Introduction
The sacroiliac joint is a large, paired joint connecting the sacrum — the triangular bone at the base of the spine — to the iliac bones of the pelvis on each side. It bears and transmits the load of the upper body to the lower extremities with every step, and it is subject to the same degenerative changes, inflammatory conditions, and biomechanical stresses that affect any weight-bearing joint. When it becomes a pain generator, the result is low back, buttock, and posterior thigh pain that is clinically indistinguishable from lumbar spine pain on history alone.
Studies suggest that the SI joint is responsible for 13 to 30% of chronic low back pain cases. [2] [5] That proportion is higher in specific populations: patients who have undergone prior lumbar fusion, post-partum women with pelvic girdle pain, and patients with inflammatory conditions such as ankylosing spondylitis or psoriatic arthritis. In the general chronic low back pain population, it is a significant contributor that is frequently missed because it is not the first structure evaluated.
The challenge is diagnosis. No imaging study confirms SI joint pain. An MRI may show arthritic changes in the SI joint, but arthritic changes are common and do not establish the joint as the pain source. Physical examination tests that provoke SI joint pain — the FABER test, the thigh thrust, the sacral sulcus test, the Gaenslen maneuver — have moderate diagnostic utility individually but improve meaningfully when used in combination. [3] The definitive diagnostic test is the fluoroscopic intra-articular injection of local anesthetic: if a precisely placed injection into the SI joint produces significant temporary pain relief, the joint is confirmed as the primary pain generator. [6]
That diagnostic injection is where we start at NYBJ. Before recommending any treatment directed at the SI joint, we confirm the diagnosis.
The Sacroiliac Joint: Anatomy and Why It Causes Pain
The SI joint is a large, C-shaped joint with a surface area of 17 to 22 cm². It is the junction between the sacrum and the ilium and is stabilized by some of the strongest ligaments in the body. Unlike the lumbar facet joints, which are true synovial joints, the SI joint has a hybrid structure: the anterior one-third is synovial (with joint fluid and cartilage) and the posterior two-thirds is syndesmotic (fibrous, ligamentous). This anatomy means that SI joint pain can originate from either the intra-articular synovial portion or from the surrounding ligamentous structures.
The joint moves very little — approximately 2 to 4 degrees of rotation and 1 to 2 mm of translation — but it absorbs significant compressive and shear forces with every step. Over time, degenerative changes accumulate. Inflammatory conditions can affect the synovial portion directly. Biomechanical disruption — from pregnancy, leg length discrepancy, prior lumbar fusion that alters load transfer, or asymmetric gait — can overload the joint and produce pain.
| Condition | How It Affects the SI Joint | Clinical Pattern |
| Degenerative arthritis (osteoarthritis) | Cartilage loss and joint space narrowing in the synovial portion; osteophyte formation | Gradual onset; worse with prolonged sitting, standing, stair-climbing; may be bilateral |
| Post-lumbar-fusion SI joint stress | Load transferred to SI joint after lumbar fusion stiffens the levels above; accelerated degeneration | New onset low back / buttock pain after lumbar fusion; often 1–3 years post-op |
| Pregnancy-related pelvic girdle pain | Ligamentous laxity from relaxin hormone; increased SI joint mobility and instability | Onset during or after pregnancy; posterior pelvic pain; worse with single-leg loading |
| Inflammatory sacroiliitis | Inflammatory arthritis (ankylosing spondylitis, psoriatic arthritis, IBD-related) affecting SI joint | Bilateral involvement common; morning stiffness; elevated ESR/CRP; younger patients |
| Trauma / direct impact | Fall on buttocks or MVA; direct disruption of SI joint ligaments or joint surface | Acute onset following mechanism; tenderness directly over SI joint; may be unilateral |
| Leg length discrepancy | Asymmetric loading of SI joints with each step | Insidious onset; unilateral SI joint more affected; gait analysis helpful |
Diagnosing SI Joint Pain: Examination and the Diagnostic Injection
SI joint pain cannot be diagnosed by imaging alone. The clinical approach combines a structured physical examination using provocative tests with a definitive diagnostic injection.
Physical Examination
Several provocative tests have been validated for SI joint pain. No single test is sufficient — studies show that using three or more positive tests significantly increases diagnostic accuracy. [3] [4] I use a systematic examination approach that includes:
| Test | How It Is Performed | What a Positive Test Suggests |
| FABER (Patrick’s test) | Hip flexion, abduction, external rotation while supine. The examiner applies pressure to the knee and contralateral ASIS. | Pain in the posterior pelvis / sacral area suggests SI joint. Pain in the groin suggests hip joint pathology. |
| Thigh thrust | Supine patient. Hip flexed to 90°. Axial load applied through the femur, directing force posteriorly through the SI joint. | Posterior pelvic pain reproduces SI joint pain. One of the highest-sensitivity individual tests. [3] |
| Sacral sulcus (compression test) | Pressure applied bilaterally to the posterior ASIS with patient prone. Also performed as distraction (ASIS pressed laterally apart). | Pain or asymmetric tenderness in the sacral sulcus area. |
| Gaenslen’s maneuver | Patient supine at table edge. One hip hyperextended off the table, contralateral hip flexed. Creates torsional stress on SI joint. | Posterior pelvic pain on the hyperextended side. |
| Fortin finger test | Patient identifies pain location with one finger. Pain consistently localized within 1 cm inferomedial to the PSIS. | Highly specific when positive: 94% of patients with confirmed SI joint pain point to this area. [6] |
| The examination threshold I use: Three or more positive provocative tests, with pain reproduction in the characteristic posterior pelvic distribution, establishes sufficient clinical probability to proceed to a diagnostic injection. A single positive test is not adequate. The combination matters. [3] [4] |
The Diagnostic Injection
A fluoroscopically guided intra-articular injection of local anesthetic into the SI joint is the gold standard for diagnosing SI joint pain. [6] The injection is performed with the patient prone, using fluoroscopic imaging to guide the needle to the inferior aspect of the SI joint — the most accessible and clinically relevant portion. Contrast is injected to confirm intra-articular placement before any medication is delivered. Then local anesthetic alone is injected.
The patient tracks their pain level over the next 4 to 8 hours — the expected duration of the local anesthetic effect. If they experience 75% or greater relief of their usual pain during that window, the SI joint is confirmed as the primary pain generator. That confirmation changes everything: treatment is now directed at the correct source.
| Why fluoroscopic guidance is required: The SI joint is a complex, irregular structure. Without imaging, needle placement into the intra-articular space cannot be reliably confirmed. Studies show that injections performed without fluoroscopic guidance frequently miss the intra-articular space entirely — producing inconclusive results and leading to false-negative diagnostic outcomes. [6] At NYBJ, all SI joint injections are performed under fluoroscopic guidance with contrast confirmation as the standard. |
Who Is a Candidate for SI Joint Injection?
| Appropriate for SI joint injection | Not appropriate / different pathway indicated |
| Chronic low back and buttock pain with 3+ positive provocative examination tests | Lumbar radiculopathy with leg pain below the knee — ESI is the appropriate pathway |
| Prior lumbar fusion with new onset low back / buttock pain (adjacent segment SI joint stress) | Lumbar facet arthropathy confirmed by prior medial branch block — facet RFA is the pathway |
| Pelvic girdle pain during or after pregnancy | Hip joint pathology (groin pain, positive FABER with groin reproduction) — intra-articular hip injection is the pathway |
| Inflammatory sacroiliitis (ankylosing spondylitis, psoriatic arthritis, IBD-related) | Piriformis syndrome — piriformis injection is the pathway |
| Post-traumatic SI joint pain following fall, MVA, or direct impact | Patients who have not yet completed physical therapy for acute SI joint pain — PT first |
| Patients who have had partial response to lumbar injections and in whom the SI joint has not been evaluated | Patients with active infection at the planned injection site |
The Procedure: What to Expect
| Phase | What Happens | Time |
| Consultation & planning | Dr. Efime Popovitz reviews imaging, examination findings, pain history, and prior treatment responses. Whether a diagnostic-only injection (local anesthetic) or a combined diagnostic-therapeutic injection (local anesthetic + corticosteroid) is appropriate is determined at this visit. | At consultation visit |
| Pre-procedure | Arrival at NYBJ office. Brief pre-procedure assessment. No sedation or general anesthesia required. No IV access required for standard SI joint injection. | 10–15 minutes |
| Positioning & skin prep | Patient positioned prone on the procedure table. Fluoroscopic imaging positioned over the SI joint. Skin cleaned and local anesthetic applied at the entry point. | 5–10 minutes |
| Fluoroscopic needle advancement | Needle advanced under continuous fluoroscopic visualization to the inferior aspect of the SI joint. | 5–10 minutes |
| Contrast confirmation | Small amount of contrast injected through the needle. Fluoroscopic imaging confirms intra-articular spread within the SI joint space before any medication is delivered. | 2–3 minutes |
| Injection | Local anesthetic injected (diagnostic injection). Corticosteroid added if therapeutic injection is planned. Volume typically 1.5–2.5 mL total. | 1–2 minutes |
| Recovery & discharge | Brief observation period. Patient given a pain diary to track relief over the next 4–8 hours. Results of the diagnostic block are reviewed at follow-up. | 15–20 minutes |
| Post-procedure tracking | Patient tracks pain levels for 4–8 hours after the procedure using a simple 0–10 scale. 75% or greater relief confirms SI joint as the primary pain source. | 4–8 hours at home |
| From Dr. Efime Popovitz — When the MRI doesn’t tell the whole story A 76 year-old attorney came to see me with several years of persistent low back and left buttock pain that prevented him from sitting for even short periods of time at his desk without having significant pain. He had an MRI that showed moderate to severe lumbar facet arthropathy and foraminal stenosis at L4-L5 and L5-S1, along with diffuse disc bulges. When I examined him, I found all the positive maneuvers which reproduced his pain directly over the left SI joint. The distribution was lower and further off the side than typical lumbar facet pain. I suspected he had both lumbar facet arthropathy and SI joint dysfunction, but that the SI joint had been the primary generator his pain. I performed a fluoroscopic injection of local anesthetic and steroid into the left SI joint. Over the next several days, he reported 90% relief of his buttock and posterior thigh pain — the dominant component of his presentation. With the SI joint confirmed as the primary pain source, I discussed the pathway forward: if relief diminishes we could repeat the injection and ultimately proceed with lateral branch RFA. The RFA “heats” the nerves supplying the SI joint and therefore provides longer lasting relief. His case illustrates the pattern I see regularly: the SI joint is a concurrent contributor that is overlooked because the lumbar findings on imaging are more visible. SI joint arthritis and pain isn’t necessarily diagnosed with imaging studies. Therefore, a well-designed examination and a single injection changed years of partial or no treatment into a clear diagnosis and a specific plan. — Dr. Efime Popovitz, MD |
Outcomes and the Treatment Pathway After Injection
The outcome of a SI joint injection depends on whether it is a diagnostic injection or a therapeutic injection, and on the degree of relief produced. [7]
| Outcome | What It Means | Next Step |
| 75% or greater relief from diagnostic block (local anesthetic only) | SI joint confirmed as primary pain generator. Highly specific result. | Therapeutic injection with corticosteroid at same visit or scheduled separately. If good response but limited duration: consider lateral branch RFA. |
| 50–74% relief from diagnostic block | SI joint is likely a contributing factor but may not be the sole source. Clinically informative. | Therapeutic injection appropriate. Review examination for other contributing factors. May combine SI joint and lumbar treatment. |
| Less than 50% relief from diagnostic block | SI joint is less likely the primary source. Directs evaluation elsewhere. | Evaluate for lumbar facet, discogenic, or hip pathology as alternative sources. Do not proceed to therapeutic SI joint injection or RFA. |
| Good response to therapeutic injection, relief lasts 1–3 months | SI joint confirmed; steroid provides anti-inflammatory relief. | Repeat therapeutic injection when pain returns, up to standard frequency limits. If 3+ injections provide diminishing returns: evaluate for lateral branch RFA. |
| Good response to injection but relief lasts less than 4 weeks | Steroid provides relief but short duration suggests structural component. | Evaluate for lateral branch RFA. [8] Physical therapy for SI joint stabilization. |
Lateral Branch RFA for Refractory SI Joint Pain
For patients who have confirmed SI joint pain from diagnostic injection but whose relief from therapeutic injections is insufficient in duration, lateral branch radiofrequency ablation — also called SI joint RFA — offers a longer-duration option. [8]
Unlike lumbar facet RFA which targets the medial branch nerves, SI joint RFA targets the lateral branches of the dorsal sacral rami that provide sensory innervation to the posterior SI joint and surrounding ligamentous structures. The procedure is performed under fluoroscopic guidance, with the same diagnostic confirmation requirement: therapeutic injections must have demonstrated confirmed SI joint-mediated pain before proceeding.
Published studies report 6 to 12 months of meaningful relief from lateral branch SI joint RFA in appropriately selected patients. [8] Dr. Efime Popovitz evaluates candidacy for SI joint RFA at NYBJ. For full detail on RFA: /radiofrequency-ablation-nyc/
Why Choose NYBJ for SI Joint Injection?
| NYBJ Advantage | What It Means for You |
| Diagnostic-first approach | No therapeutic SI joint injection without diagnostic confirmation. A well-placed diagnostic block is the only way to confirm the SI joint as the pain source — and the only way to ensure the treatment is directed at the right target. |
| Fluoroscopic guidance with contrast confirmation as standard | All SI joint injections performed under live fluoroscopic imaging with contrast to confirm intra-articular placement. Without image guidance, needle placement cannot be reliably confirmed. [6] |
| Structured clinical examination | Three or more positive provocative tests required before proceeding to injection. No injections directed at clinical hypotheses — examination-guided, injection-confirmed. |
| Yale fellowship-trained dual board-certified specialist | Dr. Efime Popovitz’s dual certification in Anesthesiology and Pain Medicine and fellowship training at Yale specifically cover fluoroscopic-guided interventional procedures at the sacroiliac joint. |
| Full pathway in one practice | Diagnostic injection — therapeutic injection — lateral branch RFA — physical therapy for SI joint stabilization. All available within NYBJ. No referrals to external providers for any step of the SI joint care pathway. |
| Orthopedic integration | SI joint pain frequently coexists with hip pathology, lumbar spine disease, or post-surgical changes. NYBJ’s orthopedic surgeons and pain management specialist communicate directly when presentations overlap. |
| In-office procedure, no hospital required | All SI joint injections performed at NYBJ’s Upper East Side and Midtown offices. 20–30 minutes, same-day discharge. |
Risks & Considerations
SI joint injections are generally safe and well-tolerated. The most common side effects are minor:
- Temporary pain flare: Some patients experience a brief increase in SI joint pain for 1–3 days after the injection as the corticosteroid takes effect. This is expected and not a sign of a problem. Over-the-counter analgesics and ice typically manage it.
- Steroid-related effects: Temporary flushing, mild elevation in blood sugar (particularly relevant for diabetic patients), and transient insomnia are possible in the days after a corticosteroid injection. These are mild and self-limiting.
- Infection: Rare with fluoroscopic technique and sterile preparation. The risk is further minimized by NYBJ’s procedural protocols.
- Incomplete relief: Not all patients achieve the 75% relief threshold required to confirm the SI joint diagnosis. A negative or equivocal diagnostic block is clinically informative — it directs evaluation toward other pain sources.
- Radiation exposure from fluoroscopy: Minimal with standard technique. The dose from a single fluoroscopic procedure is small and well within safe limits.
At your consultation, Dr. Efime Popovitz will review the specific risks relevant to your procedure and individual health profile.
References
- AAOS. Sacroiliac Joint Dysfunction. OrthoInfo. orthoinfo.aaos.org/en/diseases–conditions/sacroiliac-joint-dysfunction
- Datta S et al. Systematic assessment of diagnostic accuracy of sacroiliac joint interventions. Pain Physician. 2009. pubmed.ncbi.nlm.nih.gov/19461828
- Laslett M et al. Diagnosis of sacroiliac joint pain: validity of individual provocation tests and composites of tests. Man Ther. 2005. pubmed.ncbi.nlm.nih.gov/15672258
- van der Wurff P et al. Reliability and validity of sacroiliac joint pain provocation tests. Eur Spine J. 2006. pubmed.ncbi.nlm.nih.gov/16648778
- Schwarzer AC et al. The sacroiliac joint in chronic low back pain. Spine. 1995. pubmed.ncbi.nlm.nih.gov/7732484
- Cohen SP. Sacroiliac joint pain: a comprehensive review of anatomy, diagnosis, and treatment. Anesth Analg. 2005. pubmed.ncbi.nlm.nih.gov/16052117
- Manchikanti L et al. Systematic review of the effectiveness of therapeutic sacroiliac joint interventions. Pain Physician. 2009. pubmed.ncbi.nlm.nih.gov/19461825
- Patel N et al. Systematic review of the literature on radiofrequency denervation for sacroiliac joint pain. Pain Med. 2012. pubmed.ncbi.nlm.nih.gov/22390409
- Foley BS, Buschbacher RM. Sacroiliac joint pain: anatomy, biomechanics, diagnosis, and treatment. Am J Phys Med Rehabil. 2006. pubmed.ncbi.nlm.nih.gov/24413363
- Hansen H et al. Sacroiliac joint interventions: a systematic appraisal of the literature. Pain Physician. 2007. pubmed.ncbi.nlm.nih.gov/17660843
