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

Latest posts by Fred Wu, MHS, PA-C (see all)

  • Sorry, I’m having trouble picturing how you would attach a syringe to the angio-cath before you started. I can’t recall the last time I saw angio-cath or similar that wasn’t part of a spring loaded system. Is there a way to do this that I am not thinking of?

    • Fred Wu

      @stethoscopenunchucks:disqus It may depend on the type of angiocatheter your institution stocks. At the end of the angiocatheter there may be a removable cap. Take off the cap and attach a syringe. You are correct…I don’t think it will work with the spring loaded systems. Our shop stocks angiocatheters which have an auto-guard after you advance the catheter over the needle.

      Thanks for commenting!

    • Fred Wu

      @Stethoscope Nunchucks

      Here is a picture to hopefully clarify the setup.

  • Matthew Pirotte

    interesting TOTD, playing devil’s advocate though: this seems like a Trick in search of a clinical scenario. With appropriate application of local anesthetic knee arthrocentesis really isn’t all that painful. I can’t imagine a scenario where a patient is going to care or know whether or not they have a needle or a cath in their joint…. Also in some bigger patients or in some approaches (e.g. sneaking the needle in right under the patella) i could imagine a scenario where the catheter could collapse you’d have to restick them. Any thoughts on this?

    • Fred Wu

      @matthewpirotte:disqus Agree that this may not work in every scenario but offered as another method of accomplishing the same goal. I once had a large patient where the angiocatheter was not long enough (not even close!).

      Thanks for commenting.

  • James Feldman

    One of our faculty Dr. Andy Dewitz developed a great modification for arthrocentesis. He uses a short iv tube connector to attach to the syringe and then needle so one is never manipulating the syringe in order to change for large volume or inject after aspiration. It seems that it is often the movement of the needle, especially when manipulating the syringe to remove it, that causes discomfort. Although a catheter is a consideration, if the catheter kinks or stops working could require another stick.

    • Great trick! I’ve used this technique a few times when there are 2 people for a peritonsillar abscess. Once manipulates the needle and the other just puts back pressure on the syringe via the connected IV tubing.

      • James Feldman

        yes, same concept. I give all credit to Dr. Dewitx- he is very creative in procedures and one of the very early leaders in ED POCUS

    • Fred Wu

      I like it! Agree that movement of the needle may cause discomfort/distress to the patient. Another pearl to add to one’s bag of tricks.

      Thanks for the tip!

  • Hina

    I have used a three way stop cock with the needle so you can easily inject your steroid, if you need to, or change syringes without having to manipulate the needle too much.