What are the best imaging modalities to rule out fractures of the femur, knee, and leg?

Best Imaging Modalities for Ruling Out Fractures of Femur, Knee, and Leg

Plain radiography (X-rays) should be the initial imaging modality for ruling out fractures of the femur, knee, and leg, with CT or MRI as appropriate second-line studies when radiographs are negative but clinical suspicion remains high. 1, 2

Initial Imaging Approach

Plain Radiography (X-rays)

• First-line imaging for suspected fractures of the femur, knee, and leg 1, 2, 3
• Minimum of two views required:
  • Anteroposterior (AP) view
  • Lateral view (with knee at 25-30 degrees flexion) 2
• Additional views when indicated:
  • Internal oblique view
  • External oblique view
  • Patellofemoral view (for suspected patellar fractures/subluxation/dislocation) 1
• Indications for knee radiographs based on Ottawa rules:
  • Focal tenderness
  • Effusion
  • Inability to bear weight 1, 2

Second-Line Imaging for Suspected Occult Fractures

Computed Tomography (CT)

• Indicated when radiographs are negative but clinical suspicion for fracture remains high 1, 2, 3
• Superior to radiographs for detection and classification of fractures 1
• Advantages:
  • 100% sensitivity for tibial plateau fractures (vs. 83% for radiographs) 1
  • Excellent for fracture characterization and severity assessment 1
  • Provides exquisite osseous detail 4
• Best for:
  • Tibial plateau fractures
  • Complex fracture patterns
  • Surgical planning 1, 3

Magnetic Resonance Imaging (MRI)

• Indicated when radiographs are negative and internal derangement is suspected 1, 2
• Superior to CT for:
  • Bone marrow abnormalities
  • Meniscal injuries
  • Ligamentous injuries 1, 2
• Should be performed after 4-6 weeks of persistent pain despite conservative management 2
• Particularly useful when both bone and soft tissue injuries are suspected 2, 3

Special Considerations

Femur Fractures

• Extended femur imaging may be needed to detect incomplete atypical femur fractures (iAFFs) 1
• Full-length femur imaging (FFI) from the lesser trochanter to the supracondylar flare is recommended 1
• Femoral shaft fractures may be associated with ipsilateral knee ligament injuries in up to 33% of cases 5
• Consider stress fractures when pain is persistent but initial radiographs are negative 4

Knee Fractures

• Some fractures around the knee may be difficult to detect even with optimal images 6
• Special views may be required for specific fracture types:
  • Tibial plateau fractures: tangential or tunnel projections
  • Segond fractures: tunnel views
  • Vertical patellar fractures: sunrise or Merchant views
  • Patellar avulsion fractures: lateral views
  • Osteochondral fractures: sunrise or internal oblique views 6

Stress Fractures

• Often not visible on initial radiographs 4
• MRI is the method of choice for stress fracture diagnosis when available 4
• Bone scintigraphy is highly sensitive but less specific and involves radiation 4

Imaging Algorithm

1. Begin with plain radiographs (minimum 2 views) for all suspected fractures
2. If radiographs are negative but clinical suspicion remains high:
   • For suspected bony injury: CT scan
   • For suspected combined bone and soft tissue injury: MRI
3. For persistent pain despite negative initial imaging:
   • MRI if symptoms persist after 4-6 weeks of conservative management
   • Consider stress fracture if pain is activity-related

Common Pitfalls

• Relying solely on standard views for subtle fractures around the knee 6
• Failing to consider associated ligamentous injuries with femoral fractures 5
• Overuse of radiography in acute knee injuries (92.4% of knee radiographs are negative for fracture) 7
• Missing stress fractures due to negative initial radiographs 4
• Failing to obtain appropriate specialized views for specific fracture types 6