Bedside ultrasound can be especially useful for assessing tendons — in trauma, repetitive motion injury, and suspected infection. Having a basic understanding of the normal and abnormal appearance of tendons on ultrasound will give the emergency physician an advantage when examining patients with suspected tendon injury, tendonitis, or tenosynovitis.
Tendons are typically discrete structures within the soft tissue, with a fibrillar appearance (meaning that the individual fibers of the tendon are discrete and visible). Examining them in their long axis is typically most helpful when examining for pathology, but it may also be helpful to evaluate the tendon in its short axis.
Tendonitis is characterized by a loss of the fibrillar appearance of the tendon. Rather than visualizing the individual fibers, the tendon will appear smudged or blurred (Image 1), representing edema within the tendon. This is usually a diffused, rather than localized, finding.
Tenosynovitis is identified by fluid surrounding the tendon, within the tendon sheath. (Image 2.) It may be marked or subtle, depending on the amount of fluid present. Typically, the tendon will appear edematous as well; it is unusual to have tenosynovitis without affecting the tendon, too. Tenosynovitis can be inflammatory or infectious, and the diagnosis typically is clarified by the clinical picture: Is there overlying erythema of the skin, induration, fever, or another sign of infection?
Tendon rupture or laceration is typically easy to identify in the acute setting. The full length of the tendon should be followed to its insertion, assessing for obvious discontinuity. (Image 3.) The proximal portion of the tendon may be retracted in the case of a full-tendon rupture or laceration, and it may be more difficult to locate. Edema is usually present around the rupture or laceration, which further highlights the diagnosis. A tendon injury can be much more difficult to identify in a subacute or chronic setting because the area of injury will be isoechoic (the same texture) to the surrounding tissue.
No discussion of tendons would be complete without a discussion of the artifact of anisotropy. Anisotropy is created by the interface between the tendon at its point of insertion. When the angle of the ultrasound beam is decreased (less than perpendicular), an anechoic (black) area frequently appears near the insertion point. (Image 4.) This is often mistaken for tendon laceration or injury. Changing the angle of the transducer to be more perpendicular to the tendon will alter this appearance, alerting the examiner to its presence. The lack of surrounding edema is also a clue that this finding represents a normal artifact, rather than an acute injury.
Here are a few tips for evaluating the tendon:
- Use a water bath for hands and feet.
- Be familiar with the anatomy to enable identification of the tendon in question.
- When in doubt, assess the same location on the unaffected side.
Next month, we'll look deeper into the soft tissue.