What imaging studies are most sensitive and specific for diagnosing forearm and elbow injuries?

Imaging Studies for Diagnosing Forearm and Elbow Injuries

MRI without contrast is the most sensitive and specific imaging modality for diagnosing soft tissue injuries of the forearm and elbow, while CT without contrast is superior for detecting occult fractures when radiographs are normal or indeterminate. 1, 2

Initial Imaging Approach

• Plain Radiographs: Should always be the first-line imaging for acute elbow and forearm pain
  • Benefits: Can identify fractures, dislocations, joint effusions (posterior/anterior fat pad signs), and avulsion fractures at tendon/ligament attachment sites 1
  • Limitations: May miss occult fractures and cannot adequately assess soft tissue injuries

When Radiographs are Normal or Indeterminate

For Suspected Fractures:

• CT Without Contrast: Recommended next step
  • Sensitivity: Detects occult fractures in 12.8% of patients with normal radiographs but positive elbow extension test 1
  • Benefits: Superior for fracture characterization, including size of fragments, displacement, and angulation 1
  • Applications: Particularly useful for radial head fractures, Essex-Lopresti injuries, and Monteggia fractures 1

For Suspected Soft Tissue Injuries (Tendons/Ligaments/Muscles):

• MRI Without Contrast: Recommended next step

  • Benefits: Superior visualization of ligaments, tendons, muscles, nerves, bone marrow, and cartilage 1, 3
  • Applications:
    • Ligament assessment: High concordance with surgical findings (87.5% for medial collateral ligament complex, 90.9% for lateral collateral ligament complex) 1
    • Tendon evaluation: Particularly useful for biceps and triceps tendon tears, can distinguish between partial and complete ruptures 1, 3
    • Special views: FABS (flexion-abduction-supination) view may help in challenging cases of distal biceps tendon pathology 1

• Ultrasound: Alternative first-line for soft tissue injuries

  • Benefits: Non-invasive, readily available, cost-effective 2
  • Diagnostic accuracy: 95% sensitivity, 71% specificity for differentiating complete vs. partial tears 2
  • Limitations: Operator-dependent, limited assessment of associated injuries

Comparative Effectiveness

1. MRI without contrast:

   • Highest sensitivity and specificity for soft tissue injuries 1, 3
   • Best for comprehensive assessment of both soft tissue and osseous structures 4
   • Superior for detecting partial tears of biceps and triceps tendons 1
   • Best interobserver agreement for lateral collateral complex injuries 1

2. CT without contrast:

   • Superior for fracture detection and characterization when radiographs are normal 1
   • Better for assessing fracture morphology, displacement, and surgical planning 1

3. Ultrasound:

   • Good first-line alternative for suspected tendon ruptures (95% sensitivity) 2
   • Limited in assessment of deeper structures and associated injuries 2

Common Pitfalls and Caveats

• MRI with contrast is not supported by evidence for routine assessment of elbow/forearm injuries 1
• Bone scans have no evidence supporting their use in acute elbow and forearm pain 1
• Delay in appropriate imaging may lead to suboptimal outcomes, especially for complete tendon tears requiring early surgical intervention 2
• The worst interobserver reliability on MRI is for ulnar collateral ligament injuries, requiring careful interpretation 1
• Ultrasound is highly operator-dependent and may miss associated injuries 2

Clinical Decision Algorithm

1. Obtain plain radiographs for all acute elbow/forearm pain
2. If radiographs are normal or indeterminate:
   • For suspected fracture → CT without contrast
   • For suspected soft tissue injury → MRI without contrast (preferred) or ultrasound (if MRI unavailable)
3. If planning surgical intervention → MRI without contrast is recommended for comprehensive assessment