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Trick of the Trade: Knee Arthrocentesis

arthrocentesis2A patient comes into the ED and you suspect septic arthritis to the knee. As you consent the patient for arthrocentesis, you can tell s/he has reservations about a needle being inserted into their knee and left in place while you aspirate. You also think in the back of your mind how tricky it is to sometimes change syringes while keeping the needle in the correct location. Is there another way of tapping the knee without a needle?


Trick of the Trade: Use the angiocatheter for knee arthrocentesis

  • Prepare for arthrocentesis in the usual fashion (anteromedial or anterolateral approach)
  • Instead of attaching a needle to the syringe, attach an 18 gauge angiocatheter
  • Insert the angiocatheter while aspirating back on the syringe
  • When synovial fluid is aspirated, advance the catheter into the joint and remove the angiocatheter needle
  • The plastic catheter is left in the joint for aspiration


  • No metal needle left in the knee, which may comfort some patients
  • No needle to secure if you need to change syringes
  • Convenient way to also administer intraarticular steroids/analgesics
  • Joint/catheter can be manipulated without fear of causing tissue injury


  • Milk the joint/effusion to facilitate fluid collecting in the joint space
  • Slight manipulation of the joint may help the fluid re-distribute into the joint space
  • Aspirate as you slowly withdraw the catheter in case there is a residual fluid pocket
  • Be aware of a kinked catheter as an extreme angle may impede aspiration

Other pearls regarding septic arthritis? Check out synovial lactate for septic arthritis and the Paucis Verbis card: Septic Arthritis.

Has anyone tried the angiocatheter technique for knee arthrocentesis? We’d love to hear about your experience!

ALiEM Copyedit

Fred: Great idea for a post. I think this would be useful primarily, as you mention, if you were doing a multi-step procedure, such as aspirating synovial fluid and instilling an agent. Other variations on the theme that weren\'t mention above including:

  1. Injection of bupivacaine or other anesthetic agent for transient pain relief after synovial fluid removal.
  2. Instillation of methylene blue to check for an open joint injury and then removing the dye as much as possible when done.

A kinked angiocatheter would be my primary concern as you mention, so if I assume that if the technique is not working smoothly, to revert back to the traditional needle-only technique. Also if I were doing just a straight aspiration of a joint, I\'d personally probably go with just a needle.

And lastly, I\'d specifically mention somewhere that this is just for a knee, which is what I\'m assuming you mean. Otherwise the angiocatheter is too short (e.g. hip) or the too big in general (e.g. elbow, fingers, wrist). Perhaps by changing the title and the Trick of the Trade header to say \"Knee Arthrocentesis\".

Michelle Lin, MD
ALiEM Editor in Chief; Associate Professor of Emergency Medicine, UC San Francisco

Expert Peer Review

Hi Fred,

This is fabulous. Can\'t wait to try it myself.

One other thing I would mention for this piece though is adding a line or two on the different approaches in regards to location of insertion of needle, and the success rate noted in literature for each location. Also, if there is any literature on the success rate of angio-catheter vs plain needle / syringe, it would be nice to know or could be a future project for an ambitious resident at Kaweah!!

Christian Herrera

Christian Herrera, MD
Attending Emergency Physician Providence Saint Joseph Medical Center (Burbank, CA)


Agree about mentioning the different access sites. I added a blurb about the 2 locations that I\'ve used. I couldn\'t find anything in the literature about using the catheter for arthrocentesis so don\'t know about success rates. It is mentioned (very) briefly in Roberts and Hedges\' but no data behind it. It would be a good project for an ambitious resident!

Thanks for the feedback!


Fred Wu, MHS PA-C
Lead PA, Department of Emergency Medicine, Kaweah Delta Medical Center (Visalia, CA)
Fred Wu, MHS, PA-C

Fred Wu, MHS, PA-C

Lead PA
Department of Emergency Medicine
Kaweah Delta Medical Center (Visalia, CA)
Fred Wu, MHS, PA-C

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