Knee X-Rays and Detecting Abnormalities

As part of the standard evaluation of your knee, your doctor will discuss the nature of the problem with you, examine your knee, and possibly obtain X-rays of the knee joint.

x-ray of someone's knees
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Why Knee X-Rays Are Done

You may have heard that an MRI is a better test for diagnosing knee problems. However, that's not necessarily true.

Many knee problems are better diagnosed by X-ray, and obtaining an X-ray as the first step is the usual course in diagnosing a knee condition.

Knee X-rays give much more useful information about knee alignment, bone quality, and the extent of any degenerative (arthritic) changes within the knee.

An MRI is a useful test as well, but doing an MRI alone won't allow a doctor to get a complete understanding of most knee problems.

Bilateral X-Rays

Sometimes your doctor may want to have an X-ray done on both knees. This is called a bilateral X-ray and is especially common if your doctor is checking for signs of arthritis.

What's On a Knee X-Ray

Your doctor will look for the following on your knee X-rays:

  • Soft-tissue changes: X-rays are best at showing bone, but there is much more besides bone that can be seen on an X-ray. They can also show signs of soft-tissue swelling and excess fluid within the knee.
  • Bone quality: X-rays aren't adequate for evaluating bone density (you need a bone density test for that), but they can detect abnormalities (e.g., certain bone disorders, bone thinning).
  • Alignment: X-rays taken while standing show the alignment of the knee joint and abnormalities in bone alignment. Malalignment can put excessive force on parts of the joint and accelerate arthritic changes.
  • Joint spaces: The space between the bones seen on X-ray is actually filled completely with cartilage. Narrowing of this joint space is the best sign of the extent of knee arthritis.
  • Early arthritis signs: Other signs of arthritis, including bone spurs, can be seen on an X-ray. Some of these early signs offer an indication of how much of your knee pain is due to early arthritis.
  • Trauma/fracture: X-rays show evidence of injury to the bone, including fractures. Not all fractures show up on X-ray, but most do. Common fractures seen on knee X-rays include tibial plateau fractures and patella fractures.

A Word From Verywell

An X-ray is a very useful test and helps provide information your doctor can use to make a diagnosis of your knee pain. While this is not as new of a test as an MRI, in some cases it's still a much more useful one and it's less costly too.

That said, for some conditions, the next step in making a diagnosis after an X-ray is complete is to do an MRI.

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Article Sources
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  1. Harvard Health Publishing. X-ray may be best screening tool for diagnosing knee pain. Published February 2017.

  2. Arthritis Foundation. X-rays, MRIs and other imaging tests for knee diagnosis.