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
Universal Images Group / Getty Images

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 Can Be Seen 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 are not adequate to demonstrate bone density (you need a bone density test for that), but they do show the normal bone architecture. Abnormalities, including certain bone disorders and osteopenia (bone thinning), can be detected by an X-ray.
  • Alignment. X-rays taken while standing up can show the alignment of the knee joint and whether or not there is an abnormality in the alignment of the bone. Malalignment can lead to excessive forces 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 will show evidence of injury to the bone, including fractures. Not all fractures show up on X-ray, but most do. Common types of fractures seen on knee X-rays include tibial plateau fractures and patella fractures.

X-Rays Are Usually the First Step

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.

Was this page helpful?
Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  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.