X-ray, ultrasound or MRI: which test for foot pain?

“Can’t I just get an MRI?” It’s a fair question. MRI sounds like the most thorough test, so why start with anything else? Because each test answers a different question, and choosing the right one starts with listening to you and examining your foot.

Start with the exam, not the scanner

Where it hurts, when it started and what makes it worse tell us a lot. So does pressing on the sore spot, testing each tendon’s strength and watching you walk. The exam narrows the likely causes, and that decides which test, if any, will help.

Not every sore foot needs a picture. After a twisted ankle, a short checklist called the Ottawa ankle rules helps decide whether an X-ray is needed; our post on sprain or fracture explains it.

X-rays: the first look at bone

An X-ray uses a very small dose of radiation to make pictures of bone, and no radiation stays in your body afterward. It’s the fastest and easiest way to check for fractures, dislocated joints and arthritis.^[3]

For many foot problems we take X-rays while you stand. Standing, or weight-bearing, X-rays show the bones under your body weight. For arthritis, they’re the most valuable test for judging severity and joint deformity; X-rays taken when you’re not standing make that hard to assess.^[5]

X-rays have limits. They show little about muscles and tendons.^[3] And an early stress fracture is often hard to see on an X-ray at first. It may show up only several weeks later, once healing bone forms around the crack.^[6] See fractures and trauma.

Ultrasound: soft tissue, in motion

Ultrasound uses sound waves, not radiation, to make pictures of muscles, tendons, ligaments, nerves and joints. It helps diagnose tendon tears and tendinitis, ligament sprains and tears, fluid in joints, ganglion cysts, and splinters or glass under the skin.^[4]

Because the images are live, ultrasound can show a tendon or joint while it moves. But it struggles with bone: sound waves have trouble passing through it, so ultrasound sees only the surface of a bone, not what’s inside.^[4]

MRI: the detailed view

MRI uses a strong magnet and radio waves, with no radiation. It can show very small tears in tendons, ligaments and muscles, and some fractures and bone bruises that don’t show on X-rays.^[2,3] That’s why, when a stress fracture is suspected but the X-ray looks normal, an MRI or a bone scan can find it earlier.^[6] See stress fractures in runners. When X-rays are normal or unclear and a cartilage or joint problem is suspected, guidelines rate MRI, or CT, as usually appropriate.^[1]

The trade-offs: an MRI can take longer, and you need to lie perfectly still. Metal implants can blur the pictures, and the magnet can interfere with some devices, such as pacemakers, so always mention them.^[2] We don’t have MRI at the office; when you need one, we arrange it at an imaging center.

CT, briefly

CT uses X-rays to build detailed cross-section pictures. It’s useful for complicated or subtle fractures and dislocations,^[3] and it can help plan surgery when a fracture needs it.^[7,6] Our colleagues at the Center for Lower Extremity Surgery (external site) explain how imaging is used before surgery.

Why “just get an MRI” isn’t always the next step

More detail isn’t always more useful. For ongoing foot pain whose cause isn’t yet clear, radiology guidelines rate MRI, CT, ultrasound and bone scans as usually not appropriate as the first test. X-rays come first.^[1]

MRI can also pick up changes that may not be causing any trouble. In one study of 294 routine foot and ankle MRIs, from people with no recorded sprain or injury to the outside of the ankle, 35% showed some change in the peroneal tendons, which run along that side. The authors note that people whose scans show changes like these, without matching symptoms or exam findings, can be reassured.^[8]

So the order matters: the exam first, then the simplest test that can answer the question, then MRI when the answer still isn’t clear.

Common questions

Can ultrasound replace an MRI?

Sometimes. After a normal or unclear X-ray, when the pain seems to come from a tendon, ligament, the plantar fascia or other soft tissue, guidelines rate both ultrasound and MRI as usually appropriate.^[1] Ultrasound is faster than MRI and you don’t have to stay completely still, but it can’t see inside bone.^[4] For a suspected hidden fracture, guidelines favor MRI or CT.^[1]

My X-ray was normal, but my foot still hurts. Now what?

A normal X-ray rules out some problems, not all. Depending on your exam, the next step may be an ultrasound at the same visit, an MRI, a repeat X-ray in a few weeks, or a treatment plan and a follow-up visit.

When to see a podiatrist