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Pearls & Pitfalls for Ultrasound Evaluation of Joints
1. Use a High Frequency Linear Transducer: Typically, because they are such superﬁcial structures, joints are best visualized using a 7-10 or 10-13 MHz, linear array transducer. For the elbow, start with your probe in the dimple between the olecranon, radial head and lateral epicondyle on the lateral side of the elbow.
2. Use Adequate Analgesia: Scanning over an inﬂamed joint may be painful for the patient. Pretreat with opiates as long as your patient will be admitted or has someone to drive them home.
3. Ceate a Good Acoustic Window: To get the best image, you may need to apply a little extra gel over bony areas or scan the joint while it is immersed in water.
4. Be Thorough: if you don’t see ﬂuid when you expect it, consider trying a different contact spot for the probe or repositioning the joint. Often, the more the joint is bent, the easier it will be to ﬁnd excess ﬂuid.
5. Compare Sides: Because most people have two elbows, any questionable ﬁndings on one side may beneﬁt from a comparison view of the other elbow. Look for dark, anechoic ﬂuid, which should not be visible by ultrasound in a normal joint.
6. Review Your Anatomy: Utilize color Doppler or spectral Doppler to ensure that the anechoic ﬂuid collection you are visualizing is not a vascular structure. Reviewing your musculoskeletal anatomy beforehand will help you identify the bones, tendons, muscles, nerves, and bursae you see on your bedside scan.
7. Consider Routine Ultrasound Prior to Tapping a Joint: Not only will this help improve your musculoskeletal ultrasound skills, it will also help you avoid wasted time and unnecessary risk and pain for your patient when there is actually no ﬂuid collection available to tap.
8. Practice: With bedside ultrasound, there’s no substitute for experience. The more scans you do, the better you will be able to differentiate abnormal from normal – even when you are unsure exactly what the abnormality is. To view a library of ultrasound images, go to the Ultrasound department within www.epmonthly.com.
Brady Pregerson manages a free on-line EM Ultrasound Image Library and is the author of the Tarascon Emergency Department Quick Reference Guide. For more information visit 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.