Annals of B-Pod: Quick Hit Case

"doc, you're not gonna believe this, but..."

An otherwise healthy teenage female presents to the emergency department (ED) with left foot pain after being dared by her friends to jump out of a second story window. She reportedly landed directly on the plantar aspect of her left foot and was unable to bear weight on that foot following the incident.  She reports no other injuries.

+ What do I see when I walk into the room?

The patient was well appearing and in no acute distress. Musculoskeletal exam was most significant for diffuse swelling and ecchymosis over the left anterior foot with tenderness over the base of the metatarsals. The foot was otherwise neurovascularly intact. Her cardiopulmonary, abdominal, and neurologic exams were within normal limits.

+ What does imaging show?

The initial x-ray of the left foot was significant for soft tissue swelling without acute osseous findings. A weight bearing x-ray was then obtained that showed a linear lucency at the base of the first metatarsal with an osseous fragment between the base of the second metatarsal and medial cuneiform, with associated widening of the Lisfranc interval, concerning for a Lisfranc fracture. A CT of the foot confirmed the diagnosis of a Lisfranc fracture of the distal aspect of the medial cuneiform with multiple small ossific fracture fragments in the Lisfranc interval.

Unremarkable initial x-ray.

Weight bearing film revealing widening of the Lisfranc interval and a small lucency on the medial aspect of the base of the first metatarsal (arrow).

+ Discussion and management

Lisfranc fractures and dislocations are rare and commonly overlooked in the ED setting. Because the standard workup is often unrevealing, approximately 20% of these injuries are missed on initial presentation.[1] Knowing the risk factors and clinical presentation of Lisfranc injuries can help providers identify when to suspect this diagnosis.

In order to assess for this injury, it is important to understand the anatomy that makes up the Lisfranc joint. This joint complex connects the midfoot to the forefoot, and is a critical area in stabilizing the arch of the foot to assist with ambulation. It is particularly crucial in ankle dorsiflexion and plantarflexion.[2] The Lisfranc joint complex consists of the five metatarsals of the forefoot articulating with the three cuneiforms and the cuboid of the midfoot.[3]

Of these bones, the second metatarsal in particular plays the largest role in stabilization of the arch and any disruption can often lead to displacement of the third through fifth metatarsals. There are multiple ligaments supporting the joint, with the strongest being the Lisfranc ligament connecting the medial border of the second metatarsal with the lateral aspect of the medial cuneiform. Additionally, there is also a transverse ligament that connects the second through fifth metatarsals. Disruption of this ligament in Lisfranc injuries characteristically results in displacement of the first metatarsal on imaging as discussed below.

The incidence of Lisfranc injuries has been reported at 1 in 55,000 per year, and it is two to four times more likely to occur in men than women. The average age of patients with this injury is in the fourth decade.[3] These injuries are often sustained by a high-energy mechanism such as a motor vehicle collision, accounting for approximately two-thirds of all Lisfranc injuries. Certain low energy mechanisms can also result in Lisfranc injuries. A frequent reported mechanism is missing a step when coming down the stairs. Patients may also report direct trauma from a large external force that strikes the foot. As in the patient above, some patients experience an indirect force such as the foot hitting a stationary object and the weight of one’s body becoming the additional force.

On physical exam, these patients usually have severe pain over the midfoot and often are unable to bear weight. One may see significant swelling throughout the midfoot or gross dorsal subluxation or lateral deviation of the forefoot. One highly specific exam finding suggestive of a Lisfranc injury is plantar ecchymosis. However, this finding is not always present in the setting of mild ligamentous strains or minor fractures.

Additionally, ecchymosis often does not appear until 24-48 hours after the injury. On rare occasions, compartment syndrome can occur due to significant swelling of the midfoot, and suspicion should be raised with pain out of proportion with passive extension of the toes. In subacute presentations, the Lisfranc joint may be dorsally subluxed with a provoked test by applying dorsal forces to the distal aspect of the midfoot while palpating the joint with the other hand.

When considering radiographic evaluation, if there is any concern for a Lisfranc injury it is important to order weight-bearing films to improve detection rates. Aggressive pain control should be pursued as obtaining true weight bearing films is often limited by patient discomfort. Anterior-posterior (AP), lateral, and oblique films should be obtained when evaluating for a Lisfranc injury.

On a normal foot x-ray, the medial cortex of the second metatarsal should form a continuous line with the medial cuneiform. Likewise, the intermetarsal joint space should be less than 2 mm. Dislocation or fracture of the Lisfranc joint complex should be suspected with a number of radiographic findings.

The AP film may show: 1) loss of linearity of the medial border of the second metatarsal with the medial border of the middle cuneiform; 2) increased intertarsal space greater than 2.7 mm; or 3) presence of a “fleck sign” at the base of the second metatarsal, which is pathognomonic for an avulsed or disrupted Lisfranc ligament.

On the oblique film, loss of normal alignment of the second through fourth tarsal-metatarsal joints will often be seen. Finally, dorsal displacement of the base of the second metatarsal may be evident on a lateral view of the injured foot.

If x-ray findings are not present, but clinical suspicion remains high, CT should be considered as even weight bearing radiographs have limited sensitivity and specificity for detecting Lisfranc injuries. One small observational study showed a miss rate of approximately 50% with weight bearing films. More recently CT has become the gold standard in imaging modalities as it demonstrates much higher detection rates. If the x-ray is diagnostic for Lisfranc injuries, a CT is not mandatory in the ED setting, although it can help with surgical planning.

Although this diagnosis does not often require emergent intervention, it is important that these patients receive timely follow up. Missed injuries can lead to osteoarthritis or debilitating deformities of the midfoot. Lisfranc injuries that would require urgent evaluation include open fractures, fracture patterns in which the soft tissue may be compromised and in danger of necrosis, or any concern for compartment syndrome.

Otherwise, it is recommended that all patients with evidence of a Lisfranc injury, whether minor or major, be evaluated by an orthopedist within one to two weeks to prevent these complications. All patients should be placed in a posterior slab splint, be made non-weight bearing, and instructed to ice and elevate the extremity.

Foot pain is a common ED complaint and Lisfranc injuries can be difficult to diagnose. Knowledge of the clinical presentation and management of these injuries can help prevent missed diagnoses and chronic complications.

Authored by Kathryn Banning, MD

Posted by Mathew Scanlon, MD