Can an X‑ray of the sacrum be performed?

Can X-rays of the Sacral Area Be Performed?

Yes, X-rays of the sacrum can absolutely be performed and are routinely used as the initial imaging modality in multiple clinical scenarios, though their diagnostic limitations must be understood. 1

When Sacral X-rays Are Appropriate

Initial Imaging for Stress Fractures

Radiographs should be the first imaging test when a sacral stress fracture is suspected, despite their low sensitivity 1. The ACR Appropriateness Criteria explicitly recommend radiography as the initial imaging evaluation because if findings are conclusive for insufficiency fracture, no further imaging is needed 1. However, you must recognize that radiographs have inherently low sensitivity due to overlying bowel gas, fecal material, vascular calcifications, sacral curvature, and copious soft tissue 1.

Inflammatory Back Pain and Spondyloarthritis

For suspected axial spondyloarthritis, radiographs of the pelvis (which include the sacroiliac joints and sacrum) are the established first-line imaging 2. The Assessment of SpondyloArthritis International Society (ASAS) specifically recommends whole pelvis radiographs to evaluate both the sacroiliac joints and hips 2.

Pediatric Spine Trauma

In children with thoracolumbar trauma, sacral fractures can be evaluated with radiographs, though they miss 35% of sacral fractures compared to CT and MRI 3.

Critical Limitations You Must Know

Poor Sensitivity

The sensitivity of sacral radiographs is notably poor:

• Only 10.5% sensitivity for detecting sacral fractures in elderly patients with blunt trauma 4
• 21.7% false negative rate when compared to CT 4
• Radiographs may be more likely negative initially in older or osteoporotic patients with insufficiency fractures 1

When X-rays Are Insufficient

If initial radiographs are negative but clinical suspicion remains high, proceed directly to MRI without contrast 1, 5. This is particularly critical for:

• Pregnant patients: MRI without contrast is preferred as the next step after negative radiographs, with an approximate fetal absorbed dose from pelvis radiograph of only 1.1 mGy 1
• High-risk fractures: When there's concern for hip or sacral insufficiency fractures that could lead to complications
• Early disease detection: MRI can detect stress fractures within hours, while radiographic changes may take weeks 1

Special Populations

For pregnant patients with suspected sacral stress fractures:

• Radiographs can be performed initially (1.1 mGy fetal dose) 1
• If negative, MRI without contrast is the next imaging study - not repeat radiographs 1, 5
• The benefit far outweighs risk for radiographs not involving the abdomen/pelvis directly 1

Practical Algorithm

1. Start with radiographs for suspected sacral pathology (stress fracture, inflammatory sacroiliitis, trauma)
2. If positive and findings are conclusive: No further imaging needed 1
3. If negative but high clinical suspicion:
   • Proceed to MRI without contrast (preferred) 1, 5
   • CT is an alternative if MRI unavailable or contraindicated 1
   • Consider repeat radiographs in 10-14 days only if advanced imaging unavailable 5

Common Pitfalls to Avoid

• Don't rely solely on negative sacral radiographs in elderly patients - they miss over 20% of fractures 4
• Don't order repeat radiographs as the next step after negative initial films when MRI is available 1, 5
• Don't assume the "Honda sign" on bone scan rules out sacral fracture if absent - only 63% of sacral insufficiency fractures demonstrate this sign 1
• Don't delay advanced imaging in high-risk scenarios (elderly, osteoporotic, pregnant patients with persistent symptoms) 1, 4

The key message: X-rays can and should be performed initially, but understand they are a screening tool with significant limitations, particularly for the sacrum 1, 6, 4.