Feature Article

Why Did My Doctor Order an MRI for My Knee Injury?

Three examples for when an MRI might be better than an X-ray

It’s no surprise that people tend to tilt their head when an orthopedic doctor recommends a magnetic resonance imaging (MRI) scan for a knee problem. After all, people with orthopedic injuries expect X-rays, and have likely had medical and/or dental X-ray scans all their life. They may also expect a CT scan. But an MRI? Not so much.

But put simply, it could be for many reasons. Doctors know that in some cases, MRIs actually produce more detailed images than X-rays or CT scans, without the radiation. It just comes down to this: What exactly are we looking for? A broken bone? A tissue tear? Extra fluid? 

So if you're wondering why your doctor ordered an MRI instead of a run-of-the-mill X-ray, it might just be one of the three common reasons below. 

1. You might have torn cartilage, called a meniscal tear.

If you're a regular athlete, you might already know about meniscal tears, the painful cartilage injury that can bench you for quite a while. Because the meniscus is a soft, squishy tissue between your thigh and shin bones, it won't show clearly (or at all) on an X-ray. However, an MRI can give the doctor a clear picture to diagnose it for sure.1

But if you're still unsure, ask the doctor if they have any sample images from both an X-ray and an MRI so that you can compare and see the difference between the two pictures. It might just help you visualize the benefit of an MRI's high-quality, detailed images that show soft tissue like cartilage. 

The sooner your doctor can diagnose the tear, the sooner they can help fix it, either through surgery or prolonged rest to help the tear recover on its own.

2. You might have a tiny bone fracture that can't be seen on an X-ray.

Sometimes, your doctor might order an MRI if they suspect that you have a very small fracture in your bone that might be hard to see, or even hidden behind another big bone in your knee. For example, you might have a tiny break in your patella (or kneecap) — or the tibia (shin) or femur (thigh) near your joint.

The MRI can help your doctor better diagnose the break through a more detailed, up-close picture of the knee.2 And just like anything else, the sooner they diagnose the issue for your pain, the sooner you can get back on your feet (or knees, that is).

3. You might have some fluid buildup or an infection in your knee. 

Your doctor might suspect that you have some excess fluid in your knee, which is common in people with a meniscal tear, arthritis, or other injuries that cause swelling. A Baker's cyst (a cyst with lots of fluid) is a major cause, but there can be other causes, too. Having a big, bulging knee might be a sign that some extra fluid is to blame, but an MRI can detect it through high-quality pictures of the knee.3

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How to prepare for an MRI

You may have fears before the MRI, and that’s perfectly normal! But know this: The procedure is painless, has no radiation, and other than having to keep still for a while, causes no discomfort.

Here's what to expect:

  • Before the MRI, your doctor may require you not to eat or drink for several hours.
  • When getting ready for the MRI, you'll be asked to remove any jewelry, coins or other metal you have with you.
  • You'll lie on your back on a table that slides into an MRI enclosure. If you have claustrophobia, your doctor may provide you a sedative to stay calm.
  • For up to an hour, you'll need to remain very still and quiet during the test.

After that, you're done — and one step closer to getting your knee injury diagnosed for once and for all.


  1. Meniscus Tears. American Academy of Orthopaedic Surgeons. https://orthoinfo.aaos.org/en/diseases--conditions/meniscus-tears. Accessed May 1, 2018.
  2. Magnetic Resonance Imaging (MRI) – Knee. Radiological Society of North America. https://www.radiologyinfo.org/en/info.cfm?pg=kneemr. Accessed May 1, 2018.
  3. Knee MRI Scan. U.S. National Library of Medicine. https://medlineplus.gov/ency/article/007361.htm. Accessed May 1, 2018.