Les Midfoot Fractures: A Franc Review
Case
A healthy 33-year-old female presents after a mechanical fall while jogging. She stumbled while stepping from the curb and fell forward into the street. She has severe right ankle and foot pain and is unable ambulate. On examination, there is diffuse swelling of her right foot and ankle with tenderness throughout, especially at the dorsal aspect of the foot. There is a small amount of plantar ecchymosis. X-rays of the foot are obtained.
What is your next move?
Do you provide the patient with and ace wrap and crutches and discharge her home? What else should be considered? Are the details of her mechanism helpful? Are there radiographic findings suggestive of occult fracture? What examination findings are suggestive of an occult pathology?
Introduction
Originally described during the Napoleonic wars without the aid of multidetector computed tomography scanners, Lisfranc injuries remain an important consideration in foot trauma but are fraught with diagnostic challenges. Often describing a fracture/dislocation to any portion of the tarsometatarsal joint complex, Lisfranc injuries can lead to significant morbidity and functional impairment if missed (which occurs in up to 20% of cases). The stability of the complex is primarily conferred by the articulation of the second metatarsal with the middle cuneiform and the Lisfranc ligament (oblique interosseous ligament) which connects the base of the second metatarsal with the medial cuneiform.
Mechanism of Injury
The key to making a correct diagnosis begins with a high index of suspicion based on history (e.g. mechanism) and exam because radiographic findings may be subtle. Direct injury is usually from blunt trauma to the dorsal foot or from crush injury. Indirect injuries are often associated with extreme hyperplantarflexion or rotation of a fixed midfoot. Other common mechanisms include motor vehicle collisions and sports that require stirrups, bindings, or foot straps. Interestingly, one third of Lisfranc injuries are associated with seemingly minor mechanisms.
Radiograph Review
Lisfranc injuries range from subtle, sometimes undetectable subluxations to obvious fracture-dislocations. A methodical review of x-rays is essential to assessing for a Lisfranc injury. Special attention should be paid to alignment and focuses on two key relationships. First, the medial borders of the second metatarsal and the middle (second) cuneiform should be well-aligned on the AP view, as should the lateral borders of the first metatarsal and the medial (first) cuneiform. Second, the distance between the first two metatarsals should be examined, as this distance is commonly increased with Lisfranc injuries. Widening between the metatarsals and/or cuneiforms may be more apparent with oblique views.
Suggestive Exam Findings
- Inability to ambulate or stand on toes
- Significant pain/swelling of the midfoot
- Plantar ecchymosis
- Positive pronation-abduction test (pain with forefoot abduction and pronation with fixed hindfoot)
Suggestive Radiographic Findings
- Widening between the first and second metatarsals and/or medial and middle cuneiforms – Image 3
- Malalignment of the first and second metatarsals with the medial and middle cuneiforms, respectively, on the AP view (as described above) – Image 4
- Malalignment of the medial and lateral borders of the third metatarsal and lateral cuneiform on the oblique view
- Malalignment of the medial borders of the fourth metatarsal and cuboid on the oblique view
- Fleck sign (avulsion fracture of second metatarsal base) – Image 5
- Step-off sign (dorsal metatarsal displacement) on lateral view
- Cuboid or cuneiform fractures
Image 3: Radiograph demonstrating widening between the first and second metatarsals (Click to expand)
Image 4: Radiograph demonstrating malalignment of the medial and lateral borders of the third metatarsal and lateral cuneiform (Click to expand)
Image 5: Radiograph demonstrating the "fleck sign." Indicative of an avulsion fracture of the base of the second metatarsal (Click to expand)
Role of CT
Interpretation of radiographs may be limited secondary to suboptimal positioning and the inherent overlapping bony articulations of the midfoot. Classically, weight-bearing views are suggested; however, adequate weight-bearing views are often limited by pain. Advanced imaging is advantageous in these cases and allows for visualization of subtle findings in multiple planes. A CT should be obtained if the diagnosis remains in question despite normal-appearing radiographs if there are suggestive exam findings or the patient is unable to bear weight.
Management
When improperly managed, Lisfranc injuries can lead to pes planus deformity and functional limitations secondary to arthritis and pain with weight bearing. Stable ligamentous injuries (with displacement <2mm) may be managed conservatively with short leg casting and non-weight bearing for 6 weeks. Stability can be reassessed with weight bearing radiographs at two weeks. Prior to proceeding with non-operative management, advanced imaging should be considered to better evaluate the extent of injury. Unstable or displaced injuries are typically managed with open reduction and internal fixation. In the emergency department, orthopedic consultation is recommended in all suspected or confirmed cases of Lisfranc injury.
Key Points
- A high index of suspicion must be maintained to identify subtle Lisfranc injuries. Foot pain and swelling after trauma, especially when associated with inability to bear weight, should be suspected of having a Lisfranc injury.
- The second metatarsal base should always be carefully assessed for displacement, avulsion, and fracture. The alignment of the second metatarsal with the middle cuneiform and spacing between the first and second metatarsals are the most consistent and easily assessed relationships on AP radiographs.
- CT scan should be obtained in cases of normal-appearing radiographs when there is remaining clinical suspicion.
- Missed Lisfranc injuries can result in long-term disability.
Faculty Reviewer: Jefferey Feden, MD
Image Credits
- Courtesy Dr. Henry Knipe, radiopedia.org
- Courtesy Dr. Henry Knipe, radiopedia.org
- Courtesy RMH Core Conditions, radiopedia.org
References
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