Part 2 of a Series
Our series on joint care has given you a basic overview on knee arthrocentesis. Typically, it is not necessary to have an orthopedic consultant come to the bedside in the emergency department to do this procedure. Arthrocentesis is a procedure you can do well and feel confident about your technique.
Take a moment to review our last blog post on knee pain before reading this post and watching the accompanying video. (http://bit.ly/1Q7dG4h.) As always, review the anatomy; it plays a key part in successful bedside technique. Ultrasound-guided arthrocentesis is always a favored approach.
Although emergency physicians and advanced practitioners can complete this procedure at the bedside, we suggest contacting the surgeon involved for post-op patients before starting arthrocentesis. Most surgeons (if in-house at the time) will want to see a hot post-op knee. The surgeon may want to complete the procedure herself or omit a procedure if she does not feel it is necessary. Surgeons also may have concerns about antibiotics use (or misuse) and follow-up care for their patients.
n Identification of knee effusion on physical exam
n Identification of knee effusion on plain radiograph
n Localized anesthesia prior to arthrocentesis of the knee
n Arthrocentesis of the knee
n Send laboratory testing including (but not limited to) cell count with differential, crystal analysis, Gram staining, bacterial culture(s), and sensitivity analysis.
n Suspected or definitive infection overlying the joint
n Obtain the following materials:
o 27 g needle x1 (for local anesthetic)
o 10 mL syringe x1 (for local anesthetic)
o 20 mL syringes x3 (for aspiration)
o 18-20 g needle x1 (for aspiration)
o Sterile gloves
o Antiseptic of choice
o Sterile perforated drape
o Three-way stopcock
o Sterile testing tubes and/or containers
o Bandages and/or dressings of choice
n Identify all landmarks.
o Landmarks include the medial edge of the surface of the patella or at the middle or superior aspect. Note: The medial approach is typically the first-line approach, although a lateral approach is also an option.
n Position the patient lying supine and extend the knee as far as possible, keeping in mind that flexing the knee to a 20- to30-degree angle may assist with quadriceps relaxation.
n Cleanse the patient’s skin with antiseptic. Recommendations include clorhexidine or Betadine. Remember, if you use Betadine, you should remove the excess using an alcohol swab prior to injection to prevent Betadine from going into the joint itself. Entrance of Betadine into the joint can cause inflammation and should be avoided.
n Apply a sterile fenestrated drape.
n Use a 27 g needle to create a small wheal of anesthetic to the appropriate area. You may use 1% or 2% lidocaine in combination with sodium bicarbonate, approximately a total of 10-15 mLs. The solution is 1:10 mL of bicarb and lidocaine.
n Hold the patella firmly with your non-dominant hand.
n After a wheal is created, position your dominant hand so that it is parallel to the stretcher. Inject the anesthetic slowly into the skin and along the entire track of the aspiration of the needle. Infiltrate the skin down to the area of the joint capsule. The injection track should be dispensed between the posterior portion of the patella and the intercondylar femoral notch.
n Use your non-dominant hand to milk the effusion from the suprapatellar pouch above the patella. This will force fluid into the joint. This will aid in fluid removal as you aspirate.
n Do not forget to aspirate as the needle is advanced.
n Use a large syringe (20 mL is suggested) because there may be a larger-than-expected effusion present. The knee can hold up to about 50-70 mL of fluid.
n Place all fluid into appropriate tubes, and send to the laboratory.
(Adapted from Roberts JR, Hedges JR. Clinical Procedures in Emergency Medicine, 6th edition, Philadelphia: Saunders/Elsevier, 2014.)
n If this is your first time completing the procedure, consider using an ultrasound-guided technique to be certain you have the correct landmarks.
n If your first syringe is filled to its entirety, remove it and place a new empty syringe onto the needle. To do this, hold the needle that is in the joint with a hemostat to maintain the correct position. This also stabilizes the needle so you can remove the syringe.
n Another technique is to use a three-way stopcock applied to the needle to allow you to change the syringes without having to remove the needle.
n The procedure can be almost painless to the patient and you can limit his distress if anesthesia is appropriately used. Tense patients with tense muscles do not allow for solid technique, so be sure to aid in patient comfort. As always, we feel patient comfort is half the battle!
n Sedation is rarely required, but may be prudent in some patients. This is not routine practice.
n Always try to remove as much blood or fluid as possible. Large amounts of pus may clog the needle, and the joint may not be totally drained. If this occurs, inject a small portion of the aspirated fluid into the space from the syringe and attempt minor position changes. Do not forget to push down on the suprapatellar pouch.
n Do not completely withdraw and reinsert the needle. If positioning of the needle tip needs to be altered, advance or retract the needle a few millimeters, rotate the bevel or lessen the force of aspiration or injection.
n Avoid side-to-side movements of the needle. Keep the barrel of the syringe parallel to the stretcher.
n It is easier than you think to confuse your sharps after the procedure is completed. Do not accidently toss your sample into the sharps bin.
n Apply a clean, sterile dressing with an ACE bandage to the knee post arthrocentesis.
Tip of the Week
The string test is a bedside technique to determine if the synovial fluid is inflammatory or noninflammatory fluid. Noninflammatory fluid may result from a meniscal tear. To complete this test, place a generous amount of synovial fluid onto your gloved thumb. Touch the drop with your index finger and slowly separate your fingers. A string will be formed as the fluid is stretched and manipulated. A string of approximately 1-2 cm will be evident in a noninflammatory condition. No appreciable string will be formed in an inflammatory synovial fluid such as rheumatoid arthritis. (Clinical Procedures in Emergency Medicine.)
Watch the video here.
Evidence-Based Practice Pearl
The Scandinavians seem to be doing it right. The study reported “significantly less procedural pain, improved arthrocentesis success, greater synovial fluid yield, more complete joint decompression, and improved clinical outcomes.” (Scand J Rheumatol 2012;41:66.) We also recommend reading our friend Dr. Todd Thomsen’s article, Arthrocentesis of the Knee. (New Engl J Med 2006;354e19; http://bit.ly/1fwqzIG.)
Jim weighs in: “Once you learn the technique, the knee joint is quite easy to tap. Using suprapatellar pressure maximizes fluid in the knee joint itself.”
Martha weighs in: “I always provide a rolled towel under the patient’s knee to help with relaxation and comfort to aid in proper positioning.”
Complications of knee arthrocentesis and other clinical pearls related to joints.