Archive for November, 2009

The Case of the Elusive Glass Fragment

November 22, 2009

 

For the past 2 weeks, you have had a sharp pinpoint pain in your heel every time you take a step. You decide to see your podiatrist, who suggests that you take an X-ray to make sure there are no spurs, cyst or breaks in the bone. The X-ray is shown to you, and there are no sign of abnormality in the bone. Your podiatrist then suggests exploring the heel with diagnostic ultrasound.

An ultrasound may at first seem like an unusual imaging modality to diagnose the source of foot pain, especially since most people associate ultrasound imaging with pregnancy. Surprisingly, ultrasonography is a quick and inexpensive way to evaluate pathologies of the foot. In this case noted above, the ultrasound showed a concentrated bright spot in the heel with a tail of light waves behind the spot, which indicated a foreign body in the foot. Unlike ultrasounds, X-rays can only pick up signals from metal and bone, which have denser properties compared to glass and soft tissue structures.

Science of the Ultrasound:

Ultrasound uses high frequency sound waves that are emitted from a probe that is applied to the skin. The sound waves painlessly penetrate the skin and encounter bones, ligaments and tendons.  Each tissue type is made of different components, when the waves are reflected back to the probe they appear characteristic of that particular structure. The probe is attached to a computer that compiles the various sound waves and forms an image on a screen.  Tissues that contain more water such as muscle will absorb the ultrasound wave and will send little or no waves back to the probe. These tissues that absorb the waves will appear on the screen as dark areas.  Conversely bone, which contains less water, will reflect all of the waves back to the probe and therefore will appear on the screen as a white image. Using this gradient of  relative amounts of reflected waves and a firm knowledge of the normal anatomy a trained podiatrist will be able to determine the difference between normal and damaged or injured tissues in your foot.

Other Pathology Visualized by Ultrasound:

1. Ganglions

2. Neuromas

3. Foreign Bodies (like glass or metal)

4. Achilles Tendon Rupture

5. Tendon Abnormalities

6. Rupture of the Ankle Ligaments (Sprains)

7. Fascia tears and inflammation (Heel pain)

8. Bursitis

Advantages of Ultrasound:

1. Uses no radiation like X-rays or Cat Scans

2. Can perform live active or passive range of motion

3. Cost effective, especially compared to MRI

4. Conveniently used in an office setting