SI Joint Pain or Something Else? A Guide to Differential Diagnosis

The North American Spine Society poses the question directly in its patient education materials: "What is Sacroiliac Joint Pain and How to be Sure That's What You Have?"

This framing captures the central challenge. Lower back and buttock pain is common, and the SI joint is one of many possible sources. Treating the SI joint without confirming it as the pain generator leads to unnecessary procedures and delays in addressing the actual problem. The goal of differential diagnosis is to identify the correct source before committing to treatment.

Medical source: North American Spine Society, Patient Education — Sacroiliac Joint Pain. spine.org

The SI joint, lumbar spine, and hip share overlapping pain referral patterns. A patient with buttock pain and leg radiation could have:

• SI joint dysfunction
• Lumbar disc herniation with radiculopathy
• Lumbar facet joint pain
• Hip arthritis
• Greater trochanteric pain syndrome
• Piriformis syndrome
• Hamstring origin tendinopathy
• Referred pain from other pelvic structures

Each of these conditions has a different optimal treatment. Injecting the SI joint in a patient whose pain is actually coming from the L4-5 disc will not provide relief — and may delay the correct diagnosis by months.

Similarities to SI joint pain: Buttock pain, possible leg radiation, lower back pain.

Key differences: Radiculopathy typically follows a dermatomal distribution (specific nerve root territory). Neurologic findings — reflex changes, dermatomal sensory loss, focal weakness — are more common. Symptoms often worsen with sitting and improve with walking short distances. MRI typically shows a disc herniation at the level corresponding to the neurologic findings.

Similarities to SI joint pain: Lower back pain, buttock pain, possible thigh radiation.

Key differences: Facet pain is typically worse with extension and rotation of the lumbar spine. It rarely radiates below the knee. Tenderness is often present over the facet joints on examination. Diagnostic medial branch blocks (not SI joint injections) are used to confirm facet pain.

Similarities to SI joint pain: Groin pain, buttock pain, thigh pain, difficulty with prolonged walking.

Key differences: Hip arthritis typically produces groin-predominant pain that worsens with weight-bearing and hip rotation. The FABER test (hip flexion, abduction, external rotation) reproduces groin pain with hip arthritis. X-ray of the hip typically shows joint space narrowing and osteophytes. Hip intra-articular injection confirms the diagnosis.

Similarities to SI joint pain: Lateral hip and buttock pain, worse with prolonged standing or walking.

Key differences: Pain is localized to the lateral hip over the greater trochanter and is reproduced by direct palpation. It is typically not associated with neurologic symptoms. MRI may show gluteal tendon pathology.

Similarities to SI joint pain: Buttock pain with possible leg radiation mimicking sciatica.

Key differences: Tenderness is localized to the piriformis muscle in the deep buttock. Symptoms may be reproduced by hip internal rotation under load. Neurologic findings are typically absent.

Similarities to SI joint pain: Posterior buttock and thigh pain.

Key differences: Pain is localized to the ischial tuberosity (sitting bone) and worsens with prolonged sitting, running, or hamstring loading. Tenderness is present at the ischial tuberosity on palpation.

When the clinical picture is consistent with SI joint pain but the differential remains uncertain, an image-guided diagnostic injection into the SI joint is the most reliable way to confirm the diagnosis. Substantial relief of usual pain following the injection — typically 75% or greater — provides strong evidence that the SI joint is the primary pain source.

Dr. Blythe performs a structured evaluation that includes a detailed history, lumbar and hip examination, SI joint-specific provocative testing, and review of imaging. When the diagnosis is uncertain, diagnostic injections are used to confirm the pain source before treatment is recommended. Treatment follows confirmed diagnosis — not symptom location alone.

Related articles: Where Is SI Joint Pain Usually Felt? · How Doctors Confirm That Pain Is Coming From the SI Joint · Herniated Disc vs. Lumbar Spinal Stenosis

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Medical review date: July 2026