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Blog/Sacroiliac Joint Injection
Joint Pain9 min read

Sacroiliac Joint Injections: Diagnosing the Hidden Cause of Low Back Pain

TL;DR

The sacroiliac (SI) joint — where the sacrum meets the ilium of the pelvis — is responsible for up to 30% of chronic low back pain cases, yet it is frequently misdiagnosed as lumbar disc disease or facet joint arthritis. SI joint injections deliver corticosteroid and local anesthetic directly into the joint under fluoroscopic guidance, providing both diagnostic confirmation (pain relief confirms SI joint as the source) and therapeutic relief. For patients with confirmed SI joint dysfunction, radiofrequency ablation of the lateral branch nerves offers long-lasting relief.

Key Features

  • Fluoroscopy-guided intra-articular injection
  • Dual diagnostic and therapeutic purpose
  • Confirms SI joint as pain source
  • Outpatient — 30-minute procedure
  • Pathway to lateral branch RFA
  • Covered by most insurance plans

Key Benefits

  • Identifies the true source of low back pain
  • Provides immediate therapeutic relief
  • Avoids unnecessary lumbar spine surgery
  • Guides long-term treatment planning
  • Reduces buttock and leg pain
  • Improves sitting and standing tolerance

The SI Joint: Anatomy and Why It Causes Pain

The sacroiliac joint is a large, C-shaped synovial joint that connects the sacrum (the triangular bone at the base of the spine) to the ilium (the large pelvic bone) on each side. It bears the full weight of the upper body and transmits forces between the spine and lower extremities during walking, running, and lifting. The joint is stabilized by some of the strongest ligaments in the body — but it is not immobile: it has a small range of motion (2–4 mm of translation and 2–3° of rotation) that is essential for normal gait.

SI joint dysfunction occurs when this motion becomes abnormal — either hypermobile (too much movement, causing ligament strain) or hypomobile (restricted movement, causing joint inflammation). The resulting pain is typically felt in the lower back, buttock, and posterior thigh — a pattern that closely mimics lumbar disc herniation and facet joint pain, making accurate diagnosis critical.

Recognizing SI Joint Pain: Key Signs

Pain in the lower back, buttock, or posterior thigh
Pain worse with prolonged sitting or standing
Pain with transitioning from sitting to standing
Pain with climbing stairs or walking uphill
Tenderness directly over the SI joint
Pain with single-leg standing
Positive FABER or FADIR test on examination
Pain that does not radiate below the knee (usually)

Chronic Low Back or Buttock Pain?

Find out if your pain is coming from the SI joint. Schedule an evaluation at NYC Pain Management in Rego Park, Queens.

Schedule SI Joint EvaluationView SI Joint Service