What is the preferred imaging modality, Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) scan, for evaluating foot injuries?

MRI vs CT for Foot Imaging

For acute foot trauma, start with weight-bearing radiographs, then use CT as the primary advanced imaging technique for complex fractures, polytrauma, and Lisfranc injuries, while reserving MRI for soft tissue injuries, occult fractures, and when radiographs are negative but clinical suspicion remains high. 1, 2

Initial Imaging Approach

• Radiographs are the mandatory first-line study for acute foot trauma, with weight-bearing views essential when possible 1, 2
• Weight-bearing radiographs have 99% sensitivity for detecting foot fractures when Ottawa rules are positive 1
• Non-weight-bearing films are unreliable for detecting subtle injuries, particularly Lisfranc injuries 1, 2, 3
• Bilateral imaging helps identify subtle malalignment by comparison with the uninjured side 1, 2, 3

When to Use CT

CT should serve as the primary advanced imaging technique in these specific scenarios: 1

• Acute hyperflexion injuries and high-energy polytrauma, especially when patients cannot bear weight 1, 2, 3
• Complex fractures requiring preoperative planning, particularly involving multiple metatarsal and cuneiform fractures 1, 3
• Lisfranc injuries to demonstrate the full extent of osseous injury and associated fractures 1, 2, 3
• Polytrauma patients, where approximately 25% of midfoot fractures identified on CT are missed on radiographs alone 3
• Tendon entrapment and dislocations, particularly peroneal dislocations and retinacular injuries associated with calcaneal fractures 1

CT Advantages for Bone

• Superior for detecting nondisplaced fractures and subtle osseous injuries 3
• Better than MRI for identifying water-rich fresh wood foreign bodies (63% sensitivity, 98% specificity) 1
• Provides detailed osseous anatomy for surgical planning 1

When to Use MRI

MRI is the preferred modality for these clinical situations: 1

• Suspected Lisfranc injury with normal radiographs, particularly for purely ligamentous injuries without diastasis 1, 2, 3
• Occult fractures and bone stress injuries not visible on radiographs 1
• Soft tissue injuries including ligaments, tendons, and the capsuloligamentous complex 1, 4
• "Turf toe" and plantar plate injuries requiring direct evaluation of soft tissue structures and chondral lesions 1
• Acute tendon ruptures when the specific tendon is uncertain or concomitant osseous injury is suspected (83% sensitivity for tendon and ligament injuries) 1
• Midtarsal (Chopart) sprains that frequently accompany ankle injuries 1

MRI Advantages for Soft Tissue

• Most sensitive modality for detecting occult fractures and acute bone stress changes 1
• Shows high correlation with intraoperative findings for unstable Lisfranc injuries 1, 2, 3
• 3-D volumetric acquisitions are superior to standard orthogonal imaging for Lisfranc ligamentous complex evaluation 1, 3
• Demonstrates osseous injuries not visible radiographically, including high-grade contusions associated with prolonged recovery in athletes 1
• Excellent for evaluating osteomyelitis in diabetic foot complications (77-100% sensitivity, 80-100% specificity) 2

Algorithm for Clinical Decision-Making

Step 1: Obtain weight-bearing radiographs

• Include AP view with 20° craniocaudal angulation for suspected Lisfranc injuries 1, 2, 3
• Obtain bilateral views for comparison 1, 2, 3

Step 2: If radiographs show complex fractures or polytrauma

• Proceed directly to CT for complete osseous evaluation and surgical planning 1, 2, 3

Step 3: If radiographs are negative but clinical suspicion remains high

• Choose CT for suspected occult fractures in high-energy mechanisms or inability to bear weight 1, 3
• Choose MRI for suspected soft tissue injuries, ligamentous Lisfranc injuries, or when tendon/plantar plate pathology is suspected 1, 2, 3

Step 4: If both osseous and soft tissue evaluation needed

• CT and MRI are complementary; CT excels at bone detail while MRI provides superior soft tissue characterization 4

Critical Pitfalls to Avoid

• Never rely solely on non-weight-bearing radiographs for suspected Lisfranc injuries, as this leads to missed diagnoses 1, 2, 3
• In diabetic patients with neuropathy, standard clinical tests are unreliable and patients may bear weight despite fractures—image more liberally 1, 2, 5
• Do not use CT or MRI as first-line imaging when radiographs are appropriate and sufficient 1
• Remember that conventional radiographs including weight-bearing images are not sufficient for routine workup of acute hyperflexion injuries—CT should be primary 1, 3
• Ultrasound has limited utility for foot trauma evaluation, with low grading scores for talus and bony avulsion assessment 1

Special Considerations

• For foreign body detection, CT is superior to MRI (63% vs 58% sensitivity), particularly for radiopaque materials 1
• MRI and ultrasound have similar sensitivity for acute soft-tissue trauma including ligamentous and tendinous disruption 1
• Post-traumatic arthritis occurs in approximately 25% of Lisfranc injuries despite anatomic reduction, requiring long-term radiographic surveillance 2