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Arthrocentesis Of The Knee


John Kiel DO, MPH
Assistant Professor of Emergency Medicine
Assistant Professor of Orthopedic Surgery
University of Florida College of Medicine – Jacksonville


  • Arthrocentesis of the knee can be performed with or without ultrasound
  • Use of ultrasound improves accuracy, decreases pain scores, allows aspiration of more synovial fluid, and decreases the total time of the procedure
  • Emergency medicine physicians should be comfortable using ultrasound to augment arthrocentesis of the knee
Transducer and needle are positioned along the suprapatellar recess in short axis to the limb. This is well visualized on ultrasound.[1]Image courtesy of, “PoCUS Guided Knee Arthrocentesis


  • The knee is the most commonly effused joint in the human body from both traumatic and atraumatic causes.
  • It represents the largest synovial cavity in the body and is likely the easiest to aspirate.
  • Knee joint aspiration can be used for diagnostic and therapeutic purposes.
  • Due to its common presentation in the emergency department, it is critical that physicians be familiar with the technical skills to perform this procedure.


  • The knee can be defined as a hinged synovial joint.
  • Four bones stabilize the joint: the patella, femur, tibia and fibula.
  • Knee extension is aided by the extensor complex which consists of the quadriceps tendon, patella, patellar tendon and its insertion on the tibial tubercle.
  • The joint capsule begins in tibiofemoral space and extends into the suprapatellar bursa or recess which runs deep to the extensor apparatus.
Anatomy of the knee joint. The suprapatellar bursa (red box) is contiguous with the joint.[2]Image courtesy of, “Prepatellar Bursa”
  • It is critical to recognize that the suprapatellar bursa is contiguous with the joint itself.
  • Thus, aspiration or injection from the suprapatellar bursa is synonymous with placing the needle in the tibiofemoral joint space.

Ultrasound Evaluation

  • There are some key views on knee ultrasound that can help you identify your landmarks.
  • The suprapatellar bursa communicates with the knee joint and appears on US as a thin hypoechoic line no more than 2 mm wide extending approximately 6 cm above the patella, inferior to the quadriceps tendon.[3]Valley VT, Stahmer SA. Targeted musculoarticular sonography in the detection of joint effusions. Acad Emerg Med. 2001;8(4):361-367. doi:10.1111/j.1553-2712.2001.tb02114.x
  • Fluid in the joint appears as an anechoic stripe in this area, with abnormal fluid filling the suprapatellar bursa and lateral joints recesses.[4]Lee D, Bouffard JA. Ultrasound of the knee. Eur J Ultrasound. 2001;14(1):57-71. doi:10.1016/s0929-8266(01)00146-x
  • Acute effusions are typically anechoic, whereas chronic effusions may demonstrate fibrous adhesions and echogenic debris, representing inflammatory or hemorrhagic material or fat globules.[5]Finlay K, Friedman L. Ultrasonography of the lower extremity. Orthop Clin North Am. 2006;37(3):245-275, v. doi:10.1016/j.ocl.2006.03.002
Transducer position in long axis.
Transducer position in short axis.
Normal suprapatellar bursa in long axis. Note there is no joint effusion so the bursa is “closed”.
Normal suprapatellar bursa in short axis. Note there is no joint effusion so the bursa is “closed”.
Suprapatellar bursa demonstrating a moderate sized joint effusion. A linear transducer is used and is in long axis to the knee.
Suprapatellar bursa demonstrating a very large joint effusion. A curvilinear transducer is used and is in long short axis to the knee.


  • Landmark vs. Ultrasound Guided Approach
    • Wu et al published systematic review comparing landmark (LM) and ultrasound (US) based approach to knee arthrocentesis.[6]Wu T, Dong Y, Song HX, Fu Y, Li JH. Ultrasound-guided versus landmark in knee arthrocentesis: A systematic review. Semin Arthritis Rheum. 2016;45(5):627-632. … Continue reading[7]Ahmed I, Gertner E. Safety of arthrocentesis and joint injection in patients receiving anticoagulation at therapeutic levels. Am J Med. 2012;125(3):265-269. … Continue reading
  • Determine area of perceived maximum fluid
    • Use milking maneuver or ballottement test to find best insertion point
Patient and needle position for palpation guided knee arthrocentesis.
Demonstration of ‘milking maneuver’ to move the suprapatellar fluid behind the knee and perform the ballottement test. Note that this technique can also be used to move the synovial fluid towards the needle to maximize aspiration volume.
  • Suprapatellar bursa
    • Can be superolateral (first choice) or superomedial
    • Approximately 1 cm superior and 1 cm lateral to patella
    • Inferolateral or inferomedial not recommended unless contraindication to suprapatellar approach
  • Contraindications: abnormal anatomy, overlying cellulitis or soft tissue injury
  • Apply local anesthetic at needle insertion site
    • Can inject extra anesthetic into soft tissue and joint space
  • Angle needle approximately parallel to the femur, directed medially, into the suprapatellar bursa while actively aspirating
  • Continue needle insertion until joint fluid returns in syringe
  • Aspirate until no more fluid is collected
    • Assistant can continue to ‘milk’ fluid in the suprapatellar recess towards needle tip
  • After the needle is removed, apply appropriate pressure and bandage at end of procedure

Ultrasound Guided Technique

  • General
    • Need two providers or one provider with an assistant
    • One provider performs arthrocentesis, second provider holds transducer and manages ultrasound
    • Strongly recommend suprapatellar approach
  • Patient positioning
    • The patient should be supine with the knee should be in approximately 15-20 degrees flexion.
  • Identify suprapatellar bursa including point of needle insertion
    • Ultrasound should be oriented in transverse axis over suprapatellar bursa
  • Synovial fluid will appear as anechoic or hypoechoic collection deep to the quadriceps tendon
  • Local anesthetic should be injected
    • Can inject extra anesthetic into soft tissue and joint space
  • Under ultrasound guidance
    • The needle should be directed into the hypoechoic collection while maintaining negative pressure with the syringe
    • The needle should be visualized in long access, in plane
  • Aspirate until no more fluid is collected
    • Assistant can continue to milk fluid towards needle tip
  • After the needle is removed, apply appropriate pressure and bandage at end of procedure
Transducer position and needle position seen clinically as well as visualized on ultrasound.[8]Image courtesy of, “PoCUS Guided Knee Arthrocentesis
Video demonstration with needle in plane and needle tip within the suprapatellar effusion.

Additional Considerations

  • Challenges to Landmark-based approach
    • Body habitus
    • Multiple attempts made to isolate fluid pockets due to small effusions or difficult anatomy Inadvertent striking of nearby bony or cartilaginous surfaces
    • Incomplete aspiration of joint fluid
    • Benefits of Ultrasound-guided approach
  • Technically easy
    • Maximize the amount of fluid retrieved
    • Increase the successful aspiration and total volume of knee joint fluid
    • Decrease patient discomfort at time of procedure and at 2 weeks follow up
    • Increase the practitioner’s sense of ease in performing the procedure
    • Could decrease total procedure duration.

Pearls & Pitfalls

  • If the patient complains of pain during the procedure, you may pause to inject more local anesthetic. Also consider providing PO, IM or IV medication prior to the procedure depending on their degree of discomfort.
  • Patients with a larger body habitus may be more challenging to aspirate. In these cases, be sure to have staff available to help manipulate soft tissue and have longer needles.
  • Palpate lateral or medial side of suprapatellar recess to manipulate the soft tissue planes and better clarify needle target if any degree of uncertainty
  • Periprocedural, assistant can manipulate suprapatellar recess and push fluid towards needle to minimize degree of needle movement and maximize volume of aspirate