Diagnostic Radiology/Musculoskeletal Imaging/Trauma/Lisfranc fracture-dislocation
The Lisfranc joint, named after a field surgeon in Napoleon's army who described a new technique of forefoot amputation for soldiers with gangrene related to frostbite, defines the boundary between the midfoot and forefoot. The joint can be disrupted traumatically by axial loading, with rotational forces directed either medially or laterally. This classically occurs when patients get their foot caught in something, such as stirrups when horse riding. Disruption of the lisfranc joint is also seen in the Charcot joint in diabetics.
The presention of patients with a traumatic lisfranc injury is variable depending on its severity. While some patients will present with obvious physical foot deformities, others may present with only midfoot pain with weight bearing. The typical clinical signs include midfoot plantar echhymosis, midfoot instability, and pain along the TMT joints with motion.
The 5 TMT joints form the Lisfranc joint. Important ligaments transverse these joints, critical for support and strength. Ligaments connect the bases of each of the metatarsals to each other, except the first two. There is also an oblique ligament between the medial cuneiform and the base of the 2nd metatarsal.
The initial radiological work-up consists of an AP, lateral, and medial oblique views. If these views fail to demonstrate a lisfranc injury and there is high clinical suspicion, getting full weight bearing views or stress views if the patient is unable to weight bear is essential. A CT scan can also be obtained, which may show an occult injury.
The following should be considered when evaluating radiographs for a Lisfranc fracture-dislocation:
- Perhaps the most important alignment is along the second metatarsal and second cuneiform. A step-off between these two bones is indicative of a Lisfranc disruption.
- Malalignment of the fourth metatarsal and cuboid can also be diagnostic of a Lisfranc injury.
- The medial cuneiform-second metatarsal space should be evaluated for the "fleck sign" indicating avulsion of the Lisfranc ligament.
Fig. 1 Example of a Lisfranc fracture, demonstrating incongruity of the medial shaft of the 2nd metatarsal and middle cuneiform.
Fig. 2 Lisfranc fracture demonstrating lateral dislocation.
Fig. 3 Lisfranc fracture demonstrating medial dislocation of the 1st metatarsal.
Anatomically stable injuries can be treated conservatively, whereas unstable injuries or malalignment requires surgery. Generally, surgery involves open reduction and fixation with screws across the affected TMT joint(s). Screws are typically left in for 6 months.