Radiology #2: Twisted

The Patient

A 65 year old man presents following a twisting injury to his right foot after tripping over in the garden. As a (very) minor mechanism of injury, he is seen in the Pit. He tells you he has been unable to weight-bear at all since the injury several hours ago. The midfoot looks swollen, but there is no tenderness over either malleoli and he can both plantarflex and dorsiflex comfortably. He still cannot weight-bear when you see him in TEU. You obtain the following plain film images:

The Pictures

What do you think?

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The AP film is concerning for a Lisfranc injury. The distance between the 1st and 2nd metatarsal (M1-M2) is appreciably wider than it should be, as is the distance from the medial cuneiform to the 2nd metatarsal (C1-M2) where the Lisfranc ligament runs. Otherwise there is some calcaneal entheseopathy and mild osteoarthritis of the ankle joint.

The patient had the contralateral foot imaged for comparison views. Have a look at the two non-weightbearing images next to each other and you'll see that the injury becomes much more obvious:

An M1-M2 distance >4mm (>5mm on weight-bearing views) or a C1-M2 distance >3mm (>5mm on weight-bearing views) are suggestive of a Lisfranc injury [1].

A subsequent CT confirmed the presence of a cortical avulsion fracture from the dorsolateral aspect of the medial cuneiform. This is the "fleck sign" that can be seen on either plain film or CT, and is pathognomonic. The CT was reported as suspicious for a Lisfranc injury, and patient made non-weight bearing prior to a review by the orthopaedic team.

For trauma interns seeing undifferentiated patients in the Pit, this is an easy diagnosis to miss, and a crucial one not to. Because while the mechanism may seem innocuous and the radiologic findings can be subtle, the injury itself is serious. They tend to occur when there is rotation around a fixed forefoot (the classic mechanism being a fall from a horse with a foot trapped in the stirrups, but it can also occur following a trivial trip or stumble, as in this case). They can also occur in high energy trauma when there is crush injury or axial loading through a plantarflexed foot (like falling from a height and landing on the ball of the foot). The Lisfranc ligament is central in maintaining the midfoot arch that is crucial for stability when weight-bearing, and injuries often go on to cause post-traumatic arthritis. This means they can result in chronic pain and permanent loss of function, and in rare cases can also also be complicated by compartment syndrome of the midfoot and distal ischaemia due to dorsalis pedis injury. They often require open reduction and internal fixation or arthrodesis, and so missing one can have serious consequences for the patient.

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Thanks to Dr Nick Chapman for submitting this case.

References

click to see references

[1] Lustosa L. Lisfranc injury - an approach. Radiopaedia [internet]. 2022. Accessed 11th May 2025. Available from: https://radiopaedia.org/cases/lisfranc-injury-an-approach

[2] Grewal US, Onubogu K, Southgate C, Dhinsa BS. Lisfranc injury: a review and simplified treatment algorithm. Foot (Edinb). 2020:45:101719.