Is a computed tomography (CT) scan warranted over a magnetic resonance imaging (MRI) scan for a patient with suspected fracture in the right foot?

CT vs MRI for Suspected Foot Fracture

For a patient with suspected foot fracture, CT is warranted over MRI as the advanced imaging modality of choice when radiographs are insufficient or in specific high-risk scenarios, though plain radiographs remain the mandatory first-line study. 1, 2

Initial Imaging Approach

• Plain radiographs (three-view: AP, lateral, and oblique) are the mandatory first-line imaging study for any suspected foot fracture, with 99% sensitivity when Ottawa rules are positive. 3, 2

• Weight-bearing views are essential whenever possible, as non-weight-bearing films are unreliable for detecting subtle injuries, particularly in the midfoot. 2

• Bilateral imaging should be obtained to help identify subtle malalignment by comparison with the uninjured side. 2

When CT is Warranted Over MRI

CT should be the primary advanced imaging technique in the following clinical scenarios:

High-Energy Trauma and Polytrauma

• CT is essential for appropriate treatment planning in polytrauma patients, as approximately 25% of midfoot fractures identified on CT are overlooked on radiographs. 1, 2

• The American College of Radiology recommends CT as the primary imaging technique for high-energy polytrauma patients, especially when the patient cannot bear weight. 1, 2

Complex Fracture Evaluation

• CT is commonly used to evaluate the true extent of osseous injury in complex fractures and is particularly valuable for preoperative planning. 1, 2

• Studies report only 25%-33% sensitivity of radiographs for detecting midfoot fractures in Level 1 trauma patients, making CT critical in these cases. 1

Acute Hyperflexion Injuries

• For patients with acute hyperflexion injuries to the foot, conventional radiographs including weight-bearing images are not sufficient, and CT should serve as the primary imaging technique. 1

• CT is advocated as the primary technique for suspected Lisfranc injuries when patients cannot bear weight, as it demonstrates multiple metatarsal and cuneiform fractures associated with ligamentous injuries. 1, 2

Practical Advantages of CT

• CT provides faster diagnosis with patients spending less time in the emergency department (average 430 minutes) compared to MRI (502 minutes). 4

• CT is readily accessible in the vast majority of hospitals, whereas MRI availability is often limited. 5

• Approximately 26% of elderly patients have at least one contraindication to MRI, making CT the only viable option. 4

• CT is superior for evaluating bony abnormalities and nondisplaced fractures. 2, 6

When MRI May Be Preferred

MRI should be considered in specific scenarios where soft tissue evaluation is paramount:

• MRI is the most sensitive modality for detecting occult fractures and acute bone stress changes when radiographs are negative and clinical suspicion remains high. 1, 2

• For suspected purely ligamentous Lisfranc injuries without diastasis and normal radiographs, MRI is recommended as it has high correlation with intraoperative findings. 1, 2

• MRI is preferred for evaluating soft tissue injuries including ligaments, tendons, and the capsuloligamentous complex when radiographs are noncontributory. 1, 2

• However, MRI is not routinely used as the first imaging study for acute foot trauma in settings of peripheral neuropathy, penetrating trauma, or polytrauma. 1

Clinical Algorithm for Decision-Making

1. Obtain weight-bearing radiographs first (three views: AP, lateral, oblique), including bilateral views for comparison. 3, 2

2. If radiographs show complex fractures, polytrauma, or high-energy mechanism → proceed directly to CT for complete osseous evaluation and surgical planning. 1, 2

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

   • Choose CT for suspected occult fractures in high-energy mechanisms, inability to bear weight, or when rapid diagnosis is needed. 2, 5
   • Choose MRI only for suspected soft tissue injuries, purely ligamentous Lisfranc injuries, or when tendon/plantar plate pathology is specifically suspected. 2

Critical Pitfalls to Avoid

• Never rely solely on non-weight-bearing radiographs for suspected midfoot or Lisfranc injuries, as this leads to missed diagnoses. 2

• In patients with diabetic neuropathy, standard clinical tests are unreliable and patients may bear weight despite fractures—image more liberally and do not apply Ottawa rules. 1, 2

• Do not use CT or MRI as first-line imaging when radiographs are appropriate and sufficient. 2

• For acute hyperflexion injuries, conventional radiographs including weight-bearing images are insufficient—CT should be the primary modality. 2

Cost-Effectiveness Considerations

• An MRI-selective protocol with initial CT scanning is more cost-effective than performing MRI in all patients, with studies showing significant cost savings (estimated 66,805 Euro over 4.5 years). 5

• CT provides faster time to diagnosis (3 hours vs 40 hours for CT+MRI protocol), reducing overall healthcare costs and emergency department burden. 5