Tips & Tricks for the Ultrasound Evaluation of a Joint Effusion
01 Look before You Leap: Ultrasound can be used to help you delineate whether a patient has a joint effusion or not. It is more sensitive than x-ray and can also help you localize the best area to tap. It may be prudent to perform a bedside ultrasound prior to an arthrocentesis attempt when physical exam findings are equivocal.
02 Go Linear: For most joints use a 5 to 7.5 MHz linear array transducer. Apply a large amount of ultrasound gel to improve your acoustic interface. If the patient is thin and devoid of much subcutaneous fat, you may need to utilize an acoustic standoff pad or water submersion to improve your sonographic window.
03 Take Multiple Views: Always obtain images in multiple planes (longitudinal, transverse, oblique) to help define the borders of the structure you are looking at and avoid mistaking vascular structures for a joint effusion. Apply color or spectral Doppler if there is any concern that you may be looking at a vascular structure. Use ultrasound to find the best and largest fluid pocket to tap.
04 Compare Sides: Utilize contra-lateral limbs for comparison views, especially when unsure of what you see. If you see a similar structure on the asymptomatic limb, you may need to look again.
05 Don’t Move: Avoid changing the position of the joint between performing the bedside ultrasound and performing the arthrocentesis. Fluid may move with joint repositioning. If you decide to perform a dynamic ultrasound-guided joint aspiration, make sure you prep and drape the probe in a sterile fashion prior to beginning your procedure.
Brady Pregerson manages a free on-line EM Ultrasound Image Library and is the editor of the Emergency Medicine Pocketbook series. For more information visit EMresource.ORG.
Teresa S. Wu is the Associate Residency Director, and Director of Ultrasound and Simulation Programs and Fellowships, for the Maricopa Emergency Medicine Program in Phoenix, Arizona.