What are the steps to evaluate a Lisfranc injury on x-ray?

Radiographic Evaluation of Lisfranc Injury

Obtain a three-view radiographic series (anteroposterior, oblique, and lateral) as your initial imaging study, with weight-bearing views being absolutely essential for accurate diagnosis. 1, 2

Step-by-Step X-ray Evaluation Protocol

1. Initial Radiographic Views

• Obtain three standard views: anteroposterior (AP), oblique, and lateral projections of the foot 1
• Add a fourth AP view with 20° craniocaudal angulation to improve visualization of the Lisfranc joint 1, 2
• Weight-bearing radiographs are mandatory when the patient can tolerate them—non-weight-bearing images are unreliable and will miss subtle injuries 1, 2
• Include bilateral foot imaging on AP views to compare the injured side with the uninjured contralateral foot for detecting subtle malalignment 1, 2

2. Key Radiographic Findings to Identify

Primary Signs of Lisfranc Injury:

• Diastasis between the first and second metatarsal bases: Look for widening of the space between M1 and M2 bases 1, 2, 3
• The "fleck" sign: A small avulsion fracture fragment in the first-second intermetatarsal space, representing avulsion of the Lisfranc ligament 1, 2, 3

Alignment Assessment:

• On AP view: The medial border of the second metatarsal base should align with the medial border of the middle cuneiform 1
• On oblique view: The medial border of the fourth metatarsal base should align with the medial border of the cuboid 1
• On lateral view: Assess for dorsal displacement of the metatarsal bases relative to the cuneiforms 1

3. Critical Pitfall to Avoid

Never rely solely on non-weight-bearing radiographs—this is the most common reason for missed diagnoses, as purely ligamentous injuries without diastasis will not be visible without weight-bearing stress 1. If the patient cannot bear weight due to pain or other injuries, proceed directly to advanced imaging rather than accepting negative non-weight-bearing films 1.

4. When to Proceed to Advanced Imaging

CT Imaging Indications:

• When radiographs are normal but clinical suspicion remains high (midfoot pain, swelling, plantar ecchymosis, inability to bear weight) 1
• For acute hyperflexion injuries or high-energy polytrauma 1
• When multiple metatarsal and cuneiform fractures are present 1
• To evaluate the true extent of osseous injury and detect nondisplaced fractures 1
• In polytrauma patients: Approximately 25% of midfoot fractures identified on CT are overlooked on radiographs 1

MRI Imaging Indications:

• For purely ligamentous injuries when radiographs are normal but clinical suspicion persists 1
• For direct visualization of the Lisfranc ligamentous complex, with 3D volumetric acquisitions superior to standard sequences 1
• MRI shows high correlation with intraoperative findings for unstable Lisfranc injuries 1

5. Special Patient Populations

• Neuropathic patients require heightened vigilance as they may be able to bear weight despite significant fractures 1
• Polytrauma patients warrant a lower threshold for CT imaging given the high rate of missed injuries on plain radiographs 1

The algorithmic approach prioritizes weight-bearing radiographs first, followed by CT for osseous detail when radiographs are equivocal or in high-energy trauma, and MRI specifically for suspected purely ligamentous injuries 1. This stepwise progression maximizes diagnostic accuracy while avoiding the common pitfall of accepting negative non-weight-bearing films in a clinically suspicious presentation.