Appropriate X-ray Ordering for Post-Fall Buttock Pain
For a patient with buttock pain after a fall and preserved ROM, order "X-ray pelvis AP and lateral sacrum" rather than just "sacrococcygeal region," as this provides comprehensive evaluation of both sacral and pelvic structures that commonly fracture together. 1
Why This Specific Order Matters
The Standard Imaging Protocol
- Anterior-posterior (AP) pelvis radiographs combined with lateral lumbar spine views should be the initial imaging approach for patients presenting with low back or pelvic pain after trauma 1
- This combined approach is critical because patients with suspected sacral fractures often have concomitant pelvic fractures, including pubic rami fractures, which would be missed with isolated sacrococcygeal views 2
- The pelvis view allows comparison to the contralateral side, improving diagnostic accuracy 2
Why "Sacrococcygeal Region" Alone Is Inadequate
Plain radiographs of the sacrum have inherently low sensitivity due to overlying bowel gas, fecal material, vascular calcifications, sacral curvature, and soft tissue 1
- Standard sacrum/coccyx radiographs miss approximately 35% of sacral fractures 1
- In one study, sacrum and coccyx radiographs showed only 8.4% positivity rate and had no quantifiable clinical impact on ED management 3
- These isolated views are so limited that some experts recommend eliminating dedicated sacrum/coccyx radiographs from ED practice entirely 3
The Clinical Reality of Sacral Fractures
Common Presentation Patterns
- Sacral fractures frequently occur after low-energy trauma (80% of cases) and present with local pain even without neurologic deficits 4
- Only 4.8% of isolated transverse sacral fractures present with neurologic impairment 4
- Approximately 30% of sacral fractures are identified late due to inadequate initial imaging 5
When Initial Radiographs Are Negative
If your AP pelvis and lateral sacrum views are negative but clinical suspicion remains high:
- CT of the pelvis/sacrum is superior to radiography, missing only a small fraction of fractures that plain films miss 1
- Every sacral fracture in one series was confirmed with sacrococcygeal CT scan when plain films were equivocal 4
- MRI is also superior to radiography but is typically reserved for cases requiring soft tissue evaluation 1
Critical Pitfall to Avoid
Do not rely on preserved range of motion or absence of severe pain to exclude fracture. Clinical examination for spine fractures has only 81% sensitivity and 68% specificity 1, 6. Sacral insufficiency fractures particularly have insidious onset with vague symptoms that can be dismissed as "arthritis" 7.
Practical Ordering Recommendation
Write your order as: "X-ray pelvis AP and lateral sacrum" or "X-ray pelvis AP and lateral lumbar spine" to ensure adequate visualization of the entire sacropelvic region 1. If these are negative and pain persists, proceed directly to CT pelvis/sacrum without contrast rather than repeating plain films 1, 4.