What can be diagnosed with ultrasound in the hands and feet? Tendon injuries, tendonitis, tenosynovitis, abscess, paronychia, felon, foreign body, fracture ... just to get started.
A water bath is extremely helpful in evaluating the fingers and toes. The hands or feet can be immersed in a basin, with the transducer just hovering over the area of interest. (Image 1.) This small amount of step-off improves the resolution of the superficial structures and greatly aids in distinguishing normal from abnormal.
Placing the transducer along the long axis of the finger is usually the most helpful place to start an exam because the normal structures (skin, subcutaneous tissue, tendon, bone, joint) can be more easily identified in this orientation. (Image 2.) Evaluating the fingers in short axis can be helpful in evaluating abnormal-appearing structures. Multiple fingers can also be evaluated side by side in transverse, making differentiation between normal and abnormal easier.
Many pathologies can be evaluated with ultrasound, but let's focus on my personal favorite: felons. I find it very frustrating to go through the painful process of anesthetizing and incising a suspected felon only to yield little or no pus. A quick ultrasound can quickly rule in or out a drainable fluid pocket. The increased resolution provided by a water bath makes it easier to identify a fluid collection deep to the fingertip as an anechoic (black) area. (Image 3.) Felons can be distinguished from simple cellulitis, which will appear as soft tissue thickening without focal fluid collection.
The soles of the feet provide a particular challenge for ultrasound because they are not accessible using the water bath. Using a glove filled with water, a small bag of saline, or a large amount of gel can provide enough step-off to visualize the most superficial areas.
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