frequency sound waves. Ultrasound is safe and painless, and produces pictures of the inside of the body using sound waves. Ultrasound examinations do not use ionizing radiation (as used in x-rays). Because ultrasound images are captured in real-time, they can show the structure and movement of the body's internal organs, as well as blood flowing through blood vessels.

Ultrasound imaging is a noninvasive medical test that helps physicians diagnose and treat medical conditions.

What are some common uses of the procedure?

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Hip ultrasound images are typically used to help evaluate:

• abnormalities of the muscles, such as tears and soft-tissue masses.
• bleeding or other fluid collections within the muscles, bursae and joints.
• small benign and malignant soft tissue tumors.
• early changes of rheumatoid arthritis.

• developmental dysplasia of the hip (DDH), which in infants can range from the ball not in the cup (complete dislocation) to just a shallow cup (acetabular dysplasia).

• fluid in a painful hip joint in children.

Ultrasound of the hip can be performed on infants with DDH up to six to eight months of age.

How should I prepare?

You should wear comfortable, loose-fitting clothing for your ultrasound exam. You may need to remove all clothing and jewelry in the area to be examined.

In the case of an infant, it may be helpful to feed the baby just prior to the exam. It is also possible to bottle feed the infant during the exam. If you are present in the room during the procedure, standing where the infant can see you and hear your voice may make him or her more relaxed.

What does the equipment look like?

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Ultrasound scanners consist of a console containing a computer and electronics, a video display screen and a transducer that is used to do the scanning. The transducer is a small hand-held device that resembles a microphone, attached to the scanner by a cord. The transducer sends out inaudible high frequency sound waves into the body and then listens for the returning echoes from the tissues in the body. The principles are similar to sonar used by boats and submarines.

The ultrasound image is immediately visible on a video display screen that looks like a computer or television monitor. The image is created based on the amplitude (loudness), frequency (pitch) and time it takes for the ultrasound signal to return from the area of the patient being examined to the transducer, as well as the composition of body tissue through which and the type of body structure the sound travels through.

How does the procedure work?

Ultrasound imaging is based on the same principles involved in the sonar used by bats, ships and fishermen. When a sound wave strikes an object, it bounces back, or echoes. By measuring these echo waves, it is possible to determine how far away the object is and its size, shape and consistency (whether the object is solid or filled with fluid).

In medicine, ultrasound is used to detect changes in appearance of organs, tissues, and vessels or detect abnormal masses, such as tumors.

In an ultrasound examination, a transducer both sends the sound waves and receives the echoing waves. When the transducer is pressed against the skin, it directs small pulses of inaudible, high-frequency sound waves into the body. As the sound waves bounce off of internal organs, fluids and tissues, the sensitive microphone in the transducer records tiny changes in the sound's pitch and direction. These signature waves are instantly measured and displayed by a computer, which in turn creates a real-time picture on the monitor. One or more frames of the moving pictures are typically captured as still images. Small loops of the moving “real time” images may also be saved.

How is the procedure performed?

For most ultrasound exams of the hip, the patient is seated on an examination table and asked to lie on his or her back or side.

Almost all of the ultrasound studies of infants and children are performed with the child lying on his or her back on the examination table.

A clear water-based gel is applied to the area of the body being studied to help the transducer make secure contact with the body and eliminate air pockets between the transducer and the skin that can block the sound waves from passing into your body. The sonographer (ultrasound technologist) or radiologist then presses the transducer firmly against the skin in various locations, sweeping over the area of interest or angling the sound beam from a farther location to see an area of concern better.

When the examination is complete, the patient may be asked to dress and wait while the ultrasound images are reviewed.

This ultrasound examination is usually completed within 20 minutes, but may occasionally take longer.

What will I experience during and after the procedure?

Ultrasound examinations are painless, fast and easily tolerated by most patients.

After you are positioned on the examination table, the radiologist or sonographer will apply some warm water-based gel on your skin and then place the transducer firmly against your body, moving it back and forth over the area of interest until the desired images are captured. There is usually no discomfort from pressure as the transducer is pressed against the area being examined.

If scanning is performed over an area of tenderness, you may feel pressure or minor pain from the transducer.

The radiologist or sonographer may ask you to move the hip being examined or may move it for you to evaluate functions of the hip joint, muscle, ligament or tendon.

For infants, both hips are usually examined. The hip is checked in different positions and planes at rest and sometimes with gentle stress, this is painless.

Once the imaging is complete, the clear ultrasound gel will be wiped off your skin.

After an ultrasound examination, you should be able to resume your normal activities immediately.

Who interprets the results and how do I get them?

A radiologist, a physician specifically trained to supervise and interpret radiology examinations, will analyze the images and send a signed report to your primary care physician, or to the physician or other healthcare provider who referred you for the exam, who will share the results with you. In some cases the radiologist may discuss results with you at the conclusion of your examination.

What are the benefits vs. risks?

Benefits

• Most ultrasound scanning is noninvasive (no needles or injections).
• Occasionally, an ultrasound exam may be temporarily uncomfortable, but it is almost never painful.
• Ultrasound is widely available, easy-to-use and less expensive than other imaging methods.
• Ultrasound imaging is extremely safe and does not use any ionizing radiation.
• Ultrasound scanning gives a clear picture of soft tissues that do not show up well on x-ray images.
• Ultrasound provides real-time imaging, making it a good tool for guiding minimally invasive procedures such as needle biopsies and needle aspiration.
• In some cases, ultrasound may be able to evaluate the tendon structure more accurately than MRI.
• The hip joints of infants, unlike those of adults, are largely made of cartilage, which allows excellent dynamic views of the entire hip joint using ultrasound.

Risks

• For standard diagnostic ultrasound, there are no known harmful effects on humans.

What are the limitations of Ultrasound Imaging of the Hip?

Ultrasound has difficulty penetrating bone and, therefore, can only see the outer surface of bony structures and not what lies within (except in infants who have more cartilage in their skeletons than older children or adults). For visualizing internal structure of bones or certain joints, other imaging modalities such as MRI are typically used.