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Arthrocentesis Of The Acromioclavicular Joint


Calvin Eric Hwang, MD CAQ-SM
Clinical Assistant Professor
Department of Orthopaedic Surgery
Stanford University School of Medicine


  • Acromioclavicular (AC) joint aspiration and/or injection can be significantly easier with ultrasound guidance or assisted localization.
  • AC joint steroid or anesthetic injection can greatly decrease pain/symptoms in acute AC injuries.
Standard probe position for AC joint arthrocentesis or injection. (A) shows the joint in long axis and (B) shows needle placement for out-of-plane approach.[1]Mikell C, Gelber J, Nagdev A. Ultrasound-guided analgesic injection for acromioclavicular joint separation in the emergency department. Am J Emerg Med. 2020;38(1):162.e3-162.e5.


  • Septic arthritis in the acromioclavicular (AC) joints) is uncommon, but can present atypically so a high index of suspicion is necessary when evaluating someone with fever, shoulder pain, and limited range of motion.
  • US guided shoulder arthrocentesis can be performed by emergency physicians to diagnose septic arthritis and crystal arthropathies[2]Nagdev A. Ultrasound-Guided Glenohumeral Joint Evaluation and Aspiration. ACEP Now. 2016;35(6)..
  • Conversely, US guided AC steroid injections can be considered in patients presenting with suspected AC joint arthritis and sprains.


  • The shoulder girdle is composed of the proximal humerus, scapula and clavicle.
  • The AC joint is a synovial joint formed by the medial acromion and the distal tip of the clavicle.
  • It is stabilized by the acromioclavicular and coracoclavicular ligaments.
Anatomy of the acromioclavicular joint.[3]Image courtesy of, “The Acromioclavicular Joint” (click to enlarge)

Ultrasound Evaluation

  • A high-frequency linear or hockey stick probe should be used for evaluation.
  • The patient should be in the seated position and their arm resting at their side or in their lap.
  • The ultrasound probe should be placed on the superior aspect of the AC joint in long axis.
  • Significant AC joint effusions can be seen with distension of the capsule though up to 3 mm of distension is normal.
Ultrasound of normal acromioclavicular joint in long axis.
Effusion of the acromioclavicular joint in long axis.[4]Adhikari S, Stolz L, Amini R, Blaivas M. Impact of point-of-care ultrasound on quality of care in clinical practice. Rep Med Imaging. Published online 2014:81.


  • Landmark vs. Ultrasound Guided Approach
    • Both landmark and ultrasound-guided approaches to acromioclavicular joint arthrocentesis have been described.
    • Studies of ultrasound-guided vs landmark-guided approaches to the AC joint have shown a much higher success rate (100%) when compared to landmark-guided (40-66%)[5]Aly A-R, Rajasekaran S, Ashworth N. Ultrasound-guided shoulder girdle injections are more accurate and more effective than landmark-guided injections: a systematic review and meta-analysis. Br J … Continue reading.
    • For this reason, we strongly encourage emergency medicine physicians to utilize ultrasound when performing procedures involving the AC joint.
  • Materials
    • 18 gauge draw needle
    • 1.0 – 1.5 inch, 25 gauge needle for aspiration and injection
    • Note: small joint but may require larger gauge for aspiration
    • 3 – 5 cc syringe
    • Local anesthetic
    • Sterile equipment (gauze, skin prep, gloves, probe cover, etc)

Palpation Guided Technique

  • General
    • Can be performed without assistance
    • Procedure should be done with strict sterile technique
  • Position
    • Patient should be in seated position
  • Approach
    • Palpate medial acromion and distal clavicle.
    • Mark site of injection with pen or impression
    • Insert needle on superior aspect of skin between the medial acromion and distal clavicle.
Demonstration of the palpation guided approach with the joint space marked and the acromion and clavicle outlined.[6]Image courtesy of, “Acromioclavicular Joint”
  • Other
    • Because it is blind, the needle may require multiple redirections until you feel it “drop” into the joint, you aspirate fluid and/or injection becomes very easy

Ultrasound Guided Technique

  • General
    • Can be performed without assistance
    • Procedure should be done with strict sterile technique.
  • Position
    • Patient should be seated or supine with the affected arm at the patient’s side
  • Ultrasound
    • Prior to starting the procedure, place the probe in long axis to the joint and identify the medial acromion, lateral clavicle, and AC joint, then rotate the probe to visualize the joint in short axis.
Demonstraiton of ultrasound guided arthrocentesis of acromioclavicular joint
Demonstration of probe position and view of ultrasound guided approach. Joint space and target marked (*) with arrows indicating joint capsule. Supraspinatus is marked SS.[7]Image courtesy of, “ULTRASOUND GUIDED SHOULDER INJECTIONS”
    • Excess synovial fluid will appear as an anechoic collection bulging superiorly out of the AC joint.
  • Under ultrasound guidance
    • Probe: This can be performed in short axis or long axis (recommended)
    • Needle: The needle can be in plane or out of plane
    • A 25-gauge needle should be inserted with direct visualization into the AC joint.
    • Negative pressure with the syringe should be maintained throughout.
    • Aspirate until all visible fluid has been collected.
  • Other
    • A small gel ‘standoff’ or ‘step off’ can be used to create a window and improve visualization of the needle as it approaches the joint space
    • Injection can be performed using the same approach.
Video demonstration of the in plane approach.
Video demonstration of the out of plane approach.

Additional Considerations

  • Benefits
    • Easy to visualize joint and effusion.
    • Procedure is performed with direct needle visualization throughout
    • Arthrocentesis and injection can each be both diagnostic and therapeutic.
    • Can speed time to diagnosis and disposition.

Pearls & Pitfalls

  • Due to the superficial nature of the AC joint, this procedure can easily be performed in short or long axis and in or out of plane
  • If indicated, medication (e.g. steroid or anesthetic) can be injected into the acromioclavicular joint using the same approach.