Pearls & Pitfalls for Ultrasound of Tendon Lacerations
1. It can often be difficult to determine whether tendon injury or disruption has occurred. On physical exam, normal function can be seen even with a 90% tendon disruption.
2. Ultrasound can augment clinical findings and help expedite the diagnosis, especially when the physical exam may be limited secondary to pain, swelling, or lack of patient cooperation.
3. If the target area is superficial, it is often useful to create your own acoustic window. Water immersion of the target structure can enhance visualization of superficial structures. Simply float the ultrasound probe in the water a few centimeters above the target structure. On your ultrasound screen, the acoustic layer of water will appear as a dark, anechoic line in the nearfield. The target structure will appear just farfield to this anechoic line.
4. Scan superficial structures with a high frequency (7.5 to 10 MHz) linear array transducer.
5. Begin by scanning in the longitudinal axis. Skeletal muscle will appear hypoechoic with interwoven echogenic striations and hyperechoic fascial planes. Adjacent tendons will appear brightly hyperechoic with visible linear fibers on long-axis scanning.
6. Any hypoechoic or anechoic interruption in the hyperechoic tendon fibers should raise the suspicion of a tendon disruption. The hypoechoic or anechoic area may represent blood or granulation tissue where the tendon fibers have torn apart. (Figures 3 & 4)
7. Subtle tendon damage may display an increase in the tendon cross-sectional area due to localized edema in the absence of actual tearing of the tendon fibers. Compare the area of interest to adjacent segments.
8. If the ultrasound beam is not aimed directly parallel to the tendon fibers, a false hypoechogenicity artifact may be noted (anisotropy). This artifact is most prominent in tendons that run in an oblique course and can occur when you are scanning near the insertion site. To avoid this error, make sure you obtain multiple views in two scanning planes.
9. With bedside ultrasound, you can often visualize both the proximal and distal ends of a complete tendon laceration, which are often difficult to find during beside exploration attempts.
Brady Pregerson manages a free on-line EM Ultrasound Image Library and is the editor of the Emergency Medicine Pocketbook series. www.EMresource.ORG
Teresa S. Wu is the Associate Residency Director, and Director of Ultrasound and Simulation Based Training for the Maricopa Emergency Medicine Program in Phoenix, Arizona.