What is the recommended imaging protocol for diagnosing sacroiliac (SI) joint pain?

Recommended Imaging Protocol for Diagnosing Sacroiliac (SI) Joint Pain

Conventional radiography of the SI joints should be the first imaging method used for diagnosing sacroiliac joint pain, followed by MRI with fluid-sensitive sequences if radiographs are negative or equivocal and axial spondyloarthropathy is suspected. 1

Imaging Algorithm for SI Joint Pain

First-Line Imaging

• Plain radiography (X-ray) of the SI joints
  • Provides baseline assessment of structural changes
  • Can detect advanced sacroiliitis, erosions, sclerosis, and joint space narrowing
  • Limited sensitivity for early disease (changes may lag 7+ years behind symptom onset) 1
  • Anteroposterior view of the pelvis to visualize both SI joints

Second-Line Imaging (if radiographs are negative/equivocal)

• MRI of the SI joints
  • Essential for detecting early inflammatory changes 1
  • Required protocol elements:
    • T1-weighted sequences (for structural lesions)
    • Fluid-sensitive sequences (T2-weighted fat-saturated or STIR) to identify bone marrow edema and inflammatory changes 1
    • Gadolinium contrast is optional and not required for routine assessment 1
  • Evaluates both active inflammatory lesions (bone marrow edema) and structural lesions (erosions, new bone formation, sclerosis, fat infiltration) 1

Alternative Second-Line Imaging (if MRI contraindicated)

• CT scan without contrast
  • Higher sensitivity than radiographs for detecting subtle erosions and bony changes 1
  • Provides excellent visualization of SI joint anatomy 1, 2
  • Useful when radiographic findings are equivocal 1
  • Limited in detecting active inflammation compared to MRI 1

Special Considerations

For Young Patients or Those with Short Symptom Duration

• Consider MRI as the first imaging method rather than radiography 1
• This approach may detect early inflammatory changes before structural damage occurs

For Suspected Axial Spondyloarthropathy

• If SI joint MRI is negative but clinical suspicion remains high:
  • Consider MRI of the spine (includes sagittal STIR or T2-weighted fat-saturated sequences) 1
  • Isolated spine involvement occurs in 6-23% of cases 1

For Post-Procedural Evaluation (e.g., SI joint fusion devices)

• CT is the gold standard for evaluating hardware position and complications 3
• Provides detailed assessment of implant position relative to neural structures 3

Pitfalls to Avoid

1. Relying solely on radiographs - May miss early inflammatory changes, leading to delayed diagnosis and treatment 1
2. Performing spinal MRI before SI joint imaging - SI joint MRI should be prioritized in suspected axial spondyloarthropathy 1
3. Omitting fluid-sensitive sequences in MRI protocols - Standard spine protocols may not include the fat suppression necessary for detecting inflammatory features 1
4. Overuse of gadolinium contrast - Not shown to significantly increase diagnostic accuracy for sacroiliitis 1
5. Frequent repeat imaging - For monitoring structural changes, radiographs should not be repeated more frequently than every 2 years 1

By following this evidence-based imaging protocol, clinicians can effectively diagnose SI joint pain, which affects up to 25% of patients with axial low back pain 4, and initiate appropriate treatment to improve patient outcomes.