Sound Bite 4 - Knee Effusion

Author: Dr Gokul Sagar Bailur Editor: Dr Nick Mani

Gentleman in his 70s presents to Emergency Department with an acute painful swollen hot knee joint with significant reduction in range of motion, and unable to weight bear on it.

Lab bloods sent from triage show WCC 12.2, NO 7.1, CRP 150.

You elect to perform ultrasound guided knee arthrocentesis as there is a large knee effusion (clinically/sonographically): -

Panel 1 Short axis of knee joint with needle insertion (with reverberation artefact) into the large anechoic effusion in-plane with linear probe

Panel 2/3 Long axis of knee joint demonstrating large anechoic effusion before aspiration, with acoustic shadowing artefact of the patella not to be mistaken for effusion (QT- Quadriceps Tendon, SPFT- Supra-Patellar Fat Pad)

Case Resolution-

The ultrasound guided knee arthrocentesis was performed safely without any complication in ED. Septic arthritis was diagnosed by microscopy without any delay, awaiting culture & sensetivities, and the patient was admitted to the orthopaedics.

Take Home Message-

Confirm the diagnosis of knee effusion on ultrasound, and perform the procedure safely and without any delay under ultrasound guidance.

References-

Poonja, Z., Ahn, J.S. & Kim, D.J. Just the facts: ultrasound guidance for arthrocentesis. Can J Emerg Med 23, 737–739 (2021). https://doi.org/10.1007/s43678-021-00184-x