Knee X-Rays and Detecting Abnormalities

As part of the standard evaluation of your knee, your healthcare provider 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 healthcare provider to get a complete understanding of most knee problems.

Bilateral X-Rays

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

What's On a Knee X-Ray

Your healthcare provider 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 healthcare provider 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.