What Is Sacroiliac (SI) Joint Pain?
The sacroiliac joints connect the sacrum (the triangular bone at the base of the spine) to the iliac wings of the pelvis. They are strong, relatively immobile joints whose primary function is load transfer from the spine to the lower extremities during ambulation. Despite their limited motion (approximately 2–4 degrees of rotation), the SI joints are richly innervated and a significant source of chronic pain when they become inflamed, arthritic, or dysfunctional.
SI joint dysfunction is estimated to be the primary pain generator in 15–25% of patients presenting with chronic low back pain — making it one of the most frequently missed diagnoses in pain medicine. The pattern of SI joint pain closely mimics lumbar disc herniation and hip pathology, which contributes to underdiagnosis. Dr. Qureshi has specific expertise in SI joint evaluation and uses a systematic approach including provocative clinical tests and diagnostic injection to definitively confirm or rule out the SI joint as a pain source.
Causes of SI Joint Pain
- Degenerative arthritis (sacroiliitis) — age-related cartilage degeneration in the SI joint, often alongside lumbar degenerative disc disease and facet arthritis
- Inflammatory arthritis — ankylosing spondylitis, psoriatic arthritis, and reactive arthritis frequently involve the SI joints bilaterally, causing significant morning stiffness and inflammatory pain
- Pregnancy and postpartum changes — the hormone relaxin increases SI joint ligamentous laxity during pregnancy; combined with altered biomechanics and increased load, this can cause significant SI joint pain
- Trauma — falls onto the buttock, motor vehicle accidents, and athletic injuries can acutely strain the SI joint ligaments
- Post-fusion syndrome — lumbar spine fusion, particularly at L5-S1, increases stress on the SI joints and accelerates degeneration in a significant proportion of patients
- Leg length discrepancy — even small discrepancies (greater than 1 cm) alter load distribution through the pelvis and can stress one SI joint asymmetrically
Symptoms
- One-sided low back pain just below the belt line, often with specific tenderness at the PSIS (posterior superior iliac spine)
- Pain in the buttock, posterior hip, and sometimes the posterior thigh — rarely extends below the knee, distinguishing it from lumbar radiculopathy
- Pain worsening with transitional movements — sitting to standing, rolling over in bed
- Increased pain with prolonged sitting or standing
- Pain with stair climbing or single-leg stance (loading one SI joint)
- Morning stiffness that improves with activity (characteristic of inflammatory sacroiliitis)
- Difficulty sleeping on the affected side
- Groin pain in some patients (referred from the anterior SI joint)
How SI Joint Pain Is Diagnosed
Diagnosis relies on a combination of clinical assessment and diagnostic injection. Provocative physical examination tests — including FABER, Gaenslen's test, posterior shear (thigh thrust), and compression and distraction tests — are used in combination. When three or more tests are positive on one side, SI joint pathology is suspected. The gold standard for diagnosis is a fluoroscopically guided, intra-articular SI joint injection: if the patient experiences 50% or greater pain relief, the diagnosis is confirmed. This diagnostic injection also serves as a therapeutic treatment and often provides weeks to months of relief.
Treatment Options
- Fluoroscopic-guided SI joint injection — delivers corticosteroid and local anesthetic directly into the SI joint under X-ray guidance; confirms diagnosis and provides therapeutic relief; typically provides 1–4 months of benefit per injection cycle
- Sacral lateral branch blocks — the SI joint is innervated primarily by the sacral lateral branches (S1–S3 dorsal rami); blocking these nerves is the diagnostic step before proceeding with RFA
- Sacral lateral branch radiofrequency ablation (RFA) — for patients with confirmed SI joint pain who achieve positive diagnostic blocks; provides long-lasting relief (typically 12+ months) by disabling sensory nerves supplying the SI joint
- PRP therapy — regenerative injections targeting SI joint ligamentous laxity; particularly useful in younger patients with hypermobility-related SI joint instability
- SI joint stabilization belt and physical therapy — pelvic stabilization exercises reduce SI joint stress and improve function as an adjunct to injection therapy
- Trigger point injections — for piriformis and gluteal trigger points that can mimic or coexist with SI joint dysfunction
SI joint pain is frequently confused with lumbar spine conditions. Read our guide on how to tell if your back pain is serious to understand the key differences.