How Lisfranc Injuries Are Diagnosed: X-ray vs. CT vs. MRI

sarangndesai
4 days ago
9 min read

Updated: 12 hours ago

By Sarang Desai, DO

Fellowship-Trained Orthopedic Foot and Ankle Surgeon | Sports Medicine Specialist

McKinney and Flower Mound, Texas | Serving the Dallas-Fort Worth Metroplex

If you injured the middle of your foot and someone told you your X-rays were "normal" — but you still can't walk on it — this article is for you.

Lisfranc injuries are one of the most commonly missed injuries in the foot. Up to one-third of them are misdiagnosed on the first visit.[1] The reason isn't carelessness. It's that the standard imaging most patients get is the wrong test for this particular injury.

As a fellowship-trained orthopedic foot and ankle surgeon in McKinney and Flower Mound, I see the downstream consequences of this all the time. A patient comes in six weeks after a "midfoot sprain," still limping, and the correct imaging finally shows what was there the whole day of the injury.

This article walks through exactly how Lisfranc injuries are diagnosed — which test to get, when, and what each one actually shows.

---

Quick Answer: Which Imaging Test Do You Need?

Bilateral weight-bearing X-rays are the first and most important test. If those are normal or unclear but suspicion remains, CT or MRI is the next step. CT is better for bone. MRI is better for ligaments.

Here's the short version:

Imaging Test	What It Shows Best	When It's Used
Non-weight-bearing X-ray	Obvious fractures and dislocations	Often the first test done — but can look completely normal in subtle injuries
Bilateral weight-bearing X-ray	Instability revealed under load; side-to-side comparison	The single most important test. First-line for any suspected Lisfranc injury
CT scan	Small fractures, bone fragments, precise joint alignment	When X-rays are equivocal, for surgical planning, or in high-energy trauma
MRI	Lisfranc ligament integrity, bone bruising, soft tissue	When distinguishing a stable sprain from an unstable ligament tear
Weight-bearing CT	Combines 3D bone detail with loading	Emerging technology; not yet universally available

---

Why Regular X-rays Miss This Injury

This is the single most important concept to understand.

A standard foot X-ray is taken while you're lying down or sitting, with no weight on the foot. In a subtle Lisfranc injury, the ligaments are torn but the bones haven't shifted yet — because nothing is pushing them apart. The X-ray looks normal.

The moment you stand up, your body weight drives the second metatarsal away from the medial cuneiform, and the gap becomes visible.

The research on this is clear. A study comparing weight-bearing and non-weight-bearing X-rays in patients with confirmed ligamentous Lisfranc injuries found that on non-weight-bearing films, the step-off between the intermediate cuneiform and second metatarsal was essentially the same as in uninjured controls — a difference of 0.39 mm, not statistically significant. On weight-bearing films, that same measurement showed a difference of 1.98 mm and became highly significant.[2]

Reliability improves dramatically too. Interobserver agreement for interpreting weight-bearing radiographs was above 0.90, compared with 0.61 to 0.80 for non-weight-bearing films.[2]

Translation: weight-bearing X-rays don't just show more — different readers actually agree on what they're seeing.

---

Bilateral Weight-Bearing X-rays: The Gold Standard First Test

Two words matter here: bilateral and weight-bearing.

Weight-bearing means standing on the foot during the X-ray. Yes, it hurts. It's also the only way to reveal the instability.

Bilateral means we X-ray both feet, side by side, on the same image. Normal midfoot anatomy varies from person to person. Your uninjured foot is the perfect control. A 2 mm gap might be normal for you — or it might be 2 mm wider than your other side, which is diagnostic.

The 2024 International Foot and Ankle Sports Consensus, developed through a modified Delphi process with 32 international foot and ankle surgeons, reached unanimous agreement that bilateral weight-bearing radiographs should be the initial imaging study for suspected Lisfranc injuries in athletes.[3]

What We're Measuring

Several specific findings suggest an unstable Lisfranc injury:

- C1-M2 distance — the gap between the medial cuneiform and the base of the second metatarsal. A side-to-side difference greater than 1 mm carries about 92% sensitivity for injury requiring surgery.[4]

- The fleck sign — a small bone fragment sitting in the space between the first and second metatarsal bases. This is an avulsion — a piece of bone the Lisfranc ligament pulled off as it tore. It's essentially diagnostic.

- Loss of alignment — on the AP view, the medial border of the second metatarsal should line up with the medial border of the middle cuneiform. On the oblique view, the medial border of the fourth metatarsal should line up with the medial border of the cuboid. On the lateral view, the metatarsals should not be dorsally displaced relative to the cuneiforms.[5]

The American Academy of Family Physicians summarizes this well: obtain weight-bearing radiography when possible, and if suspicion is high but the patient cannot bear weight, order a CT scan.[5]

What If You Can't Stand On It?

Sometimes patients simply cannot tolerate standing. Options include:

- Repeat weight-bearing films in 5-10 days after swelling and pain improve

- Proceed directly to CT

- In some cases, stress radiographs under anesthesia

What is not an acceptable option is accepting a normal non-weight-bearing X-ray as proof that nothing is wrong.

---

CT Scan: When Bone Detail Matters

A CT scan takes thin cross-sectional slices and reconstructs them into a 3D picture. For Lisfranc injuries, CT excels at:

- Detecting small, non-displaced fractures that plain films can't resolve

- Quantifying subluxation with millimeter precision

- Surgical planning — knowing exactly which joints are involved changes the operation

- High-energy trauma, where the injury pattern is complex

A systematic review of Lisfranc imaging concluded that CT is more useful than radiography for detecting non-displaced fractures and minimal bony subluxation.[6]

The Important Caveat About CT

CT alone is not a perfect substitute for weight-bearing X-rays, because a standard CT is done lying down — no load on the foot. The same problem that makes non-weight-bearing X-rays unreliable applies to non-weight-bearing CT.

One emergency department study of 117 patients with suspected Lisfranc injury found that when the initial weight-bearing radiograph was positive, 54% of subsequent CT scans were read as equivocal or negative. The authors concluded that CT provided limited additional benefit in the initial ED evaluation and advocated for bilateral weight-bearing radiographs as the first-line investigation.[7]

That said, CT becomes far more useful when both feet are scanned for comparison. A study using bilateral foot CT found that side-to-side differences at multiple measurement points reliably distinguished patients who needed surgery from those who didn't.[4]

Newer CT Findings

Three-dimensional CT reconstruction has introduced new diagnostic signs — the Mercedes sign, the peeking metatarsal sign, and the peeking cuneiform sign. In a study of 102 feet with intraoperatively confirmed diagnoses, these signs showed sensitivity of 92-97% and specificity of 92-93%, with excellent reader agreement. The Mercedes sign performed best.[1]

Weight-bearing CT — where the scan is performed while standing — combines the advantages of both approaches. It's promising, and validation studies are ongoing, but it's not yet available everywhere.[8]

---

MRI: The Test That Sees the Ligament

X-rays and CT show bone. MRI is the only test that directly visualizes the Lisfranc ligament itself.

MRI is the best modality for detecting ligament abnormalities.[6] It shows:

- Whether the Lisfranc ligament is intact, partially torn, or completely ruptured

- Bone marrow edema (bone bruising) at the joint surfaces

- Injuries to surrounding ligaments and joint capsule

- Associated cartilage damage

Why This Changes Treatment

The single most important treatment decision in a Lisfranc injury is: is this stable or unstable?

The 2024 International Foot and Ankle Sports Consensus reached unanimous agreement that stable, nondisplaced injuries with an intact Lisfranc ligament on MRI may be managed nonoperatively with close monitoring.[3] In that consensus, athletes with stable ligamentous injuries returned to sport in 2.8 months on average, with 96.8% returning overall.[3]

Conversely, an MRI showing a complete Lisfranc ligament rupture — even with X-rays that look borderline — tells us this foot will not stay aligned under load, and surgery is likely needed.

The same consensus specified CT or MRI for evaluating low-grade instability after initial weight-bearing radiographs.[3]

The Limitation of MRI

MRI shows the anatomy of the ligament but does not directly measure stability under load. A ligament can be partially torn on MRI and still be functionally stable — or look reasonably intact and still allow displacement when you stand. This is why MRI is interpreted alongside weight-bearing imaging and physical exam, never in isolation.[6]

---

What Ultrasound Can and Can't Do

Ultrasound can visualize the dorsal Lisfranc ligament and measure the C1-M2 distance. It's fast, inexpensive, and involves no radiation.

However, its accuracy for diagnosing Lisfranc instability remains unproven.[6] It's highly operator-dependent, and it cannot see the deeper plantar ligaments, which are the most biomechanically important part of the complex. Ultrasound is not a substitute for weight-bearing X-rays, CT, or MRI in this setting.

---

My Diagnostic Algorithm

Here's how I actually work through this in clinic:

Step 1 — History and exam. The mechanism matters: axial load or twisting through a plantarflexed foot.[3] On exam, I'm looking for midfoot tenderness, pain with the squeeze/pronation-abduction test, inability to bear weight, and — most specifically — plantar ecchymosis (bruising on the sole of the foot). That last finding is a Lisfranc injury until proven otherwise.[9]

Step 2 — Bilateral weight-bearing X-rays. Always. Both feet. Standing. If the patient truly cannot stand, I plan for repeat films once pain improves, or go to CT.

Step 3 — If X-rays are clearly abnormal: proceed to CT for surgical planning and to define the full injury pattern.

Step 4 — If X-rays are normal or borderline but clinical suspicion remains: MRI to assess ligament integrity, or CT if I'm more concerned about an occult fracture. Per the ACR, these are considered equivalent alternatives in this scenario.[10]

Step 5 — If everything is still equivocal but the patient can't walk: I do not discharge them with a "sprain" diagnosis. I immobilize, keep them non-weight-bearing, and repeat weight-bearing imaging in 2-3 weeks. Instability that isn't visible on day one often declares itself as swelling resolves.

The cost of over-investigating is an extra scan. The cost of under-investigating is a collapsed midfoot arch, post-traumatic arthritis, and an operation that could have been avoided.

---

Questions to Ask Your Doctor

If you have a suspected midfoot injury, these are reasonable questions:

1. Were my X-rays taken while I was standing?

2. Was my other foot X-rayed for comparison?

3. Was a Lisfranc injury specifically considered and ruled out?

4. If my X-rays are normal but I still can't walk, what's the next step?

5. Should I see a foot and ankle specialist?

---

When to Get a Specialist Opinion

See a fellowship-trained foot and ankle surgeon if you have:

- Midfoot pain that isn't improving after a week

- Inability to bear weight after a foot injury

- Bruising on the bottom of your foot

- "Normal" X-rays but persistent significant pain

- A diagnosis of "midfoot sprain" that isn't getting better

Early, accurate diagnosis is the difference between a straightforward recovery and a complex reconstruction. Lisfranc injuries do not get easier to treat with time.

---