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Ultrasound · Shoulder

Acromioclavicular (AC) Joint Injection

shoulderac jointdistal claviclesprain

Treats

  • AC joint arthritis/sprain
  • Distal clavicle osteolysis
  • Isolated AC pain

Contraindications

  • Active local skin infection or cellulitis at the entry site (absolute)
  • Suspected septic joint (absolute)
  • Bacteremia (absolute)
  • Known allergy to local anesthetic, steroid, or antiseptic prep
  • Therapeutic anticoagulation — review case-by-case
  • Uncontrolled diabetes (relative)

Pre-procedure checklist

  • Confirm patient identity (two identifiers)
  • Confirm procedure, side, and site — mark with patient awake
  • Review allergies and anticoagulation
  • Confirm informed consent
  • Pre-scan to confirm joint orientation and rule out incompetent capsule
  • Time-out immediately before needle entry

Positioning

  • Patient seated; arm relaxed at side
Positioning

Probe

  • High-frequency linear probe (10-15 MHz)
Probe

Landmarking — find the view

  • Start mid-clavicle; slide laterally to the gap; continue to acromion; translate to center the joint gap

The correct ultrasound view

  • Two flat bones (clavicle/acromion) with thin dark joint line centered
The correct ultrasound view

Needle corridor

  • Superior approach: between superior capsule (below) and subcutaneous tissue (above) → tiny joint space, angled to match the oblique joint plane
Needle corridor

Avoid

  • Acromial branch of thoracoacromial artery
  • Overfilling (very small capacity)

Steps

  1. 1In-plane SUPERIOR approach along the oblique joint plane; angle the needle to match the joint line rather than the skin surface.
  2. 2Confirm trajectory by tilting probe to reveal the joint cleft orientation before entry.
  3. 3Inject 0.5-1 mL total; stop if resistance or pain rises.
  4. 4STOP IMMEDIATELY if the patient reports electric, shooting, or paresthetic sensations.

Tips

  • Use minimal local anesthetic to save space for steroid.
  • Limit corticosteroid to ≤ 3 per joint per year.

Resident pearls

  • Don't 'fill up' the joint with local if you plan to use steroid; the capacity is often < 1 mL.
  • Total injectate volume ≤ 1 mL — pre-mix steroid and small lidocaine aliquot in the same syringe before approaching the joint.
  • If pressure is low, the capsule may be incompetent (post-trauma/surgery), leaking into SA space.
  • Look for the Geyser sign: fluid tracking from GH joint up through the AC joint.

Supplies

  • 3 mL Syringe
  • 25G 1.5" Needle (default); 27G 1" only for lean patients — 27G deflects before reaching the joint in larger patients
  • 18G Drawing Needle
  • 1% Lidocaine (0.5 mL)
  • Triamcinolone 20-40 mg OR Dexamethasone 4 mg (0.25-0.5 mL)
  • Alcohol Swabs (vial tops)
  • Betadine/Chloraprep
  • Sterile Gloves
  • Sterile 4x4 Gauze Pads
  • Sterile Towels & Drapes
  • Adhesive Bandage (Band-Aid)
  • Washcloth/Towel (gel cleanup)
  • Needle Disposal Safety Cap
  • Sterile probe cover & gel

Post-procedure

  • Apply a clean dressing; remove after 24 hours.
  • Local anesthetic relief for 1-4 hours; steroid begins 24-72 hours.
  • Steroid 'flare' in 2–10% — manage with ice and acetaminophen.
  • Rest 24-48 hours.
  • Return immediately for: spreading redness, swelling, fever, or disproportionate pain.
  • Diabetics: expect 50-100 mg/dL glucose rise for 3-5 days.
  • Maximum 3 injections per joint per year.