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Indications & Patient Selection
Indications
- Axial low back pain with SI joint origin — duration ≥3 months, failed conservative therapy (NSAIDs, physical therapy, sacral belting)
- SI joint pain characteristics: pain below L5, buttock pain, PSIS tenderness, groin pain; worsened with single-leg stance; Gaenslen test positive; FABER (Patrick) test positive
- Sacroiliitis: ankylosing spondylitis, psoriatic arthritis, reactive arthritis, post-partum SI dysfunction, post-lumbar fusion SI stress
- Diagnostic injection: ≥50% pain relief after intra-articular steroid/anesthetic confirms SI joint etiology
- Post-fusion SI pain: up to 40% of patients develop SI joint pain within 5 years of lumbar fusion — low threshold for injection in this population
Contraindications & Workup
- Absolute contraindications: Active infection over injection site · Uncorrectable coagulopathy · Pregnancy · Allergy to contrast or corticosteroids
- MRI pelvis: evaluate for sacroiliitis, subchondral erosions, bone marrow edema (STIR sequences), bridging or ankylosis
- X-ray SI joint: sclerosis, joint space changes, bridging osteophytes
- ESR / CRP: elevated in inflammatory arthropathy (ankylosing spondylitis, psoriatic arthritis)
- HLA-B27: obtain if ankylosing spondylitis suspected — guides long-term management and biologic therapy referral
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Pre-Procedure Checklist
Imaging guidance. Fluoroscopy (preferred for most cases) or CT guidance. CT preferred when ankylosis is present (ankylosing spondylitis) or when fluoroscopic access is difficult due to body habitus.
Needle selection. 20–22G, 3.5-inch spinal needle. Use 20G if ligament is particularly tough or for larger patients. Have a longer needle (5") available for obese patients.
Injectate preparation. 1 mL triamcinolone 40 mg + 1 mL bupivacaine 0.5% = total 2 mL. Joint capacity ~2–2.5 mL — do not exceed to avoid periarticular extravasation.
Contrast. Iohexol 180 (dilute) for arthrogram confirmation. Pre-draw 1 mL for test injection. Arthrogram confirmation before steroid injection is mandatory.
Positioning. Patient prone; pillow under pelvis for comfort and mild pelvic flexion, which can open the inferior SI joint space.
Anticoagulation (SIR Category 1 — low risk). No routine holds required. Warfarin: continue if INR ≤3.0 (no correction needed for Cat 1). DOACs: no hold required (optional 12–24h hold for therapeutic dosing at operator discretion). Aspirin and clopidogrel: continue — P2Y12 inhibitors do NOT need to be held for Category 1 procedures. Therapeutic anticoagulation: brief optional hold (IV heparin 2–4h; LMWH hold 1 dose) if clinically feasible.
Diabetic patients. Warn about transient glucose elevation for 24–48h post-steroid. Arrange home glucose monitoring. Check recent HbA1c if available.
Consent discussion points. Post-injection pain flare (10–20%), infection (<0.1%), foraminal injection with nerve injury, glucose elevation in diabetics, limited benefit in ankylosed joints, potential need for lateral branch RFA if repeated injections provide only short-term relief.
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Relevant Anatomy
SI Joint Structure
- Diarthrodial synovial joint (anterior inferior portion) — true joint with hyaline and fibrocartilage, synovial lining in the lower 2/3, and thick fibrous capsule
- Posterior syndesmosis — fibrocartilaginous/ligamentous component (dorsal, interosseous, iliolumbar ligaments); primary stability source
- Joint space: 2–4 mm; irregular margins; widest inferiorly — the inferior joint is the primary injection target
- Joint capacity: ~2–2.5 mL; overfilling causes periarticular extravasation and reduces efficacy
- Synovial lining in lower 2/3 renders it susceptible to inflammatory arthropathies (ankylosing spondylitis, psoriatic arthritis)
Innervation & Nearby Structures
- Innervation: L4–S3 dorsal rami (posterior SI ligament) + sacral plexus branches (anterior capsule); explains why lateral branch RFA at L4–S3 is effective
- Key target landmark: posterior inferior joint line at S3–S4 level — most accessible entry point on oblique fluoroscopy
- Sacral foramina (S1–S4): medial to joint; inadvertent foraminal injection causes nerve root irritation — the critical error to avoid
- Sciatic notch: inferior and lateral — avoid
- Iliac vessels: anterior to joint — relevant for anterior approaches; use CT if anterior access required
- Fluoroscopic challenge: oblique joint orientation + overlapping iliac and sacral cortices → ipsilateral oblique view mandatory to separate joint lines
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Technique
Default RadCall approach · share your own below
Supplies
22G 3.5" spinal needle
C-arm fluoroscopy
Iohexol 180 (dilute contrast)
1 mL + 3 mL syringes
Extension tubing (primed)
Triamcinolone 40 mg/mL
Bupivacaine 0.5%
ChloraPrep
Sterile drape
Pillow for under pelvis
Sterile dressing
Approach — Intra-Articular Fluoroscopy-Guided Injection
Steps
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Position & AP fluoroscopy
Patient prone with pillow under pelvis. Obtain AP fluoroscopic view to identify the SI joint region. On AP, the SI joint typically appears as 2–3 overlapping lines due to the oblique orientation — this view alone is not sufficient for needle guidance.
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Ipsilateral oblique view
Rotate C-arm 10–25° toward the ipsilateral (same) side. This opens the inferior SI joint space into a single clear, accessible lucent line. The inferior 1/3 of the joint at the S3–S4 level is the target — it is widest and most accessible.
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Target the inferior joint margin
Under oblique fluoroscopy, identify the posterior inferior joint line. Align the needle trajectory with the posterior joint margin on the oblique view. Apply local anesthesia to skin and subcutaneous tissue.
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Advance needle to posterior joint line
Advance 22G spinal needle (3.5") to the posterior joint line using coaxial technique. You will feel a distinct tactile change as the needle transitions from fibrous posterior ligament into the joint space. Confirm depth on lateral view if needed.
▶ CT-guided SI joint needle placement
CT-guided SI joint injection: needle at posterior inferior joint margin — CT confirms position when fluoroscopy obscured by overlapping ilium; inject contrast before therapeutic agent.
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Arthrogram confirmation
Inject 0.3–0.5 mL dilute iohexol 180 under live fluoroscopy. Correct intra-articular position: contrast fills the inferior joint pouch with linear tracking along the posterior joint margin. STOP if contrast flows into S1–S4 foramina (too medial) or shows vascular pattern (redirect immediately).
▶ Fluoroscopic SI joint arthrogram
Fluoroscopic arthrogram: contrast tracks along the SI joint interspace — anterior and superior spread confirms intra-articular position; periarticular spread is acceptable if injecting ligament.
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Inject therapeutic mixture
Once intra-articular position is confirmed: inject 1 mL triamcinolone 40 mg + 1 mL bupivacaine 0.5% (total 2 mL) slowly. Monitor patient comfort throughout — significant pain may indicate intra-osseous needle position. Do not exceed 2–2.5 mL total volume.
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Withdraw & recover
Remove needle; apply sterile bandage. Recover patient for 20 minutes. Log pain score at 30 minutes post-injection. A significant immediate reduction confirms local anesthetic effect and is a positive diagnostic finding. Instruct patient on pain diary tool for post-procedure tracking.
Optional — Periarticular (Extra-Articular) Injection
For patients with predominantly posterior ligamentous SI pain (rather than intra-articular). Also consider when intra-articular access is obstructed by ankylosis.
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Target posterior SI ligament
Under fluoroscopic or CT guidance, direct a 22G needle into the posterior SI ligament along the posterior joint margin. No joint entry required.
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Inject periarticular
Inject 1–2 mL of steroid/anesthetic mixture into the posterior ligamentous complex. No arthrogram confirmation required; spread in periligamentous tissue is acceptable and therapeutic.
SI Joint RFA Escalation Pathway
If repeated injections provide only temporary relief (<3 months per injection), refer for lateral branch radiofrequency ablation of L4–S3 dorsal rami. This is a separate procedure targeting the nerve supply to the posterior SI ligament and joint capsule. Escalate to RFA after 3 injections with inadequate duration of relief.
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Fluoroscopic Landmarks
View-by-View Guide
- AP view: SI joint appears as 2–3 overlapping lines due to the oblique joint orientation and superimposed iliac/sacral cortices. Not adequate for needle guidance alone.
- Ipsilateral oblique (15–25°): Separates the joint into a single clear lucent line. The inferior portion is most accessible. This is the primary working view for needle advancement.
- Lateral view: Useful to confirm needle depth at the posterior joint line. Tip should project at the posterior margin of the joint, not through to the anterior compartment.
- CT guidance: Preferred when ankylosis is present (ankylosing spondylitis) or when the joint is not well visualized fluoroscopically. Allows direct visualization of needle tip in the joint space.
Arthrogram Interpretation
- Correct intra-articular: Contrast fills the inferior joint pouch; linear tracking along the posterior joint margin; gradual spread within the irregular joint contours
- Foraminal injection (too medial): Contrast flows into S1–S4 foramina — linear contrast extending medially from the sacral side; STOP, withdraw, redirect laterally
- Intra-osseous position: "Bone blush" — diffuse opacification of cancellous bone without joint space filling; STOP, withdraw, redirect
- Vascular uptake: Linear streaming contrast disappearing rapidly; STOP and reposition before injecting steroid
- Periarticular spread only: Diffuse pooling around joint without joint cavity filling; may still be therapeutic for ligamentous pain (periarticular injection)
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Troubleshooting
Problem
Needle does not enter the joint
Likely cause: Starting point too superior; insufficient oblique angulation; tough posterior ligament in older or ankylosed patients.
Next step: Try a more inferior starting point — the inferior 1/3 of the joint is widest and most accessible. Increase oblique angulation to 25°. If ligament is very tough, upsize to 20G needle. Consider CT guidance if fluoroscopic access remains difficult.
Problem
Contrast flows into sacral foramen
Likely cause: Needle tip too medial — sitting in or adjacent to S1–S4 foramen on the sacral side of the joint.
Next step: Withdraw needle and redirect laterally. On the oblique view, target the middle or lateral aspect of the inferior joint line rather than the medial margin. Reconfirm arthrogram before injecting steroid.
Problem
Pain with injection / intra-osseous needle
Likely cause: Needle tip within sacral or iliac cancellous bone. Contrast will show a "bone blush" — diffuse opacification of bone without joint cavity filling. Patient typically reports sharp, deep aching pain with injection.
Next step: STOP injecting. Withdraw needle 2–3 mm and reconfirm with small contrast injection. If arthrogram confirms joint entry, proceed. If still intra-osseous, withdraw fully and reposition.
Problem
Only extra-articular spread on arthrogram
Likely cause: Needle is periarticular rather than intra-articular. Patient may have predominantly ligamentous SI pain rather than pure intra-articular disease. Also seen in partially ankylosed joints.
Next step: Periarticular injection is still therapeutic for posterior ligamentous SI pain. Proceed with injection of 1–2 mL steroid/anesthetic into the periarticular tissues. Document that injection was periarticular — this affects interpretation of diagnostic utility (articular vs. ligamentous etiology).
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Complications
Immediate / Periprocedural
- Post-injection flare (10–20%) — transient pain increase 24–48h post-injection; resolves with NSAIDs and ice; warn patient before discharge; does not indicate failed procedure
- Intra-foraminal injection with nerve injury — rare with fluoroscopic guidance and arthrogram confirmation; presents as acute radiculopathy; avoid by redirecting laterally when foraminal contrast spread is seen
- Vascular injection — risk primarily with anterior approach without CT guidance (proximity to iliac vessels); use posterior fluoroscopic approach routinely
- Vasovagal reaction — manage with supine positioning, IV fluids, atropine if needed
Delayed
- Septic sacroiliitis (<0.1%) — fever, escalating joint pain, elevated WBC/CRP; MRI with contrast for diagnosis; broad-spectrum IV antibiotics; IR or surgical drainage if abscess forms; strict sterile technique prevents this
- Steroid side effects: glucose elevation (diabetics — monitor 24–48h), facial flushing (transient, 24–48h), adrenal suppression with repeated use (limit to 3 per region per year), skin/subcutaneous atrophy from superficial deposition
- Hematoma — rare in Category 1 procedure; usually self-limited; standard anticoagulation hold minimizes risk
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Critical Pearls
✶
Oblique view is mandatory — the SI joint is invisible on pure AP. The SI joint's oblique orientation means AP fluoroscopy only shows overlapping joint lines. Always obtain an ipsilateral oblique view (10–25°) before attempting needle entry. Trying to access the joint on AP alone is a common cause of failed or intra-osseous injections.
✶
2 mL maximum injectate — the joint holds only 2–2.5 mL. Excess volume causes periarticular extravasation, dilutes the steroid, and reduces efficacy. Prepare exactly 2 mL (1 mL triamcinolone 40 mg + 1 mL bupivacaine 0.5%) and do not add more. If the patient reports escalating discomfort with slow injection, stop at 1.5 mL.
✶
Confirm arthrogram before injecting steroid — intra-articular confirmation is the entire point. A 0.3–0.5 mL contrast injection takes 30 seconds and prevents foraminal nerve injury and intra-osseous steroid injection. Never skip this step. Look specifically for foraminal contrast flow (medial redirect needed) and bone blush (withdraw and reposition needed).
✶
Ankylosing spondylitis patients often have fused joints — intra-articular injection may be impossible. In partially or fully ankylosed SI joints, the joint space is obliterated and intra-articular access cannot be achieved. These patients should receive periarticular ligament injection or lateral branch blocks. CT guidance helps confirm needle position when fluoroscopic anatomy is distorted.
✶
Post-lumbar fusion SI pain is increasingly common. Up to 40% of patients develop SI joint pain within 5 years of lumbar fusion, due to altered biomechanics and stress transfer to the SI joint. Maintain a low threshold for SI joint injection in post-fusion patients with new axial low back and buttock pain below the fusion level.
✶
If 3 injections provide <3 months relief each, refer for lateral branch RF ablation of L4–S3. Repeated short-term relief (but not durable relief) indicates confirmed SI joint etiology but insufficient lasting response to steroid. Lateral branch RFA targeting L4–S3 dorsal rami denervates the posterior SI ligament and joint capsule and is the definitive next escalation step.
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Community Cards
Institutional and personal technique variations
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REF
References
Citations
- Prologo JD, Ray CE Jr., eds. Advanced Pain Management in Interventional Radiology: A Case-Based Approach. Thieme; 2024. Ch. 25 (Dalili D, Dalili DE, Isaac A, Fritz J).
- Rupert MP, Lee M, Manchikanti L, Datta S, Cohen SP. Evaluation of sacroiliac joint injection methods: systematic review. Pain Physician. 2009;12(2):399–404.
- Simopoulos TT, Manchikanti L, Gupta S, et al. Systematic review of the diagnostic accuracy and therapeutic effectiveness of sacroiliac joint interventions. Pain Physician. 2015;18(5):E713–E756.
- Zheng P, Schneider BJ, Yang A, McCormick ZL. Image-guided sacroiliac joint injections: an evidence-based review of best practices and clinical outcomes. PM R. 2019;11 Suppl 1:S98–S104.
- Foley BS, Buschbacher RM. Sacroiliac joint pain: anatomy, biomechanics, diagnosis, and treatment. Am J Phys Med Rehabil. 2006;85(12):997–1006.
- SIR Standards of Practice Committee. Consensus Guidelines for Periprocedural Management of Coagulation Status. J Vasc Interv Radiol. 2012;23(6):727–736.
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References & Resources
Primary sources · Key data · Related procedures
Key Guidelines
- ISIS Practice Guidelines for SI Joint Procedures
- ASIPP Evidence-Based Guidelines for SI Joint Interventions
- ACR Appropriateness Criteria for Low Back Pain
Primary References
- Prologo JD, Ray CE Jr., eds. Advanced Pain Management in Interventional Radiology. Thieme; 2024. Ch. 25: SI Joint Injection.
- Manchikanti L et al. An update of comprehensive evidence-based guidelines for interventional techniques in chronic spinal pain. Pain Physician. 2013;16(2 Suppl):S49-283.
- Cohen SP. Sacroiliac joint pain: a comprehensive review of anatomy, diagnosis, and treatment. Anesth Analg. 2005;101(5):1440-1453.