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Ultrasound · Hip

Sacroiliac (SI) Joint Injection

hipsi jointsacroiliaclow back paindiagnostic injection

Treats

  • Suspected SIJ-mediated pain (single intra-articular block is one of several diagnostic tools — fluoroscopic confirmation with contrast remains more rigorous than US for true intra-articular placement)
  • Therapeutic injection after failed conservative care

Contraindications

  • Active local skin infection at entry site (absolute)
  • Known allergy to local anesthetic, steroid, or antiseptic prep
  • Therapeutic anticoagulation — review case-by-case
  • Uncontrolled diabetes (relative)
  • Active sacroiliitis from inflammatory arthropathy in flare (relative — coordinate with rheumatology)

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: identify the synovial portion in the inferior third (S2-S3) and the dorsal sacral foramina to avoid
  • Time-out immediately before needle entry

Positioning

  • Prone; pillow under abdomen to minimize lumbar lordosis
Positioning

Probe

  • Curvilinear 2-5 MHz; linear may suffice in thin patients
Probe

Landmarking — find the view

  • Visual Cue: The 'Synovial Cleft' — Identify the sacroiliac gap in the inferior 1/3 of the joint.
  • Transverse over sacral hiatus → move laterally to sacral edge → follow cephalad ONLY to the inferior third (approx S2-S3) where the SI cleft becomes visible. Do NOT go higher — the upper two-thirds of the posterior SIJ is a ligamentous syndesmosis with no synovial space.
  • Rock the probe to maximize the 'opening' of the posterior joint cleft.
  • Identify the thick posterior sacroiliac ligaments overlying the cleft.

The correct ultrasound view

  • Two bony lines (sacrum medial, ilium lateral) with posterior SI joint cleft between; posterior SI ligament complex superficial
The correct ultrasound view

Needle corridor

  • In-plane lateral → medial through posterior SI ligament complex into synovial cleft (inferior third — S2-S3 level — most accessible)
Needle corridor

Avoid

  • S1–S4 sacral nerve roots (exit via posterior sacral foramina medially — intraforaminal injection delivers anesthetic/steroid directly onto a nerve root and can cause transient lower extremity weakness, sensory change, or bowel/bladder dysfunction). If the sacral cortex disappears from view on the medial side of the needle path, stop and re-scan — you may be over a foramen.
  • Superior and middle cluneal nerves (posterior rami crossing the posterior iliac crest and sacral region — direct injection may cause persistent posterior hip/buttock pain)
  • Superior gluteal artery/vein and gluteal nerve branches laterally

Steps

  1. 1Advance in-plane to joint cleft; test inject a small bolus for separation.
  2. 2Inject therapeutic volume (often ~1-2 mL) under real-time visualization.
  3. 3STOP IMMEDIATELY if the patient reports electric, shooting, or paresthetic sensations into the leg or pelvis.

Tips

  • Success improves with experience; aim for inferior synovial region if cleft is narrowed in older adults.
  • If color Doppler shows a vessel directly in the planned path, abandon and re-plan.
  • Limit corticosteroid to ≤ 3 per joint per year.

Resident pearls

  • Approach lateral-to-medial through the posterior SI ligament complex.
  • The inferior synovial cleft (S2-S3 level) is the most reproducible entry point — the upper two-thirds is posterior syndesmosis only (no synovial target).
  • Confirm positioning by visualizing the cleft opening during test bolus.

Supplies

  • 5 mL Syringe
  • 22G 3.5" (89 mm) spinal needle — standard for SI joint depth in most adults
  • 18G Drawing Needle
  • 1% Lidocaine (1-2 mL)
  • Triamcinolone 40 mg OR Dexamethasone 4-10 mg
  • 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; resume normal activity as tolerated thereafter.
  • Return immediately for: spreading redness, swelling, fever, disproportionate pain, OR new leg weakness, foot drop, or numbness.
  • Diabetics: expect 50-100 mg/dL glucose rise for 3-5 days.
  • Maximum 3 injections per joint per year.