Best Imaging to Rule Out Lisfranc Fracture
Weightbearing radiographs of both feet (bilateral AP, oblique, and lateral views) are the best initial imaging to rule out a Lisfranc fracture, as they increase detection of subtle injuries by accentuating diastasis at the tarsometatarsal joint that may be missed on non-weightbearing films 1.
Initial Imaging Approach
Start with bilateral weightbearing radiographs including:
- Standard three views (AP, oblique, lateral)
- Optional AP view with 20° craniocaudal angulation for enhanced visualization 1
- Both feet must be included on AP views to compare subtle malalignment against the uninjured side 1
Why Weightbearing Matters
Non-weightbearing radiographs are unreliable for detecting subtle Lisfranc injuries because they fail to demonstrate instability that becomes apparent under physiologic load 1. Weightbearing views increase abnormal alignment at the Lisfranc joint, making injuries easier to identify 1. One study found that when weightbearing radiographs were positive, 54% of subsequent CT scans were equivocal or negative, while only 12% of patients with negative weightbearing films had positive CT scans 2.
When Weightbearing Films Are Not Possible
If the patient cannot bear weight due to pain or polytrauma:
CT is the Next Best Option
- CT demonstrates superior sensitivity for detecting subtle displacement that radiographs miss 3
- In cadaver studies, all 1-mm dislocations and two-thirds of 2-mm dislocations were invisible on routine radiographs but visible on CT 3
- CT revealed additional occult fractures in 46% of cases with true positive radiographs 4
- Novel 3D CT signs (Mercedes sign, peeking metatarsal sign, peeking cuneiform sign) show 92-97% sensitivity and 92-93% specificity 5
- CT is particularly valuable in polytrauma patients where 25% of midfoot fractures are missed on radiographs 1
MRI for Equivocal Cases
If radiographs are normal but clinical suspicion remains high, both MRI and CT are supported for further evaluation 1:
- MRI directly visualizes the Lisfranc ligament complex with high correlation to intraoperative findings 1
- MRI detects purely ligamentous injuries without diastasis 1
- 3D volumetric MRI acquisitions show superiority over standard sequences 1
Key Radiographic Measurements
On weightbearing AP views, measure the diastasis between the medial cuneiform and second metatarsal base (C1-M2):
- Express as a ratio compared to the uninjured side
- Mean ratio requiring surgery: 1.53 vs. 1.11 for non-operative injuries 2
- Diastasis ratio correlates strongly with need for surgical intervention (R = 0.576, P < 0.001) 2
Common Pitfalls to Avoid
Don't skip weightbearing views - This is the single most important factor in detecting subtle injuries that lead to chronic instability and post-traumatic arthritis if missed 1, 6, 7
Don't order CT first in ambulatory patients - Weightbearing radiographs provide better functional assessment of instability 2
Don't forget bilateral comparison - Subtle malalignment is often only apparent when compared to the contralateral foot 1
Don't dismiss clinical suspicion with negative non-weightbearing films - Up to one-third of Lisfranc injuries are initially missed 5, 6
Clinical Context Exceptions
Polytrauma or high-energy mechanisms: Use CT as primary imaging since weightbearing is impractical and radiographs miss 25% of midfoot fractures in this setting 1, 4
Persistent pain with normal weightbearing films: Proceed to MRI to evaluate for purely ligamentous injury without diastasis 1