What X-ray is recommended for a patient who fell onto their buttocks and broke a step?

X-ray Imaging for Patient Who Fell onto Buttocks

For a patient who fell onto their buttocks with sufficient force to break a step, obtain an anteroposterior (AP) pelvis radiograph immediately as the initial imaging study. 1

Initial Imaging Approach

• Start with a portable AP pelvis radiograph as the first-line imaging study for any patient with direct buttocks trauma, particularly when the mechanism involves high-impact force (such as breaking a step during the fall). 1, 2

• The AP pelvis view is specifically designed to evaluate for unstable pelvic ring injuries, sacral fractures, and hip dislocations that commonly occur with direct buttocks impact. 1

• This single view can identify life-threatening pelvic injuries including "open book" fractures, vertical shear injuries, and posterior ring disruptions that may require immediate stabilization. 1

Clinical Decision-Making Algorithm

If the patient is hemodynamically unstable (systolic BP <90 mmHg, heart rate >100 bpm, or requiring fluid resuscitation):

• Obtain portable AP pelvis radiograph immediately in the trauma bay without delay. 1
• Do NOT wait for CT scanning if the patient shows signs of shock. 1
• The portable pelvic X-ray helps identify injuries requiring immediate external fixation or angiography. 1

If the patient is hemodynamically stable:

• Begin with AP pelvis radiograph, then proceed to CT pelvis with IV contrast if any fracture is identified or if clinical suspicion remains high. 1
• CT scanning is the gold standard for characterizing pelvic fractures but should follow, not replace, the initial plain film. 1, 3
• CT has 100% sensitivity and specificity for pelvic fractures and will detect 32% of fractures missed on plain radiographs alone. 4, 5

Additional Views to Consider

• Inlet and outlet views are no longer routinely necessary in the acute setting if CT scanning will be performed, as CT reconstructions provide superior detail of posterior pelvic ring injuries. 3

• Lateral hip views should be added if there is focal hip pain, inability to bear weight, or concern for hip dislocation or proximal femur fracture. 1

Common Pitfalls to Avoid

• Do not skip the initial AP pelvis radiograph even if planning CT scan—the plain film provides rapid triage information and may identify unstable fractures requiring immediate intervention before CT. 1, 4

• Do not rely solely on physical examination to exclude pelvic injury—up to 32% of pelvic fractures are missed on plain radiographs, and clinical examination alone is even less sensitive. 4, 5

• Recognize that sacral fractures and posterior ring injuries are frequently missed on plain films (sensitivity only 68%) but are clearly visible on CT, so maintain high suspicion and proceed to CT if mechanism suggests significant force. 1, 4

• Age matters: Patients over 55 years warrant imaging even with minimal symptoms due to increased fracture risk and potential for occult injuries. 6, 7

When to Proceed to CT Imaging

Obtain CT pelvis with IV contrast (portal venous phase at 70 seconds) if: 1

• Any fracture is identified on plain radiograph
• High-energy mechanism (fall from height >15 feet or equivalent force to break a step)
• Persistent pain despite negative radiograph
• Blood at urethral meatus, perineal hematoma, or inability to void (suggesting urethral injury)
• Gross hematuria (requires CT cystography with bladder contrast)

The CT should include 3D bone reconstructions to better characterize fracture patterns and guide surgical planning if needed. 1