Systematic Approach to Foot/Ankle X-ray Interpretation
Initial Imaging Protocol
Always obtain weight-bearing radiographs as your first-line study, as non-weight-bearing films are unreliable for detecting subtle injuries, particularly Lisfranc injuries. 1, 2, 3
Standard Views Required
- Three-view series: anteroposterior (AP), oblique, and lateral projections 1
- Additional AP view with 20° craniocaudal angulation to improve visualization of the Lisfranc joint complex 1, 2
- Bilateral imaging with both feet on AP radiographs to detect subtle malalignment by comparing to the uninjured side 1, 2, 3
Lisfranc Injury Interpretation
Positive Radiographic Findings
- Diastasis between the first and second metatarsal bases (>2mm widening) 1, 4
- "Fleck" sign: small avulsion fracture fragment between the base of the first and second metatarsals, representing avulsion of the Lisfranc ligament 1, 4
- Loss of alignment between the medial border of the second metatarsal base and medial border of the middle cuneiform on AP view 4
- Loss of alignment between the medial border of the fourth metatarsal and medial border of the cuboid on oblique view 4
- Associated metatarsal and cuneiform fractures 5
Critical Relevant Negatives
- Normal alignment of the medial border of the second metatarsal base with the middle cuneiform 4
- No diastasis between first and second metatarsal bases (<2mm spacing) 1
- Absence of fleck sign 1, 4
- Intact Lisfranc joint space on all three views 1
When to Advance Beyond X-ray
If radiographs are normal but clinical suspicion remains high (midfoot swelling, plantar ecchymosis, inability to bear weight), you must obtain advanced imaging—do not stop at negative X-rays. 1, 3
- CT is your primary advanced imaging for acute hyperflexion injuries, high-energy trauma, polytrauma patients, or those unable to bear weight 5, 1, 3
- CT detects 25% of midfoot fractures missed on radiographs in polytrauma patients 1, 3
- MRI is indicated when radiographs are normal but you suspect purely ligamentous injury without diastasis 1, 2, 3
- MRI with 3-D volumetric acquisitions shows high correlation with intraoperative findings for unstable Lisfranc injuries 5, 1, 3
Ankle Fracture Interpretation
Positive Radiographic Findings
- Fracture lines involving the medial malleolus, lateral malleolus, or posterior malleolus 6
- Widening of the mortise (>4mm medial clear space or asymmetric tibiofibular clear space) indicating syndesmotic injury 6
- Talar shift or subluxation within the ankle mortise 6
- Associated fibular fracture location (helps classify injury pattern per Lauge-Hansen) 6
Critical Relevant Negatives
- Intact medial clear space (should be ≤4mm and symmetric with superior clear space) 6
- Normal tibiofibular overlap on AP view (≥6mm) and mortise view (≥1mm) 6
- Concentric talar position within the mortise on all views 6
- No cortical disruption of malleoli or tibial plafond 6
Classification Approach
Use three views (AP, mortise, lateral) to identify the position of the foot at injury and direction of deforming force per Lauge-Hansen classification. 6
Jones vs Pseudo-Jones Fracture Interpretation
Jones Fracture (True Jones)
- Transverse fracture at the metaphyseal-diaphyseal junction of the fifth metatarsal, 1.5-3cm distal to the tuberosity 3
- Fracture line extends into the intermetatarsal articulation between the fourth and fifth metatarsals
- No extension into the tarsometatarsal joint
Pseudo-Jones (Avulsion Fracture)
- Avulsion fracture at the base of the fifth metatarsal tuberosity (proximal to Jones fracture location)
- Fracture line oriented transversely or obliquely through the tuberosity
- May extend into the fifth metatarsal-cuboid joint
- Caused by peroneus brevis tendon avulsion
Critical Relevant Negatives
- No cortical disruption at the base of the fifth metatarsal 3
- Normal soft tissue contour without swelling over lateral midfoot
- Intact fifth metatarsal-cuboid articulation
Critical Pitfalls to Avoid
Most Common Diagnostic Errors
- Never rely solely on non-weight-bearing radiographs for suspected Lisfranc injuries—this is the leading cause of missed diagnoses 1, 2, 3
- Up to 20% of Lisfranc injuries are missed or diagnosed late, especially low-energy purely ligamentous injuries 7, 8
- In diabetic patients with neuropathy, standard clinical tests are unreliable and patients may bear weight despite fractures—image more liberally 2, 3
- Radiographs have only 25-33% sensitivity for midfoot fractures in Level 1 trauma patients 5
When Initial X-rays Are Negative
Do not stop at negative radiographs if clinical suspicion is high—conventional radiographs including weight-bearing images are insufficient for acute hyperflexion injuries. 5, 3
- Proceed to CT for high-energy mechanisms, polytrauma, or inability to bear weight 5, 1, 3
- Proceed to MRI for suspected soft tissue injuries, ligamentous Lisfranc injuries, or occult fractures in athletes 5, 3
- CT reveals additional occult fractures in 46% of cases with positive radiographs and 35% of cases in other parts of the foot/ankle 9