Knee X-Rays and Detecting Abnormalities

Getting an X-ray of the knee is often a first step in diagnosing a knee condition. In many cases, knee X-rays can help find the cause of pain, tenderness, or swelling. X-rays are best at showing bone, but can also reveal soft tissue changes and signs of arthritis.

The results can help determine a treatment for your knee or may lead to additional testing.

This article explores why knee X-rays are done and what the images can show.

x-ray of someone's knees
Universal Images Group / Getty Images

Why Knee X-Rays Are Done

Many knee problems are diagnosed by X-ray, an image that shows internal structures like bones and soft tissues.

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.

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

Magnetic resonance imaging (MRI) is a useful test as well. However, doing an MRI alone won't allow a healthcare provider to get a complete understanding of most knee problems that cause pain.

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: 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.) However, 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.

2 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.

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

By Jonathan Cluett, MD
Jonathan Cluett, MD, is board-certified in orthopedic surgery. He served as assistant team physician to Chivas USA (Major League Soccer) and the United States men's and women's national soccer teams.