What is the diagnostic approach to an avulsion fracture of the pubic rami?

Diagnostic Approach to Avulsion Fracture of the Pubic Rami

The optimal diagnostic approach for avulsion fracture of the pubic rami begins with radiography of the pelvis and hip, followed by MRI if radiographs are negative but clinical suspicion remains high. 1

Initial Imaging

Primary Imaging

• Anteroposterior (AP) pelvis radiograph plus orthogonal views of the symptomatic hip (typically a cross-table lateral view)
  • This combination allows visualization of the entire pelvic ring and comparison with the contralateral side 1
  • Standard approach at most institutions due to accessibility, speed, and cost-effectiveness
  • Allows detection of approximately 90% of fractures 1

Important Considerations

• Radiographs alone cannot exclude fracture due to limitations in sensitivity and specificity 1
• Pubic rami fractures often coexist with other pelvic ring injuries that may be missed on initial radiographs
  • In one study, 96.8% of patients with pubic rami fractures had additional posterior pelvic ring injuries detected on CT scans 2
• Overlying bowel gas, fecal material, vascular calcifications, and soft tissue can obscure fractures, particularly in elderly or osteoporotic patients 1

Secondary Imaging (if radiographs are negative but clinical suspicion remains)

MRI of Pelvis and Affected Hip

• First choice for secondary imaging when radiographs are negative but clinical suspicion remains high 1
• Advantages:
  • Near 100% sensitivity for fracture detection 1
  • Can detect bone marrow edema, stress reactions, and soft tissue injuries 1
  • Provides prognostic information - trabecular injuries (like pubic bone) are associated with longer recovery times 1
  • No radiation exposure

CT Scan

• Alternative when MRI is contraindicated or unavailable 1
• Benefits:
  • Better visualization of fracture morphology for treatment planning 1
  • Can detect associated pelvic hematomas or other injuries 1
  • Particularly useful for evaluating the posterior pelvic ring 2
• Limitations:
  • Less sensitive than MRI for detecting occult fractures 1
  • Radiation exposure

Bone Scintigraphy (Nuclear Medicine)

• Generally not recommended as first or second-line imaging 1
• Limitations:
  • Time-consuming
  • Lacks specificity (can be positive with synovitis, arthritis, degenerative joint disease)
  • May be falsely negative in elderly patients, especially within the first few days after injury 1
  • Often requires supplemental imaging with MRI or CT for conclusive diagnosis 1

Special Considerations

Avulsion Fractures vs. Insufficiency Fractures

• Avulsion fractures typically occur at muscular attachment sites:
  • Hamstrings at ischial tuberosity
  • Adductor muscles at inferior pubic symphysis
  • Gluteal muscles at greater trochanter 1
• Insufficiency fractures occur in patients with abnormal bone (osteoporosis, irradiated bone) 1
  • Often have insidious onset with intractable pain
  • Common sites include sacrum, supra-acetabular ilium, superior and inferior pubic rami 1

Associated Injuries

• Pubic rami fractures are often associated with additional injuries:
  • 68% of patients with pelvic fractures had concomitant internal or skeletal injuries 3
  • Bilateral pubic rami fractures have higher prevalence (33%) of additional injuries 3
  • Potential for life-threatening hemorrhage, particularly in elderly patients on anticoagulants 4

Clinical Implications

• Pubic rami fractures are associated with prolonged pain, bed rest, and increased morbidity and mortality 2, 5
• Higher 1-year mortality compared to age-matched controls, especially in patients ≥90 years 5
• 30% of patients with dorsal pelvic injuries associated with pubic rami fractures eventually require surgical intervention 2

Diagnostic Algorithm

1. Initial Assessment: AP pelvis radiograph + orthogonal views of symptomatic hip
2. If radiographs positive: Assess for displacement and associated injuries
3. If radiographs negative but clinical suspicion remains:
   • Proceed to MRI of pelvis and affected hip (preferred)
   • If MRI contraindicated: CT scan of pelvis
4. After diagnosis: No additional imaging is typically needed; patients are followed clinically until pain-free 1

Remember that pubic rami fractures should not be dismissed as isolated, stable injuries, as they frequently represent part of a more complex pelvic ring injury pattern that may require comprehensive management.