Ultrasound-Guided Knee Arthrocentesis
- Sterile ultrasound sheath and gel
- 18g 1.5 needle attached to a 5–10 mL syringe
- Sterile drape
- Sterile gloves
- 30 g tuberculin syringe filled with 1–2% lidocaine or ethyl chloride spray
*Pictures are for educational purposes, and sterile precautions (sterile probe cover, gloves, drapes, etc.) should be used for all joint aspirations.
For ultrasound-guided arthrocentesis, we recommend a lateral to medial in-plane technique. With the linear probe in the prepatellar fossa, rotate the probe marker (clockwise) to the patient’s right to obtain a transverse view of the prepatellar space (see Figure 3). A large area around the suprapatellar space should be cleaned and draped in a sterile manner. The ultrasound transducer should be placed in a sterile sheath and then on the sterile field. The ultrasound system should be positioned opposite to the provider so the screen is in the direct line of sight. Using a 10 mL syringe attached to a standard 18g needle, enter the skin in plane and just lateral to the probe at a shallow angle (see Figure 4). The needle will traverse between the iliotibial band (superiorly) and vastus lateralis (inferiorly) without risk for vascular puncture. Clear needle visualization can be achieved by slowly advancing just under the transducer. Gentle aspiration of synovial fluid with needle tip being visualized within the fluid collection will confirm violation of the joint space.
Point-of-care ultrasound can be a useful adjunct in the evaluation of the patient with a swollen, painful knee. Ultrasound can identify a suspected knee effusion as well as assist with arthrocentesis. A simplified in-plane technique can easily be incorporated into the evaluation of the patient with a suspected septic knee.